Emergency Generator ground protection

[EPC]

I have been assisting an engineering firm that does work in the data center field. They have an emergency generator 480V, 3760A, solidly grounded, and they indicated that the code does not allow them to have ground trip on the generator that trips but only to alarm. They refer to NEC 700.6(D) and 700.26 which uses the word 'indicate'.
The generator came with phase and ground overcurrent trips. There is no way to disable the ground trip without replacing the trip at a cost of $7000. Are they interpreting the code correctly?

To me it does not make since not to trip with the ground overcurrent function. Most likely the ground fault is going high enough that the phase overfunction is going to trip the breaker any way.

 

[charlie b]

Neither of those two articles forbid the use of a ground trip. 700.26 says that you are not required to have a ground trip, but it does not say that you must not have one. 700.6(D) (2011 NEC) says you need an alarm, but it does not also say that you must only have an alarm.

 

[mayanees]

The NEC doesn't prohibit the use of ground-fault tripping for Gens, but allows the gf requirement to be met by alarming only.
It's a concession that allows critical power systems to run while the ground-fault is being investigated.
Activation of the ground-fault trip function at the main breaker is acceptable, IMO, and meets NEC requirements.
John M

 

[don_resqcapt19]

Is that generator really covered by Article 700?

 

[iwire]

Is that generator really covered by Article 700?

At 3000 plus amps it seems very unlikely to me.

 

[mayanees]

That's a real good question.. is 700 applicable. The OP states that it's a Data Center, so it's probably NOT!
That suggests the OP has the right breaker, and should just set the gf pickup per NEC requirements of 1200 amps for 1 second, or whatever the breaker allows near the NEC max.

 

[charlie b]

I took the OP's description of "emergency generator" as meaning that it supplies some emergency loads (e.g., egress lighting) and a whole lot of optional standby loads. The question thereby makes sense, in that the 700 rules would come into play.

For my part, I prefer to call the machine a "backup generator," and then in a separate sentence state whether it supplies 700, 701, or 702 loads, or a combination thereof.