Why no 90C breakers?

[Jim Bob 4820]

Idle Saturday morning contemplation. What prevents the industry from making breakers with 90C terminals/connections? Is it a materials limitation - eg can’t dissipate heat from copper in the limited surface area of a breaker - or is it lack of market or something else?

Just thinking we’ve had 90c then around forever, and with the price of copper, it seems like there would be a good cost driver for 90c components that could let us work with smaller wire sizes.

 

[ImOld]

It is acceptable to use conductors with a higher insulation rating than what is marked on the breaker, but the ampacity must be based on the conductor temperature rating marked on the breaker. So, circuit breakers marked for use with 75 deg. C rated conductors may be used with conductors rated for 90 deg. C if the conductors are sized per their 75 deg. C ampacity.

Also note:

Circuit breakers with a current rating of 125 A or less may be marked as being suitable for 60°C, 75°C only or 60/75° C rated conductors.
Circuit breakers with a current rating of more than 125 A are considered to be 75 deg. C terminated devices, regardless of the temperature rating of the lugs.
Circuit breakers intended for continuous operation at 100% of rated current may be marked to be connected with 90°C rated wire with the size based on 75°C ampacity.

This is per the NEC, breaker and wire manufacturer's.