Todays' Service Call (Solve this service call)

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480sparky

480sparky

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OK, let's get one thing out up front: This is a 'solve this service call' thread. It's NOT a "I just posted, so spill the beans" thread. There are others who want to help solve the issue and they're not online ATM, so the solution won't be revealed right away.


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Got a call this morning from the owner of a restaurant. He stated whenever his AC is running, his lights work. But when it turns off, he loses half the building lights.

OK, I think he's lost one leg of the service, so I hop in the war wagon and head there. Two minutes later, he calls back, saying the problem seems to have corrected itself. So I can forget it.

I tell him, No, it sounds like you've got an intermittent problem, and while it's all working fine now, it won't get any better.

Upon my arrival, I pull the cover off the main panel to check voltages............ and the first thing I see is this:

 
OK. Not a solution, but maybe some steps along the path.

1. It sure looks like the conduit is carrying substantial neutral current. When it stops carrying that current, he should have the full raft of compromised neutral problems, not lost leg problems.
2. Less significantly, I wonder what that "spare" lug lying in the bottom of the cabinet once connected to. :)
3. Is this single phase or three phase? With three insulated conductors coming in, the most likely answer is single phase. 120-0-120?
4. The fact that the A/C, presumably 240V, runs at all means that he has not lost an ungrounded leg, even while experiencing the problem.
 
A noodle problem was my first thought. But I couldn't get any weird voltages regardless of which circuits I shut off.... even if I turned off every one of a given phase.

At this point, I made two phone calls. One to the POCO to check their connections. The other to someone I know with an IR camera.
 
Observations:

High-leg Delta, obviously. I see no fourth conductor.

The conduit appears to be carrying neutral current.

A/C should be line-to-line, thus should have no effect on lighting.

A/C affects lighting, should mean a bad line or main breaker pole.

WAG: A/C has a ground fault on a conductor past the contactor.

2nd WAG: A/C blower motor is 120v and has a ground fault.
 
I think I would switch off breakers until the arcing stopped to narrow it down to the culprit circuit.

Either a high resistance ground fault from a hot (not enough to trip breaker) or neutral is bonded (accidentally or intentionally) at the device or somewhere along the way. (Could be a skinned neutral insulation in pipe.)

The grounding is good otherwise there would be no current flow for arc.

Locknut at panel is loose. If the locknut at the panel was tight, no arcing would be visible. (Stating the obvious.)
 
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I can only think of so many reasons current returns on grounds (or mettalics) , which is why i suspect an impared mbj, noodle, or combination of both


~RJ~
 
I can think of a few reasons for neutral current on the nipple. I'm having trouble thinking of a reason that also explains the A/C lighting interaction. I conclude there's more than one problem. Intermittent hot-leg loss along with a resistive ground fault somewhere?
 
LarryFine said:
Observations:

High-leg Delta, obviously. I see no fourth conductor.

The conduit appears to be carrying neutral current.

A/C should be line-to-line, thus should have no effect on lighting.

A/C affects lighting, should mean a bad line or main breaker pole.

WAG: A/C has a ground fault on a conductor past the contactor.

2nd WAG: A/C blower motor is 120v and has a ground fault.
Click to expand...
I agree conduit is likely carrying neutral current. AC is line to line and shouldn't impact line to neutral loads. A/C blower may very well be 120 volts and does change the load balance to neutral when running and would impact 120 volt lighting performance.

First guess would be to check neutral upstream from this point, or even the main termination in this panel that we haven't seen yet. If the conduit locknut were tight this problem may not get noticed until something else failed. If this were metal raceway back to a meter socket it could very easily become neutral path if the neutral failed.
 
jaggedben said:
I can think of a few reasons for neutral current on the nipple. I'm having trouble thinking of a reason that also explains the A/C lighting interaction. I conclude there's more than one problem. Intermittent hot-leg loss along with a resistive ground fault somewhere?
Click to expand...

OK, here's the AC / lighting issue: The owner had it all screwed up in his head.

He noticed the furnace was blowing air, but not cold air. So he checked the breaker. It was tripped. He reset it, and it tripped the breaker feeding the subpanel that had the AC breaker in it. This killed the entire subpanel which had that side of the building's lights in it. We tried resetting it, but it tripped immediately. I crawled up on the roof and took the cover off the compressor. There was a boost capacitor added. So my guess is it was toast and that's what is causing the breaker to trip.... too much current trying to start the compressor.

So we had the owner contact his HVAC guy. But we still have the glow-in-the-dark wiring to deal with.

The POCO arrives and finds the noodle splice at both the weatherhead and at the transformers out on the pole were not correct. It appeared they weren't crimped far enough and we could see burn marks on them. So those were replaced by the POCO.

But we still had arcing after that.
 
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