3P breaker with neutral contactor Vs 4 Pole breaker

[GadreP]

Hi guys, I just want your opinion about a system:

I have a turbing generator star connected. The supplier is suggesting a 3 Pole ACB with neutral contactor. The ACB rating is 630A, 415V.

What will happen if I use 4 Pole ACB without neutral contactor?

Please suggest whether a system will work:
1) If I use 4P ACB without contactor?
2) Or I have to use 3 Pole ACB with neutral contactor?
3) Or I can go ahead with 4 pole ACB with neutral contactor?

Please suggest about this..

 

[rbulsara]

Depends on a few factors, especially how the system is earthed. If the generator neutral is independently grounded, you need 4-pole devices. If the two system neutrals are tied together and grounded at one point you can use 3-pole devices.

While using a 4 pole device, the neutral contact shall be first to close and last to open (called overlapping neutral in the ANSI world).



Rafiq Bulsara

http://www.srengineersct.com

 

[waross]

The first question is why are you switching the neutral? The most dependable system is a solid neutral but there may be compelling reasons to switch the neutral.
Switching with a separate contactor will be a code violation in many jurisdictions. Consider the impact on your system when the contactor fails and leaves your neutral open.
A 4 pole breaker with overlapping neutral is your best choice if you must switch the neutral. Some jurisdictions will accept a 4 pole breaker without overlapping neutral if the 4 poles operate simultaneously.


Bill
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"Why not the best?"
Jimmy Carter