Service equipment enclosure is energized

[jimingram]

On a service call to repair the boiler circuit I became aware the steel enclosures of the service equipment, meter bank, and house panel were energized. The grounding electrode conductor has 38 amps flowing over it to the incoming cold water pipe. The boiler circuit conductors had burned because the conduit and jbox had overheated due to current flow over them.

It is an apartment building part of a multibuilding complex. It was built in the late sixties, early seventys. The 400 amp, 1 phase, service entrance conductors are in two parallel PVC conduits. They are not properly wired. There are two neutrals and two ungrounded conductors (same phase) in one conduit. There are two ungrounded conductors (same phase), no neutral, in the other conduit.

The conductors land on individual lugs. There is no problem with the lugs (corrosion, tightness.etc.).

The neutral is properly bonded to the enclosure. The pipe clamp on the incoming water pipe needs replacement. I'm assuming it is still operational because of the current flow on the ground wire.

The utility did a visual check on the transformer and found everything in order. An engineer also came out and confirmed the problem. He set up instruments for a couple of days. He said it doesn't look like an open neutral at the transformer. The neutal is carrying the unbalanced load from the service equipment.

He told me to check the other buildings as the problem may be elsewhere.

I would appreciate your suggestions how to resolve this matter

 

[don_resqcapt19]

Jim,
By energized, do you mean voltage to earth or just the fact that you have current flow on the GEC?

The boiler circuit conductors had burned because the conduit and jbox had overheated due to current flow over them.

Is the conduit metallic? Does the boiler have a metal water pipe to it?

He told me to check the other buildings as the problem may be elsewhere.

Are the other buildings in the area bonded to the metal underground water pipe system? Can you shut off the main and check for current on the GEC with the main open? My first guess is an open neutral on another service in the area assuming that the neutral at this service is ok.
Don

 

[ptonsparky]

Are the parrallel neutrals actually carrying current and of equal amounts? I agree, sounds like a bad neurtral somwhere.

 

[brian john]

My number one guess would be a neutral to ground connection somewhere down stream from the main service.


1.Perform a zero sequence reading on the service and feeder conductors, (use a large CT like a LEM or split core and measure the phase and neutral/grounded conductor). Readings if all is correct (which it isn?t) should be zero in your case it may be 38 amps. That means you have a downstream ground on the neutral, most likely.
2.Check the water pipe and other utilities that may interconnect this building to other structures. You may have a parallel path with the service neutrals and the interconnecting water pipes (or other utilities).
3.If #1 pans out you can take a volt meter and amp meter doing zero sequence readings and take readings voltage readings when you are close to the neutral to ground short the voltage should be close to ?0? volts.
4.Also check distribution equipment for the obvious neutral to ground connections.


If you do not have a large CT you can use a standard current clamp (if current readings are stable) and utilize the following formula:

N=√(Asq*Bsq*Csq)-(A*B+B*C+C*A)

5. Not picking on the engineer but if he knew what he was doing this issue should have been resolved. Test equipment in the hands of the inexperienced is, well shooting in the dark.

 

[don_resqcapt19]

Brian,

My number one guess would be a neutral to ground connection somewhere down stream from the main service.

That should not put the current on the GEC. Also, unless there is a bad feeder neutral I can't see a downstream grounded to grounding connection creating enough current flow in the grounding path to cause the heat damage on the boiler conductors. My bet is still on a bad utility neutral, either on this service or another service that is bonded to the same metal undergound water piping system.
Don

 

[George Stolz]

I think Don's statements in post #2 are right on the money. A clamp-on ammeter won't tell you the direction the current is going, so it could be that a neighboring service is using the affected building's good neutral as the path for it's unbalanced neutral current.

 

[Smart $]

...utilize the following formula:

N=√(Asq*Bsq*Csq)-(A*B+B*C+C*A)

Ummm... OP stated single phase!

...400 amp, 1 phase, service entrance conductors ...

Even so, the neutral current formula is only good on a three phase wye cconductors where there are no Line to Line loads.

BTW, your formula is incorrect. The correct formula is, where each letter designates the current of 3? wye conductors:

N = √(A^2 + B^2 + C^2 - A?B - B?C - C?A)​

...which can also be written...

N = √[A^2 + B^2 + C^2 - (A?B + B?C + C?A)]​

 

[ptonsparky]

I think Don's statements in post #2 are right on the money. A clamp-on ammeter won't tell you the direction the current is going, so it could be that a neighboring service is using the affected building's good neutral as the path for it's unbalanced neutral current.

I disagree, an amp clamp in conjunction with some math will tell you which direction the current is flowing.
Example:
Clamp L1= 225, clamp L2 = 260, net imbalance should be about 35. If your clamped neutral = 70 then you know current is from someplace else. Clamped neutral = 5, then your building is adding significant current flow to the water pipe and its neutral is suspect.

 

[brian john]

Don: It is not unusual to have net current show up on the GEC. .Additionally an EGC carrying excessive current can damage feeder conductors.

Well it is not a good idea to approach a problem with blinders, I almost always start by performing the steps I listed for several reasons.

The miswiring of the feeders in PVC should be also be checked and corrected, this will result in damaged conductors, unless conduits land on a sloted interance or PVS plate.

1.More that 95% of the buildings we work in have neutral ground issues and while it is not unusal for there to be more than one discrepancy that results in an electrical discrepancy, resolving the grounded neutral issue will minimize present and future problems.
2.By starting an inspection at the service and working out one should look for any electrical discrepancies. Induction, ground current, and it?s source, thermal issues, improperly wired equipment, ect?
3.I have never not been able to locate and/or solve any electrical problems, that I have been confronted with (not always by myself). But the key is to be open minded and check everything, it has always worked for me.


And George knowing if there is a net current issue is critical in any PQ investigation, proper tools make it easier, if necessary math can be of assistance. (I did over look the single phase reference), and with single phase the math gets a bit simpler.

 

[Bill Swain]

Had this kind of problem before, try telling the fire dept. to cut the water pipe, thats what set the house on fire.

Street light feed swinging in the wind welded itself to the bridge, which was carrying a waterpipe, fed through low resistance to my customes house, then through the neutral, gas pipe, etc. when we cut the service neutral and it didn't stop, I was puzzled, then the oil burner and feed pipe began to smoke. Chief I said, cut the water pipe. Why he said. Because I don't want to be here when the oil TANK catches fire.

But this does sound like an energized system not grounded, I have seen cut insulation, to a screw holding the trough covers on penetrate the taped connection. If this is the case start with shut off the main, and test, if it's gone it's inside, if not it's outside, but could still be your feeders.