Single-phase electric power

Because the voltage of a single phase system reaches a peak value twice in each cycle, the instantaneous power is not constant.

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.

In the United Kingdom a single-phase household supply may be rated 100 A or even 125 A, meaning that there is little need for three-phase in a domestic or small commercial environment.

Typically a third conductor, called ground (or "safety ground") (U.S.) or protective earth (UK, Europe, IEC), is used as a protection against electric shock, and ordinarily carries significant current only when there is a circuit fault.

Single-phase is sometimes divided in half at the distribution transformer on the secondary winding to create split-phase electric power for household appliances and lighting.