NEMA 4 Enclosure

Probably Polycarbonate or fiber-reinforced polyester depending on the application environment and other desired features.

I have used a grade of Noryl (PPO) in the past. It was low cost and was easy to mold. I think you will need a UL94 V-0 or 5-V (flame retardant) rated material. I think it also has to have a minimum arc tracking rating, too. The material manufacturers would be able to give you their recommendations. Try looking up the web pages for Sabic (formerly GE Plastics), Bayer, Monsanto, or other major plastic material suppliers.