IEC 309 (now IEC 60309, 1999) is an international standard from the International Electrotechnical Commission for "plugs, socket_outlets and couplers for industrial purposes". It specifies a range of mains power connectors with circular housings, and different numbers and arrangements of pins for different applications. The highest voltage allowed in the standard is 690 volts DC or AC, the highest current 250 amperes, and the highest frequency 500 hertz. The temperature range is -25°C to +40°C.

In the United Kingdom the standard has been adopted as BS 4343:1992. In Europe it is EN 60309.

Keying

IEC 60309 connectors are produced in many variants, designed so that a plug of one type can only be inserted into a socket of the same type. Different current ratings (such as 16 A, 32 A and 63 A) are distinguished by different diameters of the circular housing.

Different voltage and frequency combinations are distinguished by the location of the ground pin (or a plastic projection called the minor keyway, for connectors with no ground pin), as shown in the following table. The ground pin can be in one of twelve locations spaced at 30° intervals around the circle on which all the pins lie. Position 6 is at the same angle as the major keyway, a projection on the plug casing that aligns with a notch on the socket. The ground pin has a larger diameter than the other pins, preventing the wrong type of plug being inserted in a socket.

The background colour of each cell in the table shows the colour coding of the connectors.

A six-phase plus earth (6P+E) version also exists.

Reference

Catalogue 1SKC000013C0201 from ABB Industrial Plugs and Sockets (http://www.eg.abb.com/global/egabb/egabb103.nsf/0/023386178d2b3ce642256eb6003c0184/$file/Industrial+plugs+and+Sockets.pdf)