Optional Standby Generator Ground Fault Protection

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Richard S

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We have a project where there is a 3000kW generator that is serving as "Optional" Standby System per Article 702 of the NEC. This generator feeds a switchgear that has a pair of breakers that serve as an ATS to switch between utility and generator (see attached partial single line diagram). The generator feeder terminates in a 4000A breaker with ground fault function. The generator does not have an output circuit breaker between the alternator and the breaker in the switchgear. The generator has a controller and voltage regulator that has overcurrent (50/51) protection, but not ground fault. The generator has EPO that is lockable and we are not paralleling so this satisfies the Disconnecting Mean Required per 445.18 exception. Since the generator breaker in the switchboard has ground fault protection, everything downstream would be protected in the event of fault to ground. My question is if this would suffice for the Ground-Fault Protection of Equipment requirement Per 240.13? Do I need to add Ground Fault Relay at the generator that will shut down generator? The only issue I see is if there was a fault to ground between the generator and switchgear. The feeder will be underground in PVC, but there will be a ground conductor. Generator output is 3Ø3W no neutral.
 

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Is the generator controller listed as overcurrent protection like the high end cummins controller, or does it just have built in overcurrent protection like most do for self protection?

20' is a long way from the alternator to the first listed overcurrent protection.

You might need listed 50/51 and GF protection at the alternator.
 
ron said:
Is the generator controller listed as overcurrent protection like the high end cummins controller, or does it just have built in overcurrent protection like most do for self protection?

20' is a long way from the alternator to the first listed overcurrent protection.

You might need listed 50/51 and GF protection at the alternator.
Click to expand...

Yes high end controller. CAT EMCP 4.2. Generator about 40-50' away within line of site.
 
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ron said:
Unfortunately the CAT EMCP is not listed for overcurrent protection. :(
The 10 sets of 600s for 40-50' are technically unprotected and need both phase and ground OCPD.

The Cummins Power Command / AmpSentry is a UL Listed Protective Relay.
http://productspec.ul.com/document.php?id=NRGU.E243454
Click to expand...

Thanks Ron. That's good knowledge. Now that I look, I see that the CAT EMCP4.2 is UL recognized. I've requested information with regards to their listing to confirm. I appreciate the input.
 
Richard S said:
Thanks Ron. That's good knowledge. Now that I look, I see that the CAT EMCP4.2 is UL recognized. I've requested information with regards to their listing to confirm. I appreciate the input.
Click to expand...
Unfortunately I do not believe it is UL Recognized as a protective relay.

It is an issue I run into all the time during design and I struggle to find a spot within 10' (my choice to consider the feeder tap rules even though it is not a tap) of the alternator to place the 1st downstream circuit breaker.

http://productspec.ul.com/search.php?type=listing&listing=NRGU

The controller is probably UL recognized as a FTPM (Controls for Stationary Engine-driven Assembly).[h=3][/h]

[h=4][/h]
 
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