Discussion:
Fixed my porch light, not sure how
(too old to reply)
TimR
2012-05-15 23:21:14 UTC
Permalink
Raw Message
The back porch light stopped working, a new bulb didn't help.

So. I put a meter on the socket. 0 V.

I pulled the switch plate off (just a normal single pole). 80 V
terminal to terminal. Hmmm?

Killed the power, put an ohmeter terminal to terminal, infinite
resistance at both switch positions. Diagnosis bad switch, supported
by the fact that before it died completely, flipping the switch
several times made it work. Besides I've always had a CFL in that one
and I suspect the capacitor shortens the switch life due to arcing.

Okay, a new switch is $1.29, no big loss if wrong. Took the old
switch off, turned the power back on and checked wire to wire just for
grins, still 80 V. Uh oh.

Put the new switch in. Turned power on, checked the socket, 120 V.
Put bulb in, (CFL), lights up fine.

Well, I have a working porch light again, but I'm left with the 80 V
mystery. I don't know any way to get 80 V on a normal residential
power setup. The meter was a digital Radio Shack multimeter. If I'd
had time I'd have checked again with the Simpson analog, digitals
sometimes give funny readings, but I've never seen 80 V. What am I
missing?
Sjouke Burry
2012-05-15 23:40:33 UTC
Permalink
Raw Message
Post by TimR
The back porch light stopped working, a new bulb didn't help.
So. I put a meter on the socket. 0 V.
I pulled the switch plate off (just a normal single pole). 80 V
terminal to terminal. Hmmm?
Killed the power, put an ohmeter terminal to terminal, infinite
resistance at both switch positions. Diagnosis bad switch, supported
by the fact that before it died completely, flipping the switch
several times made it work. Besides I've always had a CFL in that one
and I suspect the capacitor shortens the switch life due to arcing.
Okay, a new switch is $1.29, no big loss if wrong. Took the old
switch off, turned the power back on and checked wire to wire just for
grins, still 80 V. Uh oh.
Put the new switch in. Turned power on, checked the socket, 120 V.
Put bulb in, (CFL), lights up fine.
Well, I have a working porch light again, but I'm left with the 80 V
mystery. I don't know any way to get 80 V on a normal residential
power setup. The meter was a digital Radio Shack multimeter. If I'd
had time I'd have checked again with the Simpson analog, digitals
sometimes give funny readings, but I've never seen 80 V. What am I
missing?
A bad contact somewhere? Put a heavy load, an iron or vacuum cleaner on
it to make sure there is a solid feed.
If those work, stop worrying. If not, start worrying, and start checking
backward along the feed.
A lousy job, but loose contacts can cause a fire.
TimR
2012-05-16 00:07:58 UTC
Permalink
Raw Message
Post by Sjouke Burry
A bad contact somewhere?
Not sure that makes sense.

Pulling a current across a resistance, like from a bad connection,
should cause a voltage drop. But no-load open circuit should be full
voltage.
c***@snyder.on.ca
2012-05-16 01:45:34 UTC
Permalink
Raw Message
Post by TimR
Post by Sjouke Burry
A bad contact somewhere?
Not sure that makes sense.
Pulling a current across a resistance, like from a bad connection,
should cause a voltage drop. But no-load open circuit should be full
voltage.
OP said they measured across the switch.

Learn how to use a meter for troubleshooting, and what the reading
mean.

The problem IS FIXED. There was a BAD SWITCH.
t***@optonline.net
2012-05-16 13:44:03 UTC
Permalink
Raw Message
Post by TimR
Post by Sjouke Burry
A bad contact somewhere?
Not sure that makes sense.
Pulling a current across a resistance, like from a bad connection,
should cause a voltage drop.  But  no-load open circuit should be full
voltage.
You were pulling a current through that circuit and
it had two resistances in it. One presumably was the
light bulb, otherwise measuring from terminal to
terminal of the open switch should not read anything..
The other resistance is that of the multimeter itself.
How much of the 120V in the circuit appears
across the bulb and how much across
the multimeter is proportional to their resistance.
I would expect the multimeter to have such a high
resistance that you'd read close to 120V. But with
a CFL presented with a tiny current, not able to light,
who knows what that resistance/impedance is.
c***@snyder.on.ca
2012-05-16 01:44:22 UTC
Permalink
Raw Message
Post by Sjouke Burry
Post by TimR
The back porch light stopped working, a new bulb didn't help.
So. I put a meter on the socket. 0 V.
I pulled the switch plate off (just a normal single pole). 80 V
terminal to terminal. Hmmm?
Killed the power, put an ohmeter terminal to terminal, infinite
resistance at both switch positions. Diagnosis bad switch, supported
by the fact that before it died completely, flipping the switch
several times made it work. Besides I've always had a CFL in that one
and I suspect the capacitor shortens the switch life due to arcing.
Okay, a new switch is $1.29, no big loss if wrong. Took the old
switch off, turned the power back on and checked wire to wire just for
grins, still 80 V. Uh oh.
Put the new switch in. Turned power on, checked the socket, 120 V.
Put bulb in, (CFL), lights up fine.
Well, I have a working porch light again, but I'm left with the 80 V
mystery. I don't know any way to get 80 V on a normal residential
power setup. The meter was a digital Radio Shack multimeter. If I'd
had time I'd have checked again with the Simpson analog, digitals
sometimes give funny readings, but I've never seen 80 V. What am I
missing?
A bad contact somewhere? Put a heavy load, an iron or vacuum cleaner on
it to make sure there is a solid feed.
If those work, stop worrying. If not, start worrying, and start checking
backward along the feed.
A lousy job, but loose contacts can cause a fire.
Just learn how to use the meter.
Metspitzer
2012-05-16 01:52:41 UTC
Permalink
Raw Message
Post by c***@snyder.on.ca
Post by Sjouke Burry
A bad contact somewhere? Put a heavy load, an iron or vacuum cleaner on
it to make sure there is a solid feed.
If those work, stop worrying. If not, start worrying, and start checking
backward along the feed.
A lousy job, but loose contacts can cause a fire.
Just learn how to use the meter.
Don't you have a vacuum cleaner in your tool kit?
HeyBub
2012-05-16 00:57:53 UTC
Permalink
Raw Message
Post by TimR
The back porch light stopped working, a new bulb didn't help.
So. I put a meter on the socket. 0 V.
I pulled the switch plate off (just a normal single pole). 80 V
terminal to terminal. Hmmm?
Killed the power, put an ohmeter terminal to terminal, infinite
resistance at both switch positions. Diagnosis bad switch, supported
by the fact that before it died completely, flipping the switch
several times made it work. Besides I've always had a CFL in that one
and I suspect the capacitor shortens the switch life due to arcing.
Okay, a new switch is $1.29, no big loss if wrong. Took the old
switch off, turned the power back on and checked wire to wire just for
grins, still 80 V. Uh oh.
Put the new switch in. Turned power on, checked the socket, 120 V.
Put bulb in, (CFL), lights up fine.
Well, I have a working porch light again, but I'm left with the 80 V
mystery. I don't know any way to get 80 V on a normal residential
power setup. The meter was a digital Radio Shack multimeter. If I'd
had time I'd have checked again with the Simpson analog, digitals
sometimes give funny readings, but I've never seen 80 V. What am I
missing?
You cannot believe the accuracy of a multimeter with no load on the circuit.
The reason is too complicated to divulge here, but it's a fact.

If your meter reads anything above about five volts - when it should be
120 - it really IS 120.
c***@snyder.on.ca
2012-05-16 01:49:08 UTC
Permalink
Raw Message
Post by HeyBub
Post by TimR
The back porch light stopped working, a new bulb didn't help.
So. I put a meter on the socket. 0 V.
I pulled the switch plate off (just a normal single pole). 80 V
terminal to terminal. Hmmm?
Killed the power, put an ohmeter terminal to terminal, infinite
resistance at both switch positions. Diagnosis bad switch, supported
by the fact that before it died completely, flipping the switch
several times made it work. Besides I've always had a CFL in that one
and I suspect the capacitor shortens the switch life due to arcing.
Okay, a new switch is $1.29, no big loss if wrong. Took the old
switch off, turned the power back on and checked wire to wire just for
grins, still 80 V. Uh oh.
Put the new switch in. Turned power on, checked the socket, 120 V.
Put bulb in, (CFL), lights up fine.
Well, I have a working porch light again, but I'm left with the 80 V
mystery. I don't know any way to get 80 V on a normal residential
power setup. The meter was a digital Radio Shack multimeter. If I'd
had time I'd have checked again with the Simpson analog, digitals
sometimes give funny readings, but I've never seen 80 V. What am I
missing?
You cannot believe the accuracy of a multimeter with no load on the circuit.
The reason is too complicated to divulge here, but it's a fact.
If your meter reads anything above about five volts - when it should be
120 - it really IS 120.
The OP stated "I pulled the switch plate off (just a normal single
pole). 80 V terminal to terminal. Hmmm?"

What's wrong with this situation?
What is being measured?
What is indicated by the fact there is no voltage at the socket and 80
volts across the switch?
Don't need to be a member of MENSA to figure this one out.
The voltage reading is likely accurate - accurate enough, anyway. Just
so happens it is immaterial because it is not a valid measurement. The
voltmeter was being used as an ammeter instead of a voltmeter.
Ralph Mowery
2012-05-16 01:14:57 UTC
Permalink
Raw Message
Post by TimR
The back porch light stopped working, a new bulb didn't help.
So. I put a meter on the socket. 0 V.
I pulled the switch plate off (just a normal single pole). 80 V
terminal to terminal. Hmmm?
Killed the power, put an ohmeter terminal to terminal, infinite
resistance at both switch positions. Diagnosis bad switch, supported
by the fact that before it died completely, flipping the switch
several times made it work. Besides I've always had a CFL in that one
and I suspect the capacitor shortens the switch life due to arcing.
Okay, a new switch is $1.29, no big loss if wrong. Took the old
switch off, turned the power back on and checked wire to wire just for
grins, still 80 V. Uh oh.
Put the new switch in. Turned power on, checked the socket, 120 V.
Put bulb in, (CFL), lights up fine.
Well, I have a working porch light again, but I'm left with the 80 V
mystery. I don't know any way to get 80 V on a normal residential
power setup. The meter was a digital Radio Shack multimeter. If I'd
had time I'd have checked again with the Simpson analog, digitals
sometimes give funny readings, but I've never seen 80 V. What am I
missing?
It is often normal to get strange readings with a digital meter, as someone
said, too much to go into here. Short answer is the wiring is acting like a
capacitor or transformer and the high impedance of the meter is picking up
voltage with a very small current. Almost any load and the voltage will
dissapear.. If the bulb was still in the circuit, it may be a small ammount
of feed through in the CFL.
c***@snyder.on.ca
2012-05-16 01:51:31 UTC
Permalink
Raw Message
On Tue, 15 May 2012 21:14:57 -0400, "Ralph Mowery"
Post by Ralph Mowery
Post by TimR
The back porch light stopped working, a new bulb didn't help.
So. I put a meter on the socket. 0 V.
I pulled the switch plate off (just a normal single pole). 80 V
terminal to terminal. Hmmm?
Killed the power, put an ohmeter terminal to terminal, infinite
resistance at both switch positions. Diagnosis bad switch, supported
by the fact that before it died completely, flipping the switch
several times made it work. Besides I've always had a CFL in that one
and I suspect the capacitor shortens the switch life due to arcing.
Okay, a new switch is $1.29, no big loss if wrong. Took the old
switch off, turned the power back on and checked wire to wire just for
grins, still 80 V. Uh oh.
Put the new switch in. Turned power on, checked the socket, 120 V.
Put bulb in, (CFL), lights up fine.
Well, I have a working porch light again, but I'm left with the 80 V
mystery. I don't know any way to get 80 V on a normal residential
power setup. The meter was a digital Radio Shack multimeter. If I'd
had time I'd have checked again with the Simpson analog, digitals
sometimes give funny readings, but I've never seen 80 V. What am I
missing?
It is often normal to get strange readings with a digital meter, as someone
said, too much to go into here. Short answer is the wiring is acting like a
capacitor or transformer and the high impedance of the meter is picking up
voltage with a very small current. Almost any load and the voltage will
dissapear.. If the bulb was still in the circuit, it may be a small ammount
of feed through in the CFL.
Short answer is the voltmeter was not being used properly, and the
longer answer is nobody else here caught it.
Nothing to do with inacuracies of digital meters - totally a case of
not knowing how to use a meter to troubleshoot - or knowing how to
interpret the readings when the meter is mis-connected.

