I need some help interpreting this exception to 310.15(A)(2). The way I'm reading it just doesn't make sense.
Here's the bit I'm concerned with:
"Where two different ampacities apply to adjacent portions of a circuit, the higher ampacity shall be permitted to be used beyond the point of transition, a distance equal to 3.0m (10ft) or 10 percent of the circuit length figured at the higher ampacity, whichever is less."
So, I'm thinking, if I have a circuit that passes horizontally through a high temperature area, and then extends away from that high temp area, the "away" portion should be able to be rated at a higher ampacity. Suppose that "away" portion was only 10 ft long. The above quoted section seems to be saying that after 10 ft, I can go ahead and use the higher ampacity figure. BUT, it also seems to be saying, since 10% of 10 ft (where 10 ft is the circuit length figured at the higher ampacity) is just 1 ft, that after 1 ft I can use the higher ampacity rating.
I'm thinking that they should have stipulated that you can go ahead with the higher ampacity rating so long as you extend beyond the transition point at least 10% of the LOWER ampacity portion of the circuit. So, using the above example, if the high ambient temperature portion (read as "lower allowable ampacity")was 100 ft long, you would have to extend at least 10% or 10ft beyond that hot spot before you could consider the conductor cooled down enough to allow a higher ampacity.
What am I missing?
