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Jargon Busted: Single-phase and Three-phase electrical power – what’s the difference?

The electrical world can be confusing and we’ve all come across some terms that don’t make much sense. That’s why in each issue of Wired we unravel a piece of industry gobbledygook and tell you what it means – In plain old English.

In a nutshell…

When you plug in your kettle, phone charger or any other electrical equipment at home, you are almost certainly using a single-phase electrical system.

In a small office using low-powered equipment, such as computers, photocopiers and basic lighting, single-phase systems can also be sufficient.

However, in a large office block, or if your workplace runs heavy machinery, for example a motor or an air compressor in a manufacturing or production plant, a three-phase system is required to provide the additional power needed. Three-phase systems are also used for power grids, transmission lines and data centres.


How do they work?

A single-phase system – uses one alternating current to provide electric power. This operates a cyclical flow of current and voltage, which flows in one direction then reverses.

A three-phase system – combines three independent alternating currents, which operate as a rotating magnetic field. These vary in phase by 120 degrees, which means the power delivered is almost constant and never falls to zero.

What has this got to do with lumberjacks?

Imagine a lumberjack is cutting down a tree with an axe. The action consists of hitting the tree with the axe and then a break while the axe is raised for the next swing. This is comparable to a single-phase system.

Now imagine you have three lumberjacks, who take it in turns to swing their axe, one after the other, so that the tree is constantly being chopped. This is more like a three-phase system.

What are the benefits of a three-phase system?

First, it can carry more load and is therefore more suitable for running powerful machinery.

Additionally, it’s safer to run, and cheaper to install and to maintain, as it doesn’t require as much conductor material and runs at a lower cost than a single-phase system.

Finally, a three-phase system can reduce the noise output and increase the lifespan of a motor.

However, for home use, single-phase systems are cheaper to operate, and require less wiring and equipment.

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