Lost a neutral?

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inspector 102

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At our local park ground, there is a pavillion that when the breakers are off, there appears to be 120 volts to panel, but breakers are turned on, voltage drops to about 75 volts. As an inspector, I told them it appears they lost a nuetral, but where would they start looking, supply side or load side of breaker. Any thoughts on how to locate break underground. Megger is the only way I could think of without smoke coming out of the ground. Thanks for any guidance.
 
Could be either a broken/loose neutral or hot from the description. You need to add a load to the circuit then check voltage again. Voltage drop at both line & load side of breaker would indicate the problem is upstream. There are several different ways to find the problem. Unless you have use for the equipment it is probably cheaper to hire the locate done versus buy it for a one time problem. Depending on what type of fault and where, operators that are experienced can find the location within a few inches or closer.
 
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I think maybe you need to 'splain things a little better.

Are you talking about the branch circuit breakers in a panel that is in the pavillion, being fed by the panel's main.

If so how many breakers are you turning on and off? what are they feeding? What's the load? Is the panel fed by # 14 for a half mile?

Is it a 240/120 panel? Are you talking about 120v to neutral on one or both phases? Do you have 240 phase to phase?
 
inspector 102 said:
At our local park ground, there is a pavillion that when the breakers are off, there appears to be 120 volts to panel, but breakers are turned on, voltage drops to about 75 volts. As an inspector, I told them it appears they lost a nuetral, but where would they start looking, supply side or load side of breaker. Any thoughts on how to locate break underground. Megger is the only way I could think of without smoke coming out of the ground. Thanks for any guidance.
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Megger wont tell you where, just if. You need a thumper, best to hire testing company to do this for you.
 
If both legs are dropping when you switch on the main to apply the connected load, it sounds like both hot legs are rotting out someplace. There are lots of gadgets to locate underground breaks, but your situation is different. Your "break" is still semi-conducting. A thumper is the only really good tool for that. Maybe the local utility will do that break locate for you since it's a public park as a bit of community goodwill? Worth an ask. Not so many electrical contractors own thumpers, but testing companies certainly do. How long might this run be? Is it in pipe, by chance? If it's in pipe, I might be inclined to just yank it out and replace it. If not, and it's sufficiently short to make economic sense, I might consider it for replacement rather than repair. The cost of a locate and the subsequent repair can sometimes exceed the cost of replacing some runs.
 
The op says there is 120 volts to the panel. He says nothing about both phases dropping. If I didn't know better I would say this panel has only 120 volts but I think we are not getting enough info.
 
inspector 102 said:
At our local park ground, there is a pavillion that when the breakers are off, there appears to be 120 volts to panel, but breakers are turned on, voltage drops to about 75 volts. As an inspector, I told them it appears they lost a nuetral, but where would they start looking, supply side or load side of breaker. Any thoughts on how to locate break underground. Megger is the only way I could think of without smoke coming out of the ground. Thanks for any guidance.
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Would seem the feeders have a problem unless the load is over on amperage.I suggest they call an electrician.
 
I agree with JimW in Tampa.

I seem to recall one time many moons ago finding or trying to find a bad spot in an isolated, de-energized 2400v underground cable by hooking the cable up to a sparkplug on a running truck engine, and then walking along the approximate route of the buried cable with a transistor radio.

The ticking stopped or started when the grounded spot was found... something like that. I can't remember if that really happened or I dreamed it.

Other times to find a bad wire, we would put 5 a. fuses in the fused disconnect and then go out in the field in a manhole and hold a clamp on ampmeter on the suspect wire while someone shut the door of the fused disconnect with a hot stick. Them babies would crack like a shotgun...

If you had current, you'd split what was left in half and repeat the proceedure until you no longer got current. Then we'd haul the offending piece out with a collapsible wire reel on the pole truck, splice it, and haul 'er back in. The roof on the part of the aircraft hanger near the fused disconnect was covered with blown, and I mean blown fuses.

That might be fun to do with your pavillion.;)
 
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Copperclad said:
Marc, what is your def. of URD? Im just curious.
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Underground residential distribution cable. Some people call it "underground triplex". I know, I know. Medium voltage cable is part of the URD system.
 
mdshunk said:
Underground residential distribution cable. Some people call it "underground triplex". I know, I know. Medium voltage cable is part of the URD system.
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OK,,Thx for your input, I was taught that urd was for med voltage cable, but I can see where underground resi secondary can surely be considered distribution cable.
 
I should have provided more information as stated earlier. This is a 120 volt line served from the underground system inside the park ground. The lighting fixture that is located on the line ahead of the pavilion works just fine. When the line gets to the pavillion, with the breakers (2) in the on position, I get a reading of approx. 75 volts on the load side. Yes we have already contacted a professional underground locating and service company, but I was looking very clues on whether my instinct was correct on the problem. The total run from the light to the pavillion is about 300 yards and is fed by #2 alum conductor. This line is also about 25 years old. Once it gets fixed I will post again and let everyone know the results. Thanks for all the input.
 
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