Running 2.5 mm2 T&E on top of floor insulation

[Luka]

I have decided to insulate my ground floor suspended joist floor in the living room using 140mm of rockwool duo slab (R-value 4.1 m2.K/W).

2.5 mm2 T&E is currently running under the floor and I want to place it on top of the insulation (not to bury it in) and directly under the subfloor. Will current capacity be affected to the level I need to be concerned about? Should I place it in a conduit or maybe lay it on some kind of tray to keep it vetilated and prevent it from sinking into the insulation? Optionally, since I have access to it, would it be a good idea to replace it with 4mm2 T&E or would that be overkill? It is a ring circuit with 32A breaker).

 

[Luka]

I have decided to insulate my ground floor suspended joist floor in the living room using 140mm of rockwool duo slab (R-value 4.1 m2.K/W).

2.5 mm2 T&E is currently running under the floor and I want to place it on top of the insulation (not to bury it in) and directly under the subfloor. Will current capacity be affected to the level I need to be concerned about? Should I place it in a conduit or maybe lay it on some kind of tray to keep it vetilated and prevent it from sinking into the insulation? Optionally, since I have access to it, would it be a good idea to replace it with 4mm2 T&E or would that be overkill? It is a ring circuit with 32A breaker).

After consideration, the other option would be running the cable under the insulation, possibly in a conduit (unless a conduit is not required) directly on the galvanised mesh supporting the insulation, so it would not be covered by anything from the bottom. Would that be a better option as cable would be protected from mechanical damage by nail/screw to the floor? Again, will current capacity be affected to the point where some action is required? Thanks

 

[littlespark]

Unless you have plug in heaters all over the place, the effects aren’t too great. Not got my regs book at hand to check though.

Your standard load on an rfc would be fine on a 20A breaker really.

It might be different with a kitchen though, where a lot of high load appliances are used, but not at the same time of course.


If the cables can go under the insulation, then it’s still in free air… no de rating factor needed.

 

[Luka]

Unless you have plug in heaters all over the place, the effects aren’t too great. Not got my regs book at hand to check though.

Your standard load on an rfc would be fine on a 20A breaker really.

It might be different with a kitchen though, where a lot of high load appliances are used, but not at the same time of course.


If the cables can go under the insulation, then it’s still in free air… no de rating factor needed.

Thanks.
If I run the cable under the insulation and support it my the mesh there would be about 150mm of free air under the mesh.

The attached picture shows how it would look like (option 2)

Are you saying that if its considered as in free air and no derating is needed I can stay on 32A breaker or regardless I should change to 20A to be safe? I will be happy to do it if it makes the problem solved.

Should I run the cable in the plastic conduit to protect from rodents and direct contact with the galvanised mesh?

 

[Luka]

Just a quick correction to the picture in my previous post. Its 2x70mm rockwool, not 2x75mm