Main Breaker

[Abe5gt]

Hi.
I have some electrical drawings that has a MCC with 3 control panel with a 150A breaker, 50A, 20A and a hoist with a breaker of 20A all individually connected to the same bar (sum of 240). The main breaker of the MCC is 400A. Can I lower the main breaker capacity to 250A? Is there a formula or a NEC table I should go by?

 

[GLENNSPARK]

hi.
I have some electrical drawings that has a mcc with 3 control panel with a 150a breaker, 50a, 20a and a hoist with a breaker of 20a all individually connected to the same bar (sum of 240). The main breaker of the mcc is 400a. Can i lower the main breaker capacity to 250a? Is there a formula or a nec table i should go by?

usa...?

 

[Abe5gt]

Yes USA

 

[Knobhead]

Why do you want to alter the designed rating of the MCC protection? The busbars (should) have been designed for a 400A supply.

I can’t understand what you are wanting to achieve.

 

[Guest55]

i'd probably want the main switch of the main panel to match / co-ordinate with the upstream devices / fuses regardless of design Ib.

but im not about to trawl through the 800 page NEC regs to confirm it

 

[shanky887614]

Why do you want to alter the designed rating of the MCC protection? The busbars (should) have been designed for a 400A supply.

I can’t understand what you are wanting to achieve.

probably wants to charge them when the mainswitch is fubar.

 

[Abe5gt]

Why do you want to alter the designed rating of the MCC protection? The busbars (should) have been designed for a 400A supply.

I can’t understand what you are wanting to achieve.

Cost in wiring (can downsize the wire gage) and main breaker. I have to wire to the MCC, it is 700 feet to the MCC.