Induced voltage in circuir that is shut off????

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Thanks -- as pointed out in another post, I ended up tracing problem back to loose wire nut (that was just installed by a licensed electrician no less).
I hope that this explains everything, including the dimly lit compact flourescent, so that there are no other problems I need to look for now that everything seems to be fixed and working properly.
Interesting about the Analog meter -- my parents were going through some of my childhood stuff and found my circa 1974 20+ range Archer multimeter (there were no digital ones then). I would have thrown it out other than for sentimental reasons, though it sounds now like I should keep it!
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writes:

etc.......
in
and
bit
co.
as
generally )

Suggest do the testing as I described anyways just to be certain--though I havent followed this thread completely and so its unclear to me what you did find as the cause.
But yes I do prefer to use the older meters. I dont much care for having to de-cipher phantom readings, or having deal with a scale value that won't settle in to some reading that actually makes sense...with an older meter, the needle generally swings into position reliably and repeatably.
--
SVL





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Good point! I did indeed find 30 volt both hot-to-ground and neutral-to-ground.
However, I believe I can explain the neutral-to-ground voltage very simply. The reason I was opening up the junction boxes in the basement and checking voltages was that I was having some wacky behavior with most of the circuit out but a few of the compact flourescents dimly lit. It turns out that one of the neutrals had slipped out of the wire nut. This could explain the induced current in both the neutral and the hot since with the breaker off they were both effectively "floating".
Let me know though if you think I am missing something.
Thanks.
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blueman wrote:

Roger that, I think you're on track now. If you reconnected that neutral wire nut and left the breaker open I'd bet dollars to donuts that you'd still measure "something", but now less than 30 volts, with that meter between hot and neutral or hot and ground, but nada between neutral and ground. (Because the capacitance between the hot and neutral in that run would form the lower leg of a capacitive voltage divider and shunt some of that stray current to ground.)
Glad you got it fixed though!
Jeff
--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)
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Not if he measured it with a digital meter, no.

Digital meters can read voltages at *extremely* low currents. *Any* device that produces a magnetic field can induce an electrical current on wires that pass near it. Unexpected currents of less than line voltage, when read by digital meters, should be verified with an analog meter before leaping to the conclusion that there is "a serious defect in the home's wiring."
-- Regards, Doug Miller (alphageek at milmac dot com)
Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?
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Doug Miller wrote:

No question that magnetic fields can induce voltages Doug, but they are unlikely to be anywhere near as large as 30 volts in house wiring because the outgoing and return current carrying conductors are so physically close to each other that their magnetic fields cancel almost completely and don't leave much of a net ac magnetic field to induce a voltage in another nearby conductor. And, I would expect that since the ground lead is also in close proximity to the hot and neutral leads in typical house wiring that magnetic field would induce a near equal voltage in it too, bucking out the voltages induced in the other two wires, leaving little voltage to measure between them.
It's genberally capacitive coupling which causes those "phantom low current voltages" on disconnected conductors in houses.
Things can be different in industrial applications where currents can be much higher and the wire runs a lot longer. For example, running a three phase circuit between two boxes in three separate pieces of metal conduit instead of a single larger conduit because a hack installer didn't have any large enough pipe with him (and didn't know any better) might not seem dangerous at first thought. But, as soon as some significant currents are put through those conductors they induce currents in the three conduits, which, since they're electrically onnected together at both ends by the walls of the boxes, act like a shorted 3 phase transformer secondary. The three conduits can get hot and often will start arcing where they join onto the boxes.
At any event, the OP found the problem, an open connection in the neutral lead at a wire nut. The degree of "seriousness" of that defect in his house wiring is debatable.
Peace,
Jeff
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
"As long as there are final exams, there will be prayer in public schools"
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_Even_ with a digital meter. Hint: neutral and ground are _supposed_ to be shorted together at the panel. Unless there's a break in the neutral or ground, even a digital meter shouldn't see that much difference between ground and neutral.
Showing 30V hot to ground or neutral, when the breaker is off, is where the impedance of the meter matters.
[Worst case difference between neutral and ground, assuming the circuit is in operation is about 1.5% (allowable voltage drop at full current thru the neutral).]
The OP's measurement of .7ma is also too high for impedance effects. It'd be a few microamps or less.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
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It takes about 70 volts to set off the neon bulb testers. It also takes almost no current for them. Induced voltage will very easy light them up. I use the testers almost every day at work in a large plant. I have seen the tester light up, read about 100 volts on a Fluke digital meter and about 20 volts on the good old Simpson 260 analog meter . While I don't think it will really hirt you, I can tell you that it will make you hirt yourself, especially if you are hot and sweaty.
If a nutral is loose and feeding back on it, you can get almost the full voltage and almost the full current of the circuit it is connected to.
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