Fire pump 120v power

Does anyone know why the code (NFPA 20) requires voltage to not be reduce no more than 125 volts on fire pumps internal controls? Some one asked me that question, but all I really could come up with was maybe there was voltage drop LOL. or maybe 125 v is just a better control voltage?? but those reasons really wouldn't make any difference though.

Does the NEC have any restrictions on that issue? I'm surprised I did not find that in the NEC, unless I'm missing something.

marti smith

Senior Member
695.7 Voltage Drop.

(A) Starting. The voltage at the fire pump controller line terminals shall not drop more than 15 percent below normal (controller-rated voltage) under motor starting conditions.

Exception: This limitation shall not apply for emergency run mechanical starting. [20:9.4.2]

(B) Running. The voltage at the motor terminals shall not drop more than 5 percent below the voltage rating of the motor when the motor is operating at 115 percent of the full-load current rating of the motor.


Senior Member
Most line voltage fire pump controllers fail in the "on" position, so control power voltage drop is not critical, just motor starting. I don't know about the reduced voltage or Delta/Wye controllers.