Fire Pump Overcurrent

Status
Not open for further replies.
L

l3city

Senior Member
Hi fellas, I am sizing the overcurrent protection for a fire pump as required by NEC 695.4(1). The code says that I I shall size the OCPD to the motor locked rotor ampacity (inrush) current. The motor is a rated 200HP, 1450 Amps (LRC),
480V, 3-phase.

On the other side this fire pump is connected to a control box, which manual reads that the fire pump will be started at 40% of the Pump's LRC (580 Amps). Question: Shall I size the OCPD based on 1450A, or at 580A?

Thanks in advance for any input.:)
 
It's not the inrush or starting current that you size it to. It is the locked rotor current and other loads.

(1) Overcurrent Device Selection. The overcurrent protective device(s) shall be selected or set to carry indefinitely the sum of the locked-rotor current of the fire pump motor(s) and the pressure maintenance pump motor(s) and the full-load current of the associated fire pump accessory equipment when connected to this power supply.
 
Size it according to the locke rotor current.


Here is a picture of a fire pump disco. 900A fuses, 500 Kcmil conductors.
100Sheldrake-Lippolis119.jpg
 
Pierre C Belarge said:
Size it according to the locke rotor current.


Here is a picture of a fire pump disco. 900A fuses, 500 Kcmil conductors.
100Sheldrake-Lippolis119.jpg
Click to expand...
That wire looks awfully small to be 500. Is it just my eyes here?
 
Size your (Supervised Condition) disconnect at LRC located 430.251(B) table and your conductors at 125 percent of pump motors FLA based on table 430.250....im sure you mean 460V in regards to the motor rating.
 
Status
Not open for further replies.
Top