Yes as long as he has fused down. Using a switched fuse connection unit (FCU) as the light switch is a common method.
The rules state that it must be protected with a MCB/RCBO/Fuse to no greater that 16A so direct into the ring without a fuse is non complainant as a ring is 32A.
Also switches and ceiling roses are often rated at 5/6 amp so normally lighting is supplied with a 6A or less protective device.
314.1 Every installation shall be divided into circuits, as necessary, to: (iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit.
This is why we have two RCD's at least in a house what is clearly unwanted is for you to get a shock and then compound the problem by plunging you into darkness.
However for years with extensions and conservatories it has been a common practice to only take on supply and use a switched FCU as the light switch. We should do a risk assessment and where should the power circuit trip you would get enough light from rest of house or outside to avoid danger then often only a single supply is used.
However with extensions you also need to re-assess the rest of the house. The room it extends from could now be a danger with power failure.
The chance of a lighting MCB tripping at same time as a power MCB is rare and clearly a area power cut can cause both to trip at the same time anyway what ever you do.
However the chance of a RCD feeding both lights and power tripping are much higher and so the risk is also higher of loss of power resulting in danger.
Today the major problem for electricians is after every job they need to issue either an installation certificate for new circuits or a minor works certificate for alterations to existing circuits. So their name is against the work done.
The Emma Shaw case found the foreman guilty some 7 years after the installation and not for the work done but because the guy who tested it was not qualified to do the testing.
Part P requires for every job there must be paper work. The notifying of the local council is only required for some jobs but the raising of installation or minor works certificates is required for all.
So you may have two certificates an installation certificate and a compliance or completion or just one but always there will be paper work with some test results.
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