4-Pole Circuit Breakers

[faresos]

Hello Everyone/;

I'm working on a project that will require to utilize power circuit breakers type Automatic transfer switch. The main service is 1200A at 480Y/277V. The main switchboard will have three main breakers configuration (Utility-Gen1-Gen2). Generator 2 is used as a back up only for Gen1 if it didn't start. My question, do I need 4-pole breakers to switch the neutral since our service is 1200A (LSIG)?

Thanks,

 

[ron]

Will the loads be 4 wire or 3 wire?

If 3 wire load, then you bond the N-G at the gens and the service and do not bring the grounded conductor from the gens to the Main SWBD, then 3 pole CBs are fine.

If the loads are 4 wire, the 4 pole CBs are the best for transfer. Be sure each source is setup as a SDS with the N-G bonded at each (or once at the Main SWBD if there are no disconnects upstream) and you bring a 4W service / feeder to the Main SWBD

 

[faresos]

Will the loads be 4 wire or 3 wire?

If 3 wire load, then you bond the N-G at the gens and the service and do not bring the grounded conductor from the gens to the Main SWBD, then 3 pole CBs are fine.

If the loads are 4 wire, the 4 pole CBs are the best for transfer. Be sure each source is setup as a SDS with the N-G bonded at each (or once at the Main SWBD if there are no disconnects upstream) and you bring a 4W service / feeder to the Main SWBD

Thanks Ron for your reply

The system will have 4-wire loads but I think can make it 3-wire loads if this will simplify it. I can provide 480-480Y/277V for the lighting loads (277V). The generators will have it's own output breaker which to me I will need 4-pole breakers for the generators in the switchboard, correct? Do I also need 4-pole breaker for the utility main at the switchboard as well?

Thanks,

 

[ron]

If you can take care of the 4 wire loads downstream separately, that makes everything easier.

Then the three input breakers in the main SWBD would be 3 pole, the gen mounted breakers would be 3 pole, and N-G bond at each first disconnect (at gens or the alternator connection box for the gens).

No grounded conductors (3 wire only plus EGC) brought from gens to main SWBD.

 

[faresos]

Thanks Ron!