The Black Outdoor Ground Box cover assembly is prewired with a single NEMA L15-30R corrosion-resistant locking receptacle. - - CAUTION: All ground box electrical circuits must be protected by a Ground Fault Circuit Interrupter upstream from the ground box. - NOTE: Cover must be closed while in use. Use only molded plug and cord assemblies that are rated for outdoor use. - NOTE: Maximum length of plug allowed at end of cord is 3 (76mm).