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.
Question: What size conductor is required for a 25 hp, 208V three-phase fire pump motor? Figure 695-1
(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.
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.
(a) 4 AWG (b) 3 AWG (c) 2 AWG (d) 1 AWG
Answer: (b) 3 AWG
Conductors sized at 125 percent of the motor's 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 75A°C 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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