DIY Home Improvement, Remodeling & Repair Forum > DIY Home Improvement > Electrical and Wiring > HOT and NEUTRAL both reading 120V???




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Old 08-04-2010, 12:46 PM  
jsbeckton
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Default HOT and NEUTRAL both reading 120V???

Hello everyone, I have been remodeling an old house for about 4 months and this will be my first post. A contractor moved a wall and the wiring in it, while adding some new recessed lighting and an outlet. He said that the old power supply was in the ceiling which he ran over to the wall where the 3-way switches are.

From the switch box he has wires going to the other switches on the 3-way lights (2 sets) and wires going to the refrigerator receptacle. Everything was working great for about a month and a half an then all of a sudden the refrigerator and lights stopped working. I pulled out the refrigerator and plugged my wiring tester in. The tester read “Hot/Ground reversed”. I then took readings with my mulitmeter and measured ~120V from the hot the ground, ~120V from the neutral to the ground, and obviously 0V between the hot and the neutral. My initial thinking is that there has to be a hot wire touching a neutral somewhere to make that 120V. Is this correct? I have tried changing out all of the switches and the receptacle with no luck.

Curiously, I also found that on the red wires (travelers?) between the 3-way switches there is only an 85V reading between them and the ground while the hot to ground reads 120V.

I have tried everything that I can think of here and still no luck. Anybody have any idea what is going on? Is there any other possibility than a hot/neutral contact somewhere and if so what is the best way to find this because I have checked everything on the circuit that I can think of.

Any help would be GREATLY appreciated!

Thanks in advance.



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Old 08-04-2010, 09:18 PM  
GregC
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Hi, sounds like someone wire both black and white leads to a breaker/fuse? ...creating 240 volt? did you trace back to the breaker box to see if white is attached to breaker/fuse instead or neutral/ground post? Its a thought, hard to understand without looking at it. Worth a try.



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Old 08-05-2010, 07:02 AM  
john4153
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I agree with GregC. There are a lot of possibilities. For example, black could be attached to ground, white and ground to the other terminals, etc. So, there are a lot of questions that might help sort it out.

1) How widespread is the problem in your house? Or, is only one outlet affected?
2) What prompted you to check that outlet?
3) Have you located the circuit breaker or fuse for that outlet?
4) Do you have a wire/circuit tracer. That is, a little tool that you can attach to a wire. It injects an audio signal that you can trace with the appropriate receiver.
5) Have you looked inside the outlet box to see what color wires are attached to what?

Finally, remember that a voltmeter puts almost no load on the circuit being tested. Sometimes, things change with a load. You might consider making something that will apply a load to the circuit being tested. A regular (incandescent) 60W bulb and a couple of alligator clips will work.

John

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Old 08-05-2010, 07:23 AM  
JoeD
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Hot ground reverse is the indication of an open neutral. 120volts measured on the neutral confirms that indication.
Look for a loose connection on the neutral wire. Sounds like the problem is back in the junction box where the feed comes from to the feed the switch box.

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Old 08-05-2010, 08:36 AM  
jsbeckton
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*** UPDATE ***

Found the problem! It turns out that the contractor didn’t mount the lighting wires far enough away from the surface of the joists. When he installed the drywall one of the screws missed the joist and punctured through the wires insulation. After a month it finally tore the insulation enough to short the neutral and the hot causing both to be at 120V upstream of this point. Therefore the problem was the neutral being in contact with the hot, just as I suspected.

Thanks for the replies.

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Old 08-05-2010, 08:40 AM  
jsbeckton
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Quote:
Originally Posted by john4153 View Post
I agree with GregC. There are a lot of possibilities. For example, black could be attached to ground, white and ground to the other terminals, etc. So, there are a lot of questions that might help sort it out.
The hot being attached to the ground woudln't make the neutral line 120V. Also, I couldn't have had a 120V potential between the hot and the ground if this were the case.

Thanks anyways.
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Old 08-05-2010, 08:44 AM  
jsbeckton
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[QUOTE=JoeD;47312]Hot ground reverse is the indication of an open neutral. 120volts measured on the neutral confirms that indication.
Look for a loose conenction on the neutral wire.[QUOTE]

See above, I was able to fix this but still have a question about your post.

When you say open neutral do you mean a neutral not connected to the terminal? How would this cause the neutral line to be 120V? If anything I would expect to have an open circuit and no voltage but I can't imagine how I woudl have 120V on the neutral?

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Old 08-05-2010, 09:40 AM  
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Quote:
Originally Posted by jsbeckton View Post
The hot being attached to the ground woudln't make the neutral line 120V. Also, I couldn't have had a 120V potential between the hot and the ground if this were the case.

Thanks anyways.
I am glad you solved your problem before it caused a much bigger problem.

As for my comment, I was referring to wiring of a single receptacle. If Black is wired to ground and ground to where Black should be (i.e., the connections are reversed at the receptacle), from the receptacle side, you most definitely will see 120 V between what should be hot and ground and between neutral and ground. There will be zero volts (or close to it) between hot and neutral, as hot is actually ground in that situation. That was only one possibility, but it is why I asked whether you had pulled the receptacle from the wall.

A short between white and black should blow the breaker, if it is low resistance. If it is high resistance, you would have detected that by putting a load on the pin with the "wrong voltage," as that would create a voltage drop across the resistance.

John
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Old 08-05-2010, 10:45 AM  
jsbeckton
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Quote:
Originally Posted by john4153 View Post
I am glad you solved your problem before it caused a much bigger problem.

As for my comment, I was referring to wiring of a single receptacle. If Black is wired to ground and ground to where Black should be (i.e., the connections are reversed at the receptacle), from the receptacle side, you most definitely will see 120 V between what should be hot and ground and between neutral and ground.
Ok, sorry I misunderstood what you were saying. I did mention that it was working for over a month so that couldn't have been the problem because it never would have worked in the first place.


If somebody accidentially puts a hot on a receptical ground they should be banned from further work! I can see a hot/neutral reverse but not a hot or neutral on the ground!

(But I am sure it happens...)
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Old 08-05-2010, 05:29 PM  
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Quote:
Originally Posted by jsbeckton View Post
Quote:
Originally Posted by JoeD View Post
Hot ground reverse is the indication of an open neutral. 120volts measured on the neutral confirms that indication.
Look for a loose connection on the neutral wire.
See above, I was able to fix this but still have a question about your post.

When you say open neutral do you mean a neutral not connected to the terminal? How would this cause the neutral line to be 120V? If anything I would expect to have an open circuit and no voltage but I can't imagine how I would have 120V on the neutral?
A neutral not connected somewhere can cause a reading of 120 volts on the neutral to ground. The voltage flow through any device that is plugged in. The device does not work because there is no current flowing.

I also wonder why the breaker did not trip if the white and black were shorted. More likely the white was just cut by the screw.


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