I have an existing facility with a 480V, 60HP fire pump. This fire pump is fed upstream from the Utility, goes through a 600A rated disconnect and through a 100A Fire Pump ATS. The emergency side of this Fire Pump ATS is fed off of a generator with a 600A breaker.
The Locked Rotor Current of a 60HP motor is approximately 435A per NEC Table 430.251(B).
According to NFPA 20:
And NEC Article 695:
It appears that this ATS is undersized. How can an ATS supply power to the Fire Pump under locked rotor conditions, in this case 435A, when the rating of the ATS is only 100A? Would this ATS not fail as a result?
A local rep says that the locked rotor conditions are built into the fire pump controller. But that still doesn't explain how this ATS will continue to operate.
What am I missing here?
The Locked Rotor Current of a 60HP motor is approximately 435A per NEC Table 430.251(B).
According to NFPA 20:
10.8.3.4 Horsepower or Ampere Rating.
10.8.3.4.2 Where rated in amperes, the power transfer switch shall have an ampere rating not less than 115 percent of the motor full-load current and also be suitable for switching the motor locked rotor current.
And NEC Article 695:
NEC 2005: Article 695 ? Fire Pumps
695.3 Power Source(s) for Electric Motor-Driven Fire
Pumps. Electric motor-driven fire pumps shall have a reliable
source of power.
(A) Individual Sources. Where reliable, and where capable
of carrying indefinitely the sum of the locked-rotor current of
the fire pump motor(s) and the pressure maintenance pump
motor(s) and the full-load current of the associated fire pump
accessory equipment when connected to this power supply,
the power source for an electric motor-driven fire pump shall
be one or more of the following.
It appears that this ATS is undersized. How can an ATS supply power to the Fire Pump under locked rotor conditions, in this case 435A, when the rating of the ATS is only 100A? Would this ATS not fail as a result?
A local rep says that the locked rotor conditions are built into the fire pump controller. But that still doesn't explain how this ATS will continue to operate.
What am I missing here?