In article , Chris Friesen wrote:
Don Klipstein wrote:

Since resistance increases with temperature, actual ampacity does not
increase much with an increase in temperature rating. And ampacity
according to the code does not increase at all.

I'm going to have to disagree with that.

For simplicity, look at the "single conductor in free air" tables. (The
other tables show it too, just the absolute values are lower.)

With 60-90C rated insulation, a #14 wire is rated for 20A. With
110-125C rated insulation, that same size wire is rated for 40A. If you
go up to 200C insulation, you can put 45A through it.

Somehow, I suspect that upgrading from 110 or 125 C insulation to 200 C
insulation only improving ampacity from 40 to 45 amps supports my point!

Meanwhile, also consider that wiring in a building is usually not single
conductor in free air, but 2 at least current-carrying conductors close to
each other and heating each other up with a sheath around them and the
environment outside the sheath usually not being "free air".

Add to this the fact that extra high temperature rating wire is used
more where ambient temperature is higher, and I see good reason for AWG 14
romex to be only allowed by code to be used in circuits up to 15 amps
regardless of temperature rating.

- Don Klipstein )