The readings are accurate
HeyBub
2012-05-16 11:48:49 UTC
Permalink
Raw Message
Post by c***@snyder.on.ca
Post by Ralph Mowery
It is often normal to get strange readings with a digital meter, as
someone said, too much to go into here. Short answer is the wiring
is acting like a capacitor or transformer and the high impedance of
the meter is picking up voltage with a very small current. Almost
any load and the voltage will dissapear.. If the bulb was still in
the circuit, it may be a small ammount of feed through in the CFL.
Short answer is the voltmeter was not being used properly, and the
longer answer is nobody else here caught it.
Nothing to do with inacuracies of digital meters - totally a case of
not knowing how to use a meter to troubleshoot - or knowing how to
interpret the readings when the meter is mis-connected.
The readings are accurate
The readings are NOT accurate. The indicated voltage is a phantom.

Consider your assertion that the meter is "mis-connected:" The meter has two
probes. There are two wires. There are two and only two possible ways to
connect the meter and the wires. Which of the two, according to you, is the
correct way to connect all this stuff? If both of the two possibilities
yield the same result, where is the "mis-connection"?
bud--
2012-05-16 14:08:54 UTC
Permalink
Raw Message
Post by HeyBub
Post by c***@snyder.on.ca
Post by Ralph Mowery
It is often normal to get strange readings with a digital meter, as
someone said, too much to go into here. Short answer is the wiring
is acting like a capacitor or transformer and the high impedance of
the meter is picking up voltage with a very small current. Almost
any load and the voltage will dissapear.. If the bulb was still in
the circuit, it may be a small ammount of feed through in the CFL.
Short answer is the voltmeter was not being used properly, and the
longer answer is nobody else here caught it.
Nothing to do with inacuracies of digital meters - totally a case of
not knowing how to use a meter to troubleshoot - or knowing how to
interpret the readings when the meter is mis-connected.
The readings are accurate
The readings are NOT accurate. The indicated voltage is a phantom.
Consider your assertion that the meter is "mis-connected:" The meter has two
probes. There are two wires. There are two and only two possible ways to
connect the meter and the wires. Which of the two, according to you, is the
correct way to connect all this stuff? If both of the two possibilities
yield the same result, where is the "mis-connection"?
The OP was measuring across an open switch with no load (no bulb). One
might expect zero volts. What was measured was a "phantom" voltage, as
Hey says, caused by capacitance between switched and neutral wires to
the light and the high impedance of the meter as Ralph said. It is a
rather well know quirk (inaccuracy) of digital meters.

The measurement across the switch would be meaningful with an
incandescent bulb installed. Or a low impedance meter would measure zero
volts (which would tell the OP nothing).
--
bud--
c***@snyder.on.ca
2012-05-17 03:29:47 UTC
Permalink
Raw Message
Post by bud--
Post by HeyBub
Post by c***@snyder.on.ca
Post by Ralph Mowery
It is often normal to get strange readings with a digital meter, as
someone said, too much to go into here. Short answer is the wiring
is acting like a capacitor or transformer and the high impedance of
the meter is picking up voltage with a very small current. Almost
any load and the voltage will dissapear.. If the bulb was still in
the circuit, it may be a small ammount of feed through in the CFL.
Short answer is the voltmeter was not being used properly, and the
longer answer is nobody else here caught it.
Nothing to do with inacuracies of digital meters - totally a case of
not knowing how to use a meter to troubleshoot - or knowing how to
interpret the readings when the meter is mis-connected.
The readings are accurate
The readings are NOT accurate. The indicated voltage is a phantom.
Consider your assertion that the meter is "mis-connected:" The meter has two
probes. There are two wires. There are two and only two possible ways to
connect the meter and the wires. Which of the two, according to you, is the
correct way to connect all this stuff? If both of the two possibilities
yield the same result, where is the "mis-connection"?
The OP was measuring across an open switch with no load (no bulb). One
might expect zero volts. What was measured was a "phantom" voltage, as
Hey says, caused by capacitance between switched and neutral wires to
the light and the high impedance of the meter as Ralph said. It is a
rather well know quirk (inaccuracy) of digital meters.
Except the OP had a CFL in the socket when they tested the voltage
across the switch.
Post by bud--
The measurement across the switch would be meaningful with an
incandescent bulb installed. Or a low impedance meter would measure zero
volts (which would tell the OP nothing).
Because the meter was, as I said, misconnected for the rquired test.
HeyBub
2012-05-17 12:08:55 UTC
Permalink
Raw Message
Post by c***@snyder.on.ca
Post by bud--
Post by HeyBub
Post by c***@snyder.on.ca
Post by Ralph Mowery
It is often normal to get strange readings with a digital meter,
as someone said, too much to go into here. Short answer is the
wiring is acting like a capacitor or transformer and the high
impedance of the meter is picking up voltage with a very small
current. Almost any load and the voltage will dissapear.. If
the bulb was still in the circuit, it may be a small ammount of
feed through in the CFL.
Short answer is the voltmeter was not being used properly, and the
longer answer is nobody else here caught it.
Nothing to do with inacuracies of digital meters - totally a case
of not knowing how to use a meter to troubleshoot - or knowing
how to interpret the readings when the meter is mis-connected.
The readings are accurate
The readings are NOT accurate. The indicated voltage is a phantom.
Consider your assertion that the meter is "mis-connected:" The
meter has two probes. There are two wires. There are two and only
two possible ways to connect the meter and the wires. Which of the
two, according to you, is the correct way to connect all this
stuff? If both of the two possibilities yield the same result,
where is the "mis-connection"?
The OP was measuring across an open switch with no load (no bulb).
One might expect zero volts. What was measured was a "phantom"
voltage, as Hey says, caused by capacitance between switched and
neutral wires to the light and the high impedance of the meter as
Ralph said. It is a rather well know quirk (inaccuracy) of digital
meters.
Except the OP had a CFL in the socket when they tested the voltage
across the switch.
Post by bud--
The measurement across the switch would be meaningful with an
incandescent bulb installed. Or a low impedance meter would measure
zero volts (which would tell the OP nothing).
Because the meter was, as I said, misconnected for the rquired test.
Again I ask, in a slightly different form, what, in your expert opinion, is
the proper way to connect two probes to two wires?
c***@snyder.on.ca
2012-05-18 00:14:23 UTC
Permalink
Raw Message
Post by HeyBub
Post by c***@snyder.on.ca
Post by bud--
Post by HeyBub
Post by c***@snyder.on.ca
Post by Ralph Mowery
It is often normal to get strange readings with a digital meter,
as someone said, too much to go into here. Short answer is the
wiring is acting like a capacitor or transformer and the high
impedance of the meter is picking up voltage with a very small
current. Almost any load and the voltage will dissapear.. If
the bulb was still in the circuit, it may be a small ammount of
feed through in the CFL.
Short answer is the voltmeter was not being used properly, and the
longer answer is nobody else here caught it.
Nothing to do with inacuracies of digital meters - totally a case
of not knowing how to use a meter to troubleshoot - or knowing
how to interpret the readings when the meter is mis-connected.
The readings are accurate
The readings are NOT accurate. The indicated voltage is a phantom.
Consider your assertion that the meter is "mis-connected:" The
meter has two probes. There are two wires. There are two and only
two possible ways to connect the meter and the wires. Which of the
two, according to you, is the correct way to connect all this
stuff? If both of the two possibilities yield the same result,
where is the "mis-connection"?
The OP was measuring across an open switch with no load (no bulb).
One might expect zero volts. What was measured was a "phantom"
voltage, as Hey says, caused by capacitance between switched and
neutral wires to the light and the high impedance of the meter as
Ralph said. It is a rather well know quirk (inaccuracy) of digital
meters.
Except the OP had a CFL in the socket when they tested the voltage
across the switch.
Post by bud--
The measurement across the switch would be meaningful with an
incandescent bulb installed. Or a low impedance meter would measure
zero volts (which would tell the OP nothing).
Because the meter was, as I said, misconnected for the rquired test.
Again I ask, in a slightly different form, what, in your expert opinion, is
the proper way to connect two probes to two wires?
Each wire in turn, to neutral or ground. VoltMeter across a switch is
a pretty lame attempt to troubleshoot the problem, because no matter
what reading he gets, it doesn't mean SQUAT.

You are obviously unable to grasp the concept.
bud--
2012-05-17 15:10:01 UTC
Permalink
Raw Message
Post by c***@snyder.on.ca
Post by bud--
Post by HeyBub
Post by c***@snyder.on.ca
Post by Ralph Mowery
It is often normal to get strange readings with a digital meter, as
someone said, too much to go into here. Short answer is the wiring
is acting like a capacitor or transformer and the high impedance of
the meter is picking up voltage with a very small current. Almost
any load and the voltage will dissapear.. If the bulb was still in
the circuit, it may be a small ammount of feed through in the CFL.
Short answer is the voltmeter was not being used properly, and the
longer answer is nobody else here caught it.
Nothing to do with inacuracies of digital meters - totally a case of
not knowing how to use a meter to troubleshoot - or knowing how to
interpret the readings when the meter is mis-connected.
The readings are accurate
The readings are NOT accurate. The indicated voltage is a phantom.
Consider your assertion that the meter is "mis-connected:" The meter has two
probes. There are two wires. There are two and only two possible ways to
connect the meter and the wires. Which of the two, according to you, is the
correct way to connect all this stuff? If both of the two possibilities
yield the same result, where is the "mis-connection"?
The OP was measuring across an open switch with no load (no bulb). One
might expect zero volts. What was measured was a "phantom" voltage, as
Hey says, caused by capacitance between switched and neutral wires to
the light and the high impedance of the meter as Ralph said. It is a
rather well know quirk (inaccuracy) of digital meters.
Except the OP had a CFL in the socket when they tested the voltage
across the switch.
I read the original post as not having any bulb in the socket. From the
OP's post yesterday that is correct.
Post by c***@snyder.on.ca
Post by bud--
The measurement across the switch would be meaningful with an
incandescent bulb installed. Or a low impedance meter would measure zero
volts (which would tell the OP nothing).
Because the meter was, as I said, misconnected for the rquired test.
Bullcrap. There is nothing wrong with measuring the voltage across the
switch if there is an incandescent lamp in the socket.

From the OP's post yesterday there is no neutral or ground at the
switch. It makes even more sense to measure the voltage across the
switch (with a lamp). Repeating Hey's question - how do you connect two
probes to two wires, no ground, no neutral.

I have, for instance, measured the voltage across cartridge fuses. If
there is voltage the fuse is open. If there is no voltage further checks
are required. (But then the US does not have fuses that "weld themselves
back together and work for a while".)
--
bud--
c***@snyder.on.ca
2012-05-18 00:52:37 UTC
Permalink
Raw Message
Post by bud--
Post by c***@snyder.on.ca
Post by bud--
Post by HeyBub
Post by c***@snyder.on.ca
Post by Ralph Mowery
It is often normal to get strange readings with a digital meter, as
someone said, too much to go into here. Short answer is the wiring
is acting like a capacitor or transformer and the high impedance of
the meter is picking up voltage with a very small current. Almost
any load and the voltage will dissapear.. If the bulb was still in
the circuit, it may be a small ammount of feed through in the CFL.
Short answer is the voltmeter was not being used properly, and the
longer answer is nobody else here caught it.
Nothing to do with inacuracies of digital meters - totally a case of
not knowing how to use a meter to troubleshoot - or knowing how to
interpret the readings when the meter is mis-connected.
The readings are accurate
The readings are NOT accurate. The indicated voltage is a phantom.
Consider your assertion that the meter is "mis-connected:" The meter has two
probes. There are two wires. There are two and only two possible ways to
connect the meter and the wires. Which of the two, according to you, is the
correct way to connect all this stuff? If both of the two possibilities
yield the same result, where is the "mis-connection"?
The OP was measuring across an open switch with no load (no bulb). One
might expect zero volts. What was measured was a "phantom" voltage, as
Hey says, caused by capacitance between switched and neutral wires to
the light and the high impedance of the meter as Ralph said. It is a
rather well know quirk (inaccuracy) of digital meters.
Except the OP had a CFL in the socket when they tested the voltage
across the switch.
I read the original post as not having any bulb in the socket. From the
OP's post yesterday that is correct.
Post by c***@snyder.on.ca
Post by bud--
The measurement across the switch would be meaningful with an
incandescent bulb installed. Or a low impedance meter would measure zero
volts (which would tell the OP nothing).
Because the meter was, as I said, misconnected for the rquired test.
Bullcrap. There is nothing wrong with measuring the voltage across the
switch if there is an incandescent lamp in the socket.
OK. EXACTLY what ic onnecting the meter across the switch telling
you? If you get a non 120 volt reading either a)- there is no power
to the switch B) the switch is shorted or closed, C) the bulb is
open, D) there is a bad connection between the switch and the bulb, E)
there is a bad connection between the bulb and the neutral buss on the
panel, F) the meter is defective.

Take your pick - you really have not learned anything of value.

If on the other hand you get a 120 volt reading, you know the switch
is open and there is a measure of continuity between the switch and
the neatral buss, as well as between the switch and the fuse/breaker,
which is supplying power.

If the test is done with no bulb in the socket - (no load) there is no
valid reading that tells you ANYTHING.

