Feeder ampacity

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mikehughes8

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I have a 3p 4wire system. A 4/0 feeder is supplied by a 250Amp breaker. The 4/0 conductor terminates in a 225A sub-panel. Table 310.16 assigns 4/0 an ampacity of 230Amps. Is this install legal. If so does somebody have a specific code reference that allows this. It seems to me that the breaker supplying the feeder would need to be 225Amps but I am not 100% sure.

Thanks
 
Look at 240.4 (B). As long as your calculated load does not exceed the ampacity of the wire then the 250 amp breaker is okay.
 
...and as long as adjustment and derating, if any, does not take the ampacity down to 225A or lower, being 225A is the next lower standard overcurrent rating.
 
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I agree with the others if the panel has a 225 main in it.

If the panel is main lug only there is a violation of 408.36
 
iwire said:
I agree with the others if the panel has a 225 main in it.

If the panel is main lug only there is a violation of 408.36
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The service has a 400 Amp main with (3) 250A feeder breakers each supplying 4/0 feeders. Each feeder lands on a 225Amp main on a sub-panel.
 
Twoskinsoneman said:
Are the 250a breakers even needed? Seems like you could go from the main and tap right to the panels....

Am I correct here?
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This is a SquareD I-Line panels and I don't have any provisions to tap off the bus.
The reason this whole issue exists is because the contractor who installed this applied 4/0 at it's 90c rating as opposed to the 75c rating.
So basically, if the 250A breaker is incorrect either 225A breakers need to be installed or taps could be used like you mentioned. The other option is to replace the cable with 250mcm which is an expensive option.
This problem applies to about 100 different installations so I only hope it is somehow legal. I don't want to call out the contractor but they have been in the news lately for the work they have done for the military.
This is not a safety issue because the service lateral and feeders are oversized for the load. I am not worried about an overload condition.
 
mikehughes8 said:
This is a SquareD I-Line panels and I don't have any provisions to tap off the bus.
The reason this whole issue exists is because the contractor who installed this applied 4/0 at it's 90c rating as opposed to the 75c rating.
So basically, if the 250A breaker is incorrect either 225A breakers need to be installed or taps could be used like you mentioned. The other option is to replace the cable with 250mcm which is an expensive option.
This problem applies to about 100 different installations so I only hope it is somehow legal. I don't want to call out the contractor but they have been in the news lately for the work they have done for the military.
This is not a safety issue because the service lateral and feeders are oversized for the load. I am not worried about an overload condition.
Click to expand...

It's already been mentioned but your install IS legal. The 4/0 is sized for the 225a panel. The 250a CB is not an issue. As you your self said it doesn't need to be there if you tapped. Beside that, as has been mentioned, your 4/0 is rated for the load so since your 4/0 are at 230a nec 240.4(B) allows them to be protected at the next higher ampacity OCPD which is 250 anyway....
 
I'm confused??,.. what is the rating of the panel board ??? If it is 225 amps then the panel needs to be protected at a max of 225 amps
 
mikehughes8 said:
Each feeder lands on a 225Amp main on a sub-panel.
Click to expand...

M. D. said:
I'm confused??,.. what is the rating of the panel board ??? If it is 225 amps then the panel needs to be protected at a max of 225 amps
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Pierre C Belarge said:
One cannot supply a panel rated at 225A with a 250A overcurrent device, regardless of the load.

It can be the other way around, say a 225A overcurrent device/circuit supplying a 250A rated panel
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The panel board is protected by the 225a breaker within the panel board as allowed by 408.36.
 
Pierre C Belarge said:
...and the 225A CBer in the panel is being supplied by a 250A CBer...this is not permitted.
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If that were the case, feeder taps would not be permitted.

Say in the case of this thread the main buss is protected to 400A and the feeders to the three panels were still 4/0 but tapped directly to the buss (and met all the criteria for a valid tapping). This would be a legal installation while the panel feeders are protected by the 225A panel mains, yet supply overcurrent protection would be at 400A.

Bringing up feeder taps was the topic of my first post but I changed it... but I had the feeling :D it would come back to it eventually!
 
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Pierre C Belarge said:
...and the 225A CBer in the panel is being supplied by a 250A CBer...this is not permitted.
Click to expand...

Why not?

The feeder conductors are properly sized.

What your saying doesn't make sense... you can never have any OCPDs of a lower apacity downstream of a higher ampacity OCPD. What about the 400A CB Main? The 250s are be protected by it.....so are the 225s within the PB so are the 15s and 20s on the BC...
 
Smart $ said:
If that were the case, feeder taps would not be permitted.

Say in the case of this thread the main buss is protected to 400A and the feeders to the three panels were still 4/0 but tapped directly to the buss (and met all the criteria for a valid tapping). This would be a legal installation while the panel feeders are protected by the 225A panel mains, yet supply overcurrent protection would be at 400A.
Click to expand...

Exactly. This would be a legal install even without the 250a CB as long as the 240.21(B) provision were met
 
Pierre C Belarge said:
...and the 225A CBer in the panel is being supplied by a 250A CBer...this is not permitted.
Click to expand...

O.K. now I'm really confused,...

Pierre ,.. let's assume the calculated load is less than 230 amps... the 4/0 feeder is allowed to be protected by a 250 amp breaker.... if the rating of the panel board is 225 amps you are saying that we cannot protect it with a 225 amp breaker??
The Feeder is protected and the panel board is protected ,.. were is the problem???
 
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