Fire Pump Overcurrent Protection

[Shujinko]

I have a project where I designed the fire pump over current protection as follows:

A pad mounted service transformer feeds into a 300A/3ph/3wire service entrance enclosed circuit breaker which feeds into a fire pump controller. The enclosed circuit breaker is sized 6 x FLA. The service entrance enclosed circuit breaker is not part of the fire pump controller, it's separate. I specified the enclosed circuit breaker as a magnetic trip only type circuit breaker. My questions are the following:

1. The electrician and switchgear vendor are saying that in my electrical distribution layout I can't spec a magnetic only type circuit breaker because it is a code violation. Is this true? What code section does it violate?

2. The electrician/vendor want to provide a service entrance rated thermal-magnetic trip enclosed circuit breaker (300A/3ph/3wire) instead of the magnetic trip only enclosed circuit breaker. Is this a violation of NEC 695.6(C) which prohibits automatic protection against overloads on a fire pump?

In my opinion both my design and the electrician/vendor's suggestion meet the requirements of the NEC. Since the enclosed circuit breaker is sized to the Locked Rotor Amps (6xFLA) a thermal magnetic trip breaker could be used, since it is basically not providing any overload protection even if the circuit breaker is thermal magnetic trip type. LRA is way higher than what is considered an motor overload per NEC 430.32(A)(1). Thoughts???

 

[texie]

I have a project where I designed the fire pump over current protection as follows:

A pad mounted service transformer feeds into a 300A/3ph/3wire service entrance enclosed circuit breaker which feeds into a fire pump controller. The enclosed circuit breaker is sized 6 x FLA. The service entrance enclosed circuit breaker is not part of the fire pump controller, it's separate. I specified the enclosed circuit breaker as a magnetic trip only type circuit breaker. My questions are the following:

1. The electrician and switchgear vendor are saying that in my electrical distribution layout I can't spec a magnetic only type circuit breaker because it is a code violation. Is this true? What code section does it violate?

2. The electrician/vendor want to provide a service entrance rated thermal-magnetic trip enclosed circuit breaker (300A/3ph/3wire) instead of the magnetic trip only enclosed circuit breaker. Is this a violation of NEC 695.6(C) which prohibits automatic protection against overloads on a fire pump?

In my opinion both my design and the electrician/vendor's suggestion meet the requirements of the NEC. Since the enclosed circuit breaker is sized to the Locked Rotor Amps (6xFLA) a thermal magnetic trip breaker could be used, since it is basically not providing any overload protection even if the circuit breaker is thermal magnetic trip type. LRA is way higher than what is considered an motor overload per NEC 430.32(A)(1). Thoughts???

Sorry, but you lose this one. Magnetic only (AKA instantaneous) can only be used as part of a listed assembly such as a combination motor starter per 430.52(C)(3). I don't think that mag only breakers are even "listed", but rather a "recognized" component to be used in a listed final product.
To satisfy Article 695 (if you are putting an OCPD ahead of the fire pump controller) you need to use an inverse time breaker ( or other type of OCPD) sized to carry LR indefinitely.

 

[gadfly56]

Are you sure that you are sizing the OCPD correctly? If you are using 6xFLA as a rule of thumb you may be too low. There is a table in NFPA 20 that gives you LRC as a function of horsepower.

 

[Shujinko]

Are you sure that you are sizing the OCPD correctly? If you are using 6xFLA as a rule of thumb you may be too low. There is a table in NFPA 20 that gives you LRC as a function of horsepower.

View attachment 16639

The fire pump is 25HP @ 460V and the Jockey pump is 2HP @ 460V. Looks like the table in your post is for motors at a utilization voltage of 230V.