What is two phase?

Answer 1

In what context? Typically people want to know this because someone referred to a residential service as 'two phase', meaning there are two hot wires and a neutral. Technically, there is no such thing as two phase power. Commercial sites are often wired in three phase power, and residences are actually using a special type of single phase power called 'Split single phase'. This has to do with the way the voltage for the hot leads is created. Residential step-down Transformers on the ground or on poles use a transformer with a center tapped secondary, making each hot wire about 120 volts. The center tap point becomes the neutral wire. A phase to phase measurement gives you about 240 volts. This is technically created with only one phase from the power generation point, as opposed to commercial services which actually use all three phases. A phase to phase measurement in a commercial service yields 208 volts instead of 240.

AnswerA two-phase system is very rare these days, as it pre-dated three-phase systems. It consisted of a generator with two phase windings, physically displaced by an angle of 90 degrees, giving two phase voltages displaced by 90 electrical degrees. The resulting line voltage is 1.414 times the phase voltage.

A two-phase system should not be confused with the split-phase system used for North American residential supplies.