Phil,
There is no such thing as a double insulated cable.
Cables are insulated and sheathed.
This is why it is so naughty to utilise the bare cpc in a flat twin & cpc cable as a live conductor.
Whilst the sheathing may be made from a very similar grade of pvc to the insulation, the standards do not require it to have any dielectric strength, and as such it is not required to be tested nor inspected for its insulating properties.
I agree BS7671 is not the be all and end all, in fact most of the electrical work I do does not come under the scope of BS7671 a all!
I have done something similar with SY.
It must just be realised by those installing that they are deviating from the regulations, they may remain within the spirit, but not the letter, so they must record a deviation and be prepared to justify that with a design FMEA.
Remember, that the signatory is signing a legal document and can be held accountable in a court of law for their design and workmanship.
If you have deviated, but not stated that, then you have technically potentially falsified a legal document.
Whilst BS7671 is not law, EAWR is, and there is contract law also.
It's all down to the weasel wording.
My bad, insulated and sheathed, lol, that's what comes of trying to type and hold a phone conversation, while trying to look at a book.I think it's one of my pet hates when people are afraid to think out of the box, along with the people who state if it doesn't comply with 7671 then it's "illegal" lol, if you are confident about what you are doing, know that it is safe, and suitable for the situation, then get on with it, I'd rather do something correctly, even if it wasn't in "the book" rather than try a bodge, that people think will comply, as you say, it's about being able to justify what you did and why you did it that way. Although I think the spark that wired a cabin that I saw on a recent site visit would have struggled.he'd connected an swa to a temp supply, no rcd, this was too short to reach the cabin, so it was joined to a length of sy, using a 32A 110v, trailing plug and socket, outdoors in the mud and wet! I wonder what his justification for that would have been?
Speaking of using a cpc as a live conductor, a mate of mine had bought a council house, he'd been thinking of buying it for ages, but hung off because it was about to have a major refurb. Eventually he bought it, new windows, bathroom, rewire, central heating etc, and he got it for a good price, a few months later and he gets a problem with the heating, I go round to look at it and it got rather interesting. It was only a motorised valve that had failed, however I discovered that during the install they'd used a 4 core flex instead of a 5 core, this meant they'd sleeved a green/yellow core with red sleeving, I wasn't happy, especially as inside the box were several G/Y'S and this had only about 10mm of red sleeving on it.
I really enjoyed ringing the council to tell them what I'd found, they were not happy! at the end of the day you either use the correct cable or don't do it, I've seen a number of 2 way switching set ups done using the earth, the other favourite one seems to be when they want a 2 gang switch instead of a 1 gang, dis the earth and use it as a live. I remember seeing one and it had to have been done by a spark, a 3 core red! I couldn't believe it, never seen one before, when I actually dismantled the wiring at the switch, it was a twin red, someone had put red sleeve on the earth, but they'd pushed it into the outer sheath! It looked at first glance like a proper cable, I wish we'd had camera phones years ago, we could have had a proper rogues gallery if we did.
