Ashu
Member
- Location
- Hunt Valley, USA
- Occupation
- Electrical Engineer
I have applied NEC article 430.62 to calculate the size of the Main circuit breaker as a feeder (Pleas see attached picture) then I came across article 215.3 which suggests a different calculation. Now I am little confused which one of these two codes to follow. Motors shown in the attached picture are going to be running all the times but the load may vary slightly based on the product running through the machine. I will appreciate any help clarifying this. Thank you!
NEC 215.3
Overcurrent Protection. Feeders shall be protected
against overcurrent in accordance with the provisions of
Part I of Article 240. Where a feeder supplies continuous
loads or any combination of continuous and noncontinuous
loads, the rating of the overcurrent device shall not be less
than the noncontinuous load plus 125 percent of the continuous
load.
NEC 430.62 Rating or Setting — Motor Load.
(A) Specific Load. A feeder supplying a specific fixed motor
load(s) and consisting of conductor sizes based on
430.24 shall be provided with a protective device having a
rating or setting not greater than the largest rating or setting
of the branch-circuit short-circuit and ground-fault protective
device for any motor supplied by the feeder [based on
the maximum permitted value for the specific type of a
protective device in accordance with 430.52, or 440.22(A)
for hermetic refrigerant motor-compressors], plus the sum
of the full-load currents of the other motors of the group.
Where the same rating or setting of the branch-circuit
short-circuit and ground-fault protective device is used on
two or more of the branch circuits supplied by the feeder,
one of the protective devices shall be considered the largest
for the above calculations.
NEC 215.3
Overcurrent Protection. Feeders shall be protected
against overcurrent in accordance with the provisions of
Part I of Article 240. Where a feeder supplies continuous
loads or any combination of continuous and noncontinuous
loads, the rating of the overcurrent device shall not be less
than the noncontinuous load plus 125 percent of the continuous
load.
NEC 430.62 Rating or Setting — Motor Load.
(A) Specific Load. A feeder supplying a specific fixed motor
load(s) and consisting of conductor sizes based on
430.24 shall be provided with a protective device having a
rating or setting not greater than the largest rating or setting
of the branch-circuit short-circuit and ground-fault protective
device for any motor supplied by the feeder [based on
the maximum permitted value for the specific type of a
protective device in accordance with 430.52, or 440.22(A)
for hermetic refrigerant motor-compressors], plus the sum
of the full-load currents of the other motors of the group.
Where the same rating or setting of the branch-circuit
short-circuit and ground-fault protective device is used on
two or more of the branch circuits supplied by the feeder,
one of the protective devices shall be considered the largest
for the above calculations.