ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Recent Posts
Al Hildenbrand - Minneapolis - obituary
by Bill Addiss - 02/03/23 07:38 PM
by renosteinke - 01/27/23 09:52 PM
Does NEC 551.71 (F) apply to dwellings?
by BigB - 01/20/23 10:46 AM
Power submeter connections
by HotLine1 - 01/19/23 09:09 AM
New in the Gallery:
Burger King crown sillyness
Burger King crown sillyness
by wa2ise, December 11
240/208 to a house
240/208 to a house
by wa2ise, October 9
Who's Online Now
1 members (Scott35), 40 guests, and 14 robots.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
#214124 10/08/14 03:23 PM
Joined: May 2010
Posts: 30
Bravo Offline OP

I am working on a design for the installation of a new fire pump/room and want to make sure my design intent meets code. I will try to keep my description short as possible.

The client site is a multibuilding campus-style complex with fire pump in one building so power source will be a feeder, not a utility service so 695.3(A)(1) will not apply. There is a onsite generator that will be used as an alternate source per 695.3(B)(1).

My intent is to tap the bus ahead of the load center main breaker to a disconnect switch (DS) rated 1200A. The DS will be within 25ft & the tap conductors will be rated for 400A (600MCM).

The DS will be installed seperate and not within the equipment that feeds other fire pump loads and will be located between the power source and the listed fire pump controller. The DS will be supervised per 695.4(B).

The DS will be sized for lock rotor but the generator breaker will be sized to run the motor.

My question, is my design intent in any violation of Art 695? Would you make any suggestions or have any problems with the design intent?

Thank you in advance

Stay up to Code with the Latest NEC:

2020 NEC & Related Reference & Study Guides
2020 NEC & Related Reference & Study Guides
Pass Your Exam the FIRST TIME with these Exam Prep Combos:

>> Master Electrician Exam Prep     >> JourneyMan Electrician Exam Prep

Joined: Jun 2004
Posts: 1,273
Off hand...

The FIRST issue is whether the fire pump is deemed auxiliary or life-safety essential and critical.

If you don't know that status, then you can't begin your design.

Auxiliary fire pumps are installed because the fire insurance company gives the facility a nice price break on insurance. Such an installation provides FULL performance in the sprinkler array. Any fire gets snuffed out QUICK. This is deemed essential (on the economics) if, say, a warehouse is loaded with inflammable goods. (furniture storage, ...)

An essential and critical life-safety fire pump is not oriented towards goods just people. Any structure that is sure to hold very large numbers of the general public is held to this standard. This is why all new football stadiums are built out of steel and concrete. A century ago, the norm was wood; it's so much cheaper and quicker to erect.

If the design is held to the higher standard, then the prime mover (engine) for the fire pump gets bumped up. How much it gets bumped is usually outside the NEC. Your Fire Marshall is the AHJ. There's really nothing we can say about it.

The folks that build fire pumps usually have a pretty solid handle on what's involved and are your best design source.

Typical issues don't even turn on conductor sizes, which most guys figure pretty quick. Instead, RACEWAYS are the issue. These systems are VERY picky about protecting the conductors. Generally they have to be encased in concrete and rigid metallic conduit (long runs) or buried in rigid non-metallic conduit or rigid metallic conduit, exposed.(limited distances, ask AHJ) The only exception to this is the final whip to the motor, itself. That will be in Sealtite.

Other BIG issues turn on how you're going to enter the frame of the fire pump controller and getting the voltage right. (208Y120 is NOT acceptable for a 240V rated controller and pump. This trips up MANY.)

Getting underground conduits in before the slab is poured can save you an ocean of money.


As for your conductor math it looks way off. C/Bs for fire pumps are set at melt-down levels. So a 200A normal draw (3/0-4/0 conductors, distance de-rated) is mated with a 1200A C/B. The disconnecting means is used for service purposes only. So in this case, the switch would be a 200A frame size beast. (NEMA1 or NEMA3R)

Unless you run a LOT of RMC, stay with thread-less connectors. Yes, they are very expensive. They are also virtually idiot proof.

