230.90(A) and 430.62(A) - Is it required

[plevymcs]

In a MCC with a bus design of 1600A and where the main section qualifies as a service entrance, per 230.90(A), can I size the OCP in the main entrance based upon the ampacity of the conductors (in this case FLA of the motors + 125% of the largest motor) or am I required to use exception (1). The exception is "permitted" but does not appear to be required.

Assistance is appreciated.

 

[jtester]

You are not required to use the Exception, but depending on the size and # of motors, you might find it necessary. The main will see the same current as the current dealt with in either 430.62 or 430.63 depending on which is applicable. If you don't size it according to the exception, you need to be sure you don't have a motor starting problem.

Of course, if you do use the exception, the bigger main usually requires larger service conductors.

Jim T

 

[plevymcs]

215.2(A)(1) vs 220.50

215.2(A)(1) vs 220.50

The feeder to the MCC is also a service entrance.

215.2(A)(1) requires a minimum sizing of 125% of the continuous loads. The motors in the MCC run continuously.

However, 220.50 advises that motor loads "shall be" calculated per 430.24, 430.25 etc.

Since the MCC is a multiple motor load, and 430.24 says the conductor sizing "shall" not be "less than" the sum of the motor ampacities + 25% of the largest motor, it appears that 215.2(A)(1) conflicts.

Does 215.2(A)(1) supercede 430.24 if 215.2(A)(1) is > 430.24 (in an MCC 215.2(A)(1) would always exceed 430.24)?

Or does 215.2(A)(1) not apply to an MCC since the feeder is considered as NOT supplying branch circuit loads? If so, is 220.50 the applicable section (note: 220.50 refers one to 430.24).

Your review is appreciated.