One Way Switch

One way lighting circuit using in-line switching 

Line diagram of a one way lighting circuit using in line method (fig 1).

Fig 1

A one way light switch is quite easy to wire up.

fig 2

The cable going to the light switch is connected as follows (fig 2). The red wire from the feed cable is connected to the top terminal, the red wire going to the light is connected to the bottom terminal, the black wires from both cables are connected together in a plastic terminal block and the earth wires are 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.

A two way light switch can also be used in in place of a one way light switch, in this instance the red wire from the feed cable is connected to the common (C) terminal and the red wire going to the light is connected to the (L1) terminal. The (L2) terminal is unused.

A metal light switch must be earthed as seen below. 

fig 3

If you are using metal light switches (fig 3) make sure you connect the earth wire to the earth terminal on the switch and fit an earth link wire from the switch to the earth terminal in the back box.

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. 

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.

 

 sources:http://www.diyhowto.co.uk/projects/one-way-light-switch