You'll find that EVERY C/B in the series going up the line has to be sized large enough to permit the pump motor to melt down.
In this way, they flow current until a bolted-short condition -- ie the feeder conductors break down and short directly across or to ground.
A bolted-short will trip even a heft C/B. (When the NEC standards are followed.)
The power available from a step-down transformer tapping the primary distribution loop must also be great enough for the fire pump. As a practical matter, it always is.
It's also common for a specific Service to be established for the Fire Pump Room. It will be fed by underground conductors directly tapping the Poco's transformer.
It will be sized large enough to melt down the fire pump C/B wise -- which means that its frame size will also be hefty. A 200A motor load will get a 1200A or 1600A dedicated Service! The U/G feeders to that service will be hefty, too. But they can be aluminum.
The run to the motor from the dedicated Service must be in copper -- typically unbroken (no splices at all) -- it can have K-taps. (Buchanan, as above.)
If the Poco is unable to supply power, the gen-set has to fire right up.
The typical Fire Pump Controller has this logic integrated into its scheme. But, since these are actually custom builds, I can provide no guarantees.
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Having built a few, I can assure you the ringers turn on raceway assembly. You don't begin to have the normal degree of freedom. Most j-men find such restrictions a real trial.
Even RMC -- exposed -- is limited in length.
The Fire Marshall will NOT be held to anything he said before. Understand that. He'll only approve the install if everything is professionally done and totally squared away.
You'd better have language in your contract that allows you to pass on Fire Marshall change orders. Yes, they happen all the time. If your Fire Pump Room is truly totally dedicated, he may give you some slack.
You'll also find that any layout has to accomodate the entry door. The Fire Pump Control has to be set -- just so -- versus the entry door. Putting it along the far wall will be rejected.
In this, the thinking is very similar to elevator control rooms. The AHJ wants emergency responders to have idiot-obvious direct line of sight to the controller. All He!! may have broken loose before the responder arrives. He may have had to axe the door.
These are the kinds of hang-ups that don't make the NEC -- and are only brought up late in the game. The only folks that are truly 'hip' are the fire sprinkler boys. Sadly, they may not show up until you're totally committed to a design.
I'd put them on speed dial during the design phase. They can make or break you.
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You get a break on conductor sizing -- but not on the GROUNDING CONDUCTOR. It has to be sized for the C/Bs -- and they are monsters.
THIS ^^^^ commonly results in design error. The grounding conductor gets (erroneously) sized for the cross section of the conductors -- like they were Service feeders.
Then, the j-man is puzzled as to why the grounding lug is so massive. Then the job is red-tagged for a grossly undersized grounding conductor. Whenever that happens, the EC wants to shoot himself as he has to upsize his raceway.
Last edited by Tesla; 10/09/14 02:53 PM.
