Fire Pump Motor Overcurrent Protection Sizing

I did the wiring for a 75 horsepower 480 volt three phase fire pump motor with a nameplate full load current rating of 94 amperes. If a transformer supplies an electric fire pump motor size it at least 125 of the sum of the fire pump and pressure maintenance pump s motor loads and 100 of the ampere rating of the fire pump s accessory equipment 695 5 a. So for a 250hp fire pump motor its ocpd rating would be 2000a.

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Nec Rules For Fire Pumps Ec M

Power To The Pump Ec M

Code Quandaries Ec M

Nec Article 695 Fire Pumps

Motor Calculations Part 2 Feeders Ec M

Consulting Specifying Engineer Power For Fire Pumps

You cannot provide secondary overcurrent protection.

Fire pump motor overcurrent protection sizing.

To size its ocpd we size it based on the locked rotor current of the fire pump per nec 695 4 b 1. The overcurrent protection complies with the earlier requirements in that it is intended only for short circuit fault protection and is set. To size its conductor ampacity we calculate it as 1 25 times the fire pump fla 302a x 1 25 377a 400a ampacity. The transformer can only have primary side overcurrent protection.

Power wiring 695 6 size conductors that supply fire pump motors and accessory equipment for no less than 125 percent of the sum of the motor full load currents as listed in table 430 148 and or 430 150 plus 100 percent of the ampere rating of the fire pump accessory equipment. Secondary overcurrent protection is not permitted 695 5 b. See example 3 to size a transformer. It must be sized for 125 of the fire pump motors and jockey pump and 100 of the remaining loads.

The feeder conductors to the fire pump are 1 awg copper with thwn insulation in 1 25 inch rigid metal conduit and liquid tight flexible metal conduit. If you install overcurrent protection devices ahead of the feeder pump circuits in the power supply for either utility or customer owned supply systems these protective devices shall be capable of carrying the locked rotor current of the fire pump motor s and the pressure maintenance pump motor s and associated fire pump accessory equipment.