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Illustrated Changes to the NEC, 2005 Edition - Part 2

Article 695

Fire Pumps

695.6 Power Wiring

The text was revised to alert the Code user that the branch circuit conductors for a fire pump motor are sized in accordance with 430.22. In addition, branch circuit conductors must be sized to accommodate the voltage drop requirements of 695.7.

(C) Conductor Size.
(1) Fire Pump Motors and Other Equipment. Conductors supplying fire pump motors and accessory equipment must be sized no less than 125 percent of the sum of the motor full-load currents as listed in Table 430.248 or 430.250, plus 100 percent of the ampere rating of the fire pumps accessory equipment.

(2) Fire Pump Motors Only. Conductors supplying a single fire pump motor must be sized in accordance with the requirements of 430.22.


Authorís Comment: This means that the branch circuit conductors to a single fire pump motor must have a an ampere rating of not less than 125 percent of the fire pump motor full-load current (FLC) as listed in Table 430.248 or 430.250.
Question: What size conductor is required for a 25 hp, 208V three-phase fire pump motor? Figure 695-1
(a) 4 AWG (b) 3 AWG (c) 2 AWG    (d) 1 AWG

Answer: (b) 3 AWG

Conductors sized at 125 percent of the motorís FLC as listed in Table 430.250
FLC of 25 hp = 74.8A, Table 430.250
Conductor = 74.8A x 1.25
Conductor = 93.5A
3 AWG at 75įC is rated 100A

Note: Fire pump motor circuit protective device size must be set to carry indefinitely the sum of the locked-rotor current of the fire pump motor. According to Table 430.151(B), the locked-rotor current of a 25 hp, 208V three-phase motor is 404A.

In addition, branch circuit conductors for a fire pump motor must be sized to accommodate the voltage drop requirements of 695.7.


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