Wiring a Light Switch


This FAQ has been written to explain the different types of light switches, circuits and terminologies that are used in modern day lighting installations. Ranging from simple one way switches to more advanced keypads that are used in home automation systems such as Lutron.

Any electrical wiring should be done by a qualified electrician. We are not electricians and have taken all the diagrams from the instructions that are supplied with the products we sell. Basic safety procedures should always be followed such as switching off the mains supply before commencing any work. The maximum current rating should also be adhered to; this is usually 6 to 10 amps per switch for on/off switches and for dimmer switches its 250 or 400 watts or 1-10 LEDs.

If you’re attempting to wire anything more complicated like upgrading a four gang light switch to a four gang dimmer switch it may be worth taking a quick photo first just in-case you get muddled up with the wires and need to revert back.

Wiring a One Way Switch

A one way light switch has two terminals which is a common marked as COM or C. The common is for the live wire that supplies the input voltage to the switch. The other terminal is marked as L1 and is the output to the light fixture.

When you’re wiring decorative light switches such as chrome or stainless steel etc, you’ll find that the switch will also have an L2 terminal which means it’s a two way switch. If you’re circuit is only one way, you can ignore this terminal and it will still work. This is because two way switches can also be used on one way circuits. Manufacturers don’t make decorative one way switches.

Wiring a Two Way Switch

Two way switching means you can switch the same light fixture from two switches that are located in different sides of a room.  Two way switches have a COM terminal as well as L1 and L2 terminals. 

  • When L1 is off L2 would be on.
  • When L1 is on L2 would be off.

There are two wiring options for this:

More advanced dimmer switches like Varilight Eclique and Lightwave RF have an S terminal instead. The S terminal can only be linked up to a corresponding slave and won't work with an ordinary two way switch. Here is an image of a Lightwave RF dimmer switch shown from behind:

Intermediate Switch Wiring

Intermediate switching is similar to two way but allows a third switch to be integrated. An example of this would be having one switch at the bottom of a staircase, one at the top and one in the middle. It’s not known as three way switching because you can also add more switches for four way switching or more.

Intermediate switches have terminals marked L1, L2, L3 and L4. Check out the diagram below that shows how to way a three way switch:

Two Way Dimming

Two way dimming allows you to dim a light fixture from two locations. You can’t use ordinary rotary dimmer switches to do this because you could potentially dim the light down to 10% with one dimmer, then walk over to the other dimmer and attempt to dim the light to below 0%. Or vice-versa you could be attempting to brighten the light above 100%. This would cause major instability on the circuit, like the time when the ghost busters crossed the beams!

You can have a dimmer switch and an on/off switch on the same circuit. The dimmer will do the dimming and the two way switch will be able to switch it on and off. If you've dimmed the lights to 50% the switch will keep switching it and off at that level until you dim it again.

Up until fairly recently two way dimming was quite expensive, it could be done using Lutron Rania. With the arrival of Varilight Eclique and Lightwave RF it doesn't cost as much. With any of these brands you need to use a combination of master and slave dimmers for it to work. The dimmers are then linked together usually by a terminal marked as S or S link. Multiple slaves can be added to the circuit to provide three way dimming or more. The slave(s) essentially sends the command to the master and the master dims or switches the lights, this ensures a chain of command and a range of no more than 0-100% is attempted.

When wiring a Lightwave RF master dimmer to a slave, the voltage isn't mains voltage it's low voltage so be careful not to connect 240V into it otherwise permanent damage will be caused. 

Wireless Switches

Wireless switches usually require an additional receiver for them to work. The receiver (shown in the diagram below) is positioned in the ceiling void near to the lights. It receives an RF (radio frequency) signal from the switch to tell the receiver what to do. If you've already got wires in place you can still use a wireless switch by terminated the wires. The market leaders for wireless switches are Rako and Lightwave RF. A wireless switch is battery powered and can be either screwed into a standard UK back box or it's lightweight design allows it to be stuck to a surface.

These images show the a 1 gang wireless dimmer from the front and from behind which shows the battery and no terminals. The diagram shows how to wire the receiver:

As a wireless dimmer doesn't require mains voltage they can be used inside bathrooms allowing you to create a bathroom dimmer switch. All you need is the following product codes: 

  • JSJSLW201WH  - 1 gang dimmer switch in white. Also available in other finishes.
  • JSJSLW831  - 250W dimming receiver
  • You could also have an additional remote control that would allow you to dim the lights while in the bath, but make sure you don't drop it in the water!

Smart Phone Dimming

If you want to control your lights from a smart phone the easiest and most cost effective way of doing this is with Lightwave RF. All you need is a master dimmer switch, the Lightwave RF Wi-Fi hub  and the App which is free to download. The master dimmer receives the signal from the App and can dim or switch the lights. The same can be done with power sockets, heating controls and other Lightwave RF add-ons.

Lutron QS Keypad Wiring

One of the main advantages of using a home automation system over traditional dimmer switches is that you can replace those big clunky looking double plate three and four gang dimmer switches with trendy looking keypads. Lutron keypads have up to 10 buttons which can be programmed to the lighting scenes of your choosing. Here is an example of engraved 5 button keypad in satin nickel.

Once you’ve decided on the function of each scene you can get the buttons engraved by completing a form and sending back to Lutron, this is included in the price of the keypad. You could either have something simple like Scene 1, Scene 2 etc or try something more adventurous like 'All On', 'TV Watching', 'Party Time', 'Reading' and 'All Off' like in my example. A scene can be a mixture of multiple lighting circuits that are all set to different dimming levels. 'TV Watching' could dim your main LED downlights down to 10%, your wall lights down to 30%, your cove LED strip lights down to 50% and even switch a table lamp on, all at the touch of one button.

