Running cables in loft - can I do this?

[The Jeep]

Hi guys & gals

Does anyone know if it's OK (i.e. Part P & BS 7671 compliant) to run circuits across joists in a loft (i.e. on the surface, not down the side of the beams). The loft is heavily insulated and I would prefer to run the cables over the top, using narrow planks across the joists to clip the cables to. The planks would be securely nailed to the beams.

The only possible conflict I see is to do with mechanical protection. The loft is not floored, by the way. Any ideas?

 

[Job_n_knock]

Wouldnt it be easier to drill holes ?

 

[Pensdown]

Hi guys & gals

Does anyone know if it's OK (i.e. Part P & BS 7671 compliant) to run circuits across joists in a loft (i.e. on the surface, not down the side of the beams). The loft is heavily insulated and I would prefer to run the cables over the top, using narrow planks across the joists to clip the cables to. The planks would be securely nailed to the beams.

The only possible conflict I see is to do with mechanical protection. The loft is not floored, by the way. Any ideas?

That is a perfect solution to ensure the cables are kept away from the insulation.

 

[The Jeep]

So no problem with any of the regs? All agreed?

By the way, drilling holes through the joists would still mean running the cables at least partly in contact with the loft insulation (don't you HATE that stuff?!!), which then derates the cable a bit (Method 4 as opposed to Method 1).

 

[Pensdown]

Unless someones going to dream up another regulation, take my word for it, your solution is perfect.

Which regulation in particular are you worried about?

 

[The Jeep]

Can't remember, but last year when I was rewiring some lights in a loft, I had some cables clipped to the top of a joist and then changed them to run along the vertical side - I must've come across something somewhere saying that running them on top was not good, but I can't remember where I read it.

Anyway, unless I hear otherwise I'm going to proceed as planned. Thanks for the advice!

 

[Pensdown]

Running the cable along the side is better but then you have the problem with the insulation. If your worried about people walking on the cables use a wider plank and nail a piece of 2x1 timber down the middle. With the cables clipped down each side they would be out of harms way if someone walked on the plank as their foot would be on the 2x1 and not the cables

 

[Adam_151]

Method of cable installation across the joists in our loft : http://www.electro-zone.co.uk/other/diynot/home/mainsloft.jpg

I'm gradually sorting stuff out, recently found a lighting circuit that was bundled with those for about 3 metres past where it needed to go, doubled back on itself ("bend radius", "whats that then?") came back those 3 metres and draped across to a JB, which fed a JB down further down the loft, which fed the rest of the loop in system, and also a branched leg back to a JB next to the first (thus cabling rested in the gap where the struts from the pre-formed roof trusses met at the loft floor)

A lot of stuff here is like that, probably not that many violations, but very messy!

Its like it was installed by a bloody spider... , or someone ordered a delivery of T&E and asked the driver to spread it around the loft in a random kinda fashion

 

[JohnD]

the electrician had a bad back, and didn't like to bend down.

 

[Lectrician]

Drilling timbers in a loft is BAD idea.

Generally, the timbers are VERY SMALL, and engineered precisely. Drilling them is NOT GOOD.

 

[the_jinj]

Drilling timbers in a loft is BAD idea.

Generally, the timbers are VERY SMALL, and engineered precisely. Drilling them is NOT GOOD.

Agreed drilling holes randomly can be bad for joist strength....
OSG recommends (non armoured) min 50mm from top or bottom of joist and max diameter of 0.25 x joist depth. They should be on centre line between 0.25 and 0.4 x span of joist. Holes in same joist should be 3 diameters apart.

 

[Pensdown]

Its like it was installed by a b****y spider... , or someone ordered a delivery of T&E and asked the driver to spread it around the loft in a random kinda fashion

You must live in a bungalow like me. If you ventured into my loft you would find every cable clipped at 300mm, 300mm segregation between power data, voice and TV, lighting to 350lux and bonding of all services.

And if you believe that you'll believe anything