I occasionally have to design control panels for exterior use (NEMA 4X) which also may have to be UL listed (UL508). The last time I did that, the UL inspector had a problem with the insulation that I used on the interior panel surfaces. I typically use a 100W Hoffman heater for anti-condensation. The insulation I use is 1/2" foam sheet (Nomaco K-Flex). I suppose one of the options I have is to forget the insulation and oversize the heater (Maine winter conditions).

Does anyone have a different approach to this problem? Thanks.

What was the inspectors issue? Can you insulate the outside of the box instead?

We use Reflectix. It's awesome. All you need is scissors and double sided tape. It really reduces heater requirements too. You can get it at Home Depot...or probably any other building supply store. I see a lot of other panel builders use it too.

Thanks for the link. This stuff looks a lot better than what we are currently using. I wouldn't be surprised if it appeared in our next outdoor panel.