Sizing protection for firepump

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shortcircuit1

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My understanding is that to size the protection for the fire pump we take the LRA from NEC table 430.251(B) corresponding to the HP of the motor and the voltage and then use that to size the protection. But the table applies to motor design letters B,C,D. Most of the big fire pump motors are now either H or J. How do we size the protection for those design letters?
 
shortcircuit1 said:
My understanding is that to size the protection for the fire pump we take the LRA from NEC table 430.251(B) corresponding to the HP of the motor and the voltage and then use that to size the protection. But the table applies to motor design letters B,C,D. Most of the big fire pump motors are now either H or J. How do we size the protection for those design letters?
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No, you will look at table 9.5.1.1 in NFPA 20 (2013), Standard for the Installation of Stationary Pumps for Fire Protection and follow the information thereafter.
 
shortcircuit1 said:
Thanks!Thats pretty much the same as NEC code letters.
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True, but some of the requirements might not get you to the same place as if you went from the NEC. For 3-phase voltages other than 460, you ratio the voltages rather than calculate the kVA which might move you up or down a letter for close cases.
 
When dealing with fire pumps keep this thought in the back of your mind and you will never go wrong, “I want that motor to be running 10 days after this building is burnt to the ground.”
 
jwelectric said:
When dealing with fire pumps keep this thought in the back of your mind and you will never go wrong, “I want that motor to be running 10 days after this building is burnt to the ground.”
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A slight exaggeration, but only slight.
 
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