Circuit Breaker Raing and Motor FLA
Circuit Breaker Raing and Motor FLA
(OP)
Hi everyone,
We are asked to use circuit breaker to protect a 6kV motor, not a fuse. So how to decide the rating of Circuit breaker?
I use 1.2 x full load current of motor as a minimum to choose CB rating for LV system. For MV sytem like 6kV, what is the criteria?
Paul2gh
We are asked to use circuit breaker to protect a 6kV motor, not a fuse. So how to decide the rating of Circuit breaker?
I use 1.2 x full load current of motor as a minimum to choose CB rating for LV system. For MV sytem like 6kV, what is the criteria?
Paul2gh






RE: Circuit Breaker Raing and Motor FLA
In MV the rating selected are much higher than equivalent LV ratings. You adjust the protection using the relay settings.
RE: Circuit Breaker Raing and Motor FLA
Because of the inrush of Motor starting current( 6 x FLA), do I need to use a larger CB to protect a motor?
For example, if the motor's FLA is 630A, can I use a CB rated at 630A to protect it?
Paul2gh
RE: Circuit Breaker Raing and Motor FLA
At 6kV it won't matter as minimum CB rating you can get is 1200A. To answer an hypothetical question, you really need to check the duty rating of the breaker with mfr. But certainly you need not use 6xFLA rated breaker, may be 2X. NEC is says "suitably" rated device..so I think it will be a matter of experience and professional judgment based on information the mfr can provide.
This again is only for MV system.