ClemsonME
Member
- Location
- Simpsonville, SC, USA
Hello All! I am looking for help interpreting NEC 430.63.
I have a panel with a 480VAC, 3 phase feeder that will contain motor starters and 20 amp time delay fuses for three motors that are 5 HP each (7.6 FLA). 20 amp fuses picked according to Table 430.52 (175% times 7.6 FLA = 19; next size fuse up is 20 amps). The panel will also have a 120VAC - 1KVA transformer (2.08 FLA) with primary and secondary fusing.
I have sized the feeder as a #10 according to 430.24 for motors with other loads. Minimum conductor ampacity is 1.25 X 7.6 + 2 X 7.6 + 1.25 X 2.08 = 27.3 amps. Therefore #10 wire will work.
I then use 430.63 to calculate feeder OCPD for combination non-motor and motor loads.
430.63(3) for two or motor motors states to use 430.62, along with Exception No. 1 to determine the motors contribution to the calculation. The calculated value is 34.2 amps. This is calculated from 19 amps (430.52 calculated OCPD for largest motor) + 2 X 7.6 amps (all other motors).
430.63, would then use 34.2 amps + 2.08 amps (for the transformer).
End result is 430.63 gives a calculated OCPD of 36.28 amps for the feeder.
Now here is where my struggle begins. 430.63 states "the feeder protective device shall have a rating NOT LESS than that required for the sum of the other load(s) plus the rating permitted by 430.62.
I interpret this as I need to round up to the next largest circuit breaker NOT round down as you would when applying 430.62 for motor only feeders.
- So, I would put a 40 amp circuit breaker on the feeder?
- Does this mean I also have the freedom to put an even larger circuit breaker (assuming I increase my feeder conductor sizes accordingly)? There is the possibility in the future that additional motors could be added to this panel. It would be nice if i could put a larger feeder circuit breaker and feeder conductors for this possible addition of motors.
- 430.62(b) also seems to imply that I can increase the feeder circuit breaker size IF the feeder conductors are sized according to the larger breaker. Is this correct?
I apologize for the long post, but this one is perplexing me.
I have a panel with a 480VAC, 3 phase feeder that will contain motor starters and 20 amp time delay fuses for three motors that are 5 HP each (7.6 FLA). 20 amp fuses picked according to Table 430.52 (175% times 7.6 FLA = 19; next size fuse up is 20 amps). The panel will also have a 120VAC - 1KVA transformer (2.08 FLA) with primary and secondary fusing.
I have sized the feeder as a #10 according to 430.24 for motors with other loads. Minimum conductor ampacity is 1.25 X 7.6 + 2 X 7.6 + 1.25 X 2.08 = 27.3 amps. Therefore #10 wire will work.
I then use 430.63 to calculate feeder OCPD for combination non-motor and motor loads.
430.63(3) for two or motor motors states to use 430.62, along with Exception No. 1 to determine the motors contribution to the calculation. The calculated value is 34.2 amps. This is calculated from 19 amps (430.52 calculated OCPD for largest motor) + 2 X 7.6 amps (all other motors).
430.63, would then use 34.2 amps + 2.08 amps (for the transformer).
End result is 430.63 gives a calculated OCPD of 36.28 amps for the feeder.
Now here is where my struggle begins. 430.63 states "the feeder protective device shall have a rating NOT LESS than that required for the sum of the other load(s) plus the rating permitted by 430.62.
I interpret this as I need to round up to the next largest circuit breaker NOT round down as you would when applying 430.62 for motor only feeders.
- So, I would put a 40 amp circuit breaker on the feeder?
- Does this mean I also have the freedom to put an even larger circuit breaker (assuming I increase my feeder conductor sizes accordingly)? There is the possibility in the future that additional motors could be added to this panel. It would be nice if i could put a larger feeder circuit breaker and feeder conductors for this possible addition of motors.
- 430.62(b) also seems to imply that I can increase the feeder circuit breaker size IF the feeder conductors are sized according to the larger breaker. Is this correct?
I apologize for the long post, but this one is perplexing me.
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