Hmmm..... your profile says you are an electrical engineer... but yet you don't know how to size a circuit breaker for a motor...??? Though it's just my opinion, I believe it's time for you to learn how.Can anyone help me figure out the required circuit breaker size for a heat pump (5hp compressor motor + 10KW heater) for a 3 phase, 460V circuit?
thank you!
Full load Current @460V (values obtained from NEC 430.250)
5HP = 7.6A
10KW heater = 10000/(1.732*460V) = 12.55A
Total FLA = 20.15A
the disconnecting means must be greater than 115 percent
115% of 20.15A = 23.17 (therefore minimum of 30A breaker)
Does this seem right?
Afraid not. Wouldn't a lower rated overcurrent protection device (ocpd) afford better protection against a surge or short circuit? What other reason might there be for using a larger ocpd?For maximum overcurrent protection
locked Rotor Current @460V (values obtained from NEC 430.250(B))
5HP = 46A
10KW heater = 10000/(1.732*460V) = 12.55A
Total current = 58.55A
Therefore maximum breaker size is 60A. We need to know the maximum to protect the motor from getting damaged due to any surge in current (from a short circuit of some kind)
Am i correct?
sorry about putting you through it this way, but this is no different than someone studying for a test and wanting us to just give them the answer without them demonstrating any effort or learning on their part.