Jeff Wisnia wrote:
....
I clim(b)ed up and looked at the paper label inside the GE fused disconnect
last nnite (Cat #TG3222-MOD6 to be specific). Off at the bottom of the
label in type so small I had to work hard to pick it out, it reads,
"Contact current not to exceed 80% of fuse rating for other than motor
circuits." ...

Note that NEC requires no more than 80% of rated amperage for virtually
all boxes, irrespective of manufacturer. It's a good rule of thumb that
many don't adhere to.

Another thing during this thread (that hadn't popped to the fore in my
mind until last night for some reason) is that in the attic you may not
have adequate (or any to speak of) air flow around the box so that the
ambient temperature ratings may not be valid since they're based on
"normal" air circulation. If the box is in an area where there isn't a
convection path over/around it, it may well have an internal temperature
rise well above that you observed w/ the brief open box test you did.

I think the upgrade to a 100 A box would solve the issue plus, perhaps,
if there is a restriction around where it is presently mounted, moving
it to a more open area couldn't hurt (and just might solve the problem
w/o the other box).