wiring of split-phase electric power (unknown in Europe). This allows one to choose single-phase AC power at either 110–120 volts between phase and neutral or 220–240 volts between phase and phase. Since these two modes do not need three phases there is also a dark yellow-orange four-pin connector available designed for a single-phase 110–120 or 220–240 volt load. It is best to connect the high leg adjacent to the earth pin, so that it will not be misplaced by phase-swap plugs. Switched-socket outlets with interlocks Switched-socket outlets with interlocks are described in IEC 60309-4 standard and are commonly used to enhance electrical safety in industrial plants. The interlock cuts power to the socket when nothing's plugged in and locks any plug in the socket until the power is turned off. See also Industrial and multiphase power plugs and sockets IEC 62196 for electric vehicles Perilex, obsolescent DIN connector IEC 60906-3 a series of smaller 16 A low-voltage connectors with a superficially similar appearance References External links IEC 60309-1 Plugs, socket-outlets and couplers for industrial purposes - Part 1: General requirements IEC 60309-2 Plugs, socket-outlets and couplers for industrial purposes - Part 2: Dimensional interchangeability requirements for pin and contact-tube accessories IEC 60309-4 Plugs, socket-outlets and couplers for industrial purposes - Part 4: Switched socket-outlets and connectors with or without interlock 60309 Mains power connectors