The international standard IEC 60446 Basic and safety principles for man-machine interface, marking and identification - Identification of equipment terminals, conductor terminations and conductors was a standard published by the International Electrotechnical Commission (IEC) that defined basic safety principles for identifying electrical conductors by colours or numerals, for example in electricity distribution wiring. The standard has been withdrawn; the fourth edition (IEC 60446:2007) was merged in 2010 into the fifth edition of IEC 60445 along with the fourth edition, IEC 60445:2006.

The standard permits the following colours for identifying conductors:

The colours green and yellow on their own are only permitted where confusion with the colouring of the green/yellow protective conductor is unlikely. Combinations of the above colours are permitted, but green and yellow should not be used in any of these combinations other than as green/yellow for the protective conductor.

If a circuit includes a neutral or midpoint conductor, then it should be identified by a blue colour (preferably light blue ). Light blue is the colour used to identify intrinsically safe conductors, and must not be used for any other type of conductor.

The preferred colours for AC phase conductors are:

For a single AC phase: brown

The colour combination green/yellow is always and exclusively used to identify the protective conductor. On any 15 mm length of the conductor, one of these two colours should cover between 30% and 70% of the area and the other the remaining area.

Insulated PEN conductors (combined protective earth + neutral in TN–C systems) should be marked: