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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 ...
In commercial construction, three-phase circuits are often used. Common 3 phase configurations within a building are 208v/120 wye, 120/240 center tapped delta and 480v/277v wye. Lighting is usually fed by 277 V or 120v. Countries such as Mexico may adopt the NFPA standard as their national electrical code, with local amendments similar to those ...
Household wiring does not usually use three-phase supplies and the clash only occurs in three-phase systems. Wiring to the old standard can be detected by use of a red wire. The new standard colour code does not use red. Where new wiring is mixed with old, cables must be clearly marked to prevent interchange of phase and neutral.
In the United States, colour-coding of three-phase system conductors follows a de facto standard, wherein black, red, and blue are used for three-phase 120/208-volt systems, and brown, orange or violet, and yellow are used in 277/480-volt systems. (Violet avoids conflict with the NEC's high-leg delta rule.)
The cable core colours are described in IEC 60304 (1982-01), Standard colours for insulation for low- frequency cables and wires. The three-phase phase colours are brown, black and grey instead of red, yellow and blue. Where a circuit includes a neutral or mid-point conductor identified by colour, the colour used shall be blue.
Conductors of a three-phase system are usually identified by a color code, to facilitate balanced loading and to assure the correct phase rotation for motors. Colors used may adhere to International Standard IEC 60446 (later IEC 60445 ), older standards or to no standard at all and may vary even within a single installation.
A wire or cable has a voltage (to neutral) rating and a maximum conductor surface temperature rating. The amount of current a cable or wire can safely carry depends on the installation conditions. The international standard wire sizes are given in the IEC 60228 standard of the International Electrotechnical Commission.
In the United States it is not usually used for three phase power but for the high leg delta wiring of split-phase electric power (unknown in Europe). This allows one to choose single-phase AC power at either 110–120 volts between phase and neutral or 220–240 volts between phase and phase.