Limited Service Fire Pump

[infinity]

I have a 30 HP fire pump in the machine room on the top of the building. Local code calls this a limited service fire pump. Information is somewhat limited and this is not mentioned in the NEC, what is the actual application of these fire pumps and how do they differ from a standard fire pump? Here's the local definition as it applies to the electrical code:

Limited Service Fire Pump. For the purposes of this section, a Limited Service Fire Pump is a fire
pump located above street level with a motor rating not exceeding 30hp and connected to a limited
service fire pump controller.

 

[packersparky]

I don't know that the pump itself is a limited service fire pump. Everything that I know about Limited service has to do the the controllers. The controllers are limited to 30 hp or less, have to start the pump across the line, and the motor has to be a squirrel cage type motor. I believe they were more prevalent a few years ago as they were cheaper than a regular fire pump controller, but there is not much difference in price anymore.

 

[drktmplr12]

I have a 30 HP fire pump in the machine room on the top of the building. Local code calls this a limited service fire pump. Information is somewhat limited and this is not mentioned in the NEC, what is the actual application of these fire pumps and how do they differ from a standard fire pump? Here's the local definition as it applies to the electrical code:

UL Paper

Full Service Fire Pump Controllers are themost common controller type for an electricmotor pump and are intended for use withstandard-size, electric-driven centrifugal firepumps utilizing squirrel-cage or wound-rotormotors rated 600-volts or less. Controllersfor squirrel-cage motors may be across-thelinestarting or reduced-voltage starting asindicated in the individual Listings.

Limited Service Fire Pump Controllersare restricted to use with across-the-linetype squirrel-cage motors rated 30 hp orless, 600-volts or less. AHJs should beconsulted before installing limited servicecontrollers since ANSI/NFPA 13, Standardfor the Installation of Sprinkler Systems,has specific limitations on where and howlimited service fire pump controllers maybe used.

https://iaeimagazine.org/magazine/2005/03/16/limited-service-controllers/

NFPA 20 mandates, among other things, that motor protection provided by fire pump controllers be of the non-thermal type, be immediately re-settable and that it provide short-circuit and locked-rotor protection only (no overload protection). These requirements are tempered for the LSC so that it performs more like a specialized industrial motor controller than a fire pump controller. Motor protection for the LSC is permitted to be of the thermal type that may require cooling time in order to be re-settable. Locked rotor overcurrent protection for the LSC is addressed in paragraph 10.7.2.1 of NFPA 20 (2003)—””the locked rotor overcurrent protection shall be permitted to be achieved by using an inverse time nonadjustable circuit breaker having a standard rating between 150 percent and 250 percent of the motor full-load current.”” This may produce performance considerably different than the desired and required 8–20 seconds locked-rotor current tolerance time before tripping that is unique to fire pump controllers.

Thus, under certain circumstances, the limited-service controller may trip too quickly to adequately start a distressed pump, take too long a time to reset under fire conditions, or protect the motor from damage. AHJs, in making their decisions, must also realize that the LSC does not contain an isolating switch, which is required in fire pump controllers. Thus, if service on the thermal-magnetic circuit breaker is required, loss of fire protection may be prolonged since often the LSC is connected directly to utility power.

Personally I would do two things-first call the AHJ and see what requirements they have, if any. Second, treat it like a regular fire pump and provide an isolation switch sized per NEC for flexibility.

 

[infinity]

Here's the problem, the local code uses the definition below for a Fire Pump which doesn't apply to the 30 HP pump in question. That leaves the other definition outlined in the OP. So basically we have two pumps, one 40 HP below street level and one 30 HP near the roof.

Fire Pump. For the purposes of this section, a fire pump is any Manual Standpipe Fire Pump,
Automatic Standpipe Fire Pump, Sprinkler Booster Pump, Special Service Fire Pump, Spray Mist Fire
Pump or Foam Fire Pump located at or below street level or with a motor rating exceeding 30hp.

Limited Service Fire Pump. For the purposes of this section, a Limited Service Fire Pump is a fire
pump located above street level with a motor rating not exceeding 30hp and connected to a limited
service fire pump controller.

The question arises because the LSFP is limited to an OCPD set at 150% of the motor current (local code) but the engineer is setting it higher like a fire pump at 300% (local code 300%-600%). I realize that some of these numbers differ from the NEC but they're dictated by the local code.