215.2 Feeder Exception Question

[Wrd4spd]

215.2(A)(1) requires one to include an additional 25% of the continuous load when sizing feeder conductors. As I understand, this additional "headroom" is added in so that heat can be more easily dissipated at the terminations. Exception #1 of the above section states that I do not have to include this extra 25% if I use a 100% rated breaker. My question is - How does providing a 100% rated breaker mitigate this extra heat in the conductor/termination?

 

[iwire]

A 100% rated breaker can only be used by itself in its own enclosure with venting.

 

[kwired]

My question is - How does providing a 100% rated breaker mitigate this extra heat in the conductor/termination?

You are looking at it the wrong way, the standard device depends on the conductor to sink some of the heat, the 100% breaker doesn't necessarily need to depend on the conductor to sink any heat.

As Bob mentioned most of these breakers are also going to be in their own enclosure and not something you will find in a panelboard with multiple breakers on a common bus.