Two situations I have found in my son’s recently purchased house:

Ring-main cables running side-by-side on top of concrete floor (suspended rather than in contact with ground – house was convertion from a former industrial building). On each side of the cables there is 25mm solid microfoam insulation with silvery foil coating – looks similar to material used in cavity walls. On top of that 35mm rockwool and on top of that floorboards. So the cables are in an insulated ‘tunnel’. Is this ok?

Lighting cables in loft. There is no thermal insulation at present. Packing on rockwool insulation just bought says “electric cables not to be covered, must be lifted carefully so that they run on top of insulation”. Most of the cables are clipped to the sides of the joists between 30 – 50mm down from top of joists and in many places pass through drilled holes in the joists and cross-bracing timbers. The rockwool will come to the top of the 170mm joists. To comply with instruction would be a major rewire of 18 50w halogen lamps. The circuit with the most lamps is serving 8 lamps. The cable is 1mm rather than 1.5 which I think is now commonly used. Some people, who may not be up to date on these matters, have told me lighting cables can be covered with any amount of insulation provided they are in contact with ceiling, joists, or masonry - ie I can ignore the insulation manufacturer’s instruction for lighting but NOT power cables.

I’d welcome your views on these two situations please.

Many thanks for info - at least its easy to make safe the ring main quite simply as you suggest.

Thinking about the lighting - I am not quite sure if you are saying I can carry on with laying insulation in the loft against the 1mm cables clipped to the sides of the joists. The lighting circuit with the most lamps (8 x 50w) is controlled by a single switch and fed from its own 6a mcb. It is unlikely the lamps would be uprated to a higher wattage and downrating would not provide enough light.

Incidentally the insulation will be kept away from the lights (which get quite hot) with galvanised loft insulation support boxes from Click Lighting. I have no intention of covering the boxes with insulation, just cutting insulation to fit round them.

Yes, I can get on with the job with confidence now - your help much appreciated.