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 preferred colours for AC phase conductors are: For a single AC phase: brown [1] The colour combination green/yellow is always and exclusively used to identify the protective conductor.
Insulated PEN conductors (combined protective earth + neutral in TN–C systems) should be marked: The cable must have a cross sectional area of 16 mm2 (5 AWG) or greater.
The three countries United States, Canada and Japan are mentioned in a note in the standard for using different colours: British Standard BS 7671:2001 Amendment No 2:2004 adopted the IEC 60446 colours for fixed wiring in the United Kingdom [1], with the extension that grey can also be used for line conductors, such that three colours are available for three-phase installations.
This extension is expected to be adopted across Europe and may even find its way into a future revision of IEC 60446.