Couple of questions regarding loft insulation and wiring

[internet]

I am planning on putting some floor boards in the loft and so have been looking around in the loft.

I've noticed there is lighting circuit wiring , two extractor fans , electric shower cabling and red fire alarm cable.

I have noticed that not all the wiring is above the insulation and recall readig somewhere that at least certain cabling needs to be above to avoid problems associated with heating of the wire.

Can anyone tell me what wire should be above , perhaps it is all of it.

In order to do this job i intend to affix batten on top of the joist , cutting the batten where wires run over the joists (rather than cut the joists). I figure that by using the batten this will add some sort of ventilation space which may help.

The red fire alarm wire is installed such that at the moment where it connects to the alarm sensor it stands quite upright and at the moment is basically higher than the height of the joists/battens will be so. So it seems I'll need to bend the wires. I am intending to do this with two sets of plieers. One to hold the wire and isolate the bending operation to only the part of the wire requiring bending and not placing any stress etc on the alarm sensor connections etc. I intend to draw diagrams of the wiring , laminate it and leave in a prominent place and mark on the boards themselves.


Can anyone offer any advice or comments on my plans? Many thanks.

 

[telectrix]

the cable that would suffer most from being in insulation is the shower cable. these are usually run close to the limit, so any derating due to insulation could cause overheating. don't use pliers on the FP200 cable. bend by hand only, and not too sharp a bend.

 

[internet]

ok thanks. What current does the shower cable carry safely? Assuming it is the correct cable? I thought it looked similar to cooker cable and I thought that can carry 30amp. Showers must use a great deal of power then I guess.

 

[telectrix]

probably be 6mm cable. 47A max. if no insulation. down to 25A if smothered.

 

[Octopus]

This should be in the DIY forum.

 

[internet]

Well i did think that after posting but it had to be authorised by an admin.

 

[internet]

probably be 6mm cable. 47A max. if no insulation. down to 25A if smothered.

oh I see. I just looked up wattage of the shower and probably 9.5k which seems to be 40a. thanks

If it went to 25a presumably it would get hot and the shower would not work at full capacity? How hot would the cables get?

 

[telectrix]

too bloody hot. on a 9.5KW shower, 6mm is on it's limit with no insulation around it.

 

[Eddiesparks]

It could be 10mm? The way to tell if not experienced is if the earth is stranded it's prob 10mm and if it's 6mm the earth will be single core.

 

[Eddiesparks]

Ps dont cut into the cable to find this out obviously (not being patronising but i dont know your knowledge level!)Look at the fuseboard or the shower itself. Isolate and prove dead as soon as cover is off. What amp rating breaker is shower on? Prob 40.

 

[Eddiesparks]

oh I see. I just looked up wattage of the shower and probably 9.5k which seems to be 40a. thanks

If it went to 25a presumably it would get hot and the shower would not work at full capacity? How hot would the cables get?

Ps i reckon the thing that you need to worry about with overload is more the buried cable burning rather than the shower itself

 

[Darkwood]

This kind of work goes slightly beyond DIY .... There are too many unknowns here that could lead us to giving incorrect info.

Cable routing.
Cable sizing
Joists should not be notched but drilled which means stripping all wiring back and feeding it through, although insulation could be a factor to whether this is an option especially with the shower cable.

The effects of insulation and over-boarding cannot be done lightly you have to weigh up a lot more than just wires in the way, recess lights for example you need to maintain the appropriate spacing as required by manufactures guides from joists the new floor and insulation.

Existing joint boxes will become inaccessible and need changing to maintenance free and no doubt new Electrics for the loft space...

I would not advice directly or take advice off a forum on how to do it without knowing the layout and circuits effected and any other limitation that you may not realise need to be addressed.

I recommend you get the existing assessed by a local competent electrician if not just to lay down guidelines... if this is all about saving a few pence then Ill say what I always say 'What's the safety of your property and family really worth'?

 

[Eddiesparks]

Yeah what he said too!

 

[internet]

Ps dont cut into the cable to find this out obviously (not being patronising but i dont know your knowledge level!)Look at the fuseboard or the shower itself. Isolate and prove dead as soon as cover is off. What amp rating breaker is shower on? Prob 40.

It's actually on 32amp. I couldn't find the exact model of shower so perhaps this one is less wattage. i guess i could measure the diameter of the individual cables with micrometer . Does 6mm refer to the area of the live and neutral or earth too. I never have the shower above 5-6 out of 9 maybe it is lucky I didn't. If the wire will drop to 25amp if under insulation I presume that means the circuit breaker will not intervene. Is that the case and why this is dangerous? I'm going to look later anyway and pull make it above the insulation if it is not already.

 

[internet]

This kind of work goes slightly beyond DIY .... There are too many unknowns here that could lead us to giving incorrect info.

Cable routing.
Cable sizing
Joists should not be notched but drilled which means stripping all wiring back and feeding it through, although insulation could be a factor to whether this is an option especially with the shower cable.

The effects of insulation and over-boarding cannot be done lightly you have to weigh up a lot more than just wires in the way, recess lights for example you need to maintain the appropriate spacing as required by manufactures guides from joists the new floor and insulation.

Existing joint boxes will become inaccessible and need changing to maintenance free and no doubt new Electrics for the loft space...

I would not advice directly or take advice off a forum on how to do it without knowing the layout and circuits effected and any other limitation that you may not realise need to be addressed.

I recommend you get the existing assessed by a local competent electrician if not just to lay down guidelines... if this is all about saving a few pence then Ill say what I always say 'What's the safety of your property and family really worth'?

Thanks for the detailed response. Would you say that done correctly the wiring should be mostly above the boards then?