De-rating and rounding up

[ryan_618]

How does the "round-up rule" (240.4) apply to conductorsd that have been derated?

For example, NM cable. 10 current carrying conductors bundled (5 14-2's) for more than 24" requires a 50% deration. 90 degree column puts #14 at 25 amps. 50% deration factor applied, conductors are worth 12.5 amps. So, I have conductors that have an ampacity of 12.5 amps. Can I round up to the next higher standard OCPD?

 

[iwire]

Re: De-rating and rounding up

Depends on what it is you are feeding and what the load is.

240.4(B)

If these conductors are feeding multi outlet circuits your rounding down.

 

[websparky]

Re: De-rating and rounding up

Hi Ryan and Bob,

I agree with Bob, depends on the load.
Just to add a little more;

2002 NEC Handbook
Section 210.19(A) requires that branch-circuit conductors have an ampacity not less than the rating of the branch circuit and not less than the maximum load to be served. These specific requirements take precedence over 240.4(B), which applies generally.

 

[charlie]

Re: De-rating and rounding up

Ryan, the ampacity adjustment factors are just that. They adjust the ampacity of the conductors. After the adjustments have been applied, then you deal with 240.4. If the adjusted ampacity is 273 amperes and the load is less than 273, you may use the next size circuit breaker or fuse. If the load is 280 amperes, you will have to use the next size wire with the same size circuit breaker or fuse.