wiring inside fibreglass insulated walls/ceilings

[Quadroclops]

I see I shouldn't route my wiring (especially the 10mm for the shower) inside insulation -I was planning to clip it inside a cavity wall with fibreglass insulation) -I've just had the loft insulated & they've put a carpet of thick fibreglass all over the wiring. Now this is common practice I know -does anyone want to comment?

[Guest]

Hi,

Your right, cabling shouldnt be routed within insulation unless the cable/circuit has been designed using "correction factors". These factors take into account the fact that a cable of size x cannot carry as much current without overheating in insulation as apposed to being in free air. Obviously cooker/shower/socket cables are more at risk in general than lighting circuits.

The best idea for the diy'er is to avoid running cables in insulation. As for the people who have insulated your loft, they obviously do not appreciate these facts.

[Quadroclops]

What a smart uh...boy am I! Better than setting fire to my house tho' -not to mention my hard work... does anone know how to calculate the correction factors -or it about right to just double the cable size? This is just for the lighting wire in a flat-roofed bathroom -it's freezing in there, so I'm keen to insulate.

[Edited by Quadroclops on 18-12-2002 at 4:12 AM GMT]

[Edited by Quadroclops on 18-12-2002 at 8:12 AM GMT]

[Guest]

I know it's a boring answer but if you really want to know try 'The electriciens guide to the IEE wiring regs' ISBN 0-9517362-9-9 by John Whitfield.

Doubling the cable size is probably overkill - 20mm cable for a shower? That's bigger than the main incomer in many older houses.