Next size overcurrent device for feeders

[kbrandt]

Can you guys point me in the right direction.Here's my question.

I have prints that show a new 100 amp breaker (3 phase 208 volt) at the main panel and the EE has #4 wire feeding a sub panel.(#4 good for 95 amps THHN)

Now does this fall under 240.4b or is that just for branch circuits from a panel or sub panel?

Can you use the next higher standard breaker for the #4 wire on feeders?

And what section is it in the code book?

The load on the new sub panel is 30 amps. The voltage drop is fine.

Thanks in advance for any info.

 

[nyerinfl]

240.4 (B) for next size up rule. #2 in particular for your case.

 

[Dennis Alwon]

#4 is only good for 85 amps since you must use the 75C column. You could put a 90 amp breaker in the case since your load is less than the 85 amps of the wire.

You can only use the 90C for derating unless your terminals are rated 90C-- I doubt they are.

 

[Dennis Alwon]

240.4 (B) for next size up rule. #2 in particular for your case.

Actual # 3 would work if you can find it. Good for 100 amps.

 

[cadpoint]

It's back to the Assume!

If a seperate structure then, yes the rules change, if in-house yes you nailed the PQ side!

You breaker the service per the NEC, per 110 something up to 800 amps!

 

[mattsilkwood]

# 3 i think

 

[mattsilkwood]

i type way too slow:grin:

 

[jim dungar]

You can only use the 90C for derating unless your terminals are rated 90C-- I doubt they are.

You can be more positive. There are no UL listed (max 600V) overcurrent protective devices rated for conductors sized per the 90?C column.