Gen Set size w/ Fire Pump

[Sparky2791]

I found an old thread (2013) that was closed on this which helped a little but thought I would bring it up for discussion.

From my research of NFPA20 due to the by-pass handle required per NFPA20 10.5.3.2 on the controller the generator needs to be size for across the line starting. NFPA20 9.6.5 has explanatory paragraph A.9.6.5 which specifically states this. See attached snip

When you have a 200HP fire pump that is not going to be a small generator. One of those worst case scenarios we need to plan for that would only happen if we did not. We've all been there.

I understand the 15%VD requirement of NFPA20 9.4.1 does not apply when in manual bypass per 9.4.2 & 9.4.3 but you still need to demonstrate the gen set can start with the fire pump and any additional load it carries. 'Ignoring' the 15% VD is nice but in the end it will really help a whole lot. Ill be looking to work with a supplier to size it but wanted to see if anyone had any comments on this.

IMO this requirement really sells the use of a diesel FP for those large HP pumps unless you can meet the NFPA requirements of a reliable source of power and get the AHJ to agree. Something I have done only 2 times in my 25 plus years doing this.


Thanks for the replies!

 

[hillbilly1]

The generator only has to start and run the fire pump, but is not required to provide locked rotor power. A lot of engineers will interlock the fire pump with the optional standby loads, so that they are dropped to run the pump, that way a huge generator is not wasted to just run the pump.

 

[topgone]

The generator only has to start and run the fire pump, but is not required to provide locked rotor power. A lot of engineers will interlock the fire pump with the optional standby loads, so that they are dropped to run the pump, that way a huge generator is not wasted to just run the pump.

Another option: In my previous job, I have to drop the generator-pump combination altogether to do away with the high locked-rotor amps. It was easier having an engine-driven fire pump set. Once installed, it was an "install and forget thing".
Honestly, I found it hard convincing my plant manager who was not keen of buying the UL-listed fire pump set (the engine-driven one) him saying we still have to buy a smaller generator to provide power to the electric-driven jockey pump and other required emergency loads. The costs were prohibitive but we did buy that smaller genny plus the UL-listed fire pump. The positive thing was that we got lower insurance premium thereafter, almost paying off the additional cost of the new fire protection system upgrade.

 

[hillbilly1]

Another option: In my previous job, I have to drop the generator-pump combination altogether to do away with the high locked-rotor amps. It was easier having an engine-driven fire pump set. Once installed, it was an "install and forget thing".
Honestly, I found it hard convincing my plant manager who was not keen of buying the UL-listed fire pump set (the engine-driven one) him saying we still have to buy a smaller generator to provide power to the electric-driven jockey pump and other required emergency loads. The costs were prohibitive but we did buy that smaller genny plus the UL-listed fire pump. The positive thing was that we got lower insurance premium thereafter, almost paying off the additional cost of the new fire protection system upgrade.

We wired a large distribution center that had a pond and diesel driven fire pump. Maintenance would do a monthly check on it, and it wouldn’t start. Had a low fuel alarm. Banged on the day tank, it sounded empty. Opened it up, and it was. I told them they have to refill the main tank occasionally. Then it came to them, someone on a forklift hit sprinkler line one weekend, and it ran all day. Turns out, they didn’t even have a fuel supplier set up to keep it full! LOL!

 

[zbang]

"Well, there's your problem."

 

[Sparky2791]

buy a smaller generator to provide power to the electric-driven jockey pump

The jockey pump is not required to be on emergency power. What I am reading from the above posts from everyone is basically what I stated at the end of my OP. Use a diesel driven pump.

to do away with the high locked-rotor amps

I assume by your statement you mean do away with the motor in rush which is basically equal to LRA.

The positive thing was that we got lower insurance premium thereafter, almost paying off the additional cost of the new fire protection system upgrade.

This is interesting. I wonder what the reasoning is for that. Perhaps less components to fail. Something to have the client look into.

 

[Sparky2791]

We wired a large distribution center that had a pond and diesel driven fire pump. Maintenance would do a monthly check on it, and it wouldn’t start. Had a low fuel alarm. Banged on the day tank, it sounded empty. Opened it up, and it was. I told them they have to refill the main tank occasionally. Then it came to them, someone on a forklift hit sprinkler line one weekend, and it ran all day. Turns out, they didn’t even have a fuel supplier set up to keep it full! LOL!

You ever see the movie Sling Blade........'Ain't got no gas in it' 'Uh huh'

 

[Sparky2791]

The generator only has to start and run the fire pump, but is not required to provide locked rotor power. A lot of engineers will interlock the fire pump with the optional standby loads, so that they are dropped to run the pump, that way a huge generator is not wasted to just run the pump.

Yes, that is a good consideration. I realize it does not need to provide locked rotor power but it does need to be sized appropriately to carry the load on in rush of the motor which in the end could warrant the same size or close to the same size gen set. I'll have to work with the vendor to run some calcs on this.

 

[hillbilly1]

Lowes dumps the whole store on the ones that we retrofitted a generator to. Since it is an optional standby system, they still maintained the battery lights. An issue they had, is a lot of fire pumps “fail on” momentarily, so with no delay, the store would trip out, and would have no generator backup the next time. I redesigned the control circuit where both fire pump AND store had to be on generator before it would trip. That solved the problem with the fire pump transferswitch exercising, and had the manufacturer put a short delay on the fire pump run output to keep it from nuisance tripping when utility was restored.

 

[Sparky2791]

and would have no generator backup the next time

Was this because it is a manual reset on the transfer switch for optional standby loads if it tripped due to FP start?

where both fire pump AND store had to be on generator before it would trip.

So the gen set is sized to handle start of the fire pump Across The Line and the store loads simultaneously ?

 

[hillbilly1]

Was this because it is a manual reset on the transfer switch for optional standby loads if it tripped due to FP start?

So the gen set is sized to handle start of the fire pump Across The Line and the store loads simultaneously ?

1. Yes, done via shunt trip breaker. (Utility stays closed, but generator main opens)
2. No, genset can run store, or pump. But not both simultaneously.