On the contrary, 40C/104F is simply a very hot temperature for electronics to be expected to operate. I recently saw some manufacturer data (company shall remain nameless) for some sophisticated power equipment that is rated to work up to 104C, and can work even hotter if derated. The data showed a 4-fold increase in failures when going from 25C/77F to 40C/104F! It's simply a function of the chemistry of components- heat kills capacitors. I will put PLCs, panels and switchgear in conditioned spaces wherever I can- they don't put out much heat, and benefit from the controlled temperatures. And I will never put valve-regulated lead-acid batteries anywhere but an air conditioned space- their life also is cut in half ever 15F, and they die fast enough as it is.
Having to derate breakers is a pain in the ass. You can't oversize the breaker because the load equipment can't handle the larger fault current, and you can't undersize the cable because you can't count on the breaker to prematurely trip, so everything still has to be full size. The only thing you CAN do is put less load per circuit. So you end up with 20A circuits that you can't put more than 10A on, and having to feed local (air conditioned) enclosed breakers from circuit breakers and cables twice the size.
For fun sometime, run some calcs sometime to put a generator (with transformer & ATS) in the desert where ambient temps can (and do) reach 145F through indirect solar heating (the ground/roof/etc turns into an oven), and direct solar heating can push that even hotter. Temps of 194F (90C) are not uncommon. THHN just doesn't cut it, and THHHHHN is hard to find. Generator derating is ridiculous. It's sad when you have to wear gloves to keep the transformer from burning you... before you even turn it on. Suddenly, 220C insulation rating becomes worthy of careful consideration. And don't forget to spec the right NEMA enclosures for dust-tight o keep all that sand out! And everything watertight because it still rains. For fun, right?
