Dube2

How do I find a de-energized grounded neutral? I have a 4000amp 277/480volt system neutral showing ground condition. I plan on shutting down the service and start process of elimination. can somebody please offer a step by step? meter type, what I should have as far as ohm's, etc... Any bit of help will do.

Thanks in advance, Dube2

mcclary's electrical

Cue Brian/John

HARRY304E

Depending on what type of meter you are using your neutral will show that it is grounded because it is grounded at your service disconnecting meens.

Are you saying the you have a ground fault condition at your main switch gear?

Also what are you trying to acomplish a little more information would help you get the right answer to your question.

Dube2 Welcome to the forum.....

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RIVETER

Your question is an ambiguous one. A neutral is grounded whether the system is energized...or not. If you are wondering if you can find a grounded phase conductor with the system De-energized" ...yes.

wildleg

I wish I could figure out from your post what the problem is.

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mxslick

Me too, since oh, about 99.99% of systems with a neutral ground the neutral intentionally.

I find it scary that someone who doesn't get that is working on a 4000 amp 480/277 service.

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LightsOn81

If I understand it right this system/service is still hooked up. The neutral is the grounded conductor. Unless you take the neutral loose at the service it should read that it's grounded. If it were open then you would have a problem.

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brian john

What we do.



While power is up perform a visual inspection of the distribution system,, did this yesterday and of 20 loads fed from the main switch gear we found 8 loads with intentional grounds.



While doing the visual perform a zero sequence test on all feeders those with current are suspect.

During the outage.

Isolate all feeder neutrals at both ends, megger at 250 then 1000 VDC.

The feeders that megger dead short, go to the panels and isolate all branch circuit neutrals, megger at 250 and then 1000 VDC.

Tag all the shorted ones, reconnect everything and then trace out the shorted neutrals.

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Brian John
Leesburg, VA

jrannis

Brian,
This make it seem as though you routinely find intentionally grounded branch circuit neutrals. Are there certain types of installations that present this? Do you find this more in certain types of facilities?

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Dube2

I think BJ hit the nail on the head. Forgive me for not offering more info on this. Last minute,get out of the office sort of thing. Anyway, I had the breaker GFCI ground fault test performed by third party company, to perform the test they need to disconnect all feeders and neutral from the system to isolate the breaker. At that time they found a grounded noodle down streem. So I assume it's in one of the tennant panels. Process of elimination and I'm sure I will find it, but just wanted to hear what others have done in this same situation. The third party technician even said it may not be anything to worry about, but he said it in front of the building owner so now they think they have this huge problem.

So a Meggar is the answer and not a MM in the ohm's position?

Thanks Guys, Dube

brian john

We are hired several times a year to do grounded neutral investigations. Use to be more often when we used CRT monitors (more suseptical to EMF) Doing one this week end for a really really big guys support team. Think of someone I disagree with in Washington DC and it is his place.

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Brian John
Leesburg, VA

brian john

No MM.

I would bet better than 75%-95% of commercial buildings have this issue.

Short out a phase conductor trips a circuit breaker, short out a neutral and you have ground current.

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Brian John
Leesburg, VA

Dube2

well we found the problem, tek screw on neutral buss bar to can. didn't take long at all, once we isolated the indevidual panels, it was cake walk. thanks for the info guys.

brian john

And sometimes it can be a BIT*H, finding the short.

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Brian John
Leesburg, VA