THREE WAY LIGHT SWITCHING
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THREE WAY LIGHT SWITCHING |
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Here are step by step instructions on how to wire up a three way lighting circuit or to change a existing two way light circuit to a three way system, this is very useful on stairs etc. as you can have a switch at the bottom of the stairs and one at each end of the landing. Ensure 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 that are "two way", these will have three terminals.
To install a three way lighting system from scratch please see these pages-
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| Old colours | New harmonised colours |
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Here you can see the back of a light switch, in this
instance it is a two way switch being used for a one way light. A one way
switch has only a common and L1 terminal and a two way switch has a common,
L1 and L2 terminal, like this one in the picture. Note that new harmonised cable is being used (Brown and Blue) and note that Brown sleeving has been placed over the Blue wire, This signifies that it will 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 earthing terminal. The backbox will need earthing unless it is plastic and there is no earthing point. |
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For three way switching you need a length of three core
and earth cable long enough to reach from the existing light switch to the
second light switch and then a length from the second light switch to the
third light switch. This cable needs
routing via the easiest route,
here are the guidelines and permissible zones. This is not harmonised cable but the new colours are above, simply replace the colours with Grey, Black and Brown, the earth sleeving still needs using before connection as with all cable. There are no set rules for which wire does what in three way lighting, but I am going to use the most sensible option. |
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After running your cable from the first light switch to the
second, you will need to
prepare the cable. Now 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. |
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There are no fixed regulations for which wire goes where but
if 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 have slid this back a little then you 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 Yellow wire goes in the common terminal, Red in the L1 terminal and Blue goes in the L2 terminal. When ever you fasten a wire 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! |
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This is the intermediate switch, it is easy to identify as
it has 4 terminals. L1,L1 and L2,L2 The two wires from the first light switch, which are red and Blue go into the L1 and L1 terminals. The two wires that are going to the final switch, which again will be red and Blue go into the terminals marked L2 and L2. The yellow terminal is simply joined together using a terminal block, this can be taped up with insulation tape and left in the back box. Brown sleeving should be put on all wires except the earth which requires green and yellow sleeving. Harmonised cable can be used but the colours will be different, the colours are not important but what each wire does is important. |
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This is the back of the Third switch that will make the
circuit 3 way, once again the brown sleeving has been slid back for clarity. The wires in this switch should mimic exactly the three wires that you have put in the First switch. The Yellow wire goes in the common terminal, Red in the L1 terminal and Blue goes in the L2 terminal. You now have a light that can be switched on or off from 3 different locations. |
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