To enable wires to be easily and safely identified, all common wiring safety codes mandate a colour scheme for the insulation on power conductors.
Many local rules and exceptions exist per country, state or region.
Older installations vary in colour codes, and colours may fade with insulation exposure to heat, light and ageing. As of March 2011, the European Committee for Electrotechnical Standardization (CENELEC) requires the use of green/yellow colour cables as protective conductors, blue as neutral conductors and brown as single-phase conductors.The United States National Electrical Code requires a green or green/yellow protective conductor, a white or grey neutral, and a black single phase. The United Kingdom requires the use of wire covered with green insulation, to be marked with a prominent yellow stripe, for safe earthing (grounding) connections.
For this reason, three-phase control panels will often use indicator lights of the old colours.Źródło: https://en.wikipedia.org/wiki/Electrical_wiring
An electrical code is a set of regulations for electrical wiring.
The intention of an electrical code is to provide standards to ensure electrical wiring systems that are safe and unlikely to produce either electric shock or fires.Ways in which electrical codes ensure safety include ways to prevent (or mitigate) short circuits, ground faults, and overheating from inadequate current-carrying capacity (ampacity).
Appropriately rated fuses or circuit breakers are used to interrupt a circuit loop whose ampacity is exceeded to avoid overheating of wires or other fixtures.Electrical codes are usually devised by national or international technical organizations, and adopted as law to make them enforceable.Electrical codes differ based on geographic area.
See the following: DIN VDE (German Institute for Standardization) published by DIN-Norms is used in Germany National Electrical Code has been adopted for electrical wiring in the United States and for Mexico, Costa Rica, Venezuela and Colombia IEC 60364 is used as a basis for electrical codes in many European countries Canadian Electrical Code published by the CSA is used in Canada (see Electrical wiring in North America). British Standard BS 7671 is the set of regulations for electrical wiring in the United Kingdom. Australian/New Zealand Standard AS/NZS 3000:2007 Wiring Rules is used in Australia and New Zealand. NF C 15-100 (fr) is used for low voltage installations in France RGIE (fr) (Réglement Général sur les Installations Électriques) is used for installations in Belgium. AREI (nl) (Algemeen Reglement Elektrische Installaties) is used for installations in Flanders, Belgium. Źródło: https://en.wikipedia.org/wiki/Electrical_code