Routing cable through flat roof

[DomB]

Hi all,

I'm just trying to route some cable accross a kitchen which has a flat roof. I've had a look at the ceiling void and could pass a cable over the top of all the joists / rafters (there's quite a good gap between the top of the joist and the insulation) but would that contravene the regulations?

It's not really an option for me to drill holes through each of the rafters as I'd have to take down loads of the ceiling..

Any help much appreciated

 

[DurhamSparky]

sounds fine!!

 

[DomB]

Thanks - the reg's mention that unless the cable goes through the joists 50mm from top or bottom they must be "mechanically protected" - I'm guessing laying some plastic trunking over the top of teh joists and then pushing the cable through that would not be OK?

 

[DurhamSparky]

just throw them over...! sod the holes..! its a ceiling void not under floorboards or in a loft space where screws / nails may get driven through them from the boards or potential DIY loft boarding!!

 

[spud1]

As its a flat roof not much chance of anyone driving a nail through it from above so id agree with durham but i might think twice about doing the same on a angled roof where tiles/slates may get replaced in the future. Plastic capping or trunking would not constitute mechincal protection by the way. steel conduit or plates is more like it.

 

[DomB]

Cheers - this is a new circuit for my NAPIT assessment so I do have to do it to the letter.

My other option is to route the cable round the outside of the house and back into the kitchen - I guess I can just do that through plastic conduit?

 

[spud1]

Yes that is an option plastic conduit would be fine for this if that is your only option. Good luck with NAPIT !

 

[DurhamSparky]

seriously they wont fail you for throwing the cables over the joists! and i can probably safely say the examiner wont be interested in looking up into the void! he will listen to what you have done and examine your terminating at the CU and or Outlets! plastic conduit will just incurr extra cost and hassle as it open the examiner up to inspect you conduit building skills.

but its your job not mine!

all the best with napit!

 

[Spudnik]

The 50mm rule is IF the cables are being run through the joists.

You are going over so no need.

 

[DomB]

Thanks all,

It's a little confoosing. I could read the reg's (section 2.3.2 from The Electricans Guide to the Reg's) to say that"if a cable passes through joists it needs to be 50mm from top or bottom or in earther conduit". I guess I'm not passing it through joists, it's going over them, so I could argue the case it came to it (not that I want to argue with the assessor but y'know).

Going over the joists does meet the requirement that "When a cable is installed under a floor or above a ceiling it must be run in such a position that it is not liableto damage by contact with the floor or ceiling or their fixings" - no-one's going to drill from the top through the flat roof!

~sigh~, damnedRegs - I wouldn't mind if they weren't so amiguous. It's a massive route around the kitchen, going outside etc, if I don't do the ceiling ting