Nuisance tripping GFI breakers

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Electrical1234567

Member
Location
Colorado
Occupation
Electrician
I am wiring a 164 unit apartment complex and am having issues with just about every 240v gfi breaker tripping, What’s weird is just about every unit is doing it regardless if the breakers have a load or not. What’s even more strange is that when we move the breakers down 1 bussed space in the panel they no longer trip. For example A phase on the top half of the breaker B phase on the bottom then we move them down 1 space so B phase on the top half A phase on the bottom and the breakers no longer trip. None of the 120v afci/gfi breakers have any issues, and it’s a 3 phase system so it’s doing it across A,B and C phase. Any ideas on what would cause something like this?
 
mtnelect

mtnelect

HVAC & Electrical Contractor
Location
Southern California
Occupation
Contractor, C10 & C20 - Semi Retired
This is the main problem with GFCI circuits.
 

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E

Electrical1234567

Member
Location
Colorado
Occupation
Electrician
mtnelect said:
My bet, is one or more of your feeders have a crossed grounded connection(s). Re-identify your grounded feeders to each phase.
Click to expand...
I’ve chased phantom tripping arc’s and GFI’s before. This is different, breaker trips, then move the breaker down 1 bussed space in the panels and no trip. If it was a grounded conductor moving the breaker in the panel would still cause a trip. But that fact that it holds is what the real issue is. Why does it trip when it’s A on top B on bottom but not when it’s B phase on top and A phase on bottom. Nothing to do at all with grounded conductors anywhere. It’s a 4,000 amp service the 1600 amp bus way on each side of the building. We are pretty careful to not cross any of the conductors throughout the building.
 
mtnelect

mtnelect

HVAC & Electrical Contractor
Location
Southern California
Occupation
Contractor, C10 & C20 - Semi Retired
Electrical1234567 said:
I’ve chased phantom tripping arc’s and GFI’s before. This is different, breaker trips, then move the breaker down 1 bussed space in the panels and no trip. If it was a grounded conductor moving the breaker in the panel would still cause a trip. But that fact that it holds is what the real issue is. Why does it trip when it’s A on top B on bottom but not when it’s B phase on top and A phase on bottom. Nothing to do at all with grounded conductors anywhere. It’s a 4,000 amp service the 1600 amp bus way on each side of the building. We are pretty careful to not cross any of the conductors throughout the building.
Click to expand...

Unfortunately ... you will have to do it all over again, this time with permanent markings. Each grounded conductor to each phase.
 
E

Electrical1234567

Member
Location
Colorado
Occupation
Electrician
hillbilly1 said:
Is the main service 480? XO on the step down transformer may not be bonded. A fault to ground on one phase may raise the neutral voltage enough to cause problems.
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main service is 208/120. No step down transformers or anything like that. Pretty straight forward service really. The fact that they trip then moving the breakers down 1 bussed space and don’t trip is what’s really throwing me for a loop.
 
J

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
Electrical1234567 said:
main service is 208/120. No step down transformers or anything like that. Pretty straight forward service really. The fact that they trip then moving the breakers down 1 bussed space and don’t trip is what’s really throwing me for a loop.
Click to expand...
Are these breaker the plug in neutral style?
 
tortuga

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
I'd check the N-G voltage & voltage Drop with an Ideal Sure test or similar tester.
Do you have 164 unit's on the same transformer ? If so can you post a photo ?
 
E

Electrical1234567

Member
Location
Colorado
Occupation
Electrician
tortuga said:
I'd check the N-G voltage & voltage Drop with an Ideal Sure test or similar tester.
Do you have 164 unit's on the same transformer ? If so can you post a photo ?
Click to expand...
Yes 1, 5 story building. 1 transformer, 4,000 amp service. I don’t have many photos, I really should take more biggest service I’ve ever built. It would make sense that vantage drop has something to do with it, because the tripping seems to get worse the more units we energize. If we energize 1 floor we have almost no tripping but as we energize more units it get worse.

Do you think too much voltage drop would cause them to hold when we move the breakers in the panel. Seems strange to me that if we land them A on top leg B on bottom they trip but if we move the breakers down and have B phase on top and A phase on bottom they hold.

Also we upsized any of our longer runs to account for voltage drop. The only really long runs we have in the building are feeding meter banks in the electrical rooms, none of the runs from meter to unit panel are far and the. Unit wiring is even shorter.
 
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