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An Outlet in the dining room which had a microwave plugged into it stopped working. I found 120+ volts from hot to ground and 96+ from hot to neutral. Also at one point my "three light tester" showed hot-ground reversed at one point, but also good at another point.

After researching on-line I believed the problem to be an open neutral, possibly in a back stabbed outlet or loose neutral wire nut connection. I started by checking all connections on that particular circuit once I isolated it in the breaker box. I replaced both outlets,connecting to the screws not the backstabs. I also rewired light switches by disconnecting the backstabs and re-attaching to the screws although this step, in hindsight, was probably unnecessary.

Eventually I found a two wire (hot and neutral only) ceiling light fixture in an adjacent laundry room (same breaker in panel box). The plastic fixture box has four Neutral wires plus the neutral light fixture and a ground wire all in a single wire nut. When I removed the ground from the connection of five neutrals (four rolex and one light) the light stopped working and I now have 120V from hot to ground but only 16V hot to neutral at the outlet.

I really don't think I want to rewire the ground back into the neutrals and I am thinking I should continue by checking the neutral set screws on the neutral bar in the panel, but I'm a little stumped about the ground that I disconnected and re-attached to the green nut on the light mounting bracket that spans the plastic ceiling box.

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Also I think the right thing to do is find any additional grounds, rewire the grounds together, and pigtail to the mounting strap. T I may need to run a new neutral from the ceiling light neutrals back to the panel box. –  KeninBrandon Apr 24 at 23:24
    
Starting from the box closest to the breaker, check each hot/neut voltage and when you get to the box where it's down to 16v, you know the break in the neutral is at that box or the one previous (or in the wire in-between). –  Paul Apr 25 at 0:03
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It might be time to contact a local licensed Electrician. I think you're beyond the point where anybody on the internet can help you. –  Tester101 Apr 25 at 10:10
    
I have to agree with @Tester101 here. If your neutral wire is showing a high resistance (big voltage drop from 120 to 16), this presents a fire hazard if you continue to use the circuit. –  Paul Apr 25 at 14:21

4 Answers 4

Rarely do wires fail in the middle somewhere. (Well, except for aluminum wire.) Almost certainly the neutral conductor problem is at a junction.

Keep the ground disconnected from the neutral in all places. Shut off the circuit and use a DMM or other ohmmeter along with an adequately long run of wire (any gauge, even telephone wire) to directly measure the resistance of the neutral wire from point to point. In each measurement, deduct the resistance of the test wire.

It should quickly be apparent which run of wire has a problem. Probably, you'll find during measurement that there is a poor connection: once that is cleaned up, everything will work well.

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The ground conductors were probably functioning as your neutral return (just not very well) until you disconnected it at the light. So not only do you have an open (or high resistance) neutral wire, but you also have too much resistance in a ground wire. If you've checked all the boxes and terminals for loose connections, you may have a damaged wire in the structure somewhere. The high resistance will cause heat (and risk of fire) if you continue to use the circuit. I would probably contact someone who has access to test equipment that can diagnose the actual in-wall wiring. (like maybe an infrared thermometer to detect a hot spot, or a voltage detector to trace wires in the walls, or at least an ohmmeter)

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Wow! It looks like someone that predates you in that house was having the same problem and you discovered their quick fix.

Also it sounds like you don't have a small-appliance receptacle circuit in your dining room and maybe not in your kitchen either. If you don't already, and while you're getting that circuit repaired, you might also want to consider getting a new 20amp circuit into your kitchen for a receptacle or two, then maybe you can put the microwave in there.

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I have a similar problem, something my dad and I tried might help:

Shut off the breaker for that circuit and run an extension cord from a live outlet to each receptacle (one at a time) to try to follow the problem.

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I really don't understand what you're suggesting here. –  Chris Cudmore Apr 25 at 19:16
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I think he's suggesting turning off the breaker and backfeeding each outlet with a modified extension cord to see if the circuit starts working in an attempt to try to isolate the fault. Sounds exceedingly dangerous. –  Johnny Apr 25 at 22:07
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Welcome to the site. I share @Johnny's concern that you're suggesting a dangerous process. If that's not what you mean, please edit your answer to be more specific about what you're suggesting. –  TomG Apr 26 at 22:04

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