Use a 4 pole breaker if it is necessary to disconnect the neutral, ie if you need total electrical isolation for non mechanical, ie electrical maintenance or work on conductors. A removable neutral link would also suffice for electrical maintenance.
If you have three incoming wires use 3 pole, 4 incoming wires use 4 pole. Possibly the local code will specify some other numbers. Obviously somewhat different for 3 phase service verses single phase center taped.
You use what's appropriate.
When supplying a branch circuit with more than one live conductor, each live conductor must be protected by a breaker pole. Choose the one that matches how many live conductors you have in the application.
depends on how many phases of power.... 3 is usually normal.... dont put the grounded conductor under the breaker...........4 pole? sounds like a contactor
--------------A[BREAKER]---------------...
--------------B[ POLES ]----------------------------->busbar
--------------C[ 300A ]----------------------------->busbar
N--------------------------------------... BUS
Should the incoming breaker be 3 pole or 4 pole and why?
