Removal of Ground Fault Protection

[aharrigan]

An existing 4000Amp service has a 4000A breaker that feeds another part of the building. As per original design it has ground fault protection.

The building electrical system was redone in 2012 and the 4000A service was re-fed via a new 2000A breaker in the new line up.
A large load was removed from the original service.

A shorted elevator motor fed from the original buss tripped out the 4000A breaker to the other part of the building. I would guess the close proximity of the fault to common buss may have caused the trip of the 4000A breaker.

Building engineer wants to disconnect the ground fault mechanism on the 4000A under the theory that this buss is now fed from a 2000A breaker ( new electronic SQ-D ) and the 4000A does not need to be ground faulted.

Looking at 215-10 and 230-95 not sure it would be legal todo this?

 

[iwire]

It sounds fine to me.

 

[petersonra]

An existing 4000Amp service has a 4000A breaker that feeds another part of the building. As per original design it has ground fault protection.

The building electrical system was redone in 2012 and the 4000A service was re-fed via a new 2000A breaker in the new line up.
A large load was removed from the original service.

A shorted elevator motor fed from the original buss tripped out the 4000A breaker to the other part of the building. I would guess the close proximity of the fault to common buss may have caused the trip of the 4000A breaker.

Building engineer wants to disconnect the ground fault mechanism on the 4000A under the theory that this buss is now fed from a 2000A breaker ( new electronic SQ-D ) and the 4000A does not need to be ground faulted.

Looking at 215-10 and 230-95 not sure it would be legal todo this?

I think it is either a feeder CB or a service disconnect. In either case it exceeds 1000A and thus it needs to have the GF protection if it is a solidly grounded system exceeding 150V to ground.

 

[augie47]

Assuming the new service that feeds your older gear has GF protection a fault might cause the larger new service to trip if you remove the present GF entirely... so the 4000 tripping might have been a bit of a blessing.
It may well be worth your while to have a coordination study of the entire system.

 

[iwire]

I think it is either a feeder CB or a service disconnect. In either case it exceeds 1000A and thus it needs to have the GF protection if it is a solidly grounded system exceeding 150V to ground.

But it is only required to have GFP once, not at every OCPD over 1,000.

 

[Jraef]

I would guess the close proximity of the fault to common buss may have caused the trip of the 4000A breaker.

The flaw in your hypothesis lies there. The 4000A breaker tripped because of a lack of coordination in the settings of whatever was feeding the elevator, with the settings on that 4000A feeder. Performing a Coordination Study prevents this EXACT sort of thing by making sure that faults are cleared at the lowest levels possible.

 

[iwire]

For what is worth I agree with Gus and Jraef that the thing that really needs to be do is a coordination study.

 

[petersonra]

But it is only required to have GFP once, not at every OCPD over 1,000.

thats true, but the OP said the 4000A breaker feeds other things. thus it has to have the GF as well.

in fact how would you ever avoid having it on any upstream feeder?

 

[iwire]

thats true, but the OP said the 4000A breaker feeds other things. thus it has to have the GF as well.

It already has GFP from the new 2,000 feeding it.

 

[jim dungar]

Sounds like you had a ground fault, and the breaker did what it was supposed to do, protect the building from a damaging fire. Or are you saying the 4000A breaker tripped because there was a fault in the circuit next to it?

Now the recommendation is to remove the protective function so that if the upstream (2000A) main device sees a ground fault and trips causing a total outage.

Has anyone considered coordinating all of the protective device settings?

 

[petersonra]

It already has GFP from the new 2,000 feeding it.

I think I misread what the OP meant.

If the 4000A CB is fed from the new 2000A CB with GFP, I agree the GFP on the 4000A CB can be removed.

I don't get why they went to the trouble to add the new 2000A breaker just because they took out a large load. Seems unnecessary.

 

[aharrigan]

The 2000A circuit breaker was part of a major overhall of the building electrical service.
The original service 4000A was installed under the six switch rule. One of the disconnects was this 4000A breaker that fed the
West side of the building. The elevator was fed from a panel that was one of the six switches. So the fault went from the elevator
back thru the panel feeding it to the 4000A buss. The fault must have been large enough to effect the 4000A disconnect that feeds the West side of the building.

I agree that these are probably not coordinated as they should be. I am just rying to figure out if it would be legal as the engineer
wants to disconnect the GFI sensor? I hope this clarifies the situation somewhat. I have not posed the question yet to the AHJ.

 

[augie47]

Take a look at 215.10 Exception No. 2 and I believe you will find as long as you have GF on the supply to this breaker you can disconnect it's GF protection.
Keeping in mind the next short may take out the MAIN GF.