430.24 Several Motors or a Motor(s) and Other Load(s).

Feeders serving a group of motors must have an ampacity based on 125% of the largest motor FLC value plus the sum of the other motor FLC ratings in the group.
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Feeders serving a group of motors must have an ampacity based on 125% of the largest motor FLC value plus the sum of the other motor FLC ratings in the group.

Often, a feeder will supply a group of motors or a motor and another non-motor load. Once the full load current (FLC) ratings of a group of motors has been determined, the feeder conductors can be sized. NEC® Section 430.24 requires a feeder supplying a group of motors to have an ampacity based on 125% of the largest motor FLC value plus the sum of the other motor FLC ratings in the group.

One major difference between 430.22 for sizing the branch circuit and 430.24 for sizing a feeder is that Section 430.24 requires multiplying the FLC from the largest motor supplied by the feeder by 125% even if the largest motor is not used in a continuous duty application.

See the actual NEC® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to NFPA 70.

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430.24 Several Motors or a Motor(s) and Other Load(s).

Below is a Real Question from our Electrical Continuing Education Courses for Electrical License Renewal:

Determine the minimum feeder ampacity for a group of 3 motors with the following FLC values: 12 amps, 11 amps, 6 amps.

A: 32 amps.
B: 29 amps.
C: 36.25 amps.
D: 36 amps.
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