Firepump Breaker Sizing 2

[vinchii]

Hi to all guys who are working with IEC and BS standards during design stages. can you guys share if what is the counterpart of the consideration of NFPA rule on lock rotor current during Circuit breaker sizing of firepumps?

Basically that is approx. 6xFLC. On the few of my previous projects which is based in UK and Dubai. firepump specialist required only the circuit breaker to be the same or 1 size CB higher than the FLC. (with soft starter). on the NFPA point of view this is completely insufficient.

can i have your thoughts?

Regards

 

[RRaghunath]

NFPA 20 only says Locked rotor protection pickup shall not be set lower than 300% of motor full load current and shall not operate before 8 seconds.
Motor circuit breaker rating can be just over the motor full load current.

 

[dpc]

He's asking about IEC standards. I don't have NFPA 20 in front of me, but NEC 695 says:

OC device shall not open within 2 minutes at 600% of FLA
OC device shall not open with restart transient of 24 times the FLA
OC device shall not ope within 10 minutes at 300% of FLA
Trip point shall not be field adjustable.

I don't know about IEC or BS standards.

Cheers,

Dave