Fire Pump Generator

[Bjenks]

I just had someone tell me that if you have a generator feeding aa ATS that feeds a fire pump then you do not have to connect the utility to the input of the service disconnect. They say this is because if the ATS switches over to the generator then is is a being fed directly from a seperate source. Anyone heard this before? The existing system's ATS is being replaced and it presently is being fed from the panelboard after the service disconnect and then to the fire pump. I specified to have the new utility/ATS feed taken off the existing breaker and connected to the service side of the Service disconnect. However, if this new finding is true then I can keep it connect as is and only replace the ATS.

 

[Bea]

Refer to 690.3 a typical emergency generator would not be considered on site power production facility. IMO you would be required to have both emergency genertaor and another source of power. IMO if you are altering the existing supply then utility supply shoud be made a head of the main service gear but you should contact local AJH and ask them being it is existing. FYI the ATS must be fire pump rated.

 

[Bjenks]

Next question (I have never seen so many opinions of wiring fire pumps):

I am getting mixed feedback from different sources on how to size the overcurrent protection device for a generator feeding an ATS that is dedicated to the fire pump. When I read 695.4(B) it says overcurrent protective devices between an on-site standby generator and a fire pump controller shall be selected and sized according to 430.62 to provide short-circuit protection only. 430.62(A) Exception No.1 says where one or more instantaneous trip circuit breakers are used the max is based on table 430.52. So when I sized the breaker I used a Magnetic CB that was sized at 250% of the FLA. About half the people I talk to say to size it the same as the primary source protection at RLA. NFPA 20-A.9.6.5 leads me to believe I am doing this right. Any other opinions? Please back up with code.

 

[ramdiesel3500]

Let me summarize in a nutshell what the intent of the code is so it will be easier to interpret. What the code writers are trying to do is protect the conductor and up-stream equipment from a short circuit ONLY! In the event of a fire, they do NOT want an overload to cut power to the motor. They would prefer to see that motor melt completely down rather than quit pumping water on the fire! What they want is for the ocp to exceed the locked rotor current of the motor. Conductors do not have to be larger than for a normal motor installation.

 

[ramdiesel3500]

When we do fire pumps, we have a "fire pump rated" breaker installed at the generator. This breaker is sized specifically for the fire pump motor so that its overcurrent setting is just slightly higher than the locked rotor current of the motor, but otherwise the breaker lugs and case are sized for a comparable standard motor HP rating. That breaker then feeds the standby power connection in the Fire Pump ATS/Controller unit supplied by the fire pump manufacturer. The normal power side of the ATS is fed directly from the power company transformer. The Controller is always service entrance rated. Thats what we always see on the engineered plans for buildings we wire.
Hope this helps!

 

[Cavie]

IF the neutral is being switched by the ATS then itis a seperate source and must have it's own grounding.

 

[Bea]

Next question (I have never seen so many opinions of wiring fire pumps):

I am getting mixed feedback from different sources on how to size the overcurrent protection device for a generator feeding an ATS that is dedicated to the fire pump. When I read 695.4(B) it says overcurrent protective devices between an on-site standby generator and a fire pump controller shall be selected and sized according to 430.62 to provide short-circuit protection only. 430.62(A) Exception No.1 says where one or more instantaneous trip circuit breakers are used the max is based on table 430.52. So when I sized the breaker I used a Magnetic CB that was sized at 250% of the FLA. About half the people I talk to say to size it the same as the primary source protection at RLA. NFPA 20-A.9.6.5 leads me to believe I am doing this right. Any other opinions? Please back up with code.

695.3(B)(1)If the generator is a multi source for the fire pump it must be sized to carry normal starting and running of fire pump not lock rotor

695.4(B)where refers to site generator refers to 430.62 which has nothing to do with locked rotor so if you choose to size the 250% of FLA that would be correct.

 

[Bea]

Next question (I have never seen so many opinions of wiring fire pumps):

If you are refering to my post I suggest you refer you questions to AHJ in your area because they are the ones to except what is reliable that is why I used IMO my statement would be the way it would be installed in the area I work not sure about your area where ever that is.

What is the piont of an ATS if you have one source of power that being the generator.