GFI For Outdoor Lighting, Neutral Is Shared Over 3 Phases 277v

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AzViper57

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Okay here is the is the issue. Within the courtyard of a resort hotel there are about two hundred 277 volt Ballard fixtures. There are 12 circuits run to a 12 pole contactor. Three of these circuits are bad with a direct short causing the main 2000A 480 volt GFIC breaker to shutdown. Through a process of elimination I was able to locate the problem and make the repairs and all lights are back up. With the tripping of the 2000A breaker this resulted any many issues within the resort hotel. The 277/480 sub panel I found 3 tripped breakers. When each breaker in thrown individually each breaker will trip without tripping the main 2000A breaker as it should, but because and I believe when the short occurred I think 480 volts was involved this is why the 2000A blew.

My question and I have not run across this in a lighting situation. The resort is requesting that all ground lighting be placed on GFI's. Can all three phases share the same neutral or will a separate neutral be needed for each circuit.
 
The 2000 amp main is not. GFCI it is GFP.

The real solution to this problem is a coordination study to determine what the GFP and other breaker settings should be.
 
Yes, you can get a GFP breaker designed for three phase with either wye or delta single phase (line to neutral or line to line) loads on a three phase MWBC. The neutral, if one exists, will have to be connected to the three pole breaker neutral terminal.
However, if you are looking for GFCI or GFP for a two pole breaker which feeds an individual two wire circuit with no shared wires, it gets a bit more complicated. You would not necessarily need a breaker with a neutral terminal, but you could use one such and just not connect to the neutral terminal (the breaker neutral pigtail, if it has one, would have to be connected to the neutral bar though.)

The problem that I see is in what rating the breaker would have to have. I think the standard designation for the supply you have would be 480Y/277.
So if the lighting is wired line to neutral, you would use a single pole breaker rated at 277V to ground, and it would have to be designed to power the GFP circuitry from 277V.
If you share the neutral, you MUST use a three pole breaker with GFP. If you use individual neutrals you can use single pole breakers with GFP or even GFCI is you can find any.

As iwire mentioned, the serious problem is coordinating the tripping from subpanel up to main. Your problem was probably the result of the GFP on the main tripping at a ground fault current which was less than the instantaneous trip range of the branch breaker.
At least two things will be necessary.
First, you need to make sure that the trip curves for a high current fault are coordinated so that the branch breaker is more likely to trip first.
Second, you need to hold off the GFP on the main, either by putting a lower level GFP on the branch breaker and hoping or by increasing the GFP trip value on the main so that the branch breaker will trip first on GF too, even without a GFP feature.
That is just some food for thought. The actual coordination process should be left to a specialist.
 
Sorry I met to say Ground Fault Protection. Yes I understand what your saying in the GFP settings. This is a replacement rebuilt Square D 2000A breaker and the proper setting may have not been made. Amazingly this rebuilt breaker cost $19,000.00 as it is no longer made.
 
I will be contacting someone that specializes in getting the GFP set to the correct settings as the resort cannot afford to have the main panel breaker shutdown again. As for the lighting sub panel each of the 12 circuits are on individual breakers and would be a pain in the a** to pull individual neutrals but possible...
 
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