Does BS 7671 address running wiring through insulation?

[Tony K]

I may need to run some wiring through the insulation. I'm not sure if modern wiring heats up at all, but my instinct is that whilst a modern fuse board should prevent disaster, I don't want it tripping every ten minutes either.

I have established that the Building Regs do not address this issue directly (other than to require all electrical work to be done to BS standard etc), but I am struggling to access the BS regs. 

 

Does anyone know if the regs are available, or if there is a best practise model for this scenario? I am thinking perhaps of a plastic pipe to act as a conduit.

 

Thanks!

[Mr Punter]

You may need to derate the cables.  I have ended up using 4mm for sockets where we had to run through insulation.  Get the sparky to work it out or I think you can look up online.

[Rob99]

Yes, if you run cable through insulation you will need to calculate the derating so that you end up using the correct size cable. BS7671 provides all the info and methodology so your electrician should be able to work it out for you very easily. If you're going to use conduit then that's a different scenario which will give you a different result.

 

Legal copies of the BS are not available online (unless you have a BSi subscription) as British Standards are expensive to purchase and there are copyright issues uploading any extracts.

 

Is this just a one off cable or will there be many of them? If it's a one off, post the details here and I will take a look through my copy of the BS.

[Tony K]

8 minutes ago, Rob99 said:

Yes, if you run cable through insulation you will need to calculate the derating so that you end up using the correct size cable. BS7671 provides all the info and methodology so your electrician should be able to work it out for you very easily. If you're going to use conduit then that's a different scenario which will give you a different result.

 

Legal copies of the BS are not available online (unless you have a BSi subscription) as British Standards are expensive to purchase and there are copyright issues uploading any extracts.

 

Is this just a one off cable or will there be many of them? If it's a one off, post the details here and I will take a look through my copy of the BS.

 

It will be quite a few cables, so I need to devise a method I can rely on generally rather than in an isolated case.

 

When you say conduit will give a different result, am I right to think that it will help?

Edited March 23, 2023 by Tony K

[Mattg4321]

You need to derate the cable based on the installation reference method

[Rob99]

Yes, conduit (providing it is large enough) will be better than just running the cable through insulation as there will be a degree of air space around the cables

[SteamyTea]

There are often copies of the OnSite guided. They give you the derating factor.

[Tony K]

Thanks all. I have found this (old and outdated now, but useful perhaps) online:

 

file:///home/chronos/u-2b6e8d7d7f1652a64d3eab5d1ce64d2d9cb8a42b/MyFiles/Downloads/BS-7671.pdf

 

To claim to understand it would be dishonest of me, but you have all kindly confirmed that it can be done subject to the appropriate calculations, and that a conduit is a viable tool in the circumstances.

I have a good sparky lined up and will trust in him now that I know the principal is sound.

 

Again, thanks for your assistance.  

[Onoff]

You'll get the gist of it having a read here, though based on the 16th, it is in fact superceded by the 18th! The basics generally remain the same.

 

https://www.tlc-direct.co.uk/Book/4.3.6.htm

 

16 hours ago, Tony K said:

It will be quite a few cables

 

Don't forget the option of singles in trunking.