And that's no bullcrap.
Post by bud--
From the OP's post yesterday there is no neutral or ground at the
switch. It makes even more sense to measure the voltage across the
switch (with a lamp). Repeating Hey's question - how do you connect two
probes to two wires, no ground, no neutral.
I have, for instance, measured the voltage across cartridge fuses. If
there is voltage the fuse is open. If there is no voltage further checks
are required. (But then the US does not have fuses that "weld themselves
back together and work for a while".)
bud--
2012-05-18 14:55:19 UTC
Permalink
Raw Message
Post by c***@snyder.on.ca
Post by bud--
Post by c***@snyder.on.ca
Post by bud--
Post by HeyBub
Post by c***@snyder.on.ca
Post by Ralph Mowery
It is often normal to get strange readings with a digital meter, as
someone said, too much to go into here. Short answer is the wiring
is acting like a capacitor or transformer and the high impedance of
the meter is picking up voltage with a very small current. Almost
any load and the voltage will dissapear.. If the bulb was still in
the circuit, it may be a small ammount of feed through in the CFL.
Short answer is the voltmeter was not being used properly, and the
longer answer is nobody else here caught it.
Nothing to do with inacuracies of digital meters - totally a case of
not knowing how to use a meter to troubleshoot - or knowing how to
interpret the readings when the meter is mis-connected.
The readings are accurate
The readings are NOT accurate. The indicated voltage is a phantom.
Consider your assertion that the meter is "mis-connected:" The meter has two
probes. There are two wires. There are two and only two possible ways to
connect the meter and the wires. Which of the two, according to you, is the
correct way to connect all this stuff? If both of the two possibilities
yield the same result, where is the "mis-connection"?
The OP was measuring across an open switch with no load (no bulb). One
might expect zero volts. What was measured was a "phantom" voltage, as
Hey says, caused by capacitance between switched and neutral wires to
the light and the high impedance of the meter as Ralph said. It is a
rather well know quirk (inaccuracy) of digital meters.
Except the OP had a CFL in the socket when they tested the voltage
across the switch.
I read the original post as not having any bulb in the socket. From the
OP's post yesterday that is correct.
Post by c***@snyder.on.ca
Post by bud--
The measurement across the switch would be meaningful with an
incandescent bulb installed. Or a low impedance meter would measure zero
volts (which would tell the OP nothing).
Because the meter was, as I said, misconnected for the rquired test.
Bullcrap. There is nothing wrong with measuring the voltage across the
switch if there is an incandescent lamp in the socket.
OK. EXACTLY what ic onnecting the meter across the switch telling
you? If you get a non 120 volt reading either a)- there is no power
to the switch B) the switch is shorted or closed, C) the bulb is
open, D) there is a bad connection between the switch and the bulb, E)
there is a bad connection between the bulb and the neutral buss on the
panel, F) the meter is defective.
Take your pick - you really have not learned anything of value.
You may not have learned anything.

A competent technician can evaluate what is happening. The information
is combined with the test below - if there is 120V with the switch open
it leaves B.

If there is 120V in both positions the switch is bad. That is what the
OP would have found if he had an incandescent bulb in the socket. A
simple test.
Post by c***@snyder.on.ca
If on the other hand you get a 120 volt reading, you know the switch
is open and there is a measure of continuity between the switch and
the neatral buss, as well as between the switch and the fuse/breaker,
which is supplying power.
If the test is done with no bulb in the socket - (no load) there is no
valid reading that tells you ANYTHING.
You might not figure out anything. But a competent technician would
evaluate no bulb and 80V in both positions as an open switch. I believe
that is what the OP found.

I said 2 times have an incandescent bulb in the socket.
Post by c***@snyder.on.ca
And that's no bullcrap.
Only if your grasp of electrical troubleshooting is defective.
Post by c***@snyder.on.ca
Post by bud--
From the OP's post yesterday there is no neutral or ground at the
switch. It makes even more sense to measure the voltage across the
switch (with a lamp). Repeating Hey's question - how do you connect two
probes to two wires, no ground, no neutral.
You have still not answered Hey's question. The OP said there is no
neutral or ground at the switch.

You are obviously unable to grasp the concept.
--
bud--
c***@snyder.on.ca
2012-05-18 20:15:58 UTC
Permalink
Raw Message
Post by bud--
Post by c***@snyder.on.ca
Post by bud--
Post by c***@snyder.on.ca
Post by bud--
Post by HeyBub
Post by c***@snyder.on.ca
Post by Ralph Mowery
It is often normal to get strange readings with a digital meter, as
someone said, too much to go into here. Short answer is the wiring
is acting like a capacitor or transformer and the high impedance of
the meter is picking up voltage with a very small current. Almost
any load and the voltage will dissapear.. If the bulb was still in
the circuit, it may be a small ammount of feed through in the CFL.
Short answer is the voltmeter was not being used properly, and the
longer answer is nobody else here caught it.
Nothing to do with inacuracies of digital meters - totally a case of
not knowing how to use a meter to troubleshoot - or knowing how to
interpret the readings when the meter is mis-connected.
The readings are accurate
The readings are NOT accurate. The indicated voltage is a phantom.
Consider your assertion that the meter is "mis-connected:" The meter has two
probes. There are two wires. There are two and only two possible ways to
connect the meter and the wires. Which of the two, according to you, is the
correct way to connect all this stuff? If both of the two possibilities
yield the same result, where is the "mis-connection"?
The OP was measuring across an open switch with no load (no bulb). One
might expect zero volts. What was measured was a "phantom" voltage, as
Hey says, caused by capacitance between switched and neutral wires to
the light and the high impedance of the meter as Ralph said. It is a
rather well know quirk (inaccuracy) of digital meters.
Except the OP had a CFL in the socket when they tested the voltage
across the switch.
I read the original post as not having any bulb in the socket. From the
OP's post yesterday that is correct.
Post by c***@snyder.on.ca
Post by bud--
The measurement across the switch would be meaningful with an
incandescent bulb installed. Or a low impedance meter would measure zero
volts (which would tell the OP nothing).
Because the meter was, as I said, misconnected for the rquired test.
Bullcrap. There is nothing wrong with measuring the voltage across the
switch if there is an incandescent lamp in the socket.
OK. EXACTLY what ic onnecting the meter across the switch telling
you? If you get a non 120 volt reading either a)- there is no power
to the switch B) the switch is shorted or closed, C) the bulb is
open, D) there is a bad connection between the switch and the bulb, E)
there is a bad connection between the bulb and the neutral buss on the
panel, F) the meter is defective.
Take your pick - you really have not learned anything of value.
You may not have learned anything.
A competent technician can evaluate what is happening. The information
is combined with the test below - if there is 120V with the switch open
it leaves B.
If there is 120V in both positions the switch is bad. That is what the
OP would have found if he had an incandescent bulb in the socket. A
simple test.
Post by c***@snyder.on.ca
If on the other hand you get a 120 volt reading, you know the switch
is open and there is a measure of continuity between the switch and
the neatral buss, as well as between the switch and the fuse/breaker,
which is supplying power.
If the test is done with no bulb in the socket - (no load) there is no
valid reading that tells you ANYTHING.
You might not figure out anything. But a competent technician would
evaluate no bulb and 80V in both positions as an open switch. I believe
that is what the OP found.
I said 2 times have an incandescent bulb in the socket.
Post by c***@snyder.on.ca
And that's no bullcrap.
Only if your grasp of electrical troubleshooting is defective.
Post by c***@snyder.on.ca
Post by bud--
From the OP's post yesterday there is no neutral or ground at the
switch. It makes even more sense to measure the voltage across the
switch (with a lamp). Repeating Hey's question - how do you connect two
probes to two wires, no ground, no neutral.
You have still not answered Hey's question. The OP said there is no
neutral or ground at the switch.
You are obviously unable to grasp the concept.
Forget it bud. I do this diagnostic stuff a lot, and have for almost
50 years.
bud--
2012-05-19 13:38:33 UTC
Permalink
Raw Message
Post by c***@snyder.on.ca
Post by bud--
Post by c***@snyder.on.ca
Post by bud--
Post by c***@snyder.on.ca
Because the meter was, as I said, misconnected for the rquired test.
Bullcrap. There is nothing wrong with measuring the voltage across the
switch if there is an incandescent lamp in the socket.
OK. EXACTLY what ic onnecting the meter across the switch telling
you? If you get a non 120 volt reading either a)- there is no power
to the switch B) the switch is shorted or closed, C) the bulb is
open, D) there is a bad connection between the switch and the bulb, E)
there is a bad connection between the bulb and the neutral buss on the
panel, F) the meter is defective.
Take your pick - you really have not learned anything of value.
You may not have learned anything.
A competent technician can evaluate what is happening. The information
is combined with the test below - if there is 120V with the switch open
it leaves B.
If there is 120V in both positions the switch is bad. That is what the
OP would have found if he had an incandescent bulb in the socket. A
simple test.
Post by c***@snyder.on.ca
If on the other hand you get a 120 volt reading, you know the switch
is open and there is a measure of continuity between the switch and
the neatral buss, as well as between the switch and the fuse/breaker,
which is supplying power.
If the test is done with no bulb in the socket - (no load) there is no
valid reading that tells you ANYTHING.
You might not figure out anything. But a competent technician would
evaluate no bulb and 80V in both positions as an open switch. I believe
that is what the OP found.
I said 2 times have an incandescent bulb in the socket.
Post by c***@snyder.on.ca
And that's no bullcrap.
Only if your grasp of electrical troubleshooting is defective.
Post by c***@snyder.on.ca
Post by bud--
From the OP's post yesterday there is no neutral or ground at the
switch. It makes even more sense to measure the voltage across the
switch (with a lamp). Repeating Hey's question - how do you connect two
probes to two wires, no ground, no neutral.
You have still not answered Hey's question. The OP said there is no
neutral or ground at the switch.
You are obviously unable to grasp the concept.
Forget it bud. I do this diagnostic stuff a lot, and have for almost
50 years.
Forget it clare. I have been a licensed master electrician for about 40
years and do this diagnostic stuff a lot.

Still missing - an answer to Hey's question. Two wires, no ground, no
neutral.
--
bud--
t***@optonline.net
2012-05-16 15:31:57 UTC
Permalink
Raw Message
Post by HeyBub
Post by c***@snyder.on.ca
Post by Ralph Mowery
It is often normal to get strange readings with a digital meter, as
someone said, too much to go into here.  Short answer is the wiring
is acting like a capacitor or transformer and the high impedance of
the meter is picking up voltage with a very small current.  Almost
any load and the voltage will dissapear..  If the bulb was still in
the circuit, it may be a small ammount of feed through in the CFL.
Short answer is the voltmeter was not being used properly, and the
longer answer is nobody else here caught it.
Nothing to do with inacuracies of digital meters - totally a case of
not knowing how to use a meter to troubleshoot -  or knowing how to
interpret the readings when the meter is mis-connected.
The readings are accurate
The readings are NOT accurate. The indicated voltage is a phantom.
Consider your assertion that the meter is "mis-connected:" The meter has two
probes. There are two wires. There are two and only two possible ways to
connect the meter and the wires. Which of the two, according to you, is the
correct way to connect all this stuff? If both of the two possibilities
yield the same result, where is the "mis-connection"?- Hide quoted text -
- Show quoted text -
I would have tested for 120V using one test lead
on the light side of the switch and the other held
to ground. I'd use ground because that's usually
there and available without taking anything apart.
Or he could have tested from the light side of
the switch to neutral.
Ralph Mowery
2012-05-16 15:57:44 UTC
Permalink
Raw Message
Post by t***@optonline.net
I would have tested for 120V using one test lead
on the light side of the switch and the other held
to ground. I'd use ground because that's usually
there and available without taking anything apart.
Or he could have tested from the light side of
the switch to neutral.
Many times there is no neutral at the light switch or if it is, it is not
broken and easy to get a meter lead on.

I also try not to test to ground as sometimes the ground wire is left out.
t***@optonline.net
2012-05-16 16:15:19 UTC
Permalink
Raw Message
Post by Ralph Mowery
Post by t***@optonline.net
I would have tested for 120V using one test lead
on the light side of the switch and the other held
to ground.  I'd use ground because that's usually
there and available without taking anything apart.
Or he could have tested from the light side of
the switch to neutral.
Many times there is no neutral at the light switch or if it is, it is not
broken and easy to get a meter lead on.
I also try not to test to ground as sometimes the ground wire is left out.
Well if you don't like using ground and a neutral is no
good because you have to take off a wire nut, how
would you propose to do the test?
Ralph Mowery
2012-05-16 17:00:35 UTC
Permalink
Raw Message
Post by t***@optonline.net
Post by Ralph Mowery
Many times there is no neutral at the light switch or if it is, it is not
broken and easy to get a meter lead on.
I also try not to test to ground as sometimes the ground wire is left out.
Well if you don't like using ground and a neutral is no
good because you have to take off a wire nut, how
would you propose to do the test?
Often in a light switch there is no neutral to have a wire nut to take off.

