Light Wiring Diagrams

3 way light switch using a two wire control

I’m including this method for reference in case you find it used in your house wiring but would not recommend this approach in a domestic environment. If you are adding wiring for a three way light switch then use the 3 wire control system.

I have detailed, quite extensively, why a two wire control system can be problematic in the article 2 way switch with 2 wire control. All the issues raised there apply here too, especially if used in stairways and the switches are on different floors.

This method is best suited to conduit/trunking based installations where single core conductors are used.

3 way light switch schematic diagram using a two wire control

3 way light switch schematic diagram using a two wire control


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2 way switching (two wire control)

I’ve included this method of 2 way switching for reference because you may come across it in old homes but I don’t recommend you use it. If you are doing a new install or replacing a two way switch system go for the three wire control method.

You are most likely to see this 2 way lighting circuit in an industrial/commercial setting where the installation is trunking/conduit based and single core conductors are used.

two way light switching schematic using a two wire control

Fig 1: two way light switching schematic using a two wire control

Downside(s) of the two wire control system

This approach if often referred to as a ‘cable saving method’ because it only needs a two wire control. This is fine when executed correctly but here is what you need to look out for: where this is used in a stairwell where you have a switch upstair and a switch downstairs there is the danger that the neutral and the live come from different lighting circuits. See Fi2 2.

Two way swtiching with 2 wire control

Fig 2: Two way swtiching with 2 wire control (DON’T DO THIS)

The first reason this is BAD is on safety grounds; say we are working on the light upstairs, so we turn off the upstairs lighting circuit thinking we are safe.. WRONG. The live is picked up downstairs and there are still live conductors feeding the switch upstairs and if someone flipped the downstairs switch in this diagram that live feed would extend all the way to the lamp too (you’re fried baby!!).

If you see this method used in your home ISOLATE ALL LIGHTING CIRCUITS BEFORE WORKING ON ANY OF THEM. If you are not sure ISOLATE ALL LIGHTING CIRCUITS BEFORE WORKING ON ANY OF THEM.

Note: if this method were used in a long hallway where both switches were downstairs and presumably the neutral is not borrowed from another circuit (DON’T PRESUME THIS) then this safety issue would not exist. But read on..

You see this method offered on many DIY sites but the safety issues are rarely explained adequately. Here’s another reason not to do this that I have yet to find on any DIY site:

Induction loops and RF interference

As you may be aware, any current carrying conductor ’emits’ an electromagnetic field. The good thing about twin and earth cables is that the live and return are always in close proximity (in the same cable) so there is a cancelling effect.

Now consider Fig 2 again, the live feed leaves the consumer unit (fuse board) and runs round the house to the downstairs switch, it then runs upstairs to the second switch, up through the light. The path to neutral may well run around the upstairs lighting circuit before making its way back downstairs to the consumer unit. BINGO, we have just turned our home into a massive induction loop perfectly designed to interfere with all sorts of things:

  • Induction loop hearing aid systems
  • Radio receivers
  • My lovely Stratt (that’s an electric guitar if you are not a muso)
  • Computer networks

I though I was done there but while we are on the subject of why this method is not great:

Erroneous tripping of safety/circuit protection equipment

The practice of ‘borrowing’ a neutral from a circuit that did not supply the live may well play havoc with a modern consumer unit that has multiple RCD’s or RCBO’s.

So to summarise, if you don’t want to take a piss in the dark because your wife turned the kettle on downstairs use a three wire control method🙂


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3 way light switching (old cable colours)

here we have a 3 way switching lighting circuit (sometimes called two way switching with intermediate). This allows a single light to be turned on or off from any of the switches. This page shows it wired in the old cable colours if your house has the new colours you want to go here:

3 way switching (new cable colours)

This is very similar to the two way switching circuit but with and additional intermediate switch introduced into the three wire control cable that links the two end switches.

