Three Phase and Single Phase: What’s The Difference?

Ever wondered how three phase power differed from single phase power? This guide should help.

In the home and some workplaces, the UK’s electricity supply at the point of delivery is 240V at 50Hz. This is known as a single phase system. In larger premises this is 415V, again at 50Hz. The 415V supply uses a three phase system.

Where single phase varies from three phase is in its number of live wires in the mains. Single phase has one live wire, whereas three phase has three of them. As illustrated by the diagram below, current flows in a strict red-green-blue order. Each colour has a phase generator which flows towards the phase load. A neutral section links the two central ‘Y’ points.

Three Phase Flow diagram
A diagram to illustrate current flow in the three-phase system.

There are two common ways of wiring a three-phase system: that of the Wye (Y) and the Delta (Δ) configurations. A fourth wire may be added to the Wye system, whereas the Delta system only needs three.

Power Factor Correction

Efficiency is one of the main aspects of the three phase electrical system. Sometimes, the efficiency of its three phases can go wrong. This is why electricity meters for three-phase systems have Power Factor Correction.

The Power Factor is the ratio of the real power flowing to the load to the apparent power in the circuit. This is a dimensionless number between -1 and 1. Should the power factor fall below -1 or above 1, the voltage and the current waveforms are not in sync. If you have a single phase supply, this is something you don’t have to worry about.

AC or DC?

Three phase power only applies to AC electrical supplies. AC stands for Alternate Current.

Total Control and Distribution, 10 December 2016.

Image Credit:

Animation of three-phase supply current flow by BillC, 2006 (Creative Commons License – Attribution-ShareAlike Unported).

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