If there is no neutral or I suspect the ground is not connected, I use what
some may call a 'hot stick'. It is a device about the size of a cigar that
lights up and/or beebs when held next to a wire that has voltage on it.
Cutting the breaker off and on while using the hot stick usually confirms
there is power or no power at the switch. Then with the power off, I check
the switch using the ohms fuction.

I often use a Simpson 260 because I do not like the digital meters for
general testing due to the 'phantom' voltages. Another favorite is a Fluke
T2. I think that is the number. It has about 10 LEDs in it. It will check
from about 6 volts to 600 volts AC/DC and also low resistances. Just hook
up the test leads and it will show if you have power or a short.

I do admitt that I have several differant testers that most home owners do
not normally have or really need.
I also have a Fluke 87 digital meter, but seldom use it for electrical test
due to the 'phantom ' voltages. I work in industry where I have to deal
with anything from low voltage control and instruments to 480 volt 3 phase
circuits. That is the reason for having those plus several other testing
devices.
t***@optonline.net
2012-05-16 17:33:30 UTC
Permalink
Raw Message
Post by Ralph Mowery
Post by t***@optonline.net
Post by Ralph Mowery
Many times there is no neutral at the light switch or if it is, it is not
broken and easy to get a meter lead on.
I also try not to test to ground as sometimes the ground wire is left out.
Well if you don't like using ground and a neutral is no
good because you have to take off a wire nut, how
would you propose to do the test?
Often in a light switch there is no neutral to have a wire nut to take off.
Round these parts, the vast majority of them do
have neutrals. Usually the power feeds from the
panel to the switch via a romex that has both
conductors. Current NEC code now requires that
they have neutrals.

But that is why I said to just test it by holding one
lead to ground. And again, around here the vast
majority have grounds.
Post by Ralph Mowery
If there is no neutral or I suspect the ground is not connected, I use what
some may call a 'hot stick'.  It is a device about the size of a cigar that
lights up and/or beebs when held next to a wire that has voltage on it.
Yes, he could use one of those if he happened to
have it.
Post by Ralph Mowery
Cutting the breaker off and on while using the hot stick usually confirms
there is power or no power at the switch.  Then with the power off, I check
the switch using the ohms fuction.
Agree, he could do that too.
Post by Ralph Mowery
I often use a Simpson 260 because I do not like the digital meters for
general testing due to the 'phantom' voltages.  Another favorite is a Fluke
T2.  I think that is the number.  It has about 10 LEDs in it.  It will check
from about 6 volts to 600 volts AC/DC and also low resistances.  Just hook
up the test leads and it will show if you have power or a short.
I do admitt that I have several differant testers that most home owners do
not normally have or really need.
I also have a Fluke 87 digital meter, but seldom use it for electrical test
due to the 'phantom ' voltages.  I work in industry where I have to deal
with anything from low voltage control and instruments to 480 volt 3 phase
circuits.  That is the reason for having those plus several other testing
devices.
The phantom voltage issue is more of a problem
of people having a lack of understanding of circuit
fundamentals. The OP's test procedure being an
example. I don't think either of us would have
tested it the way he did. If you understand how circuits
work, it may cause you to do a second test, etc, but it's
not really confusing.
bud--
2012-05-16 19:26:30 UTC
Permalink
Raw Message
Post by t***@optonline.net
Post by Ralph Mowery
I often use a Simpson 260 because I do not like the digital meters for
general testing due to the 'phantom' voltages. Another favorite is a Fluke
T2. I think that is the number. It has about 10 LEDs in it. It will check
from about 6 volts to 600 volts AC/DC and also low resistances. Just hook
up the test leads and it will show if you have power or a short.
I do admitt that I have several differant testers that most home owners do
not normally have or really need.
I also have a Fluke 87 digital meter, but seldom use it for electrical test
due to the 'phantom ' voltages. I work in industry where I have to deal
with anything from low voltage control and instruments to 480 volt 3 phase
circuits. That is the reason for having those plus several other testing
devices.
I thought having many test devices was about having the most toys when
you die...

I am a lot more paranoid about possible failures and arc flash after
seeing some videos. Measuring on high capacity circuits, the meters
should be "category" rated. OSHA is likely to take a dim view of using
not-cat rated meters on high capacity circuits, particularly if there is
an injury. Fluke is likely to be cat rated. Not sure any Simpson 260s
are. Digital is also nice because it is more compact. (I coveted a 260
when I was about jr high school and finally got one at a garage sale
recently.)

If using a Fluke, or similar, you can substantially eliminate phantom
voltage with an accessory:
http://www.fluke.com/Fluke/usen/Accessories/Batteries,-Chargers-and-Adapters/SV225.htm?PID=56696
Post by t***@optonline.net
The phantom voltage issue is more of a problem
of people having a lack of understanding of circuit
fundamentals. The OP's test procedure being an
example. I don't think either of us would have
tested it the way he did. If you understand how circuits
work, it may cause you to do a second test, etc, but it's
not really confusing.
On the other hand, the test would have been fine if there was an
incandescent light bulb in the socket.

I agree about circuit fundamentals, and part of that is understanding
the limitations of measuring tools (like phantom voltage).

I remember the first time I saw the effect described by Ralph where the
voltage reads about the same point on the scale on different analog
ranges. I figured it out pretty fast, but it is weird.
--
bud--
Ralph Mowery
2012-05-16 19:12:54 UTC
Permalink
Raw Message
Post by bud--
I am a lot more paranoid about possible failures and arc flash after
seeing some videos. Measuring on high capacity circuits, the meters should
be "category" rated. OSHA is likely to take a dim view of using not-cat
rated meters on high capacity circuits, particularly if there is an
injury. Fluke is likely to be cat rated. Not sure any Simpson 260s are.
Digital is also nice because it is more compact. (I coveted a 260 when I
was about jr high school and finally got one at a garage sale recently.)
I do not know what year the cat ratings came out. The Simpsons I have are
way too old for that. Where I work the meters are furnished by the company
and the Flukes are rated for cat 3 and 4 if you have the fuses in them Fluke
recommends for replacement if blown. I have seen a few films on arc flash.
We even have a long coat and face shield to use while working on some
circuits. There are differant levels of protection ranging from long sleeve
natural fiber shirts to heavy coats and face protection.

While I would use one around the house, I am not sure what the ratings if
any are on the meters that I have seen sell for around $ 5 to $ 15.
I just would not use one on the stuff where I work that has very high
current capacity. I do feel safe with the old Simpsons and the newer ones
do have a cat rating.

If you want to see something scarry, I have a few pix of the after math of a
460 volt 3 phase motor starter panel that blew up when a 15 amp breaker was
turned on. It was fed with a main breaker of about 600 amps.
I did not turn it on or see it hapen,but it was where I work.
bud--
2012-05-18 15:31:41 UTC
Permalink
Raw Message
Post by Ralph Mowery
Post by bud--
I am a lot more paranoid about possible failures and arc flash after
seeing some videos. Measuring on high capacity circuits, the meters should
be "category" rated. OSHA is likely to take a dim view of using not-cat
rated meters on high capacity circuits, particularly if there is an
injury. Fluke is likely to be cat rated. Not sure any Simpson 260s are.
Digital is also nice because it is more compact. (I coveted a 260 when I
was about jr high school and finally got one at a garage sale recently.)
I do not know what year the cat ratings came out. The Simpsons I have are
way too old for that. Where I work the meters are furnished by the company
and the Flukes are rated for cat 3 and 4 if you have the fuses in them Fluke
recommends for replacement if blown. I have seen a few films on arc flash.
We even have a long coat and face shield to use while working on some
circuits. There are differant levels of protection ranging from long sleeve
natural fiber shirts to heavy coats and face protection.
While I would use one around the house, I am not sure what the ratings if
any are on the meters that I have seen sell for around $ 5 to $ 15.
I just would not use one on the stuff where I work that has very high
current capacity. I do feel safe with the old Simpsons and the newer ones
do have a cat rating.
If you want to see something scarry, I have a few pix of the after math of a
460 volt 3 phase motor starter panel that blew up when a 15 amp breaker was
turned on. It was fed with a main breaker of about 600 amps.
I did not turn it on or see it hapen,but it was where I work.
One of the smartest electricians I know wanted to measure the current
for a motor in a food processing plant. It was a possibly explosive
atmosphere so there was a motor control center in a purged room. He
defeated the interlock on the module door and amp-clamped a motor wire -
an absolutely standard procedure. No one knows what happened - maybe a
loose screw faulted the busbars, but there was an arc flash. He was
badly injured (including condensed copper on him) and was in the
hospital quite a while. The facility was buying distribution voltage
power from the utility and one of the fuse holders was destroyed in the
event - I have no idea how that could happen. (Arc flash was not an
issue back then.)

At a trade show a manufacturer field engineer had a seminar. As an
aside, he was working for a major company like Westinghouse and the
client wanted a module for a motor control center or switchgear. The
space was open so he was measuring the size with a steel tape. The next
thing he knew he was on his back on the other side of the room. If he
hadn't been thrown he might be dead. At least in that case he did
something dumb.

Some of the required inservice classes have covered arc flash. They had
an arcflash suit - pants, top, hood and gloves. (And the protection
includes the natural fiber clothes inside.) Don't know how you do useful
work in something like that. Someone brought in copies of the labels at
his facility that are required to evaluate what protection is required.
One of them said something like "No safe approach is possible" (with
protective panels removed).

The default standard for worker electrical safety is NFPA 70E. Your
plant must have a copy and I wouldn't be surprised if you have read it.
Interesting information on what protection is required for different
voltages and available fault currents.
--
bud--
TimR
2012-05-18 14:53:42 UTC
Permalink
Raw Message
Post by bud--
atmosphere so there was a motor control center in a purged room. He
defeated the interlock on the module door and amp-clamped a motor wire -
an absolutely standard procedure. No one knows what happened - maybe a
loose screw faulted the busbars, but there was an arc flash.
I saw an interesting arc (but not an arc flash) yesterday.

The contactor up on the pole stuck, and the switch at the bottom would
not turn off a set of ball field lights.

The high voltage guy on the bucket truck suited up with a couple
layers of gloves, etc., and pulled the switch with his stick.

You've seen those switches on poles, look almost like a Frankenstein
knife switch. You hook them with a stick and pull hard and quickly.

As the switch opened, the arc followed it for about 12 - 15 inches.
It was a cloudy day and I could clearly see the arc.
Ralph Mowery
2012-05-18 17:06:57 UTC
Permalink
Raw Message
Some of the required inservice classes have covered arc flash. They had an
arcflash suit - pants, top, hood and gloves. (And the protection includes
the natural fiber clothes inside.) Don't know how you do useful work in
something like that. Someone brought in copies of the labels at his
facility that are required to evaluate what protection is required. One of
them said something like "No safe approach is possible" (with protective
panels removed).
The default standard for worker electrical safety is NFPA 70E. Your plant
must have a copy and I wouldn't be surprised if you have read it.
Interesting information on what protection is required for different
voltages and available fault currents.
I just retired as of yesterday. We have all the protective gear. Gloves,
coat, face shield. While we seldom use it, we have a couple of special
outfits that are rated for 100 cal. The coats we normally have are rated
for 40 cal. I was almost tempted to bring my 40 caliber Glock on the last
day and shoot at my arc flash coat and tell them it would not protect
against a 40 caliber... Almost impossiable to do useful work with that junk
on. Most of the time we can cut the power off and do a test and then take
all the stuff off.

We have lables like that all over the plant. It is a large plant and covers
many acers. A small building ( maybe 50 x 100 feet) has a motor control
center and it had a sign on it that mainly stated we could not get within
about 500 feet of it. That ment if any breaker on it tripped, it would have
to stay off. Someone finally wised up and replaced that sign with one that
was workable.

