tap rule

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quiluis57

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Riverside California United States
Hello my name is Luis and i have a question:
i have a panel rated 480 volt 400 amp feed it From main switch gear i need to install 150 Amp breaker and this panel house only 100 amp frame breakers, i install 6' of 1-1/4 conduit to a 15o breaker with an enclosure as i interpret the 240.21 i was request to install 500 mcm sizes of the wire that feed the panel I can not connect 500 mcm wire in a 150 amp braker and as my understanding of the tap 10 rule is ok to run 1/3 of the rated wire of the main feed please let me know which one is to code i appreciate your help thanks
 
You do not have to run 500 from the 400 amp panel to the 150 amp breaker.

You only have to size those circuit conductors to the load. However if you run a wire type equipment grounding conductor that will be sized based on the 400 amp feeder you are tapping but in no case does it have to exceed the size of the circuit conductors.
 
iwire said:
You do not have to run 500 from the 400 amp panel to the 150 amp breaker.

You only have to size those circuit conductors to the load. However if you run a wire type equipment grounding conductor that will be sized based on the 400 amp feeder you are tapping but in no case does it have to exceed the size of the circuit conductors.
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Bob, where is that?
 
240.21 (B)(1) allows you to use cable of ampacity not less than the rating of the OCPD supplying OR not less than the OCPD at the termination. As long as the cable is rated for more than 1/10th of the OPCD supplying the conductors (40A in this case) then you should be fine with using a 1/0 @ 150A to feed the new panel.
 
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