Motor panel Feeder OCPD

[arc_flashed]

Hoping someone can help clear up a bit of confusion.
I have a motor/vfd panel that has (2) 125HP VFDs and a small AC load. Per NEC 430.24 I've calculated my feeder conductor ampacity as 354 amps.
Does this value require that my upstream feeder breaker be sized at a minimum of 354 amps? I know the cable must be at least capable of carrying this ampacity but I am having a hard time finding the section that would determine if I need to have a 400amp breaker or if a 350amp would be acceptable by code.

 

[petersonra]

I don't recall the code specifies minimum ratings of breakers for such a case.

 

[Jraef]

There would be no cost difference between a 350A or 400A breaker, so why add risk of nuisance tripping under full load conditions? The cable size remains the same either way.

 

[arc_flashed]

There would be no cost difference between a 350A or 400A breaker, so why add risk of nuisance tripping under full load conditions? The cable size remains the same either way.

There is an existing 350amp breaker installed and we could land without an outage. Changing the CB will be a full outage so I am trying to determine if there is any code requirement saying a 400amp is required.
The only thing I can find is in section 215.3 which lists feeder OCPD as 125% of cont plus 100% of non-cont. Since my motor cabinet feeder is sized at 354 minimum, I am trying to figure out if that same 354amps applies to the feeder OCPD.

 

[wwhitney]

The only thing I can find is in section 215.3 which lists feeder OCPD as 125% of cont plus 100% of non-cont.

220.50 says "Motor loads shall be calculated in accordance with 430.24, 430.25, and 430.26 and with 440.6 for hermetic refrigerant motor-compressors."

Now 430.24, 430.25, and 430.26 don't refer to calculating loads, they refer to calculating minimum conductor ampacity. My conclusion is that 220.50 means that the load is the minimum conductor ampacity calculated per one of those sections.

Which means that if your 430.24 calculation comes out to 354A, 220.50 says the load is 354A. And then 215.3 says the OCPD has to be at least as large as the load, which means at least 354A.

Cheers, Wayne