Motor Circuit Breaker Sizing (Two or More Motors)

Jul 9 / James Stallcup
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Motor Circuit Breaker Sizing - Two or More Motors
(Based on the 2023 NEC)

Example Problem: What size overcurrent protection device is required for a feeder supplying a 10 HP, 15 HP, 20 HP, and 25 HP, three-phase, 460 volt, Design B group of motors?


Step 1: Finding FLC of motors

430.6(A)(1) and Table 430.250

10 HP = 14 A

15 HP = 21 A

20 HP = 27 A

25 HP = 34 A


Step 2: Calculating feeder OCPD

430.52(A), Table 430.52, and 430.62(A)

34 A x 250% = 85A

= 90A (round up) = 14 A

= 21 A

= 27 A

Total load = 152 A


Step 3: Selecting OCPD

430.62(A), Table 240.4(G), and Table 240.6(A)

152 A requires 150 A OCPD (round down)


Solution: The size overcurrent protection device is 150 amps.

Illustration 3

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