Kinda off topic...House electrical issue?

[hk538]

I've noticed during moving one of the wall receptacles, that when the
breaker for that circuit is shut off, I'm still showing 17-19vac on my
meter. Not exactly sure as to why I'm still showing ac on a circuit
that is supposed to be dead. I've checked a few others with the circuit
breaker off and they too are showing 17-19 vac. The only thing I can
figure is maybe some stray inductance or some sort of system ground
problem. I've checked the breakers and everything seems to be fine. 200
amp main with breakers is less than a year old and I've always heard
square-D is good stuff. Not sure....Any ideas?

Thanks,
GW

 

[James Sweet]

I've noticed during moving one of the wall receptacles, that when the
breaker for that circuit is shut off, I'm still showing 17-19vac on my
meter. Not exactly sure as to why I'm still showing ac on a circuit
that is supposed to be dead. I've checked a few others with the circuit
breaker off and they too are showing 17-19 vac. The only thing I can
figure is maybe some stray inductance or some sort of system ground
problem. I've checked the breakers and everything seems to be fine. 200
amp main with breakers is less than a year old and I've always heard
square-D is good stuff. Not sure....Any ideas?

Thanks,
GW

That's normal, if the wire is run parallel to another wire which is live
you can get a significant voltage, though there should be next to zero
current.

Square D is generally pretty good, you should measure the voltage at the
terminals into the main breaker and turn on the A/C, it shouldn't drop
more than a couple volts. If it does then you have a problem somewhere
between the panel and the pole.

 

[[email protected]]

What are you measuring with? If it is a high impedance voltmeter, the
previous poster is completely correct. Connect a 1000 ohm resistor
across the meter terminals. The voltage should be about zero. If it
is not, then there is some serious coupling going on and you chould
check further as there might be a safety issue.

H. R. (Bob) Hofmann

 

[hk538]

Hi Bob,
The meter I'm using has a 10M ohm resistance. 1K rsistor in parallel
with the meter leads, right?...Is this what's referred to as a shunt?
Correct me if I'm wrong.

Thanks again,
GW

 

[Fred McKenzie]

Hi Bob,
The meter I'm using has a 10M ohm resistance. 1K rsistor in parallel
with the meter leads, right?...Is this what's referred to as a shunt?
Correct me if I'm wrong.

GW-

That is correct. You would be turning a 10M Ohm meter into a 1K Ohm meter.

The voltage you measure might be due to leakage current through the
insulation resistance around the breaker. It might also be due to a small
series capacitance between the input and output of the breaker, or a
combination of leakage resistance and capacitance.

Either way, leakage impedance forms a voltage divider with the breaker
input and your meter. Suppose the measured voltage is 10 Volts across a
10M Ohm meter. That means the leakage current is 10/10 microamps = 1.0
microamps. The leakage impedance would be (120-10)/1.0 Megohms =110
Megohms.

Leakage current of 1 microamp would cause a 1K Ohm resistor to develop
about 1000 microvolts, or 0.001 volts. A digital meter might be able to
read this on its most sensitive voltage scale.

Fred

 

[hk538]

Thanks for the information Fred. I really appreciate it. I'm hoping to
have some time tomorrow after a Dr.'s appt to look into this a little
further. Thanks again for the suggestions. Great help.

GW

 

[hk538]

Thanks everyone

GW