Most of the arc flash junk started when a company came up with some high
dollar main breakers that were suspose to trip under certain conditions. As
many companies did not want to replace them, the arc flash hazard was
'invented'.
Metspitzer
2012-05-18 17:50:52 UTC
Permalink
Raw Message
Post by bud--
Post by Ralph Mowery
Post by bud--
I am a lot more paranoid about possible failures and arc flash after
seeing some videos. Measuring on high capacity circuits, the meters should
be "category" rated. OSHA is likely to take a dim view of using not-cat
rated meters on high capacity circuits, particularly if there is an
injury. Fluke is likely to be cat rated. Not sure any Simpson 260s are.
Digital is also nice because it is more compact. (I coveted a 260 when I
was about jr high school and finally got one at a garage sale recently.)
I do not know what year the cat ratings came out. The Simpsons I have are
way too old for that. Where I work the meters are furnished by the company
and the Flukes are rated for cat 3 and 4 if you have the fuses in them Fluke
recommends for replacement if blown. I have seen a few films on arc flash.
We even have a long coat and face shield to use while working on some
circuits. There are differant levels of protection ranging from long sleeve
natural fiber shirts to heavy coats and face protection.
While I would use one around the house, I am not sure what the ratings if
any are on the meters that I have seen sell for around $ 5 to $ 15.
I just would not use one on the stuff where I work that has very high
current capacity. I do feel safe with the old Simpsons and the newer ones
do have a cat rating.
If you want to see something scarry, I have a few pix of the after math of a
460 volt 3 phase motor starter panel that blew up when a 15 amp breaker was
turned on. It was fed with a main breaker of about 600 amps.
I did not turn it on or see it hapen,but it was where I work.
One of the smartest electricians I know wanted to measure the current
for a motor in a food processing plant. It was a possibly explosive
atmosphere so there was a motor control center in a purged room. He
defeated the interlock on the module door and amp-clamped a motor wire -
an absolutely standard procedure. No one knows what happened - maybe a
loose screw faulted the busbars, but there was an arc flash. He was
badly injured (including condensed copper on him) and was in the
hospital quite a while. The facility was buying distribution voltage
power from the utility and one of the fuse holders was destroyed in the
event - I have no idea how that could happen. (Arc flash was not an
issue back then.)
At a trade show a manufacturer field engineer had a seminar. As an
aside, he was working for a major company like Westinghouse and the
client wanted a module for a motor control center or switchgear. The
space was open so he was measuring the size with a steel tape. The next
thing he knew he was on his back on the other side of the room. If he
hadn't been thrown he might be dead. At least in that case he did
something dumb.
Some of the required inservice classes have covered arc flash. They had
an arcflash suit - pants, top, hood and gloves. (And the protection
includes the natural fiber clothes inside.) Don't know how you do useful
work in something like that. Someone brought in copies of the labels at
his facility that are required to evaluate what protection is required.
One of them said something like "No safe approach is possible" (with
protective panels removed).
The default standard for worker electrical safety is NFPA 70E. Your
plant must have a copy and I wouldn't be surprised if you have read it.
Interesting information on what protection is required for different
voltages and available fault currents.
At his day job, one of the instructors of our nightly apprentice
program at the International Brotherhood of Electrical Workers put a
wiggy on the line terminals of a 4160V switch gear once. As a
reminder, a wiggy is good for 600V.

This did not end well. I don't remember the details, but I have heard
the story a thousand different times.
///////
When I was an apprentice, my roommate was also an apprentice. He
worked for a very small company. The company was dad, son and my
roommate. The son was changing a buss fuse under load. When the two
maintenance workers that were in the area because of the outage became
aware of what the son was doing, they ran for the door. I am told
that both maintenance workers were burned on their back half of each's
bodies as they had made it to the door and were each half shielded by
the door jam as they left the room. The son was killed. He was an
experienced electrician. The rush to restore power to the building
cause him to make the error.
http://en.wikipedia.org/wiki/Peachtree_25th_Building

* wiggy = voltage tester (solenoid)
c***@snyder.on.ca
2012-05-17 03:48:28 UTC
Permalink
Raw Message
On Wed, 16 May 2012 13:00:35 -0400, "Ralph Mowery"
Post by Ralph Mowery
Post by t***@optonline.net
Post by Ralph Mowery
Many times there is no neutral at the light switch or if it is, it is not
broken and easy to get a meter lead on.
I also try not to test to ground as sometimes the ground wire is left out.
Well if you don't like using ground and a neutral is no
good because you have to take off a wire nut, how
would you propose to do the test?
Often in a light switch there is no neutral to have a wire nut to take off.
If there is no neutral or I suspect the ground is not connected, I use what
some may call a 'hot stick'. It is a device about the size of a cigar that
lights up and/or beebs when held next to a wire that has voltage on it.
Cutting the breaker off and on while using the hot stick usually confirms
there is power or no power at the switch. Then with the power off, I check
the switch using the ohms fuction.
I often use a Simpson 260 because I do not like the digital meters for
general testing due to the 'phantom' voltages. Another favorite is a Fluke
T2. I think that is the number. It has about 10 LEDs in it. It will check
from about 6 volts to 600 volts AC/DC and also low resistances. Just hook
up the test leads and it will show if you have power or a short.
I do admitt that I have several differant testers that most home owners do
not normally have or really need.
I also have a Fluke 87 digital meter, but seldom use it for electrical test
due to the 'phantom ' voltages. I work in industry where I have to deal
with anything from low voltage control and instruments to 480 volt 3 phase
circuits. That is the reason for having those plus several other testing
devices.
The simple old neon tester is still the simplest troubleshooter for
domestic wiring - the old solenoid tester to determine what line
voltage you are working with (usually 24 to 600)
c***@snyder.on.ca
2012-05-17 03:43:22 UTC
Permalink
Raw Message
On Wed, 16 May 2012 11:57:44 -0400, "Ralph Mowery"
Post by Ralph Mowery
Post by t***@optonline.net
I would have tested for 120V using one test lead
on the light side of the switch and the other held
to ground. I'd use ground because that's usually
there and available without taking anything apart.
Or he could have tested from the light side of
the switch to neutral.
Many times there is no neutral at the light switch or if it is, it is not
broken and easy to get a meter lead on.
I also try not to test to ground as sometimes the ground wire is left out.
In which case you will still have a "capacitive ground" which will
give an (inaccurate but more or less consistent) reading. The test
will still tell you if the switch is working or not. A simple neon
tester will do the same, using your pinkie as ground.
c***@snyder.on.ca
2012-05-17 03:40:45 UTC
Permalink
Raw Message
Post by t***@optonline.net
Post by HeyBub
Post by c***@snyder.on.ca
Post by Ralph Mowery
It is often normal to get strange readings with a digital meter, as
someone said, too much to go into here.  Short answer is the wiring
is acting like a capacitor or transformer and the high impedance of
the meter is picking up voltage with a very small current.  Almost
any load and the voltage will dissapear..  If the bulb was still in
the circuit, it may be a small ammount of feed through in the CFL.
Short answer is the voltmeter was not being used properly, and the
longer answer is nobody else here caught it.
Nothing to do with inacuracies of digital meters - totally a case of
not knowing how to use a meter to troubleshoot -  or knowing how to
interpret the readings when the meter is mis-connected.
The readings are accurate
The readings are NOT accurate. The indicated voltage is a phantom.
Consider your assertion that the meter is "mis-connected:" The meter has two
probes. There are two wires. There are two and only two possible ways to
connect the meter and the wires. Which of the two, according to you, is the
correct way to connect all this stuff? If both of the two possibilities
yield the same result, where is the "mis-connection"?- Hide quoted text -
- Show quoted text -
I would have tested for 120V using one test lead
on the light side of the switch and the other held
to ground. I'd use ground because that's usually
there and available without taking anything apart.
Or he could have tested from the light side of
the switch to neutral.
Correct.
c***@snyder.on.ca
2012-05-17 03:18:07 UTC
Permalink
Raw Message
Post by HeyBub
Post by c***@snyder.on.ca
Post by Ralph Mowery
It is often normal to get strange readings with a digital meter, as
someone said, too much to go into here. Short answer is the wiring
is acting like a capacitor or transformer and the high impedance of
the meter is picking up voltage with a very small current. Almost
any load and the voltage will dissapear.. If the bulb was still in
the circuit, it may be a small ammount of feed through in the CFL.
Short answer is the voltmeter was not being used properly, and the
longer answer is nobody else here caught it.
Nothing to do with inacuracies of digital meters - totally a case of
not knowing how to use a meter to troubleshoot - or knowing how to
interpret the readings when the meter is mis-connected.
The readings are accurate
The readings are NOT accurate. The indicated voltage is a phantom.
Consider your assertion that the meter is "mis-connected:" The meter has two
probes. There are two wires. There are two and only two possible ways to
connect the meter and the wires. Which of the two, according to you, is the
correct way to connect all this stuff? If both of the two possibilities
yield the same result, where is the "mis-connection"?
OK Bub - I'm make it REAL simple. And I'll type slowly so you can
understand. A switch is in series with the load. The switch has 2
contacts. Both contacts are on the "live" wire, because the neutral is
not switched. The OP measured the voltage from one terminal of the
switch to the other. IF the bulb was not in the socket, the voltage
would be ZERO, with the switch on or off. If there was an incandescent
bulb in the socket, the voltage would be line voltage - roughly 120
volts, with the switch OFF, and ZERO with the switch on. - if the
switch was any good.

However, the OP had a CFL in the socket, so thecapacitance etc. of the
electronic ballast was dropping about 40 volts across it with the
extremely low current flowing through the meter - and because the
switch was shot, the reading was the same both ways. If the switch had
been good, he would have found 80 volts across the open switch, and
ZERO across the closed switch, with the CFL lit.

The CORRECT way to test the line voltage is line to neutral, or line
to ground. If there is any ground at all the digital meter will read
the same either way, within a tenth of a volt,

I happen to have made my living using test meters for quite a few
years, so I knowwhat the OP did, what he should have done, and exactly
what the meter readings he gor mean.

You obviously do not.
charles
2012-05-16 01:26:25 UTC
Permalink
Raw Message
Post by TimR
The back porch light stopped working, a new bulb didn't help.
So. I put a meter on the socket. 0 V.
I pulled the switch plate off (just a normal single pole). 80 V
terminal to terminal. Hmmm?
Killed the power, put an ohmeter terminal to terminal, infinite
resistance at both switch positions. Diagnosis bad switch, supported
by the fact that before it died completely, flipping the switch
several times made it work. Besides I've always had a CFL in that one
and I suspect the capacitor shortens the switch life due to arcing.
Okay, a new switch is $1.29, no big loss if wrong. Took the old
switch off, turned the power back on and checked wire to wire just for
grins, still 80 V. Uh oh.
Put the new switch in. Turned power on, checked the socket, 120 V.
Put bulb in, (CFL), lights up fine.
Well, I have a working porch light again, but I'm left with the 80 V
mystery. I don't know any way to get 80 V on a normal residential
power setup. The meter was a digital Radio Shack multimeter. If I'd
had time I'd have checked again with the Simpson analog, digitals
sometimes give funny readings, but I've never seen 80 V. What am I
missing?
I had odd readings like that on one circuit, by coincidence a porch
light. Trouble turned out to be an open neutral wire, a staple had
damaged the romex and it finally, after years, gave up.
c***@snyder.on.ca
2012-05-16 01:43:42 UTC
Permalink
Raw Message
Post by TimR
The back porch light stopped working, a new bulb didn't help.
So. I put a meter on the socket. 0 V.
I pulled the switch plate off (just a normal single pole). 80 V
terminal to terminal. Hmmm?
Killed the power, put an ohmeter terminal to terminal, infinite
resistance at both switch positions. Diagnosis bad switch, supported
by the fact that before it died completely, flipping the switch
several times made it work. Besides I've always had a CFL in that one
and I suspect the capacitor shortens the switch life due to arcing.
Okay, a new switch is $1.29, no big loss if wrong. Took the old
switch off, turned the power back on and checked wire to wire just for
grins, still 80 V. Uh oh.
Put the new switch in. Turned power on, checked the socket, 120 V.
Put bulb in, (CFL), lights up fine.
Well, I have a working porch light again, but I'm left with the 80 V
mystery. I don't know any way to get 80 V on a normal residential
power setup. The meter was a digital Radio Shack multimeter. If I'd
had time I'd have checked again with the Simpson analog, digitals
sometimes give funny readings, but I've never seen 80 V. What am I
missing?
80 volts terminal to terminal on the switch means 80 volt drop across
the bulb. Same with switch o or off means the switch was no good. Feed
to ground would read approxemately 120 volts. With bad switch load to
ground would read zero. Good switch, load to ground 120.
HeyBub
2012-05-16 11:52:30 UTC
Permalink
Raw Message
Post by c***@snyder.on.ca
80 volts terminal to terminal on the switch means 80 volt drop across
the bulb. Same with switch o or off means the switch was no good. Feed
to ground would read approxemately 120 volts. With bad switch load to
ground would read zero. Good switch, load to ground 120.
Huh?

By definition, with a functioning switch energized, both sides MUST read the
same and that "same" must be zero. With the switch in the OFF position, and
using a digital voltmeter, you can get any reading from zero to 120.
c***@snyder.on.ca
2012-05-17 03:26:22 UTC
Permalink
Raw Message
Post by HeyBub
Post by c***@snyder.on.ca
80 volts terminal to terminal on the switch means 80 volt drop across
the bulb. Same with switch o or off means the switch was no good. Feed
to ground would read approxemately 120 volts. With bad switch load to
ground would read zero. Good switch, load to ground 120.
Huh?
By definition, with a functioning switch energized, both sides MUST read the
same and that "same" must be zero. With the switch in the OFF position, and
using a digital voltmeter, you can get any reading from zero to 120.
You don't read to good, Bub. I said from one terminal of the switch to
GROUND or neutral. Live side th ground will always be aprox 120.
Switched side to ground will be zero with the switch off, and 120 with
the switch on, with a functioning switch, reguardless of load.
Terminal to terminal on the switch will read zero with the switch
turned on, and non-zero with it turned off - the non-zero value
depending on the combination of load impedence and meter
impedence(sensitivity) - regardless if it is a digital or analog
meter, and if the nanalog is a symple d.arsenval movement or a VTVM.
The reeding from LINE to NEUTRAL or GROUND will NOT show your phantom
voltage, and the reading across the open switch is NOT phantom.

