Kinda off topic...House electrical issue?

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.

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

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

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

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

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

Thanks everyone:-)

GW

Modern high impedance input DVMs are a bit of a pain for measuring household wiring. An old analogue meter with about 1000 ohms per volt is much more use.

Leakage current in home wiring is often due to the presence of power factor correction capacitors in older flourescent light fixtures, and is quite normal

Arfa

And with most SMPS. However, I was meaning testing with no load. UK house wiring is Twin and Earth - all enclosed within a sheath. This is a good system to keep external fields to a minimum, but allows a degree of capacitive coupling which with a high impedance volt meter gives very misleading results.