Electric cable and insulation

[Harrier23]

How would people overcome the issue in the attached photo?

For 3 out of the 4 garage walls I will be able to use a void behind the insulation boards to run cables and have them come through the back of my back boxes which will be fixed to noggins.

The front wall however does not have enough space to run cables from behind the back boxes.

How am I best to go around having the cables avoid contact with the insulation where they enter and exit the back box?

I could have the insulation sit flush against the wood cladding, however this would mean that the cables ran in front of the insulation, which I'm keen to avoid.

Alternatively I could cut out a small gap in the insulation board to allow the cable to run through and then up the cladding behind the insulation, however I think this would run the risk of cold bridging?

Any other ideas?

 

[EFLImpudence]

If you have the cable to the font of the insulation touching the (is it?) plasterboard, this would be alright for a 32A / 2.5mm² T&E cable ring circuit.

 

[Harrier23]

Yeah it will be plasterboard on top and a radial circuit for both lights and sockets

 

[mattylad]

I would be a little concerned about the lack of any form of barrier between the back boxs and the outer of the shed, they tend to leak in places. when pi$$ed wet through.

 

[JohnD]

I would be a little concerned about the lack of any form of barrier between the back boxes and the outer of the shed, they tend to leak in places. when pi$$ed wet through.

Yes, the cladding looks like shiplap or perhaps featheredge. Gaps open up with weather changes and driving rain will penetrate, as will damp.

IMO a weather-resistant liner such as roofer's breathing membrane or even felt is necessary to protect against water, dirt, draughts and insect penetration. Insulation can be added on the dry side.

If you are lining a shed, ply or OSB will resist damp. Plasterboard won't. I'd also prefer metalclad surface boxes rather than sunk backboxes in a shed.

Also, in your pic, you have placed the socket backboxes with entry grommets in the top. This will lead any water on the cables to run into the sockets.

 

[Harry Bloomfield]

I would be a little concerned about the lack of any form of barrier between the back boxs and the outer of the shed, they tend to leak in places. when pi$$ed wet through.

Unless there is a good reason to sink cables and outlets, in a garage or shed I would run everything on the surface. If the drops need protection, a short length of Egatube works well. I think I remember there being a reg about all such sockets and switches in a garage had to be above a certain height from the floor. Personally, I like them to be at shoulder height in a garage, for easy use.

 

[Harrier23]

Yeah think I'll run some sort of water/damp proof membrane against the wood to be safe - thanks for the advice.

No real reason for sunken sockets, other than the garage is going to be more of a comfortable space so would prefer not to have surface mounted.

I think I will run the wiring behind the insulation board (50mm Kingspan) so that they are in the 20mm gap between the insulation and waterproof membrane.

I'll likely run the cable through a short length of 20mm conduit to safely pass the insulation and foam around the cut in the plasterboard to avoid any cold bridging

 

[mattylad]

I'm far from an expert on the subject but IMO it may be better to run the cable on the socket side of the insulation so there can be no moisture pulled through with it.