Generator Disconnect Confusion

[hbendillo]

Is there any case where an integral circuit breaker on a generator does not have to be service entrance rated? When an automatic transfer switch is fed from a circuit breaker that does not originate in the service entrance equipment, is there any need for the transfer switch or any breaker serving it to be service entrance rated?

 

[RUWired]

Is there any case where an integral circuit breaker on a generator does not have to be service entrance rated?

Unless it is the feeder to a building, i don't see where it is required to be service rated. And I'm not so sure it's actually the breaker, but more it's an enclosure that needs to be rated when required.

445.18 Disconnecting Means Required for Generators.
Generators shall be equipped with disconnect(s), lockable in the open position, by means of which the generator and all protective devices and control apparatus are able to be disconnected entirely from the circuits supplied by the generator except where both of the following conditions apply:
(1) The driving means for the generator can be readily shut down.
(2) The generator is not arranged to operate in parallel with another generator or other source of voltage.

When an automatic transfer switch is fed from a circuit breaker that does not originate in the service entrance equipment, is there any need for the transfer switch or any breaker serving it to be service entrance rated?

I think again only when it is serving a building.

Rick

 

[M. D.]

Not sure I fully understand the question, but I found this question in a Mike Holt Newsletter.

I thought that the OCP at the generator had to be service entrance rated or else another rated OCP would be required before entering the building: could you clarify this?

Q12. We have a standby generator with a circuit breaker mounted on the generator and an automatic transfer switch installed on the load side of the service disconnect. Is an additional disconnecting means required for the generator feeder conductors entering the building?


A12. Where an outdoor-housed generator is equipped with a readily accessible disconnecting means located within sight (within 50 ft) of the building or structure, an additional disconnecting means isn?t required on or at the building or structure for the generator feeder conductors that serve or pass through the building or structure [700.12(B)(6)].
acdcmontana May 31 2007, 7:34 pm EDT

Reply from: Mike Holt
There is no such rule to require the generator disconnect to be service rated. Sorry.

http://www.mikeholt.com/newsletters.php?action=display&letterID=391

 

[hbendillo]

I have done some further research and I think I understand now. The circuit breaker in the generator only has to be service entrance rated if the generator is serving the entire builiding or load. In that case the utility service entrance comes in one side of the transfer switch and the generator the other side. In this case the transfer switch and generator circuit breaker have to be suitable for service entrance.

I have a plans review insisting that my genertor circuit breaker has to be service entrance rated for a hospice project I am designing. She says the circuit breaker in the generator has to meet the requirements of 225-3.1. 225-3.6 states that the disconnecting means specified in 225-3.1 must be shall be suitable for use as service entrance equipment.

 

[RB1]

It doesn't matter if the generator serves the entire load or not. If the generator disconnecting means is permitted serve as the disconnecting means required by 225.31, it is required to be suitable for use as service equipment. See 700.12(B)(6).