How to wire a light switch

Types of Light Switches

There are many types of light switches, 1 way, 2 way and intermediate, then is the number of switches on a switch plate, 1 gang, 2 gang, 3 gang and so on, then there are many types of dimmer switches, leading edge, trailing edge, LED etc. There is also varying IP rated light switches.

Each type of light switch connection is different, the wiring diagram for a 1 way light switch is different to the wiring diagram for a 2 way light switch. It is important to ensure the correct light switch is selected for its intended use.

1 Gang 1 Way Light Switch

A 1 gang 1 way light switch can be used to switch on and off a light fitting, if the same light fitting needs to be switched from two different positions i.e. top of stairs and bottom of stairs then a 1 gang 2 way light switch is required, one at the bottom of the stairs and another at the top of the stairs.

1 Gang 2 Way Light Switch

A 1 gang 2 way light switch is used to switch on and off a light fitting from two different switches, for example a large room may have two entrances where you want to be able to switch the lights on and off from.

Intermediate Light Switch

An intermediate light switch is required when you wish to turn on and off a light fitting from more than two different switches, for example a large room may have three entrances where you want to be able to switch the lights on and off from each entrance.

Terminology:

• 1 gang = A switch plate with only 1 switch.
• 2 gang = A switch plate with 2 switches.
• 1 way = Is where a light only needs to be switched from 1 light switch, so a 1 way switch is used.
• 2 way = Is where a light is to be switched from more than 1 light switch (i.e. A landing light switched at the top of the stairs and another switch at the bottom of the stairs), so 2 way switches are used.
• Intermediate = An intermediate switch is required where a light needs to be switched from more than 2 separate light switches.

Light Switch Wiring Diagrams

Note the earths have been omitted for clarity, the earth core of a cable should NEVER be cut off. Connect the circuit protective conductor (earth) to the light switch metal backbox earth terminal.

If the light switch is metal then also install a fly lead from the metal backbox earth terminal to the metal light switch earth terminal.

If both the backbox or pattress and the light switch are plastic then terminate the earth cables into a suitable electrical connector, if there is more than 1 earth cable then connect all the earth cores together using a suitable insulated connector.

Light Switch Wiring Colours:

The wiring colours in the UK changed in 2006, therefore below we have set out both the old wiring colours (Red, Black, Yellow, Blue) and the new wiring colours (Brown, Blue, Black, Grey) wiring diagrams.

Two Way Light Switch Wiring:

For two way switches it doesn’t really matter what order connections are at switch No.2 as long as it matches the connections at switch No.1, shown above are the colours and order of connections commonly used.

How to Wire a Dimmer Switch

The wiring connections for dimmer switches are the same as shown in the how to wire a light switch diagrams above.

When selecting a dimmer switch it is important to ensure the correct dimmer switch is selected matching the rating and type of lamps it is to dim. Dimmer switches have a maximum load they can dim, for example a standard incandescent 100 watt dimmer switch can only dim up to a maximum of a 100 watt incandescent load.

If you exceed this maximum load it can cause the dimmer switch module to overheat and melt due to it being overloaded.

LED dimmer switches are available in many types and ratings, for an LED dimmer switch it is best to contact the manufacture of the LED lamps who can advise on the best suited LED dimmer switch.

Common Errors

A common issue is with metal light switches where the yellow core of a 3 core cable at a 2 way light switch has been connected to the earth terminal of the light switch. When the two way switches are in a certain position the yellow core of the cable will become live. thus making the metal light switch live resulting in a risk of electric shock.

As many electricians discover on a daily basis that DIY electrical works are generally dangerous, non-compliant and normally ends up costing a lot more in the long run due to the costs involved to correct and make safe the DIY works.

Another common issue electricians are finding with DIY fitted light switches is where the earth core of the cable is being used as a live conductor, which of course is non-compliant and dangerous.