Three-phase electric power

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Three-phase electric power (abbreviated 3ϕ) is the most widely used form of alternating current (AC) for electricity generation, transmission, and distribution. It is a type of polyphase system that uses three live wires, and no neutral wire in long transmission lines, thus being most economical and the standard method by which electrical grids deliver power around the world. Due to the time shift between phases, each live wire current is always cancelled out to zero by the sum of the other two, thus a common neutral wire does not carry any current if the loads are properly balanced, e.g. when a generator powers a motor locally, or in case of large transmissions grids, in which loads can be balanced closely enough. In most 3-phase cables used eg. within buildings, a fourth wire is used as a neutral return for imbalanced loads, and a fifth as protective earth. In a three-phase system, each of the three phases is offset by 120 degrees of phase shift relative to the others. This arrangement...

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