3 way switching schematic wiring diagram

fig 1: Three way switching schematic wiring diagram

The circuit consists of a two way switch at each end (top and bottom switches in Fig 2) and an intermediate switch in the middle. All three switches are connected together by a three core and earth control cable. Notice that the wire connected to the COM terminals is looped straight through the intermediate switch using a cable connector.

Three way light switching circuit diagram (old cable colours)

Fig 2: Three way light switching circuit diagram (old cable colours)

All earth wires should connect to the earth terminal in the switch back-boxes and if you are using metal switches there MUST be a loop from this earth terminal to the one on the switch plate (see note A on Fig 2)

Four way switching and more

This circuit can be extended to four, five way switching by adding additional intermediate switches (wired as shown in fig 2) anywhere along the control cable.


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3 way light switching (new cable colours)

here we have a 3 way switching lighting circuit (sometimes called two way switching with intermediate). This allows a single light to be turned on or off from any of the switches.This page shows it wired in the new cable colours if your house has the old colours you want to go here:

Three way switching (old cable colours)

This is very similar to the two way switching circuit but with and additional intermediate switch introduced into the three wire control cable that links the two end light switches.

3 way switching schematic wiring diagram

Fig 1: Three way switching schematic wiring diagram

The circuit consists of a two way switch at each end (top and bottom switches in Fig 2) and an intermediate switch in the middle. All three switches are connected together by a three core and earth control cable. Notice that the wire connected to the COM terminals is looped straight through the intermediate switch using a cable connector.

Three way light switching wiring diagram (new cable colours)

Fig 2: Three way light switching wiring diagram

All earth wires should connect to the earth terminal in the switch back-boxes and if you are using metal switches there MUST be a loop from this earth terminal to the one on the switch plate (see note A on Fig 2)

Four way switching and more

This circuit can be extended to four, five way switching by adding additional intermediate switches (wired as shown in fig 2) anywhere along the control cable.


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2 way switching (3 wire system, old cable colours)

2 way switching means having two or more switches in different locations to control one lamp. They are wired so that operation of either switch will control the light. This arrangement is often found in stairways, with one switch upstairs and one switch downstairs or in long hallways with a switch at either end.

Here we have a two way switching system that utilises two single gang two-way switches and a three wire control, shown in the old cable colours. It is possible to achieve a similar result using a two wire control which, although it saves on cable, is not recommended. This is the preferred approach.

If your circuit has the new cable colours see: Two-way switching (3 wire control, new cable colours)

Here we a have a schematic (Fig 1) which makes it easy to visualise how this circuit works. In this state the lamp is off, changing the position of either switch will switch the live to the lamp turning it on. If you now change the position of the other switch the circuit is broken once again.

Two way switching schematic wiring diagram (3 wire control)

Fig 1: Two way switching schematic wiring diagram (3 wire control)

The schematic is nice and simple to visualise the principal of how this works but is little help when it coms to actually wiring this up in real life!!

Fig 2 below shows how we achieve this configuration. Just like any loop-in loop-out radial circuit, the switch cable from the ceiling rose contains two wires, a permanent live and a switched live. This is cable C below, one wire connects to L1 and the other to L2 on the top switch.

Cable D (Fig 2) is a three core and earth, this is the ‘3 wire control’ that links the two light switches together. COM on the first switch connects to COM on the second switch, L1 on the first switch connects to L1 on the second, and L2 on the first switch connects to L2 on the second.

All earth wires should connect to the earth terminal in the switch back-box and if you are using metal switches there MUST be a loop from this earth terminal to the one on the switch plate (see note A on Fig 2)

Two way switching using a 3 wire control (shown in the old cable colours)

Fig 2: Two way switching using a 3 wire control (shown in the old cable colours)

NOTE: The blue and yellow wires in cable ‘D’ and the black wire in cable ‘C’ are switched lives and thus should be marked with red sheathing at each end as shown.

