The C-Series devices are designed and built to conform to IEC 309-2, the worldwide pin and sleeve standard established by the international Electrotechnical Commission. This is a uniform system that makes the mating of plugs and receptacles of different voltages and current ratings physically impossible as required by the National electrical Code. C-Series devices are Color-coded according to voltage rating and female grounding contact position. Within a particular voltage group, every plug and the weatherproof cap on every receptacle is identical in color. All 250 VAC devices are blue, all 480 VAC devices are red, etc.