As for meter connections, you NEVER connect a voltmeter in series with
a load. You ALWAYS connect it ACROSS the load. The OP conected
his/her meter IN SERIES with the load, so it was acting as an ameter
but reading in volts, which didn't really mean anything (without
knowing the exact sharacteristics of the meter in question)
Stormin Mormon
2012-05-16 01:43:50 UTC
Permalink
Raw Message
Sometimes, with no load, a digital meter will pick up a
"ghost load" reading. Or ghost voltage, can't remember.
The two wires next to each other have a very slight
transformer effect. Not enough to light a bulb, but
enough to read with a DMM.

Christopher A. Young
Learn more about Jesus
www.lds.org
.

"TimR" <***@aol.com> wrote in message news:2fad4ded-a0ce-4fae-9166-***@j25g2000yqn.googlegroups.com...
The back porch light stopped working, a new bulb didn't help.

So. I put a meter on the socket. 0 V.

I pulled the switch plate off (just a normal single pole). 80 V
terminal to terminal. Hmmm?

Killed the power, put an ohmeter terminal to terminal, infinite
resistance at both switch positions. Diagnosis bad switch, supported
by the fact that before it died completely, flipping the switch
several times made it work. Besides I've always had a CFL in that one
and I suspect the capacitor shortens the switch life due to arcing.

Okay, a new switch is $1.29, no big loss if wrong. Took the old
switch off, turned the power back on and checked wire to wire just for
grins, still 80 V. Uh oh.

Put the new switch in. Turned power on, checked the socket, 120 V.
Put bulb in, (CFL), lights up fine.

Well, I have a working porch light again, but I'm left with the 80 V
mystery. I don't know any way to get 80 V on a normal residential
power setup. The meter was a digital Radio Shack multimeter. If I'd
had time I'd have checked again with the Simpson analog, digitals
sometimes give funny readings, but I've never seen 80 V. What am I
missing?
N8N
2012-05-16 12:16:22 UTC
Permalink
Raw Message
Post by TimR
The back porch light stopped working, a new bulb didn't help.
So.  I put a meter on the socket.  0 V.
I pulled the switch plate off (just a normal single pole).  80 V
terminal to terminal.  Hmmm?
Killed the power, put an ohmeter terminal to terminal, infinite
resistance at both switch positions.  Diagnosis bad switch, supported
by the fact that before it died completely, flipping the switch
several times made it work.  Besides I've always had a CFL in that one
and I suspect the capacitor shortens the switch life due to arcing.
Okay, a new switch is $1.29, no big loss if wrong.  Took the old
switch off, turned the power back on and checked wire to wire just for
grins, still 80 V.  Uh oh.
Put the new switch in.  Turned power on, checked the socket, 120 V.
Put bulb in, (CFL), lights up fine.
Well, I have a working porch light again, but I'm left with the 80 V
mystery.  I don't know any way to get 80 V on a normal residential
power setup.  The meter was a digital Radio Shack multimeter.  If I'd
had time I'd have checked again with the Simpson analog, digitals
sometimes give funny readings, but I've never seen 80 V.  What am I
missing?
If you measured across the two wires that were connected to the
switch, you're measuring the potential from hot *through the bulb* to
neutral. If you want to sleep better, pull the switch off again and
measure from hot to ground, you should then read 120V or thereabouts.
If the bulb is a CFL there may be some odd effects causing an
incorrect voltage reading the way you measured it.

nate
TimR
2012-05-16 15:19:29 UTC
Permalink
Raw Message
I started with the assumption the switch was bad, did the checking
mostly out of curiosity (and of course, when trying to figure out
which breaker controls the circuit and the light is NOT working, it's
handy to have a way to know).

And yes I've had trouble with digital meters and phantom results on no
load circuits, that's why I asked (and why I have a Simpson on the
shelf, but unwinding all those probe wires is a pain, not as bad as
winding them up to get them back in the case though).

But on 120 V circuits normally that meter reads okay or floats a bit.

I left out a couple of things. The fixture had no lamp in it, so that
circuit should be open. The kitchen lights are on the same circuit,
they went out when I got the right breaker (if I'd known that ahead of
time I wouldn't need a meter, technically).

The 80V terminal to terminal on the switch was with the switch off AND
no lamp in the fixture. With switch on, it went to 0 as I'd expect.
It was consistent with several measurements and was the same as wire
to wire with the switch removed (and still no lamp in the fixture).
That surprised me. And then when I went outside and put the same
meter on the fixture and got 120 V I was suprised again.

After work tonight I'll put the analog on it and see.
Ralph Mowery
2012-05-16 15:35:19 UTC
Permalink
Raw Message
Post by TimR
The 80V terminal to terminal on the switch was with the switch off AND
no lamp in the fixture. With switch on, it went to 0 as I'd expect.
It was consistent with several measurements and was the same as wire
to wire with the switch removed (and still no lamp in the fixture).
That surprised me. And then when I went outside and put the same
meter on the fixture and got 120 V I was suprised again.
After work tonight I'll put the analog on it and see.
One thing that you can also try with the analog is to set it to the highest
voltage scale. If you show anything that is less than the next scale down,
switch to that scale, the meter will stay almost the same physical place if
a 'phantom voltage', you can then go to the next lower scale and the meter
will not move much from the same physical point.
The actual voltage the meter reads will be differant, but the physical
point will not move much.


This digital vers analog comes up almost as much as the WD-40 being oil or
not.
Metspitzer
2012-05-16 16:35:14 UTC
Permalink
Raw Message
Post by TimR
I started with the assumption the switch was bad, did the checking
mostly out of curiosity (and of course, when trying to figure out
which breaker controls the circuit and the light is NOT working, it's
handy to have a way to know).
Test the bad switch with an ohm meter
Post by TimR
And yes I've had trouble with digital meters and phantom results on no
load circuits, that's why I asked (and why I have a Simpson on the
shelf, but unwinding all those probe wires is a pain, not as bad as
winding them up to get them back in the case though).
But on 120 V circuits normally that meter reads okay or floats a bit.
I left out a couple of things. The fixture had no lamp in it, so that
circuit should be open. The kitchen lights are on the same circuit,
they went out when I got the right breaker (if I'd known that ahead of
time I wouldn't need a meter, technically).
The 80V terminal to terminal on the switch was with the switch off AND
no lamp in the fixture. With switch on, it went to 0 as I'd expect.
It was consistent with several measurements and was the same as wire
to wire with the switch removed (and still no lamp in the fixture).
That surprised me. And then when I went outside and put the same
meter on the fixture and got 120 V I was suprised again.
After work tonight I'll put the analog on it and see.
c***@snyder.on.ca
2012-05-17 03:45:52 UTC
Permalink
Raw Message
Post by Metspitzer
Post by TimR
I started with the assumption the switch was bad, did the checking
mostly out of curiosity (and of course, when trying to figure out
which breaker controls the circuit and the light is NOT working, it's
handy to have a way to know).
Test the bad switch with an ohm meter
That works - but you need to turn the power off for that test. The
voltmeter test requires removing the switch plate - and that is all
-unless you can't get your test lead to the terminals without
loosening the switch from the box - but the troubleshooting can all be
done live.
N8N
2012-05-16 18:32:00 UTC
Permalink
Raw Message
Post by TimR
I started with the assumption the switch was bad, did the checking
mostly out of curiosity (and of course, when trying to figure out
which breaker controls the circuit and the light is NOT working, it's
handy to have a way to know).
And yes I've had trouble with digital meters and phantom results on no
load circuits, that's why I asked (and why I have a Simpson on the
shelf, but unwinding all those probe wires is a pain, not as bad as
winding them up to get them back in the case though).
But on 120 V circuits normally that meter reads okay or floats a bit.
I left out a couple of things.  The fixture had no lamp in it, so that
circuit should be open.  The kitchen lights are on the same circuit,
they went out when I got the right breaker (if I'd known that ahead of
time I wouldn't need a meter, technically).
The 80V terminal to terminal on the switch was with the switch off AND
no lamp in the fixture.  With switch on, it went to 0 as I'd expect.
It was consistent with several measurements and was the same as wire
to wire with the switch removed (and still no lamp in the fixture).
That surprised me.  And then when I went outside and put the same
meter on the fixture and got 120 V I was suprised again.
After work tonight I'll put the analog on it and see.
Well if the fixture had no lamp in it you should have read 0V no
matter the position of the switch. The 80V you read was some kind of
phantom voltage.

nate
TimR
2012-05-16 23:40:50 UTC
Permalink
Raw Message
Well, I tried again.

I actually do know how wiring normally works, but that doesn't prevent
me from having a brain fart in the middle of a project.

So, bulb (CFL) in, take some measurements off the two terminals of the
switch. (note, neither switch nor box appears to be grounded; with
switch off I can't pull any voltage from either terminal to box or
ground screw on switch, and only two wires enter the box, both look to
be #12 solid, one black and one white)

Switch on. Both terminals should be at same potential, meters should
read zero. Simpson 270 reads 0, R/S digital reads roughly 10 - 14,
floats a bit.

Switch off. One terminal should be hot, one terminal should be
grounded through the lamp. Simpson reads 124, digital reads 121.

Okay, now unscrew the bulb and repeat.

Switch on, meters should read 0. Yup, both do.

Switch off. What should they read? One is hot with respect to
ground, but there is no ground in the box. The other is nothing, it
is theoretically not grounded through the lamp but just a piece of
metal in thin air. No current could flow, so intuitively the voltage
difference should be zero, but I guess since we really don't know what
potential that wire is sitting on it could be anything.

R/S digital reads 84 V. Simpson reads 25 V.

Which, if either, is real? The R/S will sometimes give me 10 V on
just one probe, if the other is capacitatively coupled, but I've never
seen phantom voltages off the analog.

I guess the test would be to put a load on and see if I could draw a
current, but I've spent enough time on this and there are other
honeydoes to get to.
c***@snyder.on.ca
2012-05-17 03:40:13 UTC
Permalink
Raw Message
Post by TimR
I started with the assumption the switch was bad, did the checking
mostly out of curiosity (and of course, when trying to figure out
which breaker controls the circuit and the light is NOT working, it's
handy to have a way to know).
And yes I've had trouble with digital meters and phantom results on no
load circuits, that's why I asked (and why I have a Simpson on the
shelf, but unwinding all those probe wires is a pain, not as bad as
winding them up to get them back in the case though).
But on 120 V circuits normally that meter reads okay or floats a bit.
I left out a couple of things. The fixture had no lamp in it, so that
circuit should be open. The kitchen lights are on the same circuit,
they went out when I got the right breaker (if I'd known that ahead of
time I wouldn't need a meter, technically).
The 80V terminal to terminal on the switch was with the switch off AND
no lamp in the fixture. With switch on, it went to 0 as I'd expect.
It was consistent with several measurements and was the same as wire
to wire with the switch removed (and still no lamp in the fixture).
That surprised me. And then when I went outside and put the same
meter on the fixture and got 120 V I was suprised again.
After work tonight I'll put the analog on it and see.
OK - I read it that you checked the voltage at the socket and found
zero, replaced the bulb and checked the voltage across the switch,
which read 80 with the switch on and off - then you replaced the
switch and got 80 and zero, and the light worked.

If, as you state now, the 80 volts was with the bulb removed,
capacitive coupling was giving you the 80 volts. (which happens not
only with digital meters, but with "sensitive" analogs as well.

You DO understand that you were not using the meter correctly? The
CORRECT measurement is line to neutral - or in absense of an available
neutral connection, line to ground. With a high impedence meter (like
most digitals) you can substitute your damp finger for ground and
usually end up within a couple of volts of accurate due to the high
capacitance of your body coupling to ground (and NO danger of a
shock).

A good switch will read line votage on the line side, both on and
off, and zero volts (or extremely close) on the load side with switch
off and load connected, and line voltage with switch on - load or no
load. I specify load connected on the OFF position because you can
get those "phantom" voltages on a "disconnected" lead - which will
dissapear if the wire is grounded through the load.
TimR
2012-05-17 12:44:59 UTC
Permalink
Raw Message
 If, as you state now, the 80 volts was with the bulb removed,
capacitive coupling was giving you the 80 volts. (which happens not
only with digital meters, but with "sensitive" analogs as well.
I'm following you, and agree, but with a caveat or two, because you're
making assumptions that are not explicit.

One is that there is no real voltage in the circuit. That is not a
given. There can be sources connected accidentally that give real
voltages between the 0 and 120 references. E.G., transformers for
doorbells (it is at the back door),

Another is, coupling to what? Hot is 120 referenced to neutral (there
is no such thing as voltage, only voltage difference) but while ground
SHOULD be the same as neutral, unless forced it may not be. The
coupling can be to ground which may be at various potentials, or at
some other object in the area - my aluminum screen door right next to
it, etc.