Switch drops from a junction box

There is a chance that if your house has these old wiring colours the switch drops may be from a loop-in-loop-out radial lighting circuit done with junction boxes rather than ceiling roses as shown in Fig 2. The switch wiring is all the same but the switch wire (cable C) leads up to a different set up.

3 way switching wired to a loop-in-loop-out radial lighting circuit done with junction boxes

Fig 3: 3 way switching wired to a loop-in-loop-out radial lighting circuit done with junction boxes


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2 way switch (3 wire system, new harmonised cable colours)

2 way switching means having two or more switches in different locations to control one lamp. They are wired so that operation of either switch will control the light. This arrangement is often found in stairways, with one switch upstairs and one switch downstairs or in long hallways with a switch at either end.

Here we have a two way switching system that utilises two single gang two-way switches and a three wire control, shown in the new harmonised cable colours. It is possible to achieve a similar result using a two wire control which, although it saves on cable, is not recommended. This is the preferred approach.

If your circuit has the old cable colours see: Two-way switching (3 wire control, old colours)

Here we a have a schematic (Fig 1) which makes it easy to visualise how this circuit works. In this state the lamp is off, changing the position of either switch will switch the live to the lamp turning it on. If you now change the position of the other switch the circuit is broken once again.

Two way switching schematic wiring diagram (3 wire control)

Fig 1: Two way switching schematic wiring diagram (3 wire control)

The schematic is nice and simple to visualise the principal of how a two way switch works but is little help when it coms to actually wiring this up in real life!!

Fig 2 below shows how we achieve this configuration. Just like any loop-in loop-out radial circuit, the switch cable from the ceiling rose contains two wires, a permanent live and a switched live. This is cable C below, one wire connects to L1 and the other to L2 on the top switch.

Cable D (Fig 2) is a three core and earth, this is the ‘3 wire control’ that links the two light switches together. COM on the first switch connects to COM on the second switch, L1 on the first switch connects to L1 on the second, and L2 on the first switch connects to L2 on the second.

All earth wires should connect to the earth terminal in the switch back-box and if you are using metal switches there MUST be a loop from this earth terminal to the one on the switch plate (see note A on Fig 2)

Two way light switching (3 wire system, new harmonised cable colours) showing switch and ceiling rose wiring.

Fig 2: Two way light switching (3 wire system, new harmonised cable colours)

NOTE: The Grey wire in cable ‘D’ is a switched live and the Blue wire in cable ‘C’ and Black wire in cable ‘D’ are permanent lives and thus should be marked with brown sheathing at each end as shown.


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Old multi-point radial lighting diagram using junction boxes

Fig 1 shows what is referred to as a radial circuit (sometimes called a ‘loop-in’ or ‘multi-point radial lighting circuit’). which uses junction boxes instead of ceiling roses. You may find this wiring arrangement in older properties.

N.B. The diagrams below shows the old cable colours as you are unlikely to find this approach taken in a modern property which would use the new ‘harmonised’ cable colours.

If your lighting circuit has all the cables terminate in ceiling roses rather than junction boxes, please refer to one of the following instead:

Multi-point radial lighting circuit with new cable colours (harmonised) or

Multi-point radial lighting circuit (old cable colours)

Multi-point radial lighting circuit using junction boxes

Fig 1: Multi-point radial lighting circuit using junction boxes

The live feed from the Consumer unit (fuse board, shown in blue in Fig 1) feeds into the first junction box (junction box A, Fig 1). This would be cable A in the diagram below (Fig 2) which shows how the junction box is terminated. This live feed now loops back out of the junction box (cable B, Fig 2) and feeds power to the next ceiling light in the radial circuit (junction box B, Fig 1). This repeats for each light in the circuit until we reach the last light.

Once we reach the last light, you can see that there is only The feed from junction box B (Fig 1), This is Cable A in the diagram below (Fig 3), which shows how the last junction box in the circuit is terminated.

