GFPE on 120/208V solidly grounded wye electrical service

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jkim780

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Working on a school addition. It has a 1600A 120/208V solidly grounded wye electrical service with 1600A MCB. It also has a GFPE at MCB. I don't know how it got there but it is there. I don't think this is a code violation because code doesn't prohibit a GFPE at 120/208V service. However, the problem is that they have nuisance trips at leaset 2-3 times a month causing the blackout of the whole school, whenver they are trying to plug something (like a vacuum cleaner) at receptacles. It has been going on almost 7 years. Now, they are trying to fix this problem while they are doing an addition. They upgraded this electrical service 7 years ago and there is no GFPE performance testing report available.

My question is

1) What will cuase the tripping? It is because the setting is too low or there is actually ground fault at the somewhere downstream?

2) what would be the best way to solve this tripping? Making the setting higher? or disable or remove the GFPE since this is not required?
 
Re: GFPE on 120/208V solidly grounded wye electrical service

Hello;
Check NEC 230-95 (1999) This should help.
 
Re: GFPE on 120/208V solidly grounded wye electrical service

check with the manufacturer of the switch to find out what the minimum trip current should be.

Also these units should be checked out. I have heard anywhere from every 3 to seven years. if the unit is not set right it will cause nuisance trips
 
Re: GFPE on 120/208V solidly grounded wye electrical service

On a 208y/120 system it's not required as one of the other guys referred to art 230.95.
Otherwise, is it a separate GF device? How is it installed? If it is a separate device it most likely trips the main breaker via a shunt trip. It senses the current by using CTs. Study the way the CT or CTs are installed. Remember that in a 3ph, 4w system either (1) CT is used where ALL phase conductors and the neutral pass through a single CT. If separate CTs are used then each line conductor and the neutral will have its own CT.
Even if there is GF integral to thew Main breaker it atill must have an external neutral CT.
What I'm saying is that the installer may have missed the neutral and the GF device is picking up the neutral current as being a ground fault. I had this happen in a large warehouse type grocery store where the 480y/277v manufacturer miswired the neutral CT and every time there was a large neutral current as a result of s 277v lighting load it would take down the entire store.
So verify that the GF is installed correctly and that is monitoring all lines and neutral and that it is not set too low.
Remember that there is no recommended setting other than coordination and that even with systems with 150v L-G they're talking about 1000a maximum but don't give a setting value lower than that.
Dave
 
Re: GFPE on 120/208V solidly grounded wye electrical service

Local school had nuisance tripping of a 208Y/120 GFP (yes it was not needed). GFP setting was 200A, which by the way will always cause a GF trip well before any 15 or 20 breaker can clear the fault.

Problem was eventually narrowed down to moisture inside of a wallpack fixture.

Good luck hunting.
 
Re: GFPE on 120/208V solidly grounded wye electrical service

Made a quick field trip today. The existing swbd is a GE spectra series 1600A 120/208V 3ph 4w solidly grounded wye. It has a 1600A Power Break Circuit Breaker which has a Micro Versa Trip trip unit as an option. It seemed that the sensor is connected to a neutral CT. Trip setting was at minimum, which is 320A. No wonder they have nuisance tripping all the time.

Another interesting finding was that there is no main bonding jumper between the neutral bus to the equipment grounding bus. There is a link for connecting both but it was not connected. I am not sure this will effect on GF operation but obviously it is code violation.

I am well aware of 230.95. My question was that would it be better off to disable or remove the GFP and forget about all the nuisance tripping since this is not required?, or
Should I try to find the cause of tripping and make it work and leave the GF device in place since it is already there? After all, it's better than nothing.

Back to the tripping problem, I know that trip setting was too low but would it be the only reason for the tripping? Could there be any other reasons? How can I track down those problem like Jim mentioned?
 
Re: GFPE on 120/208V solidly grounded wye electrical service

Posted By Jim Dungar:

GFP setting was 200A, which by the way will always cause a GF trip well before any 15 or 20 breaker can clear the fault.
Click to expand...
Don't most also have a programmable time delay also? I seem to remember something in the code about a 1000A maximum setting at a 1 sec delay. If you had a 200A setting with a 1 sec delay, I can't imagine that tripping faster than a branch breaker or even a feeder breaker?

Steve
 
Re: GFPE on 120/208V solidly grounded wye electrical service

there is no main bonding jumper between the neutral bus to the equipment grounding bus
Click to expand...
Is it possible the bonding between ground and neutral occurs elsewhere? I assume there is a GEC on the ground terminal that goes somewhere?

I've seen a service at one school catch fire. (Not that the GFPE would have stopped it, since it was at the service conductors). So I say better to be safe and leave the GFPE. Plus, what if there really is a problem? Just unhooking th GFPE would then be asking for trouble.

I wonder if the lack of the grounding conductor is a clue? If there is more than one ground-neutral bond somewhere, then that could look like a ground fault.

I would start by getting a clamp on ammeter and seeing what the current on the neutral is?

One more possibility: any chance a bunch of computers or electronics are generating harmonics that could show up on the neutral? That could cause false tripping.

STeve
 
Re: GFPE on 120/208V solidly grounded wye electrical service

jkim780,
It's nice to set the thing as low as you can set it until the nuisance tripping becomes an issue.
Just set it higher.
With regard to if there is a time delay, often this is and option which you have to spec and pay for. If there is one, it may be adjustable between 100-500ms which would give you a brief hiccup before it trips.
With regard to the bonding jumper, is the panel a service entrance? That would determine in it should be bonded there or not as I see it.
Also, I would doubt it the fact that the bonding jumper wasn't in place would cause a false trip.
Just so the neutral CT is in place and wired correctly so the at the neutral current is being monitored by the GF.
Dave
 
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