# Main breaker

1374 Views 10 Replies 7 Participants Last post by  btharmy
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?
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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?
You can look into buying a 250 amp breaker that will fit in that panel, then why not?
I was just wondering why the designer used a 400A main breaker.
I was just wondering why the designer used a 400A main breaker.
Probably just to have the power available.
1
So if it's greater that the sum of the Ampacities is OK?
Yes. As long as the bussing is rated for 400A or more.
So if it's greater that the sum of the Ampacities is OK?
The ampacity of the breakers have nothing to do with sizing the panel. The size is based on the calculated load. Why would you change a 400 amp panel into a 225 amp panel? especially if it is designed for 400 amps. Think of future use.
2
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?

Yes , there is a Load Calc for the Largest Motor ( Start fuse size ??? ) + FLAs of other Motors / and fla of other Loads ... Then you can add for future expansion if you wish . Something along that line , i would have to look it up .

Peet
I'm thinking I'd price/install as per the Electrical drawings.
2
The ampacity of the breakers have nothing to do with sizing the panel. The size is based on the calculated load. Why would you change a 400 amp panel into a 225 amp panel? especially if it is designed for 400 amps. Think of future use.

Cost
Guy said:
But isn't the customer paying for a 400a panel? This is most likely for future. I'm sure you are going to pass on the savings to the customer if you reduce the panel size?
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