240.4(B) & Parallel Conductors

[George Stolz]

Can you use the next size up rule for parallel conductors?

 

[don_resqcapt19]

If you can, do you apply the "round up" to the sum of the conductors or to each one by itself? That is, can you parallel four sets of 2/0 for an 800 amp circuit by rounding each of the conductors up to 200 amps and multiply by four, or do you add up the four sets before you do the rounding and have to use a 700 amp OCPD for the four sets of 2/0?

 

[infinity]

I said yes simply because the cutoff of 800 amps would make the rule pretty useless if you could only apply this to conductors not in parallel.

 

[ActionDave]

If you can, do you apply the "round up" to the sum of the conductors or to each one by itself? That is, can you parallel four sets of 2/0 for an 800 amp circuit by rounding each of the conductors up to 200 amps and multiply by four, or do you add up the four sets before you do the rounding and have to use a 700 amp OCPD for the four sets of 2/0?

I would think (B) (2) would make you go with 700A.

 

[charlie b]

If you can, do you apply the "round up" to the sum of the conductors or to each one by itself?

You are not rounding up the ampacity. You are not, in fact, rounding up anything at all. You are selecting an OCPD that is rated higher than the ampacity of the conductors, within a few restrictions. So in your example, the ampacity of four sets of 2/0 is 700 amps. That is what you have to protect, and it happens to match a standard OCPD rating. So you must use an OCPD not higher than 700 amps.