DIY How To

Two way light switch using 3 core cable

There are different ways to connect up two way lighting circuits, if it is a new installation the ideal way is to use a three core & earth cable between the two light switches.

Two way lighting circuit using three core & earth cable

Line diagram of a two way lighting circuit using junction boxes (fig 1).

Two way lighting circuit using junction boxes fig 1

The junction box should be wired as shown below.

Lighting junction box fig 2

Explanation of above picture. (fig 2)
The feed cable comes from a previous junction box or from the consumer unit, the red, black and earth wires are connected to separate terminals. The earth wire must be covered with green/yellow sleeving.

The cable going to the first light switch is connected as follows (fig 2). The red wire going to the switch is connected to the same terminal as the red wire from the feed cable, the black wire from the switch is connected to the spare terminal (terminal not yet used), and the earth wire is connected to the same terminal as the earth wire from the feed cable.
The black wire from the switch, should be marked with red tape or red sleeving to show it is a live wire, but in practice is often left unmarked.

The cable going to the ceiling rose is connected as follows (fig 2). The red wire going to the ceiling rose is connected to the same terminal as the black wire (marked with red tape or red sleeving) coming from the light switch, the black wire going to the ceiling rose is connected to the same terminal as the black wire from the feed cable and the earth wire going to the ceiling rose is connected to the same terminal as the earth wire from the feed cable.

The following picture is exactly the same as the picture above with the addition of another cable which provides the feed for the next junction box.

Lighting junction box fig 3

The cable going to the next junction box is connected as follows (fig 3). The red wire going to the next junction box is connected to the same terminal as the red wire from the feed cable, the black wire going to the next junction box is connected to the same terminal as the black wire from the feed cable and the earth wire going to the next junction box is connected to the same terminal as the earth wire from the feed cable.

The first two way switch can be quite difficult to wire up.

Two way light switch fig 4

The feed cable going to the first switch is connected as follows (fig 4). The red wire is connected to the (L1) terminal, the black wire is connected to the (L2) terminal and the earth wire is connected to the earth terminal.
The black wire from the feed cable, should be marked with red tape or red sleeving to show it is a live wire, but in practice is often left unmarked.

The cable going out to the second light switch is connected as follows (fig 4). The red wire is connected to the common (C) terminal, the yellow wire is connected to the (L1) terminal along with the red wire from the feed cable, the blue wire is connected to the (L2) terminal along with the black wire (marked with red tape or red sleeving) from the feed cable and the earth wire is connected to the earth terminal.

If you are using a plastic switch the earth wires will need to be connected to the terminal in the terminal box (as shown above) because there are no earth terminals on plastic switches.

The second two way light switch is a bit easier to wire up.

Two way light switch fig 5

The cable coming from the first light switch is connected as follows (fig 5). The red wire is connected to the common (C) terminal, the yellow wire is connected to the (L1) terminal, the blue wire is connected to the (L2) terminal and the earth wire is connected to the earth terminal.

A metal light switch must be earthed as seen below.

Metal light switch fig 6

Safety AdviceIf you are using metal light switches (fig 6) make sure you connect the earth wire to the earth terminal on the switch.

When using a ceiling rose on a circuit that utilises the in line switching method, again the wiring is quite easy, the difficult part is working at height and above your head.

Ceiling rose fig 4

The cable going to the ceiling rose is connected as follows (fig 4). The red wire is connected to the same terminal block that contains the brown wire going to the lampholder, the black wire is connected to the same terminal block that contains the blue wire going to the lampholder and the earth wire is connected to the earth terminal.

When using a ceiling rose on a circuit that utilises junction boxes, again the wiring is quite easy, the difficult part is working at height and above your head.

Ceiling rose fig 7

The cable going to the ceiling rose is connected as follows (fig 7). The red wire is connected to the same terminal block that contains the brown wire going to the lampholder, the black wire is connected to the same terminal block that contains the blue wire going to the lampholder and the earth wire is connected to the earth terminal.

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