Single-phase electric power
distribution of AC electric power in a system where the voltages of the supply vary in unison
Single-phase electric power (abbreviated 1φ) is the simplest form of alternating current (AC) power used to supply electricity. In a single-phase system, all the voltages vary together in unison, creating a single alternating waveform. This type of power is widely used for homes, small businesses, and other applications where the main needs are for lighting, heating, and small appliances.
Unlike three-phase systems, single-phase power does not naturally produce a rotating magnetic field, so motors designed for it require extra components to start and generally have lower power ratings (rarely above 10 kW). Because the voltage peaks twice during each cycle, the instantaneous power delivered is not constant, which can make it less efficient for running large machinery.
Most of the world’s single-phase systems operate at a standard frequency of either 50 or 60 Hz. Some specialized systems, such as traction power networks for electric railways, may use other frequencies such as 16.67 Hz.
History
Single phase power transmission took many years to develop. The earliest developments were based on the early alternator inventions of 19th-century Parisian scientist Hippolyte Pixii, which were later expanded upon by Lord Kelvin and others in the 1880s. The first full AC power system, based on single phase alternating current, was created by William Stanley with financial support from Westinghouse in 1886.
This brief starts where responsible research should: with the source description of “Single-phase electric power” as distribution of AC electric power in a system where the voltages of the supply vary in unison. Everything that follows is an evidence route, not borrowed authority.
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Vocabulary and entity names are the principal evidence signals here, because they determine the precision of every later search. The source revision retrieved here is dated Aug 26, 2026. The linked authority identifier is Q260295. None of the 0 selected statements returned an explicit reference. The first chronological checks are 1886.
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This entry incorporates text from “Single-phase electric power” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.