ECN Forum Forums General Topics of the Trade General Discussion Area Zinsco 40*C Breaker

I have an old Zinsco panel in my house with type Q breakers (not for long, will be replaced with a Murray 200A panel). It was there when I moved it, it has a 100A, then a 100A Breaker going to a sub panel. The one going to the sub says 40 degrees C. Table 310.16 only goes down to 60C. I'm just wondering what size copper wire would be used on 100A 40*C. The breaker has #2 SE cable with a #4 Neutral connected to it, which I know is illegal because 310.15 doesn't apply here.
P.S. Sorry if I used some incorrect terms, I'm an engineering student, not an electrician.
Thanks!

40C is the ambient temperature (average enclosure temperature) the breaker is calibrated for.