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Voltage on the neutral - How? Why?
Asked Feb 28, 2008, 08:04 AM
I've run into a "situation" I'd like advice on.
The job was simply replacing an outlet. Inside the outlet box are 2 12/2 cables with ground. The outlet is a standard 110V, and the top and bottom receptacles are connected (in other words, it has not been severed to form separate-circuit outlets).
My girlfriend started this job before I got there... She turned off the breaker, tested the TOP outlet with a test light, then began removing wires - neutral wires first. And one of them shocked her! So she called me to see if I could find out why.
We shut off main power and removed the old outlet (which was damaged physically, hence the replacement). Then I used a voltmeter to determine that one of the cables was controlled by the original breaker (let's call it "A"). However, with A off, there was still 110V (relative to ground) on BOTH the white and black wires of the second cable in the box.
Only after turning off a second breaker, "B", did the voltage go away.
With A and B off, I put an ohmmeter on the neutral and hot of cable 2 and found it to be in short-circuit.
Now is where it gets funny: With A and B off, all lights and outlets in the bedrooms and living area were off. With A off, B on, but the outlet removed, PART of the bedrooms and living area were still off. Part were on. With A on and B off, the outlets and lights that were off remained off... Suggesting that A does not independently control them.
The only way that everything "works" is when the outlet is reinstalled, or the neutrals and hots are connected.
How can there be 110V on the B neutral line (relative to ground or relative to A's neutral line)... But somehow it doesn't cause a short circuit when A and B are connected via this outlet?
I'm sorry this post may be confusing... I'm confused and I'm physically here seeing it. But any help is appreciated.
I've advised my ladyfriend to seek the help of a pro and see if things are "fine" or are potentially hazardous. We do not know if somebody has rewired this home previously, but we have not messed with any of it.
Note: this is a 1970s home and is fairly simple. There are no 3-way switches, sub-panels, etc in the house. If that helps.
Thanks again, look forward to your help.
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Feb 28, 2008, 09:21 AM
2 things need to be undestood:
1)Think of Hot and neutral going to light, the light works, now cut the neutral, Now the Hot is going through filiment returning on the neutral, 1 neutral will have voltage, the other neutral will be live through the element(or any load on circuit).
2) You probably have a "Multi circuit". That is 2 hots on opposite phases sharing a neutral.
Opening the neutral on these can put 240 Volts to bulbs different appliances and burn them out. Turn off power, connect Neutral, recepticles. Its fine.
Hope their was no damage. Good Luck
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Printers & Electronics Expert
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Feb 28, 2008, 10:42 AM
Just wondering, do any of the white wires have black tape wrapped around them?
Is there more than one switch in your room (any red wires). When you got the broken outlet out for inspection, did you see a Black/Whie pair on the bottom of the outlet and another at the top of the outlet? If the second pair to the top of the outlet are removed, any chance you can guesstimate where they are going.
Normally, you would find power on the lower pair as this is the line in position. Top is the line out and can to the next outlet in the string, or be past of a switch loop that controls an overhead light, or the outlet itself.
One other thing that bothers me, you said that if you turn breaker "A" off, there is still voltage on the the outlet. If you turn off breaker "B" then the circuit is dead. If that is true, then you are getting a 240 feed across the outlet. Have you measured the outlet with both breakers on, with a meter?
That's a critical test at this point in time!
Do you have any bare copper wires that ground the outlet to the gang box?
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Feb 29, 2008, 09:34 AM
I'll measure the outlet today with both breakers on. I bet you're right.
Thanks guys, much appreciated.
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Feb 29, 2008, 01:42 PM
Please don't do the test, Turn off both breakers and hook Neutral back up. Destruction of appliances, lights and fans, or fire may occue, Most are not meant to have 240 volts.
Please turn off both breakers, hook up neutral and your done.
If you are curious, remove Panel cover, turn off those 2 breakers, follow those 2 wires, may be a red and a black, then follow where they leave the panel, see if their is 1 white for the red and black.
If you had 4 circuits that were multicircuits leaving that same conduit, you would have 2 reds, 2 blacks, and 2 whites plus your ground.
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