Weird electrical problem

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I wired my finished basement myself. In general everything was fine, I had it inspected before insulating walls and ceiling and putting drywall. I have been using power in basement for over the year and nothing was wrong. However, on final inspection the electrical inspector and I found a very weird problem that I need now to correct. I have the following wiring diagram in basement:
- dedicated 20 A circuit to basement lighting, total 26 recessed lights 65 W and 50 W - dedicated 20 A circuit for basement rooms receptacles - dedicated 20 A circuit for sump pump - dedicated 20 A circuit for washer / gas dryer - dedicated 20 A circuit sewer ejector pump - dedicated 20 A circuit for basement bath - dedicated 20 A circuit for garage receptacles - 50 A basement workshop sub-panel powering 5 dedicated 115 V / 20 A, 2 220 V / 20 A shop receptacles circuits, and 1 15 A shop lights circuit
When I switched off basement room receptacles circuit breaker while all others except sub-panel which does not seem to affect the problem were on we found there is 8 V power in that circuit. Switching off some of other circuits reducing this voltage to about 2 V and only switching off all new circuits brings disconnected voltage to zero as it should be.
Can anyone give me a clue what cane be a source of this weird residual voltage in disconnected circuit?
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Alexander Galkin wrote:

Your probably using a modern DVM with a very high impedance input to measure your voltage readings. Your reading a Phantom voltage caused by the voltage induced by adjacent wires. Try a load on the circuits and i will bet it goes away. If you had a older analog meter like a simpson 260 i will be you measure zero voltage.
Bob
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Doesn't the question now become why the inspector thought it was a problem?
charls
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Charles Bishop wrote:

No, I think it becomes the inspector, if there really is one, is either an idiot or stupid. Any insptector worth his salt would know what that is, and would put a bulb or something across the wires to see if the voltage goes away. Not only that, I've NEVER seen an inspector with a meter that could read 2V ac or DC! Usually all they have is three LEDs and their heads.
Or, this isn't a real post.
Pop
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Actually, the problem was accidentally discovered by the inspector that had usual bulb light tester that does not have any scale but just light bulb. So when he plugged in his bulb tester in one of basement room receptacles the light was hardly visible (I bet we had not noticed it if the room was not dark. Then I brought my regular multimeter that I bough in RadioShack and I was able to measure the ~8V AC voltage. The receptacles circuit does not have anything on it except 5 receptacles in one room and two in another room but it wires run in the same switch boxes as two dimmer switches of light circuit. Actually, recessed lights circuit and receptacles circuit are wired using the same 12-3 cable, black wire powers lights and red one receptacles.

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Alexander Galkin wrote:

What kind of "usual bulb light tester" are you talking about? Are you talking about a little thing with three LED's or neon lights something like this:
http://www.inspectortools.com/gfciouttesbu.html
If so, it's a worthless piece of crap way to test outlets. I can't believe inspectors are allowed to use them.
If the inspector didn't use something like that, what kind of bulb and what wattage is the bulb in the tester he did use?
Did you plug in a regular lamp (turned on of course) and at the same time test to see if there was any voltage on the circuit with your multi-meter when the circuit was turned off?
--
Tony


So
> when he plugged in his bulb tester in one of basement room receptacles the
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Tony Miklos wrote:

I don't see how plugging in a lamp that is switched off should make a difference. The outlet itself is an open circuit. A lamp switched off should also be an open circuit. Please explain how the lamp should affect the open circuit voltage? I'm an EE so don't be afraid to get technical.
Matt
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Matt Whiting wrote:

Betcha the lamp was on and the circuit off.
Osmotic voltage (hope you don't mind technical jargon) does something I call "drains."
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JerryMouse wrote:

Ha, ha, ha... Good one.
Matt
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JerryMouse wrote:

Yes, I guess I'll have to learn English! ;-)
--
Tony

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wrote:

everything was fine, I had

putting drywall. I have

nothing was wrong.

I found a very

following wiring

recessed lights 65 W

115 V / 20 A, 2 220

lights circuit

breaker while all

problem were on we

some of other

switching off all new

be.
weird residual

input to

voltage caused by

circuits and i

a simpson

was a problem?
Many inspectors are clueless... especially on the less obvious issues.
Phil Scott

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Sounds as if you are bleeding back some current on a neutral some where. Check polarity issues in the problem circuits.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Keep the whole world singing . . . . DanG (remove the sevens) snipped-for-privacy@7cox.net

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You may be using a digital meter that is so sensitive that it is picking up induced current. Do you have an old analog meter you could try. I suspect it will read 0
--
Joseph Meehan

26 + 6 = 1 It's Irish Math
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Alexander Galkin wrote:

<SNIP>
If you were reading this voltage at the recept with nothing plugged in on that circuit, then the 8V is perfectly normal reading and is due to stray coupling between conductors.
Try the reading again with a lamp or other load plugged in.
Jim
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Speedy Jim wrote:

8V seems high. I rarely see more than a few hundred mV from inductive coupling alone.
To the OP: Did you test every outlet with a tester to verify that all neutrals are connected? I wonder if you have a floating neutral somewhere.
Matt
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Matt Whiting wrote:

Really? I've often seen over 50 VAC, and still with a load as small as a 7 watt night light, it went down to zero VAC.
--
Tony

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Tony Miklos wrote:

Something doesn't jive here. The voltage shouldn't go to zero unless you short circuit the wires. Any light has resistance and any resistance that has current flowing through it will have a voltage across it. The only way the voltage can be zero with current flowing is if the resistance is also zero (a dead short - with a very short piece of wire!).
How are you measuring the voltage? Across what terminals?
Matt
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Matt Whiting wrote:

Are we mixed up again? I thought we were talking about inductive coupling, not a transformer. To keep it in layman's terms, "the voltage ain't got no balls" or *amperage* to back it up. So the slightest load across the outlet will bring it to zero VAC, (close enough for this forum anyway). I've even simply touched across the two meter leads by accident, with no other load on the circuit, and the voltage went from close to 50VAC to below 1 volt. Remember, this is with the circuit off of course, and inductive coupling, not a short or an open neutral, and me as the only load, even with sweaty hands, still probably over 10K ohms.

In the outlet, from hot to neutral, with the night light in the other socket of the same outlet.
--
Tony

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The false indication of voltage caused by a high impedance voltmeter is pretty well known. If that is really the problem, it worries me that the inspector didn't pick up on it.
Charlie
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we
It sounds like transformer pickup between powered and un-powered lines.
I've seen something like this at a school once - except that time the pickup was in an earth wire.. The staff complained of shocks from metal switch plates. The meter said the plate was at 50V wrt earth. It was caused by a poor earth at the distribution board. The "disconnected" earth wire was picking up power from the adjacent power wires - enough to cause an "ouch".
When you pull the breakers the wire from the breaker to the outlets is probably left "floating" and able to pickup some volts but perhaps not much power from adjacent powered lines (or the local radio station or....)
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