Light Wiring Diagrams

Two way switching (power feed via switch)

Here is a two way switching solution posted for one of our users who had run the power feed to one of the switch boxes and had no radial circuit to pick up a neutral at the lamp holder.

Two way switching with power feed to the switch

Two way switching with power feed to the switch


Tags: , ,

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🙂


Tags: , , , , , , , , ,

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


Tags: , , , , , , , , ,

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.


Tags: , , , , , , , , ,

2 gang 2 way light switch

This switch arrangement is basically two two way switches on a single face plate.

Some brands of light switch may have slightly different labeling on the terminals (such as C L1 L2 or even L1 L2 and L3).

Double gang swith face plate

Double gang switch face plate

Double gang two way light switch

Fig 2: Double gang two way light switch

Switch mechanism

Two way light switch mechanism

Fig 3: Two way light switch mechanism

Each of the gangs (or switches) above in Fig 2 (of which there are two) work like this (Fig 3): In position 1 (when the switch is down or ‘on’), COM and L1 are connected together (just like the one way switch). In position 2 (when the switch is up or ‘off’), COM and L2 are connected together.

There are no connections between the two gangs in Fig 2. Each gang is a single discreet switch.

Just to be different:)

The terminals on your switch may be a little different to those shown above but rest assured they function just as described above but the terminal pins are in different positions. You may see the following:

double gang two way light switch terminal variation 1

double gang two way light switch terminal variation 1

double gang two way light switch 3

double gang two way light switch terminal variation 2


Tags: , , , , ,

3 gang 2 way light switch

This format of light switch has three discreet switches on a single face plate. Basically this is three Single gang 2 way switches on a single face plate.

Triple gang switch face

Triple gang switch face

Triple gang 2 way light switch

Fig 2: Triple gang 2 way light switch

Switch mechanism

Two way light switch mechanism

Fig 3: Two way light switch mechanism

Each of the gangs (or switches) above in Fig 2 (of which there are three) work like this (Fig 3): In position 1 (when the switch is down or ‘on’), COM and L1 are connected together (just like the one way switch). In position 2 (when the switch is up or ‘off’), COM and L2 are connected together.

There are no connections between the three gangs in Fig 2. Each gang is a single discreet switch.


Tags: , , , , ,