Plan on EVERY auxiliary circuit being in RMC, too. Figure on a jockey pump circuit and service lighting, a GFCI or two. These can tap the same Fire Pump Service but must do so far enough ahead to make service calls on the pump controller possible. (when the controller is de-energized) Buchanan has K-taps that are often used to feed a SDS in such layouts. If this is done, figure on another fused disconnect just for the auxiliary circuits. Figure ona Sparately Derived Service. (480Y277 Service MAIN ==> 208Y120 sub-panel; or 480V ==> 240/120V single phase (center) tapped SDS. The loads are so trivial that single phase is common; jockey pumps are typically 240-208V.

The gen-set is expected to be co-located. But it's not an absolute requirement. If it's any distance away, then you're destined to be using the same (underground/ under-slab) raceways as above.

The gen-set is also going to have issues such as: block heater engine warm 100% of the time; Diesel fuel (never gasoline) the tank sized to run X minutes natural gas is expected to be cut-off. (earthquake/ terrorism/ collision/ jet impact (9-11), etc. )

It's control circuits will also get the full raceway treatment. You'll have to attain cleanances all around the gear -- any and all of it -- so that the service personnel can do their thing without touching the field conductors. Beware.

A regular engine run test will be mandated by the AHJ if the system is deemed life-safety critical.

So, as you can see, the status of the fire pump dictates a slew of design issues that are NOT in the NEC. So stop looking there. It's a total waste of your time.

The guy who's going to really design your system is the AHJ. He'll lay out the broad strokes. THEN you can get to work. You want plenty of lead time to get your underground raceways in place dead on!

You want to enter the fire pump controller in an approved manner. No, you can't enter the chassis any way you want, anywhere you want. You'll need exact cut-sheets for it.

The mechanical layout of the fire pump is essential. Watch out, those boys can hold their stuff back to leave you scrambling to do your thing.

Your general installation standards will be right up there with elevator control rooms: super picky.

Fire pumps (essential life-safety critical) are as difficult as Division 1 chemical plants. Nothing will be fast, easy or cheap. They are designed for WWV and the Apocalypse.

Auxiliary fire pumps are only a tad easier. The only major difference being gen-set sizing. BTW, MOST of the fire pumps (in commercial locations) are auxiliary fire pumps.

You would be extremely wise to get a j-man on your job who has been down this road before -- a top notch j-man.

Joined: Apr 2002
Posts: 7,333
Likes: 7
Your synopsis sounds OK, with a few questions.

The tap conductors are considered 'unprotected' and must be treated with the usual 'outside the structure'. until they terminate in the FP room, under the controller.

The genset capacity has to be further refined, as you did not mention that it has capacity to maintain power to the pump under all conditions.

A good source to look into is a NEC Handbook; and a Tesla said, conversations with the local Fire and Electrical Officials before you finalize the drawings/design will save you time.

Last edited by HotLine1; 10/08/14 09:51 PM.

Joined: May 2010
Posts: 30
Bravo Offline OP

Thank you for your reply. The fire pump would be for life-safety.

My main concern or question is can I feed the fire pump controller from a branch breaker in a unit substation or do I have to tap the bus ahead of the main breaker to a disconnect switch?

You are correct that I should consult with the AHJ sooner than later

Joined: Jun 2004
Posts: 1,273
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.


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.


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 01:53 PM.

Joined: Jun 2004
Posts: 1,273
BTW, the term Life Safety is bandied around all the time by the trade -- even if the fire pump is actually just and auxiliary fire pump.

You'll find that there are actually various levels of over-kill within the fire pump world.

Auxiliary fire pumps dominate the market -- by far.

"Fire Saftey - Critical" is pricy. It's the Cadillac.


Link Copied to Clipboard

Tools for Electricians
Tools for Electricians

* * * * * * *
2023 National Electrical Code (NEC)
2023 NEC Now Available!
* * * * * * *

2020 Master Electrician Exam Preparation Combos
2020 NEC Electrician
Exam Prep Combos:
Master / Journeyman


Member Spotlight
Amish Country, PA
Posts: 46
Joined: March 2013
Top Posters(30 Days)
triple 3
BigB 3
Popular Topics(Views)
303,144 Are you busy
232,163 Re: Forum
216,890 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.7.5