Split phase is a mains electrical supply system mainly used in North America ( which may be incorrectly referred to as two phase). It is used occasionally in the UK in distribution situations where only two 11 kilovolt phases are available, but it is rarely taken into buildings.

A transformer providing split phase has a single phase input, and the output is centre-tapped with the neutral on the centre tap.

This means that there are two phase conductors both equidistant from the neutral. Therefore (provided the balance is good), appliances can be directly supplied with the normal voltage with some of the advantages of higher voltages, such as smaller cables and/or lower losses. It also means that appliances can be supplied that need double the normal voltage, so it is widely used for high power or European equipment in the USA.

A further variation of "split phase" is a three-phase 240 volt delta connected system in which one pair of phases has a center tap. This allows a single service to supply 120 V for lighting, 240 V single phase for heating appliances, and 240 V three-phase for motor loads (such as air conditioning compressors).

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A split phase motor is a type of induction motor designed for use on single-phase electric power, characterized by low cost, low starting torque, and high starting current. Such motors are chiefly used in blower applications. A starting winding with a higher resistance produces a small phase shift in the current, compared with the main running winding. This produces a revolving magnetic field and resulting starting torque. Once the motor reaches near full speed, the starting winding is disconnected by an automatic switch.

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