Fire Pump Over current Protective Device Sizing

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Transportation Guy

Senior Member
Location
Williamsburg,VA
Good afternoon ladies and gents. I have a project here in VA (2008 NEC) and we are providing a on site Natural Gas generator for fire pump operation ONLY. Per the 2008 Code, if i read 695.4 (1) correctly, it states we have to size the OCPD for locked rotor current. Correct?

In the 2011 cycle, it states in 695.4 (B) (2) size it for instantaneous pickup of the full pump room load (whatever that means) and shall comply with 430.62 which sends me to 430.24, 430.52, or 440.22 (A)

The pump is 40.0 H/P, 3525 RPM,
3 PHASE, 60 CYCLE, 208 VOLT,

The engineer says we need a 700AMP OCPD
The manufacturer says we need only a 400AMP

Help!
Thanks
 
The breaker for the generator source is not required to carry LR current as the normal supply does. As you noted, the 2008 and 2011 versions are different. There really is not a change here as the end result is the same-you don't have to have the generator breaker carry LR current. The reason for this is simple-the generator feeding the breaker can't carry LR anyway.
 
LRA for 208 40 hp = 641 amps per NEC. You would normally Use 700 amp breaker. However, as Tex says the Gen may not be able to supply this.
Has the MFG said the Gen is capable of starting this 40 hp motor? You did not list the Gen KVA.
 
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Fire Pump Generator

Fire Pump Generator

ron said:
As a side note, I thought fire pump emergency feeders would come from an Article 700 or 701 source, which has to have on-site storage of fuel.
Click to expand...

700.12 General Requirements

(B) Generator Set

(3) Dual Supplies
Exception: Where acceptable to the authority having jurisdiction, the use of other than on-site fuels shall be permitted where there is a low probability of a simultaneous failure of both the off-site fuel delivery system and power from the outside electrical utility company.


We had the AHJ approve the N/G.

The GenSet is a 60KW
 
Fire Pump Generator

Fire Pump Generator

bob said:
LRA for 208 40 hp = 641 amps per NEC. You would normally Use 700 amp breaker. However, as Tex says the Gen may not be able to supply this.
Has the MFG said the Gen is capable of starting this 40 hp motor? You did not list the Gen KVA.
Click to expand...

The Manufacturer recommended a soft start wye-delta starter which the fire pump manufacturer will supply for an additional $3700.00. If that wasnt an option, we would have had to go to a 175KW which would have been an additional $50k. (the owner liked $3700.00 option)
 
2014 NEC

2014 NEC

Never opened it but had a friend send this to me. He said it is from 2014 Cycle.

"The generator disconnecting means and the OCPD for the electric driven fire pump are not required to be sized for locked-rotor current of the fire pump motors. "
 
ron said:
As a side note, I thought fire pump emergency feeders would come from an Article 700 or 701 source, which has to have on-site storage of fuel.
Click to expand...

NFPA 20 (2007) 9.6.2.2 "The fuel supply connection shall be sufficient to provide 8 hours of fire pump operation at 100 percent of the rated pump capacity in addition to the supply required for other demands."
 
Transportation Guy said:
Never opened it but had a friend send this to me. He said it is from 2014 Cycle.

"The generator disconnecting means and the OCPD for the electric driven fire pump are not required to be sized for locked-rotor current of the fire pump motors. "
Click to expand...

That may be; in 2011 it looks like it might be required to carry LRC even if the generator can't supply it. I agree it doesn't make sense since NFPA 20 (2007) only requires that the generator be sized for the normal start and run of the fire pump and other connected loads (not applicable here). The only additional requirements are regarding voltage drop in 9.4.
 
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