Hardwareguy, I have seen this situation, where the ambient was high enough to matter. For example, where the panel supplied an oven's heating elements. It's rather annoying to watch 30 amps of current blow a 50 amp fuse! It's usually in such a location where I find such open panels.
Some guys get fancier, and mount little fans to the side of the enclosure. I have even seen outdoor switchgear with roof 'turbine' fans mounted on them. While this is considered a listing violation, it is an attempt to reduce the temperature inside the cabinet to something reasonable.
Wa2Wise, thx for the explanation of an EE's education. On my jobs, the engineer and I have an understanding ... he stays clear of the electric work, and I stay away from the bridge design