If you’re considering installing a full home automation such as Lutron Grafik Eye QS or Energi Savr Node (known as ESN), the corresponding keypads which are known as SeeTouch need to be wired totally differently to any of the traditional switches that we’ve mentioned. Firstly they require a 24V DC supply which can be taken directly from the Grafik Eye or ESN. The keypads can also control electronic blinds which are also available from Lutron.

Using the recommended Lutron control cable which has two pairs of cables, one pair is for power and the other pair is for signal. Additional keypads and other components can then be linked from one to the other using the QS Link terminal. You can even link a Grafik Eye QS to an Energi Savr Node and have them both on the same system.

Lighting Circuits – Loop In, Loop Out

The favoured way of wiring recessed downlights is using the loop in, loop out method. This is a form of parallel wiring that has one cable (usually twin and earth 6242Y) containing the live, neutral and earth wires looping in and then out of leach light fitting. This is an alternative to the traditional junction box system, it uses less cable and is faster to complete.

Many downlights have a loop in, loop out terminal block attached to them. For example the Ansell iCage has the largest one which was specifically designed for this type of wiring. The JCC FGLED6 has push in loop in, loop out terminals built into the attached LED driver and the new EcoLED ZEP1 has push fit loop in, loop out terminals on the terminals of its separate LED driver. The image below shows the JCC FGLED6 wiring system:

When installing downlights that don’t have their own connection system such as the Halers H2 Pro many installers create their own by using a Click Flow Connector. With this connector you wire the smaller male connector into the downlight and the corresponding female connector into your loop in, loop out circuit. Then you simply plug the downlight into the circuit and continue the process with the next ones.

Other downlights like the Aurora M Series and Click Inceptor Micro are supplied with their own Flow Connectors. The male connector is already pre-wired into the downlight so half of the work is already done for you. Another advantage of using Flow Connectors is if the downlight fails you can unplug it and get it replaced yourself without having to get an electrician back in to disconnect it and then reconnect the replacement.

Lighting Circuits – Series Wiring

Series wiring is mainly used with LED lights that are powered from the same LED driver. It is usually used with smaller LED downlights or with LED ground lights that are constant current. The most popular constant current ratings are 350ma or 700ma. This diagram below shows how it's done:

Although many of the LED downlights we offer are constant current, they are each supplied with their own LED driver with is either directly attached to them or trails behind them like an old fashioned halogen and low voltage transformer combination. If you’re wiring a mains supply into each LED driver individually it would be classed as parallel wiring and can be done using the loop in, loop out technique.

Wiring a Downlight

If you’re upgrading an existing halogen downlight installation you’ll most likely either have mains voltage GU10 or low voltage MR16 (GU5.3) halogens. Low voltage halogens will have a transformer; this will most likely need to be disconnected as it will no longer be required. The only reason you'd need to keep the transformer is if you wanted to use MR16 LEDs that operate on AC, this is a less popular option as you need to make sure the existing transformer is compatible with the LEDs and if you're dimming them, you'll need to make sure that the MR16 LED, transformer and dimmer switch are all compatible. Many installers go for the GU10 or integrated option as their are less components to consider and it often costs less.

Hole Cut Out Size

If you're replacing existing downlights you'll want your new ones to have a similar hole cut out size otherwise you'll either need to make the holes bigger or make them smaller (yes I said smaller) which would involve re-plastering your ceiling and re-cutting the holes. Matching the hole sizes is always a key decision in the selection process.

Unless specifically stated downlights are wired in parallel, downlights are only usually wired in series when multiple lights are being powered from the same LED driver. Depending on which type of downlight you choose ,you may need to set provisions to earth them. Here are two examples that explain how to wire a downlight, one is for a GU10 fire rated downlight and another explaining how to wire an integrated LED downlight, each one has it's own earthing provisions:

Wiring a Fire Rated Downlight – Ansell iCage

The Ansell has got a large loop in, loop out terminal block that allows 2x 1.5mm twin and earth cables to wired into one downlight and into the next one. The iCage is supplied with both a GU10 and a GU5.3 low voltage lamp holder.

When used with the GU10 lamp holder, the downlight is mains voltage and must be earthed. This is classified as a Class I product. If you’re using the low voltage GU5.3 lamp holder the downlight is classified as Class III and doesn’t require an earth.

Download the fitting instructions for the Ansell iCage: CLICK HERE

Wiring an Integrated LED Downlight - Halers H2 Pro

Some integrated LED downlights like the market leading Halers H2 Pro from Collingwood Lighting are SELV which stands for Safety Extra Low Voltage. This means that the voltage of the LED driver is below 12V AC or 30V DC. Voltages below 20V can’t usually be felt by the human body and are considered harmless. 

SELV light fittings don’t require an earth; they are classified as Class III constructed products. The LED driver for the H2 Pro is also double insulated which means it has two layers of insulation around the live components, this also means it doesn’t need to be earthed. The DC output voltage is separated from the AC supply voltage.

Double insulated products are classified as Class II and can be identified by this symbol:

The H2 Pro has a live and neutral wire coming off the LED driver, you'll need additional junction or connector blocks to wire them. By adding a Click Flow connector you can create your own loop in, loop out system as mentioned in the previous loop in, loop out wiring section.

Download the fitting instructions for the Halers H2 Pro: CLICK HERE

Wiring a Spotlight

This video from Philips Lighting shows how to install an LED spotlight using their 'Click Fix' system although many of the same rules apply.

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