How to Wire a Basic Light Circuit in a Domestic Dwelling

Light circuits are wired in a radial circuit configuration, unlike socket-outlets that can be wired in either radial or ring configuration. A radial circuit does not loop back to the MCB in the Consumer Unit or distribution board. The best cable to use in a domestic dwelling for a standard light circuit is 1.5mm square twin and earth PVC cable, typically from a 5A, 10A or 16A MCB depending on the load and amount of lights on the circuit. 16A MCB's lighting is more used in commercial dwellings where larger and more light fittings are used. This article will focus on a standard light circuit using 1.5mm PVC "twin and earth". Its not uncommon to use 1.0mm (square) cable for shorter circuits with smaller loads to save money on cable. By calculating the maximum circuit length and load you will be able to decide on what cable size the best is to use. Using 1.0mm (square) cable might be a bit cheaper but considering future alterations its always better to use a 1.5mm for later extensions and adding of heavier loads. A 1.5mm square cable would typically be fed from a 5A, 6A or 10A MCB and have a maximum cable length of 108, 90 and 52 meters respectively. 108 meters sound very long but once the cable is routed through your house's canvis will turn out not to be that long.

Once the radial circuit is fed through your house via each room to each light point, feed a cable (Twin and Earth) from each light point to the switch in that room.

From your radial circuit at the lighting point, you have to connect the Live (which is the cable fed to your switch) with the radial Lives on the same connector block. Connect the other end of your Live cable at the switch to the terminal in the switch marked with L1. The other two cables in your twin and earth are blue and a bare copper cable. Make sure to put Yellow / Green folding over the bare copper cable at the switch end and light fitting and do connect it to the earth terminals provided in the fittings. Remember to connect the metal cavity box to earth in the light switch. The blue cable is used as the return live connected in the switch to the terminal marked as C (common). You have to mark the blue cable (normally used as neutral) with a brown sleeving to indicate that its now a Live and do the same at the other end of the cable in the pendant connector block. The brown sleeved blue cable is now connected to the same terminal block as the cable to the lamp holder cable. Repeat this whole proses at each light point. Remember before turning your circuit on that it will need to be tested for polarity, insulation, continuity, earth continuity and finally once livened up a loop impedance test must be carried out.