, 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. Marking Where conductors are in addition identified by letters and numbers, then: letters to be used come from Latin character set, numbers must be written in Arabic numerals, digits 6 and 9 must be underlined ( and ), and a few symbols like + and − can be used. Green-and-yellow conductors must not be marked. Examples: L1, L2, L3, N, L+, L−, M, 35, 1 References External links IEC 60446:2007: Basic and safety principles for man-machine interface, marking and identification – Identification of conductors by colours or numerals, International Electrotechnical Commission, Geneva. IEC 60445:2010: Basic and safety principles for man-machine interface, marking and identification - Identification of equipment terminals, conductor terminations and conductors, International Electrotechnical Commission, Geneva. Paul Cook: Harmonised colours and alphanumeric marking. IEE Wiring Matters, Spring 2006. 60446 Electrical wiring