splitphase

Splitphase, or split-phase power, is a method of electrical power distribution that uses a center-tapped transformer to supply two voltages that are equal in magnitude but opposite in phase. In typical North American service, this arrangement provides 120 V from each hot conductor to neutral and 240 V between the two hot conductors. The neutral carries the unbalanced current between the legs, enabling both standard 120 V loads and higher-power 240 V appliances from a single transformer.

In practice, split-phase circuits use two hot wires (commonly black and red) and a neutral (white). Multi-wire branch circuits share a neutral across the two hot legs. To ensure safety, the circuit-breaker arrangement should disconnect both hot legs simultaneously with a two-pole breaker to prevent shock on the neutral if one leg is deenergized. Proper polarity and grounding are essential for safe operation.

Split-phase motors are a related concept in which two windings produce a phase-shifted current to create starting torque in single-phase induction motors. Designs include capacitor-start and permanent-split-capacitor configurations, among others. While split-phase wiring concerns the distribution of voltage for household devices, split-phase motor design focuses on generating a rotating field through dual windings.

Advantages of split-phase distribution include access to both 120 V and 240 V from a single transformer and relatively simple wiring for homes. Disadvantages include limited overall power compared with three-phase systems and potential neutral overloading if loads on the two legs are not balanced, requiring careful circuit design and proper breaker protection.