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Three Way Light Switching

Here are step-by-step instructions on tips on how to wire up a 3 way lighting circuit or to change a existing two way light circuit to a three way system, this may be very useful on stairs etc. as you possibly can have a switch at the bottom of the stairs and one at each end of the landing. Make sure the electricity is isolated before working on any electrical circuit! For three way switching you need a special light switch with 4 terminals, this is called a intermediate switch and is easily identifiable. You will also need two light switches which can be “two way”, these will have three terminals.

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Three way switching is just not as difficult because it first seems and must be pretty straight forwards should you follow the diagrams below. Earth wires have been omitted from all photo’s and diagrams for clarity, but must be connected in any respect earth terminals. Two-way light switches are required for 3 way switching, these can be identified by looking on the terminals on the back of the switch . There might be a Com (common) terminal a L1 terminal and a L2 terminal. You will also need an intermediate switch to slot in between the other two switches, this can easily be identified because it has two L1 terminals and two L2 terminals.

Three way light switching

(with the old wiring colours)

Three core and earth cable is required to put in two or three way switching and this must be run from the first light switch to second switch (intermediate) after which to the third switch after which wired as shown in this diagram. Switch one is the switch that contains the live wire and switched live wire.

The diagram shows single colours only. In real life these wires can be covered by an outer protective sheath and would come with a bare earth wire and could be called a cable.

Red sleeving or tape would of been placed on the wires as shown to show that they could be live in some unspecified time in the future. Brown sleeving or tape has now replaced red. Note how the Yellow wire is connected together in a terminal connector within the back box for the intermediate switch.

Three way switching with the new harmonised colours-

This is identical diagram as above, but using the new harmonised colours.

Three core and earth cable is required to install two or three way switching and this should be run from the first light switch to the second (intermediate) and then to the third switch and then wired as shown in this diagram. Switch one is the switch that contains the live wire and switched live wire. The diagram shows single colours only. In real life these wires would be covered by an outer protective sheath and would include a bare earth wire and would be called a cable.

Brown sleeving or tape would of been placed on the wires as shown to show that they would be live in some unspecified time in the future. Note how the Grey wire is connected together in a terminal connector within the back box for the intermediate switch.

How to convert a single switch to a 3 way system-

Here you possibly can see the back of a light switch, in this instance it is a two way switch being used for a a technique light. A one way switch has only a common and L1 terminal and a two way switch has a standard, L1 and L2 terminal, like this one in the image. Note that new harmonised cable is getting used (Brown and Blue) and note that Brown sleeving has been placed over the Blue wire, This signifies that it is going to be live at some point! The earth wire should always be connected to the earthing points, it has been removed for clarity here but must be connected, even on plastic light switches, unless there is no such thing as a earthing terminal. The back box will need earthing unless it is plastic and there is no earthing point.

For three way switching you need a length of three core and earth cable long enough to reach from the prevailing light switch to the second light switch after which a length from the second light switch to the third light switch.

This cable needs routing via the simplest route, listed below are the rules and permissible zones permitted wiring zones

This is not the new harmonised cable so the colours might have changing, the earth sleeving still needs using before connection as with all cable.

There are not any set rules for which wire does what in three way lighting, but I am going to make use of essentially the most sensible option.

Remove the wire which is in the common terminal and place it in the L2 terminal.

These two wires are the permanent live and switched live wires.

There are no fixed regulations for which wire goes where but should you follow the colours that I have used here, they seem to make sense!

Note how all of the wires have brown sleeving on them! I’ve slid this back a bit of then you possibly can see the actual colours of the wires. The brown wire and the blue wire that is sheathed brown are already in terminals L1 and L2, this is described above. These two wires are the Permanent live and switched live.

The Grey wire goes in the common terminal, Brown within the L1 terminal and Black goes in the L2 terminal. When ever you fasten a wire right into a terminal, always give it a gentle pull to ensure it is fastened correctly. This can save hours of work later on when the wire pops out and stops working!

That is the intermediate switch, it is simple to identify as it has 4 terminals.

L1,L1 and L2,L2 The two wires from the first light switch, that are red and Blue go into the L1 and L1 terminals. (new colours might be Brown and Black)

The 2 wires which might be going to the final switch, which again can be red and Blue go into the terminals marked L2 and L2. (new colours might be Brown and Black)

The yellow wire (new colour Grey) is solely joined together using a terminal block, this can be taped up with insulation tape and left in the back box. Brown sleeving needs to be placed on all wires except the earth which requires green and yellow sleeving. The colours are usually not important but what each wire does is important.

This is the back of the second switch that may make the circuit 2 way, once again the brown sleeving has been slid back for clarity. The wires in this switch should mimic precisely the three wires that you’ve got put in the other switch.

Old colours-

The Yellow wire goes within the common terminal, Red within the L1 terminal and Blue goes within the L2 terminal.

New colours-

The Grey wire goes within the common terminal, Brown in the L1 terminal and Black goes within the L2 terminal. You now have a light that can be switched on or off from 2 different locations.

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