Colour identification

The colour of an IEC 60309 plug or socket indicates its voltage and frequency rating. The most widespread colours are yellow 125 V, blue 250 V and red 400 V. The black 500 V version can often be found on ships.


Keying

IEC 60309-2 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, 63 A and 125 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. The various positions are referenced from the view of the open side of a socket; the 6 o'clock (180°) position is at the same angle as the major keyway, and i s oriented downwards. The major keyway is 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.