Electric Fire pump feeders 1

[EEJaime]

Hello gentlemen,
I am a consulting electrical engineer and have come across a design dilemma. We will take this to the AHJ, but I thought it would be nice to get some input from some code experts to see if I was on the right path.

We are working on an addition at a major airport and part of the scope are new generators and a fire sprinkler system with partial deluge sprinklers on some exterior curtain wall systems. This has resulted in the need for a 2000gpm system served by two new electrically driven, 125 HP fire pumps. No problem there.

What I am having a problem resolving is the number of overcurrent protective devices in the supply line to the Fire Pump controller/ATS.

ON THE GENERATOR SIDE:
The emergency power to the building is served from 2-1500kW diesel engine driven generators operating in parallel through a synchronizing switchboard. The 5000A, 480V, 3Ph, 4w, 60Hz switchboard has two draw-out type air circuit breakers that feed the two fire pumps via the ATS'. I have located these ahead of the main circuit breaker. The Life Safety, Smoke Control, Mechanical and I.T. branches are fed downstream of the main.

My first question is this. Since I have non-automatic breakers at the generators for maintenance purposes, and then the synchronization breaker at the switchgear, is it a problem to have the generator feeder breaker for the generators? NFPA 20, 9.6.1.2 states that "A tap ahead of the on-site generator disconnecting means shall not be required." So are the three disconnecting,(two being overcurrent devices), violate the limitation of the number of overcurrent devices in a Fire Pump feeder?

NORMAL POWER FEEDER:
This is more complicated. We have a 34.5kV on-site distribution system. The buildings are fed by a series of 34.5kV-480Y/277V,3Ph,4w substations which in turn feed into double ended MAIN-TIE-MAIN 480V distribution switch boards.
Normally I take the Fire Pump ATS feeders primary to the 480V main and follow standard Fire pump control protocol. My problem is in figuring out a control sequence since these switchboards are source transfer, redundant switchboards. If my Fire Pump feeders are ahead of Main #1 and everything is running normally, that is ok. But if for some reason Main #1 is opened or for any reason service #1 is off-line the system is designed to automatically transfer to service #2, and my Fire pumps are without power. Obviously that cannot happen. I can take a feed from each service, but then under normal conditions they are both hot. This cannot be a new condition, All I can see is that I need a second layer of transfer switches for the normal power feeder from the two services.

There must be some simpler way, has anyone done this? I feel I am missing something basic.

Thank you in advance for any input.
Regards,
EEJaime

 

[stookeyfpe]

I'm not an electrical engineer, and parts of this post are well beyond my technical skills.

With that said I have one question: Are the pumps on a legally required emergency power circuit and if so, why? The only time a fire pump is required to be connected to an emergency power branch circuit under International Building Code is when the building is a high-rise structure and the occupied level is more than 75 feet above the lowest level of fire department access.

 

[rbulsara]

If you have a emergency power source (generators) as the alternate source, you need not go ahead of the main on the utility side.

Likewise there is no need to go to ahead of the main of the generator main either. That is only needed if the generator is too small and you need to shed the building loads to allow the FP to run on generator.

If you have a M-T-M auto throw over scheme, a feeder breaker has greater availability than the tap ahead of the main (which is not even required).

Rafiq Bulsara

http://www.srengineersct.com

 

[EEJaime]

Gentlemen,
That is exactly the information I needed. I knew I was overthinking this situation. I appreciate your input. Sometimes I seem to "engineer" myself into a corner of my own making.
Regards,
EEJaime

 

[EEJaime]

Stookeyfpe,
The existing portion of the building was ruled a high rise. The current expansion has the highest occupied level at 74'-6" above fire department access level. It is seperated from the existing by smoke doors at the interface and physically seperated otherwise. It has complete new systems for all utilities except fire sprinkler water and other wet utilities. The building we are working on is not technically a high rise by the AHJ's read so far.
Thank you,
EEJaime

 

[stookeyfpe]

It's a sprinklered building - when will we learn. So sad.