U-Line™ Factory Sealed 20 Amp Plugs and Receptacles are used with stationary or portable electrically operated devices in hazardous locations. The ECP Interchanger plug is designed with built-in switch contacts which activate when the plug is twisted into the receptacle. This design allows the ECP plug to fit into standard NEMA 5-20R and 6-20R receptacles, but does not allow standard plugs to be used with the receptacle, ensuring that only safe connections can be made in a hazardous location. Features: Energized receptacle contacts deeply recessed to reduce danger of accidental touching; Unique blade-type, brass contacts exert constant pressure along entire contact surface and provide superior electrical contact.; Insulators provide superior dielectric and mechanical strength and lowest arc tracking; ECP plug fits any standard non-explosionproof receptacle (NEMA 5-20R, or 6-20R) as well as U-Line™ explosionproof receptacles; Choice of malleable iron receptacle and mounting box or aluminum receptacle and mounting box; Ground fault circuit interrupting cover and receptacle combinations available; U-Line™ EFSR-K receptacle covers are UL Classified when used with Killark™ SWB series mounting boxes; Intermateable with competitor's plugs of like configurations