Conductors of a 3 phase system are usually marked by color code, to allow for balanced loading and to assure the correct phase rotation for 3 phase induction motors. Colors used vary widely and may adhere to old standards or to no standard at all, and sometimes vary even within an installation. However, the current National Electrical Code (2005) does not require color identification of conductors other than that of the neutral (white or white with a color stripe), the ground (green or green with a yellow stripe), or in the case of a High Leg Delta system, the High Leg must be identified with orange.
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One voltage cycle of a three-phase system, labeled 0 to 360° ( 2 π radians) along the time axis. The plotted line represents the variation of instantaneous voltage (or current) with respect to time. This cycle will repeat 50 or 60 times per second, depending on the power system frequency. The colors of the lines represent the American color code for three-phase. That is black=VL1 red=VL2 blue=VL3
Three phase systems may or may not have a neutral wire. A neutral wire allows the three phase system to use a higher voltagewhile still supporting lower voltage single phase appliances. In highvoltage distribution situations it is common not to have a neutral wire as the loads can simply be connected between phases (phase-phase connection). |