I didn't know analog meters could have that problem, I've always
assumed when I was getting weird readings off a digital it was better
to dig out the Simpson. And cart around ten pounds of meter instead
of five ounces. Hee, hee.
 You DO understand that you were not using the meter correctly? The
CORRECT measurement is line to neutral - or in absense of an available
neutral connection, line to ground.
Well, yeah, I'll concede that one. When I opened the box I figured
I'd check both sides of the switch to ground, and I'd find one leg hot
and the other not, but of course there was no ground. And since
you're supposed to switch only a hot, no neutral either. (I knew
there was no power at the fixture, I wanted to check power to the
switch, hoping I wouldn't have to trace back any further) I guess in
hindsight I should have run a jumper to the nearest solid ground and
checked that way instead.

But it's not really correct to say I was using it as an ammeter. An
ammeter measures current in a circuit. With the meter in series, that
10 million ohm resistance is effectively an open circuit, no current
can flow. And with the bulb removed, the circuit should have been
broken at an additional place.
t***@optonline.net
2012-05-17 13:35:49 UTC
Permalink
Raw Message
Post by TimR
 If, as you state now, the 80 volts was with the bulb removed,
capacitive coupling was giving you the 80 volts. (which happens not
only with digital meters, but with "sensitive" analogs as well.
I'm following you, and agree, but with a caveat or two, because you're
making assumptions that are not explicit.
One is that there is no real voltage in the circuit.  That is not a
given.  There can be sources connected accidentally that give real
voltages between the 0 and 120 references.  E.G., transformers for
doorbells (it is at the back door),
Another is, coupling to what?  Hot is 120 referenced to neutral (there
is no such thing as voltage, only voltage difference) but while ground
SHOULD be the same as neutral, unless forced it may not be.  The
coupling can be to ground which may be at various potentials, or at
some other object in the area - my aluminum screen door right next to
it, etc.
I didn't know analog meters could have that problem, I've always
assumed when I was getting weird readings off a digital it was better
to dig out the Simpson.  And cart around ten pounds of meter instead
of five ounces.  Hee, hee.
 You DO understand that you were not using the meter correctly? The
CORRECT measurement is line to neutral - or in absense of an available
neutral connection, line to ground.
Well, yeah, I'll concede that one.  When I opened the box I figured
I'd check both sides of the switch to ground, and I'd find one leg hot
and the other not, but of course there was no ground.  And since
you're supposed to switch only a hot, no neutral either.   (I knew
there was no power at the fixture, I wanted to check power to the
switch, hoping I wouldn't have to trace back any further)  I guess in
hindsight I should have run a jumper to the nearest solid ground and
checked that way instead.
You could have just used a jumper across the
switch as a test and skipped all the meter drama.
TimR
2012-05-17 15:50:20 UTC
Permalink
Raw Message
Post by t***@optonline.net
You could have just used a jumper across the
switch as a test and skipped all the meter drama.- Hide quoted text -
Pretty incomplete test, though.

If I did that and the lamp worked, it would confirm the switch was
bad. But it wouldn't tell me what breaker to use to turn off the
power. True, you CAN replace the switch hot. But there's no point in
doing so when not under production pressure.

If I did that and the lamp did not work, I would not know if I had a
bad lamp, bad fixture, bad switch, or no power to the switch, and I
wouldn't know what breaker to turn off.
c***@snyder.on.ca
2012-05-18 00:55:17 UTC
Permalink
Raw Message
Post by TimR
Post by t***@optonline.net
You could have just used a jumper across the
switch as a test and skipped all the meter drama.- Hide quoted text -
Pretty incomplete test, though.
If I did that and the lamp worked, it would confirm the switch was
bad. But it wouldn't tell me what breaker to use to turn off the
power. True, you CAN replace the switch hot. But there's no point in
doing so when not under production pressure.
If I did that and the lamp did not work, I would not know if I had a
bad lamp, bad fixture, bad switch, or no power to the switch, and I
wouldn't know what breaker to turn off.
No, but in your case, it would have proved you had a bad switch -
and if the jumper was left on when the light went out you would have
known which breaker it was.

I hope you labelled the breaker now that you know what it controls???

You SHOULD have a detailed list showing what is on what breaker.
Ralph Mowery
2012-05-17 20:48:57 UTC
Permalink
Raw Message
Post by TimR
But it's not really correct to say I was using it as an ammeter. An
ammeter measures current in a circuit. With the meter in series, that
10 million ohm resistance is effectively an open circuit, no current
can flow. And with the bulb removed, the circuit should have been
broken at an additional place.
Actually in this case you are sort of using it as an ammeter when you put it
in series with the circuit. That is why I mentioned the 'trick' with the
Simpson of going down scale to see if the meter movement stays about the
same physical place. The impedance of the circuit is high enough that you
are getting an almost constant current of a few micro amps. There is
really no such thing as a pure ammeter or voltmeter. It is just in how you
are using it and how it is calibrated.

If you look at most of the 'good quality' analog meters, they are using a
meter movement of around 50 micro amps and resistors are switched in to make
it show a full scale of whatever is desired. The Simpson has a meter
movement of about 48 microamps (I think that is the number, or close) and
one of the first calibration steps is to adjsut a pot inside the meter so it
shows a full scale at 50 micro amps.

I don't care to do the math right now, but you can calculate how much
impedance it takes to have 10 or 20 micro amps and at what voltage.
If you knew how long the wires are and a few things about the insulation,
you could calculate the capacitance of the wiring and what voltage you
should see. Just way too much to get into here.
c***@snyder.on.ca
2012-05-18 00:45:51 UTC
Permalink
Raw Message
Post by TimR
 If, as you state now, the 80 volts was with the bulb removed,
capacitive coupling was giving you the 80 volts. (which happens not
only with digital meters, but with "sensitive" analogs as well.
I'm following you, and agree, but with a caveat or two, because you're
making assumptions that are not explicit.
One is that there is no real voltage in the circuit. That is not a
given. There can be sources connected accidentally that give real
voltages between the 0 and 120 references. E.G., transformers for
doorbells (it is at the back door),
Another is, coupling to what? Hot is 120 referenced to neutral (there
is no such thing as voltage, only voltage difference) but while ground
SHOULD be the same as neutral, unless forced it may not be. The
coupling can be to ground which may be at various potentials, or at
some other object in the area - my aluminum screen door right next to
it, etc.
I didn't know analog meters could have that problem, I've always
assumed when I was getting weird readings off a digital it was better
to dig out the Simpson. And cart around ten pounds of meter instead
of five ounces. Hee, hee.
 You DO understand that you were not using the meter correctly? The
CORRECT measurement is line to neutral - or in absense of an available
neutral connection, line to ground.
Well, yeah, I'll concede that one. When I opened the box I figured
I'd check both sides of the switch to ground, and I'd find one leg hot
and the other not, but of course there was no ground. And since
you're supposed to switch only a hot, no neutral either. (I knew
there was no power at the fixture, I wanted to check power to the
switch, hoping I wouldn't have to trace back any further) I guess in
hindsight I should have run a jumper to the nearest solid ground and
checked that way instead.
But it's not really correct to say I was using it as an ammeter. An
ammeter measures current in a circuit. With the meter in series, that
10 million ohm resistance is effectively an open circuit, no current
can flow. And with the bulb removed, the circuit should have been
broken at an additional place.
The meter WAS connected AS an ammeter. It was connected IN SERIES
with the load. A voltmeter is connected ACROSS the load.
TimR
2012-05-18 11:41:25 UTC
Permalink
Raw Message
 The meter WAS connected AS an ammeter. It was connected IN SERIES
with the load. A voltmeter is connected ACROSS the load.- Hide quoted text -
In hindsight, I did it wrong.

With no lamp in the fixture, reading across an open switch does not
give meaningful results. Although I guess if it read 120 V then the
line is shorted to ground somewhere between switch and lamp. If it
read 0 V the line could be shorted to hot and the neutral broken - too
many possibilities. (when troubleshooting, I ask 3 questions: what
does it mean, what else could it mean, how can I tell the
difference)

That the meter read anything at all is only due to the line (not the
meter) being coupled to some sink somewhere between ground and hot. I
say not the meter, because the meter didn't read 80 V until touched to
the terminal. Getting that 80 V reading made it easy to find the
breaker, but that was dumb luck; and getting a zero reading would not
have guaranteed the circuit wasn't live.

But an ammeter? Nah. An ammeter is in series with the circuit.
There was no circuit with no lamp. And I would argue there is also no
circuit with the lamp in place and a 10 million ohm resistance
(digital meter) breaking the circuit - that's effectively an open.
Even the 1 million ohm of the analog is pretty close to an open
circuit. Of course that assumes both are set to the voltmeter range;
if either are set to amps then the meter closes the circuit and I'll
agree it's an ammeter. Put a voltmeter into a normal outlet, does it
become an ammeter? Why not, you just closed the circuit, and the
meter is the load?
t***@optonline.net
2012-05-18 12:21:58 UTC
Permalink
Raw Message
Post by TimR
 The meter WAS connected AS an ammeter. It was connected IN SERIES
with the load. A voltmeter is connected ACROSS the load.- Hide quoted text -
In hindsight, I did it wrong.
With no lamp in the fixture, reading across an open switch does not
give meaningful results.  Although I guess if it read 120 V then the
line is shorted to ground somewhere between switch and lamp.   If it
read 0 V the line could be shorted to hot and the neutral broken - too
many possibilities.   (when troubleshooting, I ask 3 questions:  what
does it mean, what else could it mean, how can I tell the
difference)
That the meter read anything at all is only due to the line (not the
meter) being coupled to some sink somewhere between ground and hot.  I
say not the meter, because the meter didn't read 80 V until touched to
the terminal.  Getting that 80 V reading made it easy to find the
breaker, but that was dumb luck;  and getting a zero reading would not
have guaranteed the circuit wasn't live.
But an ammeter?  Nah.  An ammeter is in series with the circuit.
There was no circuit with no lamp.
With capacitive coupling there is indded a circuit. A basic
capacitor is two metal plates seperated by a dielectric
material. There is no DC circuit path, but there sure
is an AC one. In the case of the length of wire that is
open at the other end, it's capacitvely coupled to
other conductors, ground, building metals, etc.
Post by TimR
 And I would argue there is also no
circuit with the lamp in place and a 10 million ohm resistance
(digital meter) breaking the circuit - that's effectively an open.
See the above.
Post by TimR
Even the 1 million ohm of the analog is pretty close to an open
circuit.  Of course that assumes both are set to the voltmeter range;
if either are set to amps then the meter closes the circuit and I'll
agree it's an ammeter.  Put a voltmeter into a normal outlet, does it
become an ammeter?  Why not, you just closed the circuit, and the
meter is the load?
I agree it's hard to make the case that the voltmeter becomes
a ammeter because it's not measuring amps. But with some
finite resistance, it does exist and it's effects on what kind of
circuit you connect it too can't be ignored in all cases. Plug
it into a powered AC outlet and it reads 120V because the
effects can be ignored. Connect it as you did and the
effects can't be ignored. Again, if you understand AC and
DC circuit fundementals, what's going on is easily understood.
TimR
2012-05-18 14:47:16 UTC
Permalink
Raw Message
Post by t***@optonline.net
I agree it's hard to make the case that the voltmeter becomes
a ammeter because it's not measuring amps.  But with some
finite resistance, it does exist and it's effects on what kind of
circuit you connect it too can't be ignored in all cases.  Plug
it into a powered AC outlet and it reads 120V because the
effects can be ignored.  Connect it as you did and the
effects can't be ignored.  Again, if you understand AC and
DC circuit fundementals, what's going on is easily understood.- Hide quoted text -
Theoretically, everything is a circuit. Even the air is a conductor,
and since there an infinite number of paths in parallel, and you have
to allow for resistive, capacitive, and inductive coupling, there is
alwasy current flow.

But in real world practical circumstances any sufficiently large
resistance is an open.

The proof? Simply use two meters in series, one set to voltmeter and
the other to ammeter. Put them between the terminals of an open
switch, or an electrical outlet, and read them both. Especially read
the one set to ammeter.
Post by t***@optonline.net
Again, if you understand AC and
DC circuit fundementals, what's going on is easily understood.-
Oh really? Explain it to me then. Explain why I consistently get 80
V on that circuit. Not why I might get some phantom voltage reading,
with a high impedance meter; I understand that part. I don't
understand why THAT circuit will always read 80 V when open. Show me
the math. Feel free to use Norton or Thevenin equivalents.

