Intermittent Circuit Failure

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  #1  
Old 12-22-00, 06:08 PM
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I have a circuit that fails frequently. In the past my Three Prong tester showed an "open neutral" indication. I have solved this in the past by removing and reinstalling the affected Circuit breaker in the sub panel. Tonight it failed and I got a "hot/ground reversal" indication on the lights. I shut everything off a the panel and removed/installed the Circuit breaker and I now have an open circuit.

I was told that this could be a "bad bus". Is this common? I have looked for a loose connection in the wall switches and receptacles and have not found anything loose or "burnt".

I am out of ideas and am looking for suggestions

 
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  #2  
Old 12-22-00, 08:19 PM
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Bad Circuit

cegreek,

Man, this is a good one! Can you answer a couple of questions...

1) Does this trouble occur regularly? Is it associated with a particular event, like using a particular appliance on that circuit or at the problem plug?

2) Is the problem outlet the first on the circuit, and is it the only outlet affected?

It could be a bad outlet or a bad wire or termination. Replace the outlet and test.

If that doesn't do it, here are a few suggestions for troubleshooting--do these only if you're both familiar and comfortable with them:

-- power off to the circuit, open up the outlet box, inspect the outlet. If it looks OK, ie, no visible damage, remove the outlet, turn power on and use a DMM and a known good ground (the ground pin of an extention cord plugged into a known/tested good outlet) to check voltage from the conductor--hot to known ground, neutral to known ground, and outlet ground to known ground. You're checking for mis-wires.

You should get 120v, 0v, and 0v. If you see voltage from the N or G to known ground, use a solenoid tester (a Wiggy) or a light bulb with test clips, to check the N-G and G-G for voltage. In many cases, you'll read a voltage to ground from the N and the G when using a DMM although there's no line voltage present. This is because the internal resistance of the meter is so high, you see a "phantom" voltage due to induction from nearby live circuits to the dead one being tested.

--Next, with power off, in turn check the resistance from outlet ground, outlet neutral, and the hot to known ground. You're checking for opens. You should see very low (LT 10 ohms) resistance for the first two and infinity for hot to known ground. Do this test again with someone wiggling the circuit conductors in the panel (kill power to the subpanel first...), and at the outlet. What you're looking for here is a loose connection or a conductor broken inside it's insulation. This is called a "swinger" or intermittant fault, and is a possible cause of your problem.

I think it's possible that when you go to the subpanel and re-seat the breaker on the bus, you move the wires around enough to set things right. Then as current flows and stops in the circuit, the hot and neutral conductors heat up and cool. If either is broken, a gap will open up, so you get an open. This could be happening in any outlet or j-box upstream of the problem outlet.

Let me know what you find with this further testing.

Good luck.
 
  #3  
Old 12-22-00, 09:59 PM
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cegreek,

Reseating the breaker can have no direct effect on an open neutral. The breaker has no connection to the neutral. I agree with CAP in that if this ever works it must be an indirect effect. I suggest you follow CAP's other suggestions.

If you really have an open neutral, you must check everything connected to the neutral (i.e., all outlets and the white wire at the neutral bus bar, and nutted white wires in switch boxes).

Hot ground reversal is terrible. I think you may be bumping some wires around when you are in the panel. Shut off the breaker that feeds this subpanel and make sure all the wires in your panel are run neatly, and that all ground wires are kept well away from the bus bars, and the neutral bar. Make sure all neutral connections are well away from, and electrically isolated from, the panel housing, and from the hot bars. All connections should be tightened very tight -- check the torque. Wiggling wires around should not change anything.

Good luck, and please report back what you find.
 
  #4  
Old 12-22-00, 10:33 PM
Wgoodrich
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I agree with the two previous replies. I suspect a loose neutral on the neutral bar in the panel.

Your reverse polarity changing leads me to believe that the neutral is loose causing the circuit to flow to the end of circuit finding a form of neutral through other loads on that circuit.

Your problems should be solved by going through all connections on the neutral and grounding bar. I also think your hand is moving a wire remaking a connection for a while then the problem reappears.

Let us know how you come out.


Wg
 
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