Domestic lighting circuits are also radial circuits, but there are two types currently in use: the 'loop-in' system and the 'junction box' system. In many instances, lighting systems in the home are in fact a combination of the two. The loop-in system has a single cable that runs from ceiling rose to ceiling rose and ends at the last rose on the circuit. From the ceiling roses, single cables also run to the various light switches.
In the older junction box system, each light has its own junction box situated on the single supply cable. A cable runs from each junction box to the ceiling rose while another runs from the box to the light switch. One single circuit of 1mm sq. cable can serve the equivalent of twelve 100-watt light fittings - you can check the load by adding together all of the light bulbs on the circuit.
If you find that your load exceeds 1200 watts, then your circuit should be split to have two or more lighting circuits running from the consumer unit. If you have a very large house, needing long runs of cable, it is better to use 1.5mm sq. two-core-and-earth cable instead of 1mm sq. Lighting circuits also need to be protected by 5 amp fuses or 6 amp MCBs.
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