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Thread: 4-Pole Circuit Breakers

  1. #1
    Join Date
    Aug 2006
    Posts
    292

    4-Pole Circuit Breakers

    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,

  2. #2
    Join Date
    Feb 2003
    Location
    New York, 40.7514,-73.9925
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    4,588
    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
    Ron

  3. #3
    Join Date
    Aug 2006
    Posts
    292
    Quote Originally Posted by ron View Post
    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,

  4. #4
    Join Date
    Feb 2003
    Location
    New York, 40.7514,-73.9925
    Posts
    4,588
    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.
    Ron

  5. #5
    Join Date
    Aug 2006
    Posts
    292
    Thanks Ron!

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