Fire pump question

[Npstewart]

Just a couple of questions that resulted from confusion from article 695.

If I have a 100HP fire pump @ 208-3 phase + a 1-1/2 HP jockey pump

Fire Pump FLC = 273A
Jockey Pump FLC = 6.6A
Total @125% = 349.5
Design ampacity = 400.0


Fire Pump LRA = 1603A
Jockey Pump LRA = 44A
Total = 1647A
Design Ampacity = 1800A

So my feeder can be rated at 400amps, and my disconnect (non fused) should be rated @ 1800amp.

Questions:

Should my ground from the disconnect to the fire pump controller be sized per 250.122 (or) 250.66?

Also, if the feeder has to run inside the building what type of wire is required, as I understand it has to be rated for 2 hours.

 

[david luchini]

Just a couple of questions that resulted from confusion from article 695.

If I have a 100HP fire pump @ 208-3 phase + a 1-1/2 HP jockey pump

Fire Pump FLC = 273A
Jockey Pump FLC = 6.6A
Total @125% = 349.5
Design ampacity = 400.0


Fire Pump LRA = 1603A
Jockey Pump LRA = 44A
Total = 1647A
Design Ampacity = 1800A

So my feeder can be rated at 400amps, and my disconnect (non fused) should be rated @ 1800amp.

Questions:

Should my ground from the disconnect to the fire pump controller be sized per 250.122 (or) 250.66?

Also, if the feeder has to run inside the building what type of wire is required, as I understand it has to be rated for 2 hours.

The feeder needs to be rated not less than 349.5A. So 500mcm (380A) would be OK.

The disconnect would require fuses (or use a c/b type) per 695.4(B).

I believe the ground would be an EGC sized per 250.122.

The feeder needs to be a 2 hour protective system type (such as MI cable.) Or, it can be encased in 2" of concrete, or be protected by a 2 hour rated assembly dedicate to the fire pump feeder.

 

[Npstewart]

I didn't think it required fuses because technically I could run the fire pump directly off the transformer...The only reason why I would use a disconnect is for the poor person that has to service it would have to be VERY fast in order to avoid getting shocked lol.

 

[david luchini]

I didn't think it required fuses because technically I could run the fire pump directly off the transformer...The only reason why I would use a disconnect is for the poor person that has to service it would have to be VERY fast in order to avoid getting shocked lol.

695.4(A) allows you to connect supply conductors directly to the fire pump controller...

695.4(B) allows a single disconnecting means AND OCPD between the power source and controller (or transfer switch.)

I read that as, if you provide a disconnect it must have an OCPD.

 

[Npstewart]

Thanks everyone!

 

[iwire]

Don't forget voltage drop when sizing the conductors

695.7 Voltage Drop. The voltage at the controller line terminals
shall not drop more than 15 percent below normal
(controller-rated voltage) under motor starting conditions.

The voltage at the motor terminals shall not drop more than
5 percent below the voltage rating of the motor when the
motor is operating at 115 percent of the full-load current
rating of the motor.

Exception: This limitation shall not apply for emergency
run mechanical starting. [20:9.4.2]

 

[Npstewart]

Yea, I am now feeding the fire pump with #700s due to distance.

So if my FLC is 279.9, I have to multiply that by 125% to size my feeders etc, which puts me at 349.5. So do I need to multiply that by 115% for my voltage drop calculation, which would put me at 401?

(or)

multiply 279.9 (my original FLC) by 115% to use for my voltage drop equation?

 

[iwire]

I think for figuring the voltage drop for start up you need to use the locked rotor current.

 

[david luchini]

Yea, I am now feeding the fire pump with #700s due to distance.

So if my FLC is 279.9, I have to multiply that by 125% to size my feeders etc, which puts me at 349.5. So do I need to multiply that by 115% for my voltage drop calculation, which would put me at 401?

(or)

multiply 279.9 (my original FLC) by 115% to use for my voltage drop equation?

279.9 x 115% for the running voltage drop.