Is my fire pump controller breaker sized correctly?
Filed under Fire Pump Controllers - FAQ - Frequently Asked Questions on 3/1/2010 by Author: .

 

Question: My local electrical inspector red tagged my electrical fire pump controller. He says the circuit breaker inside the controller is too small and must be sized for locked rotor current.

 

A common misconception by electrical inspectors is that the main circuit breaker frame size in an electric fire pump controller should be sized for the locked rotor current of the fire pump motor.

The confusion comes from applying the requirements in Article 695 of the National Electric Code to the fire pump controller. Article 695.4 Continuity of Power only applies to the circuits that supply the fire pump controller. It states that if an overcurrent device is installed in the fire pump controller supply circuit then it must be set to indefinitely handle the locked rotor current of the fire pump motor and accessories. So if an overcurrent device is installed in the power supply to the fire pump controller it should be sized to handle locked rotor current of the fire pump motor and accessories.

However, the main breaker inside the fire pump controller is sized per NFPA20-Installation of Stationary Pumps for Fire Protection.  In order to pass the stringent tests of UL and FM and subsequently receive their listings and approvals the breaker inside the control panel must comply with the following:

NFPA20-2010 10.4.3.3.1 Electrical Characteristics

(1) A continuous current rating not less than 115 percent of the rated full-load current of the motor   (NOTE: This relates to the physical frame size noted on the circuit breaker, but does not determine the required trip curve)

NFPA20-2010 10.4.4 Locked Rotor Overcurrent Protection

(a) Of the time-delay type having a tripping time between 8 seconds and 20 seconds at locked rotor current

(b) Calibrated and set at a minimum of 300 percent of motor full-load current

The fire pump controller circuit breaker utilizes a shunt trip device to perform the tripping functions. A microprocessor inside the fire pump controller determines the proper tripping settings and time frames to send a trip signal to the breaker accomplishing the requirements of NFPA20, Underwriters Laboratories and Factory Mutual to be Listed as an approved fire pump controller.

Summary: Your inspector is correct that the fire pump controller breaker must handle LRC for a period of time, they just didnt realize that the breaker trip settings was being controlled from a separate device. The breaker amp rating or frame size does not tell the entire story.

 

References:

NEC2005 Handbook / NFPA70: NATIONAL ELECTRIC CODE

NFPA20-2010 Installation of Stationary Pumps For Fire Protection 



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