Junction box wiring for looped radial lighting circuit

Fig 2: Junction box wiring for looped radial lighting circuit

Notice that each of the three junction boxes in Fig 1 has, in addition to the power feeds, an additional cable that feeds down to the light switches (the switch wire). This is Cable C in fig 2 & Fig 3. Cable D (Fig 2 and Fig 3) is the feed to the light fitting.

Junction box termination for the end of a radial lighting circuit

Fig 3: Junction box termination for the end of a radial lighting circuit


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Multi-point radial lighting circuit (old cable colours)

If you are new to lighting circuits, this is a good place to start. Here we will explain how the most common lighting circuit works then we’ll move on to some variations that you may see in your home that may appear to differ from this.

N.B. The diagrams below shows the old cable colours. If the cables in your circuits are Brown and Blue please see Multi-point radial lighting circuit – new cable colours.

Fig 1 shows what is referred to as a radial circuit (sometimes called a ‘loop-in’ or ‘multi-point radial lighting circuit’).

multi point (loop-in) radial lighting circuit

Fig 1: multi point (loop-in) radial lighting circuit

The live feed from the Consumer unit (fuse board, shown in blue in Fig 1) feeds into the first ceiling rose (ceiling rose A, Fig 1). This would be cable A in the diagram below (Fig 2) which shows how the ceiling rose is terminated. This live feed now loops back out of the rose (cable B, Fig 2) and feeds power to the next ceiling light in the radial circuit (Ceiling rose B, Fig 1). This repeats for each light in the circuit until we reach the last light.

Once we reach the last light, you can see that there is only The feed from ceiling rose B (Fig 1), This is Cable A in the diagram below (Fig 3), which show how the last ceiling rose in the circuit is terminated.

Ceiling rose (old cable colours)

Fig 2: Ceiling rose (old cable colours)

Notice that each of the three ceiling roses in Fig 1 has, in addition to the power feeds, an additional cable that feeds down to the light switches (the switch wire). This the Cable C in fig 2 & Fig 3.

Radial circuit last ceiling rose (old colours)

Fig 3: Radial circuit last ceiling rose in the circuit (old colours)


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Multi-point radial lighting circuit (new cable colours)

If you are new to lighting circuits, this is a good place to start. Here we will explain how the most common lighting circuit works then we’ll move on to some variations that you may see in your home that may appear to differ from this.

N.B. The diagrams below shows the new (harmonised) cable colours. If the cables in your circuits are Red and Black please see Multi-point radial lighting circuit – old cable colours.

Fig 1 shows what is referred to as a radial circuit (sometimes called a ‘loop-in’ or ‘multi-point radial lighting circuit’).

multi point (loop-in) radial lighting circuit

Fig 1: multi point (loop-in) radial lighting circuit

The light wiring diagram shows how the live feed from the Consumer unit (fuse board, shown in blue in Fig 1) feeds into the first ceiling rose (ceiling rose A, Fig 1). This would be cable A in the diagram below (Fig 2) which shows how the ceiling rose is terminated. This live feed now loops back out of the rose (cable B, Fig 2) and feeds power to the next ceiling light in the radial circuit (Ceiling rose B, Fig 1). This repeats for each light in the circuit until we reach the last light.

Ceiling rose (new harmonised cable colours)

Fig 2: Ceiling rose (new harmonised cable colours)

Once we reach the last light, you can see that there is only The feed from ceiling rose B (Fig 1), This is Cable A in the diagram below (Fig 3), which show how the last ceiling rose in the circuit is terminated.

Notice that each of the three ceiling roses in Fig 1 has, in addition to the power feeds, an additional cable that feeds down to the light switches (the switch wire). This the Cable C in fig 2 & Fig 3.

Radial circuit last ceiling rose (new harmonised colours)

Fig 3: Radial circuit last ceiling rose in the circuit (new harmonised colours)


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