Branch Circuits

[TS6M]

An 800 kcmil copper feeder is protected with a 500 ampere overcurrent protection device. This feeder is tapped using the 25 foot tap rule (240.21B)(2)) with a 4/0 THHN copper conductor. The tap conductor terminates in an 250 ampere overcurrent protection device. The inspector turns down this job. What can be done to make this installation code compliant?



o Appeal the decision, there is nothing wrong with the installation.



o Change the OCPD to 300 amp.



o Change the OCPD to 225 amp.



o Change the OCPD to 125 amp.

 

[iwire]

4/0 copper at best is rated 230 amps.

240.21(B)(2)(2) prohibits 'rounding up'.

Change the 250 to a 225 and you should be good to go.

 

[infinity]

I agree with Bob, you could go with the 125 amp OCPD also but I'm unsure why you would want to do that. :roll:

 

[TS6M]

Thanks, The 230 is due to terminal ratings I believe, but I can't find the article?

 

[iwire]

That is correct, even with 90 C conductors the terminal rating will be 75 C limiting you to that column.

If I remember correctly 110.14(C) is the NEC section.

 

[charlie b]

What can be done to make this installation code compliant?

Can I go with "none of the above"? Can I offer the response that you start by asking the inspector the reason for the red tag?

I can't do that?

Then I'll have to agree with Bob (I was hoping to avoid that :grin: ).