This is a loop in method which can be useful where the light fitting only has three terminals, or when using downlighters.
The 'in' cable supplies power from the previous light or consumer unit. The 'out' cable continues to the next light.
The 'light' cable goes to the light fitting. There will only be three wires at the light - live, neutral and earth. Useful with a fancy (or cheap-n-nasty) fitting which only has 3 terminals inside.
The in and out cables are connected together. Earth and Neutral from the light are permanently connected to the supply.
Only the live and switched live connect to the switch. Remember that the switch simply connects two terminals together - when connected, the light is on.
As with all of the other examples. the neutral wires do NOT connect to the switch at all. They connect together in a separate terminal block.
This method can be extended for use with two way and three way switching in the same manner as shown previously. The disadvantage is the large number of wires behind the switch. It may be necessary to use a deeper backbox, and if combined with two or three gang switches, even the deepest backbox may not be enough.
A further variation is to use a 3 core and earth cable to the light. This contains neutral, earth and switched live as shown here, and the extra core connects to the permanent live (COM on this switch). This is useful where a ceiling fan is fitted. The fan is controlled by a pull cord switch on the fan itself, this requires a permanent live. The switched live operates the light on the fan.
This can also be used with outside lights with movement sensors. The permanent live powers the movement sensor, and the switched live is used to activate the light manually.
With 3-core and earth cable, the correct colours to use are:
Brown : Permanent live
Black (with brown sleeve) : Switched live
Grey (with blue sleeve) : Neutral
Bare (with green/yellow sleeve) : Earth
Existing installations may use other colour codes - always make a note of what is connected where before making modifications.