loft rewire and insulation.

[5544]

well yet another loft rewire coming up. Always find it tricky in some areas to avoid the insulation with the wiring. I would be interested to see what practical means people have to avoid the dreded insulaton affecting the cable, and keeping the cable out of the way.

 

[telectrix]

if cost is not an issue, i would rip out the insulation and replace with kingspan directly under the roof. what's the point of having a loft on which you pay rates, then stuffing it full of that crap, thus rendering it useless for anything.

 

[Engineer54]

well yet another loft rewire coming up. Always find it tricky in some areas to avoid the insulation with the wiring. I would be interested to see what practical means people have to avoid the dreded insulaton affecting the cable, and keeping the cable out of the way.

Only the old poly beads affected the PVC sheaths and insulation of cables, the newer stuff is of a different chemical composition these days that shouldn't have any affect on the plasticizing of cable sheaths etc!!

 

[netblindpaul]

E54, the problem is these days the de-rating of the cables in the brb/bgb when surrounded by insulation you could end up with having to put 2x10mm sq in for a 32A ring final cct!

 

[Engineer54]

E54, the problem is these days the de-rating of the cables in the brb/bgb when surrounded by insulation you could end up with having to put 2x10mm sq in for a 32A ring final cct!

That's a completly different matter, i was only commenting on the physical side of things regarding poly bead insulation.
As for the de-rating of cables in insulation, i always do my own assessment on cable de-rating when and where necessary. Rarely use the the BRB factors, they tend to be way over, on the safe side of things, based...on the full current rating of cables. But handy as a quick reference...

 

[5544]

well should have been a little clearer. was refering to the de rating effects of the insulation on the cable. it is a three bed semi so intend doing the lighting in 1mm, but they have 200mm insulation everywhere, and two be honest i would rather not de rate the cable by half before i start. I have in the past tried small raised wood gangways, but they end up walking on them. i have tried clipping to roof joists, but still have the loose light and switch cable going to the ceiling. also uprated the lights to 1.5mm. other options would be interesting. regards

 

[telectrix]

if you use 1.0mm, that's derated to approx. 10A covered in insulation>100mm. (table 4D5, BRB). your MCB is generally 6A, so no problem.

 

[malcolmsanford]

I'm of the same opinion of our learned friends Tel and E54 for the smaller cables such as 1.00mm 1.5mm and 2.5mm even derated @ 50% there is no way it will affect a normal domestic installation. How long are lights on upstairs I would imagine a single hall light for a young child might be left on for any period of time overnight, but if at the max of 100watt it would never get near the current carrying capacity of the cable in any circumstances. T

That is also concerning the 2.5/4mm cable used for socket circuits.

Even the heavy duty showers IMO would not be affected as if they are used for an hour during a 24 hr period I would be surprised.

Unfortunately today we have a generation of electricians that are brought up without the benefit of designing circuits for themselves, instead we have a multitude of "guides" that advise us it must be done this way or that way, and i'm afraid the NICEIC are the main culprits for this.

I don't blame these younger lads, they have not had the chance in a lot of cases to develop skills as I was given, and of course in this someone must be to blame society it is easier, simpler and perhaps safer to just do it as the guide insist.

 

[Knobhead]

But Malcolm, Tel and E54, your methods aren’t written in tablets of stone unlike the rambling of the IEE.

View attachment 8254

 

[telectrix]

on a similar, but divergent note, anyone know the respective thermal values of kingspan compared to fibreglass?