Technical advices

Plugs, socket-outlets, and couplers for industrial purposes: clock position

CLOCK POSITION EN 60309-1 and EN 60309-2

Clock position: how to distinguish among the types of industrial electrical sockets

The difference between industrial electrical sockets and home used electrical sockets lies in the different current loads withstanded.

Industrial power sockets are designed to operate safely in the most demanding environmental conditions. One of the main functions of industrial power sockets is to prevent accidental disconnection.

Industrial power sockets conforming to the IEC 309 standard are widespread in Europe.

The voltage of industrial electrical sockets is colour-coded. According to the different voltages, each socket has one or more plastic notches called 'reference points' and thanks to this method the connection of a plug into a non-compatible socket is avoided.

Knowing that the main reference point is always at 6 o'clock, sockets are identified by the position of the earth contact.

The other contacts follow the earth contact clockwise in the following order: earth, phase and neutral.

Different combinations of voltage and current correspond to different positions of the earth contact, which is placed in one of twelve different positions spaced at 30° intervals around the circle enclosing all poles.

The clock face position h is established by viewing the position of the earth contact from the front of the socket; the 6 o'clock position (180°) is oriented downwards.

The most common combinations are:


Table with colour coding for industrial electrical sockets:


Voltage range Frequency range Colour code
20– 25 V 50/60 Hz Purple
40– 50 V 50/60 Hz White
100–130 V 50/60 Hz Yellow
200–250 V 50/60 Hz Blue
380–480 V 50/60 Hz Red
500–690 V 50/60 Hz Black
- >60–500 Hz Green
none of the above Grey