I think that you are simply wrong. What is going on is NOT current
flow in a circuit, as you allege, but measurement of voltage potential
difference between two different conductors.
Ralph Mowery
2012-05-18 17:36:28 UTC
Permalink
Raw Message
Post by TimR
Post by TimR
The proof? Simply use two meters in series, one set to voltmeter and
the other to ammeter. Put them between the terminals of an open
switch, or an electrical outlet, and read them both. Especially read
the one set to ammeter.
Outside of them being marked volts or amps, how do you tell which is which ?
any volt meter takes a certain ammout of amps (usually microamps) and any
amp meter will have a certain volt burden. In your example, the high
impedance of the voltmeter will protect the amp meter. The volt meter will
probably read close to 120 volts and the amp meter will show a few
microamps. Whatever the voltage shown on the voltmeter is devided by the
resistance, minus a small ammount for the amp meter burden.

Case in point is the analog meters. They often have a meter of 50 micro
amps for full scale. If that meter is placed across a source that drives it
to full scale , it will always take the same voltage to drive it to full
scale. It could also be marked for that voltage and not for 50 micro amps.
Post by TimR
Post by TimR
Again, if you understand AC and
DC circuit fundementals, what's going on is easily understood.-
Oh really? Explain it to me then. Explain why I consistently get 80
V on that circuit. Not why I might get some phantom voltage reading,
with a high impedance meter; I understand that part. I don't
understand why THAT circuit will always read 80 V when open. Show me
the math. Feel free to use Norton or Thevenin equivalents.
Simple enough to explain. There are is a constant ammount of parallel wires
in the circuit. That makes a capacitor. It will have a constant impedance
at 60 Hz.

If I hook up the Fluke meter I have, I could measuer the capacitance,
calculate the impedance and then with the meter impedance of probably 10 meg
ohms calculate the voltage.
It could also be worked backwards. YOu meter is dropping 80 volts.
Assuming 120 volts at the breaker and the copper wire having zero
resistance, the capacitance reactance is dropping 40 volts. You can then
calculate the capacitor value.
This is the same as if you take a physical capacitor of the same value. Put
one meter lead in the 120 volt socket, the other to the capacitor and the
capacitor back to the neutral..
Post by TimR
I think that you are simply wrong. What is going on is NOT current
flow in a circuit, as you allege, but measurement of voltage potential
difference between two different conductors.
This is simply word games. To measuer the voltage potential differnace with
a common digital or analog meter, there has to be some current flow, in this
case a few micro amps.
If there was no current flow, the meter would not work.
bud--
2012-05-19 14:21:30 UTC
Permalink
Raw Message
Post by Ralph Mowery
Post by TimR
Post by TimR
The proof? Simply use two meters in series, one set to voltmeter and
the other to ammeter. Put them between the terminals of an open
switch, or an electrical outlet, and read them both. Especially read
the one set to ammeter.
Outside of them being marked volts or amps, how do you tell which is which ?
any volt meter takes a certain ammout of amps (usually microamps) and any
amp meter will have a certain volt burden. In your example, the high
impedance of the voltmeter will protect the amp meter. The volt meter will
probably read close to 120 volts and the amp meter will show a few
microamps. Whatever the voltage shown on the voltmeter is devided by the
resistance, minus a small ammount for the amp meter burden.
Case in point is the analog meters. They often have a meter of 50 micro
amps for full scale. If that meter is placed across a source that drives it
to full scale , it will always take the same voltage to drive it to full
scale. It could also be marked for that voltage and not for 50 micro amps.
Minor comment - a 50 microamp meter is "20,000 ohms per volt". On AC
ranges the same meter (including my Simpson 260) is "5,000 ohms per
volt" which is 200 microamps full scale. That means the load on the
circuit is even higher and phantom voltage will be less visible. I
believe the current is higher on AC ranges to get into a more linear
curve on the diodes.
Post by Ralph Mowery
Post by TimR
Post by TimR
Again, if you understand AC and
DC circuit fundementals, what's going on is easily understood.-
Oh really? Explain it to me then. Explain why I consistently get 80
V on that circuit. Not why I might get some phantom voltage reading,
with a high impedance meter; I understand that part. I don't
understand why THAT circuit will always read 80 V when open. Show me
the math. Feel free to use Norton or Thevenin equivalents.
Simple enough to explain. There are is a constant ammount of parallel wires
in the circuit. That makes a capacitor. It will have a constant impedance
at 60 Hz.
If I hook up the Fluke meter I have, I could measuer the capacitance,
calculate the impedance and then with the meter impedance of probably 10 meg
ohms calculate the voltage.
It could also be worked backwards. YOu meter is dropping 80 volts.
Assuming 120 volts at the breaker and the copper wire having zero
resistance, the capacitance reactance is dropping 40 volts. You can then
calculate the capacitor value.
This is the same as if you take a physical capacitor of the same value. Put
one meter lead in the 120 volt socket, the other to the capacitor and the
capacitor back to the neutral..
An additional complication in calculating what is happening is that the
voltages across the meter and capacitance are at 90 degrees.

I agree with both you and trader. It is so simple - once you understand it.

Also explained with a lot less detail but from a "reliable source":
http://www.nema.org/stds/eng-bulletins/upload/Bull_88_reaffirmed_12_15_11.pdf
Post by Ralph Mowery
Post by TimR
I think that you are simply wrong. What is going on is NOT current
flow in a circuit, as you allege, but measurement of voltage potential
difference between two different conductors.
This is simply word games. To measuer the voltage potential differnace with
a common digital or analog meter, there has to be some current flow, in this
case a few micro amps.
If there was no current flow, the meter would not work.
Another way to look at it is the resistance of the meter and the
capacitive reactance are in series and split the voltage (a voltage
divider). The meter measures the voltage drop across the meter
resistance. Might make Tim happier (but is no better than your explanation).


Congratulations (in some cases condolences) on retiring. Sounds like you
had an interesting job.
--
bud--
TimR
2012-05-19 22:14:25 UTC
Permalink
Raw Message
On May 18, 1:36 pm, "Ralph Mowery" <***@earthlink.net> wrote:
YOu meter is dropping 80 volts.
Post by Ralph Mowery
Assuming 120 volts at the breaker and the copper wire having zero
resistance, the capacitance reactance is dropping 40 volts. You can then
calculate the capacitor value.
This is the same as if you take a physical capacitor of the same value.  Put
one meter lead in the 120 volt socket, the other to the capacitor and the
capacitor back to the neutral..
Some of what various posters have pointed out is correct. I did not
think all the way through this problem.

But the above is dead wrong.

You cannot calculate the capacitor value from the above information.

You can assume the hot terminal is at 120 V referenced to neutral.

You CANNOT assume the other terminal is capacitatively coupled to a 0
reference voltage. It is coupled to something, but you don't know
what. Therefore you can't assume 120 - 80 = 40.

The other wire may be coupled to neutral, or it may be coupled to
ground (which may or may not be somewhere near neutral) or it may be
coupled to something else entirely.
bud--
2012-05-20 05:09:00 UTC
Permalink
Raw Message
Post by Ralph Mowery
YOu meter is dropping 80 volts.
Post by Ralph Mowery
Assuming 120 volts at the breaker and the copper wire having zero
resistance, the capacitance reactance is dropping 40 volts. You can then
calculate the capacitor value.
This is the same as if you take a physical capacitor of the same value. Put
one meter lead in the 120 volt socket, the other to the capacitor and the
capacitor back to the neutral..
Some of what various posters have pointed out is correct. I did not
think all the way through this problem.
But the above is dead wrong.
You cannot calculate the capacitor value from the above information.
You can assume the hot terminal is at 120 V referenced to neutral.
You CANNOT assume the other terminal is capacitatively coupled to a 0
reference voltage. It is coupled to something, but you don't know
what. Therefore you can't assume 120 - 80 = 40.
The other wire may be coupled to neutral, or it may be coupled to
ground (which may or may not be somewhere near neutral) or it may be
coupled to something else entirely.
For this problem there is no difference between ground and neutral -
they are at the same potential.

One has to make simplifying assumptions. I think what Ralph wrote is
reasonable. I would assume one end of the capacitive reactance is at
ground/neutral potential.

However, as I wrote, the voltage across the capacitance and the voltage
across the meter resistance are at 90 degrees. If the capacitive
reactance and meter resistance are equal, the voltage across each is
about 84V. Adding 84V to 84V at 90 degrees phase displacement gives
120V. With voltage across the meter at 80V the voltage across the
capacitance is around 89V.

The meter resistance has to be known to calculate further (and I don't
have the ambition to calculate).
--
bud--
TimR
2012-05-21 00:07:38 UTC
Permalink
Raw Message
Post by bud--
For this problem there is no difference between ground and neutral -
they are at the same potential.
There is no valid reason to make that assumption, and I have seen many
real world examples where that assumption was wrong.

Actually, unless forced to be true by very, very good bonding and
grounding practice, it is unlikely to be true.

Now, the ground WIRE in a box very well may be pretty close to the
neutral on any given branch circuit. But this was clearly a case with
no ground wire. And ground itself is a whole different story.
t***@optonline.net
2012-05-21 13:45:58 UTC
Permalink
Raw Message
Post by TimR
Post by bud--
For this problem there is no difference between ground and neutral -
they are at the same potential.
There is no valid reason to make that assumption, and I have seen many
real world examples where that assumption was wrong.
There is a valid reason to make that assumption and it's
because Bud is trying to be realistic and explain what you
are seeing using basic circuit theory. Sure, in many cases
there is a small difference between ground and neutral,
a volt or two. But typically not 80 volts which is what you are
seeing.
And seeing that kind of voltage when using a meter
incorrectly isn't limited to your circuit, it happens frequently.
Post by TimR
Actually, unless forced to be true by very, very good bonding and
grounding practice, it is unlikely to be true.
So, say it's a 10 volt difference. So, what? It doesn't
change the analysis that 3 of us have given you that
explains the AC coupling effect. It just means that on
the other end of the modeling capacitor instead of
being connected to 0 volts, it's now connected to
10 volts. So you have a small capacitor connected
from 120V to 10 volts. Same analysis using
a distributed R,C, L model for the wire still applies.
In this case, we focused on just the C, because unless
something very unusual is going on it's going to be the
dominating factor.
Post by TimR
Now, the ground WIRE in a box very well may be pretty close to the
neutral on any given branch circuit.  But this was clearly a case with
no ground wire.  And ground itself is a whole different story.
We've given you a logical explanation using basic circuit
theory for what you are seeing. What is your explanation
for "phantom voltage" that one sees when using a
meter like you did, ie connecting it between hot and
one end of a long length of AC cable that is open on
the other end?

t***@optonline.net
2012-05-18 17:43:57 UTC
Permalink
Raw Message
Post by t***@optonline.net
I agree it's hard to make the case that the voltmeter becomes
a ammeter because it's not measuring amps.  But with some
finite resistance, it does exist and it's effects on what kind of
circuit you connect it too can't be ignored in all cases.  Plug
it into a powered AC outlet and it reads 120V because the
effects can be ignored.  Connect it as you did and the
effects can't be ignored.  Again, if you understand AC and
DC circuit fundementals, what's going on is easily understood.- Hide quoted text -
Theoretically, everything is a circuit.  Even the air is a conductor,
and since there an infinite number of paths in parallel, and you have
to allow for resistive, capacitive, and inductive coupling, there is
alwasy current flow.
But in real world practical circumstances any sufficiently large
resistance is an open.
Except of course when you're using an instrument that
has a high enough impedance in a way that you will
see those effects. That is exactly what you are doing.
The proof?  Simply use two meters in series, one set to voltmeter and
the other to ammeter.  Put them between the terminals of an open
switch, or an electrical outlet, and read them both.  Especially read
the one set to ammeter.
I have no idea that point you're trying to make here
besides using instruments in very strange ways.
Post by t***@optonline.net
Again, if you understand AC and
DC circuit fundementals, what's going on is easily understood.-
Oh really?  Explain it to me then.  Explain why I consistently get 80
V on that circuit.
Because it's likely capacitive coupling on the
cable run. I think that has been pointed out many
times now, now? There is enough capacitance
there in that open run of wire that together with the high impedance
meter it forms an RC circuit.



 Not why I might get some phantom voltage reading,
with a high impedance meter;  I understand that part.  I don't
understand why THAT circuit will always read 80 V when open.
What exactly do you think a "phantom voltage" is?
Something that can't be explained by electrical circuits
and instead by withcraft? It's only a phantom if
you don't understand circuit basics.



 Show me
the math.  Feel free to use Norton or Thevenin equivalents.
It's most simply modeled as a circuit with one
resistor, that being the multimeter, one
capacitor, that being the distributed capacitance
of the cable, and a voltage source, that being
120V AC.
I think that you are simply wrong.  What is going on is NOT current
flow in a circuit, as you allege, but measurement of voltage potential
difference between two different conductors.
But unless you accept that the one conductor is
acting as a small capacitor in an AC circuit, then
you have no potential on that unconnected wire
going to the empty light bulb socket. If it's just
a perfect conductor with no capacitve effect,
no part of a complete circuit, etc.
then there is no potential difference and you
have no explanation for the 80V you see. When
you start to model it by what it really looks like,
which is a distributed model with R, C, and L,
then the voltage you see is no longer some
mysterious "phantom" voltage, but is instead
explainable by the circuit dynamics and the
meter.
Loading...