14. Three-Phase Electricity

Phase is used to describe Alternating Current. Phase explains the timing of the electron movements. Three-phase electricity is common worldwide because it is a cheap and easy way to transmit electricity. Most homes use only one of the phases.
DC-AC diagram - Image: Heurisko Ltd.
The international colour code for each phase of red, yellow and blue is used in this diagram. Notice how within each phase (colour) the electrons are moving back and forth but not in unison with the other phase (colour) - Image: Heurisko Ltd.

What does Phase mean?

Phase is used to describe Alternating Current.
If wires are in phase it means that the electrons move back and forth at the same time. The electrons are 'in step' or 'in time' or 'in phase'.

Single Phase Power

In single-phase electricity all electrons move back and forth, at the same time

Three Phase Power

Three-phase electricity has three sets of electron movement.

This idea of three phase electricity was discovered by the brilliant scientist Nikola Tesla (1856 -1943) over a hundred years ago.

He found it

  • is more efficient to use three circuits that are out of phase. This is because there are always electrons moving in at least one wire - there are no pauses.
  • does not need a neutral or 'return path'. This is because joining the three phases together results in no current - it is like they have cancelled each other out
  • was easier and cheaper to make a 3-phase generator than any other type.