Conductors from generator to service rated transfer switch…

[sw_ross]

We’re installing a 3-phase 480/277 80kw generator and 3-phase service rated transfer switch. The neutral and ground are bonded in the ATS.
There aren’t any 277v circuits (requiring a neutral) only 480 pump motors. There is a smaller dry type transformer that is 480 -> 120/240 for lights and outlets. But that neutral is derived from that transformer and has nothing to do with the service…, I know the transformer creates a little bit of a load imbalance since it’s only using 2 of the phase conductors.

Anyways, I’m trying to get my head around the conductors from the generator to the transfer switch. Are they feeders or service (alternative source) conductors? And should there be a neutral separate from the ground wire? The engineer plans call for 3-hots, a neutral and a ground. The way I understand things you wouldn’t bond the neutral and ground at generator (objectionable current).
There’s a neutral lug and a ground lug (chassis bond).
What purpose does the neutral serve if there’s no neutral current? Does it allow for a returning fault current for the purpose of tripping the breaker? I guess it would since the ground back to the generator is only a chassis ground…

Thanks for any input to help me better understand these conductors!

 

[Dsg319]

We’re installing a 3-phase 480/277 80kw generator and 3-phase service rated transfer switch. The neutral and ground are bonded in the ATS.
There aren’t any 277v circuits (requiring a neutral) only 480 pump motors. There is a smaller dry type transformer that is 480 -> 120/240 for lights and outlets. But that neutral is derived from that transformer and has nothing to do with the service…, I know the transformer creates a little bit of a load imbalance since it’s only using 2 of the phase conductors.

Anyways, I’m trying to get my head around the conductors from the generator to the transfer switch. Are they feeders or service (alternative source) conductors? And should there be a neutral separate from the ground wire? The engineer plans call for 3-hots, a neutral and a ground. The way I understand things you wouldn’t bond the neutral and ground at generator (objectionable current).
There’s a neutral lug and a ground lug (chassis bond).
What purpose does the neutral serve if there’s no neutral current? Does it allow for a returning fault current for the purpose of tripping the breaker? I guess it would since the ground back to the generator is only a chassis ground…

Thanks for any input to help me better understand these conductors!

You are correct even if there are no line to neutral loads the neutral must be brought to the service disconnect to the EGC/neutral bond. Without such there are no hopes of clearing ground faults.

Anything after your service rated transfer switch is considered feeders and a EGC is needed. (Assuming you are using the transfer switch as your service disconnect)

 

[augie47]

For clarification: Your transfer switch does not switch the neutral, correct ?

Some generator manufacturers call for a ground rod to be attached to the chassis. You can install one to meety their requirements but it should only connect to the chassis.

 

[sw_ross]

For clarification: Your transfer switch does not switch the neutral, correct ?

Some generator manufacturers call for a ground rod to be attached to the chassis. You can install one to meety their requirements but it should only connect to the chassis.

Yes, The transfer switch does not switch the neutral.
And yes there is a ground rod installed at the generator location.