Circuit Breaker Rating for Fire Pump Controller: Need Urgent Help

In the absence of an electrical standard to work to, play safe and install the 150A one. To hell with the additional expense.

NFPA standards are applicable.

I believe NFPA 20 & NFPA 70 is relevant in this case.

Follow the standard, then. If in doubt, consult a qualified Electrician locally. Make sure a test certificate is forthcoming after installation, recording the correct nature of the installation.

Unfortunately ,I am not clear from the standard.

Whether the standard requires circuit breaker to be sized minimum 125% i.e 63 Amp or 300% ie 150 amp?

Sorry but I am not good wit these electrical terms.:(

If this is classified as a fire pump, and built accordingly, NFPA takes precedence.

Your "electrical team" isn't correct even with regard to the NEC.

But NFPA 20 10.4.3.3.1 says circuit breaker electrical charcterstic to be minimum 115 percent of full load current only .

Is it requiring 300 percent ?

Yes. Please reread your original post, where it says that 300% for 3 minutes is required.

(The minimum of 115% does not prevent the CB from being larger, as needed to fulfill other required items.)

Now you're arguing. Stop it.

I love this attitude of maintenance electricians "it might burn out without the correct protection".

So what? The buildings on fire!

BTW I've spent all my life in electrical maintenance. I've pulled some crazy tricks to get a process back under control. Motor protection? Who gives a stuff! There's going to be a very big bang if the process gets out of control.

Per NEC/NFPA70 695 and NFPA 20 the main breaker in the controller is rated at 300%, but the supply breaker must be 6 times FLA or locker rotor. The cable is still sized per NEC 430 @ 125% of FLA. Basically you only want short circuit protection and not over current. You do not want the controller to trip out because of amps during a fire. I do this all day every day for fire protection. Please feel free to contact me if needed.

P.S. The main breaker in the controller is considered lock rotor protection breaker. If coming off a transformer the protection is on the primary side only and rated to carry locker rotor and additional pump house loads only related to fire pumps and not the secondary. It would be too costly if on the secondary side as well.

The circuit breaker is sized to protect the motor lead conductors, not the motor.

The circuit breaker must also be capable of withstanding the high motor current "inrush" during starting which is often 3 x FLA without tripping/opening and rendering the pump unavailable.

The motor lead conductor size has been designed by the manufacturer to meet NFPA and NEC requirements.

Motor protection is is provided by the motor starter and/or motor protection relay(s).

Can't see why this one got an off topic, but probably done by one of the same as usual know-alls.

The response is absolutely correct in that a circuit breaker is there only to protect the circuit conductors which should be sized to adequately carry the required circuit loading, the starter overloads are there to protect the motor.

Whilst fire protection apparatus have specific requirements regarding tripping values, the above still holds true.

Fire pump motors are not equipped with overload relays.

Does NFPA mention anything about method of stating(DOL,star delta,AT,VFD etc) for 300% FLC?.

Thanks everyone..

Its clear for me.

I am going with the 150 amp so that the electrical motor doesn't trip easily.

Thanks again..

Hi. all

The electrical equipment dedicated to emergency condition have a proper regulation in all kind of standard through the world.

I think JRaelf is right, you will've to adopt a limit in between, ie. not to create another fire in the equipment room but at same time not to trip the fire pump in the middle of the existing fire. The best you can do is to install the 150 A CB and an additional overload alarm, so on critical condition event someone will decide what action have to be take (as Salomonical decision)

Bye