What Is Half-Phase Electricity?

By Mitchell Brock, eHow Contributor

 
 
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Plugging into a single-phase outlet.

Electricity is the energy supplied throughout the power grid within many nations, including the United States. There is alternating current or direct current. The power grid used AC electricity to run the lights, appliances and other electrical systems in our homes and jobs. Three different phases have been used in an AC circuit; single-phase and 3-phase. Half-phase does not really exist but is used to describe current in one of these phases.

1. Single Phase

   • Single-phase electricity is what you use in your house with the exception of a few appliances. The lights, outlets and most appliances operate off of a single-phase circuit. The single-phase circuit only carries 120-volts through one line, but has a neutral wire and a ground wire as part of the circuit.

   2-Phase

   • A 2-phase system was developed in the 1890s, but today is obsolete. Some 2-phase electricity is used on stepper motors or specialty CPUs, but in reality, 2-phase wire does not really exist anymore. Like single-phase power, 2-phase motors were used to run the generators at Niagara Falls in 1895. The 2-phase circuit is only two independent single-phase circuits, so 240-volts could be supplied to the motors. One circuit had 120-volts with a neutral wire, while the other circuit was exactly the same. The two single-phase circuits or wires made up what electricians, at that time, called 2-phase power.
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   3-Phase

   • Modern times finds a more efficient way to supply 240-volt systems with power. The 3-phase electrical circuit was developed to operate industrial motors more efficiently. The phase has three wires that carry 120-volts each. Two of the three wires supply the voltage used by a 3-phase motor. If any voltage drops on one of the 120-volt wires, the third wire can supply the voltage required by the motor. Commercial buildings have 3-phase systems, as well as ovens, dryers, welders and large industrial equipment.

   Half-Phase

   • There is no such thing as a half-phase circuit or power supply. The only reason a half-phase terminology exists is to describe part of the power supply of a 2- or 3-phase circuit. A person describing a 120-volt line on the 2- or 3-phase circuits can describe it as half the phase or half-phase. Meaning that only half the voltage required by the motor or system is flowing through that one wire. Twice as much voltage is required to run that electrical system, but half-phase is only part of the 2- or 3-phase circuit.