It's Not The Heat, It's The... Salt
Protecting anything made of metal from salty sea air is a given if you live or work near the coast. But for utility companies in areas farther away from the coast, salty air may still turn out to be a problem despite there being no saltwater beaches nearby. And, it turns out, that goes for cities that are very far inland. If you work for a utility company in an area that doesn't have the scent of the sea hanging in the air, you should still protect your equipment as if you were just blocks from the beach.
What Salt Does to Switchgear
The problem with salt isn't so much the sodium as it is the chloride, and that goes for other airborne chlorides as well. These chlorides contribute both to smog and to corrosion on metal. So if you have switchgear in salty air, you face a faster rate of decay in your equipment.
For areas by the coast, the source of salt is obvious. Salt gets sprayed into the air from wave action, and the salt can be carried inland on air currents. What's amazing, though, is that higher levels of salt in the air have been detected in states like Colorado, in amounts similar to what scientists found when they were on a vessel at sea. The source of the extra salt can range from sea salt carried far inland to coal burning and deicing salts, among other sources.
What that means for utility operators is that any equipment outdoors has to be protected from salt and inspected more frequently.
What to Do
Any exterior casing should be rated for high corrosion resistance, higher than you think you might need in your region. Just because you can't smell the beach doesn't mean the air is not overly salty for electrical equipment.
Take care to protect equipment from moisture, be it humidity, rain, or snow. While you can't install covers over everything, use utility boxes whenever possible, even in remote areas, and try to shelter what you can.
Also, take a few minutes whenever you work on a piece of equipment to inspect the casing for spots of rust. If you find any, arrange for repair work, even if all that is, is removing the rust and repainting. You can arrange to work on issues like these on specific days -- it doesn't have to be immediate -- but if you take care of small spots now, you'll stop them from growing into bigger, utility-box-chewing problems later on.