NEC clarification

[Edawada]

I have 400 AMP rated controls enclosure, my customer electrical contracting company provided 2-250AMP breakers TO FEED MY PANEL, IS THIS ACCEPTABLE?

 

[don_resqcapt19]

Probably not, but would need a one line or other details to know for sure

 

[infinity]

As Don said the devil is in the details so more info is needed to help answer your question. Even though the controls panel is rated for 400 amps that doesn't mean that 250 amps isn't adequate. It could be a set with alternate power sources and an interlock like a Kirk Key.

 

[Edawada]

It is a UL enclosure with 266A FLA, and the largest motor is a 75HP (96 FLA), 2-30 HP,1-25HP, 1-10HP, Air conditioning, and other field instruments and devices are powered from this enclosure. Now the 2-250 A breakers are in the same distribution panel.

 

[don_resqcapt19]

It is a UL enclosure with 266A FLA, and the largest motor is a 75HP (96 FLA), 2-30 HP,1-25HP, 1-10HP, Air conditioning, and other field instruments and devices are powered from this enclosure. Now the 2-250 A breakers are in the same distribution panel.

Sounds like you are trying to parallel two 250 amp circuits to feed the control panel. That is not permitted.
Show me a one line of the system,

 

[Elect117]

I think your question is best discussed with the electrical contracting company. They could have installed two separate circuits with taps to fused disconnects at the motor locations. There are a large number of ways to make two circuits of 250A feed 266A of load and still be compliant.

As Don said, if they are parallel feeding a panel, two breakers feeding conductors that land at the same location, then that is non compliant. That would be an improper way feeding a load. Parallel conductors must originate and terminate at the same locations. We just can't tell if that is what they have actually done by the descriptions given.

 

[Edawada]

A few months back before the project installation started, the electrical contractor emailed me to ask if they could use a 250A breaker to power up my enclosure since it is rated at 266A FLA (My company does not do any wiring at all, and it is up to our client to subcontract the electrical work to a local electrical company familiar with the local code). My answer was that they should provide the 400Amp to power up the enclosure (as I have some power reserved for future expansion), I wrote it is ultimately up to them as long as they bear the responsibility. Fasting forward about 10 days ago received a phone that the 250A breaker tripped in the first 7-8 seconds after trying to bump the 75 HP motor bypassing the VFD. My answer was the same they need to provide the power from a 400AMP breaker. Two after that call revived an email stating that they had resolved the power requirement by using a second breaker located in the same distribution panel with another set of conductors (Parallel configuration if you will). My response was as follows "... in my opinion is that most local and National Electrical Codes do not allow combinations of multiple breakers to achieve a higher single feeder amperage.".
That is why I'm here and soliciting professional opinion on this matter. So far great answers and questions.

 

[roger]

See 240.8, be sure to note the last sentence.

240.8 Fuses or Circuit Breakers in Parallel. Fuses and
circuit breakers shall be permitted to be connected in parallel
where they are factory assembled in parallel and listed
as a unit. Individual fuses, circuit breakers, or combinations
thereof shall not otherwise be connected in parallel.

 

[Edawada]

Very Well. Thanks, y'all.