Q. What is the minimum size XHHW insulated feeder conductor permitted for an industrial machine, which consists of the following loads? All terminals are rated at 75°C.

• 10 each – 5 hp, 480VAC, 3-phase, squirrel-cage induction, continuous duty motors,
• 10 each – 3 hp, 480VAC, 3-phase, squirrel-cage induction, continuous duty motors,
• 10 each – 3kW, 480VAC, 1-phase, electric resistance heating loads,
• 10 each – 2kW, 480VAC, 1-phase, electric resistance heating loads.
A) 3/0 AWG XHHW
B) 4/0 AWG XHHW
C) 250kcmil AWG XHHW
D) 300kcmil AWG XHHW

Explanation: Per Table 430.250, each of the 5 hp, 480VAC, 3-phase, squirrel-cage induction, continuous duty motors produces a full load current of 7.6A and each of the 3 hp, 480VAC, 3-phase, squirrel-cage induction, continuous duty motors produces a full load current of 4.8A.

Motors:
Largest motor (one of the 5hp motors) @ 1.25 (125% as per 670.4) = 7.6A X 1.25 = 9.5A
9 each, additional 5 hp motors X 7.6A = 68.4A
10 each, 3 hp motors X 4.8A = 48.0A
Subtotal = 125.9A