The aim is to ensure lights have no more than 3% volt drop, and sockets 5% volt drop, the rules are rather vague however, but normally we assume 20 amp drawn centre of ring and 12 amp even spread so we work on 26 amp to work out volt drop on a ring final, which gives us 106 meters maximum of cable. The problem with a radial circuit is still taking 20 amp at furthest point means you need three radials to replace one ring final, which is why we still use ring finals, as they work out a lot cheaper, specially when using RCBO protection.
We should plan an install, not simply do it that way as we always do it that way, and we can have three signatures on the installation certificate one for planning, one for installing, and one for inspection and testing, however this is rare with domestic installs, in the main one signature for all.
I have never been a scheme member, so I don't know if they can use the multi-signature installation certificate? In England the Part P allows use of third party inspectors instead of using the LABC, in Wales not permitted. So to use a three signature form in Wales it would have to be done using the LABC inspectors.
The LABC inspector is responsible for site safety, so he is free to say who can do what and when, this includes who can sign the installation certificate, before the Part P was watered down in England my son did work in Liverpool, Cheshire, and Flintshire, and each county inspectors were different, Liverpool was easiest with Flintshire being a real problem, so to say what you can do is pointless as it depends on what your LABC inspector is like.
Flintshire wanted to see the test equipment and calibration certificate and our qualifications, in essence he did not want us to DIY electrics. How much down to county policy and how much down to inspector I don't know.
As to trying to read any law, often there are grey areas, which are plugged with case law, so reading the Part P English law you could get a consumer unit installed with 16 RCBO's in it and 16 sockets below it, then extend and modify each one of those circuits as you want, that may be to letter of the law, but not the spirit of the law. If your going to do tricks like that to get around the Part P law, it will not protect you from other laws like electricity at work act, every home at some point has some one doing work there, even if just the milk man or postman walking to the door.
Mothers house had two consumer units, a 45 amp MCB in main one fed the kitchen one, with SWA around outside of the house, it was done before the re-wire as kitchen needed to be altered and the rubber cable used in rest of house meant that it could not be RCD protected, but the rules required RCD protection for new sockets, so it was a method of getting around the rules. Latter when rewired the kitchen consumer unit was retained.
But we are not signing the installation certificate as the person who designed the system, and this is the stumbling block, we can debate until the cows come home, but only person who can say yes or no is the LABC inspector, and if you need to ask on a forum, then likely he will not permit you to do the wiring. Or if he does, he can make it very expensive.
It seems the LABC can use third party inspectors, which you need to pay for, so in Wales first £2000 worth of work costs £100 plus vat, but on top of that a third part inspector can charge £40 per visit, there is no fixed fee, so 10 visits, and that's £500 which starts to get to point where cheaper not to DIY.
I misplaced the paperwork for mothers house, so applied for replacements, I was told it would take 4 months, and would cost what ever time the council worker spent finding it. Open cheque it seems. Lucky I then found the originals, but so much for traceable records, maybe the coroner can get the records, should some one die due to what you have done, but one would have thought the lawyers when buying or selling a house would get copies from the LABC so you can't fiddle them, but it seems that is not the case.
The completion certificate was very vague, there was really nothing to link it to the installation certificate, which I had completed, so I could have produced another installation certificate with same date which included much more work to the original, so it is like asking to see the text message from NHS saying you have passed the Colvid 19 rapid antigen test, you told the NHS you passed, it is done on trust, so no point in showing text message your word should be enough.
So legal you must have a completion or compliance certificate, but no legal requirement for the installation certificate, regulations are not a legal requirement, so once you have a completion or compliance certificate it would be hard to show what was really covered, mothers house had three completion or compliance certificates some of the work was covered by two certificates, this house I was given the certificate on buying the house, and only found out latter it only covered a small part of the house.
So in real terms with owner occupied house it would need some one to be seriously injured or killed before anyone looks at paperwork, rented houses very different, and where social services visit the house, maybe they would check, however when the Flintshire social services did work in mothers house, in spite of trying to get copies, we never got any paperwork for the work done, in Wales that was a new circuit to power door bell that included a 13 amp socket which was not RCD protected and fitted after the time when RCD protection was required. Since then whole house was rewired, but if the council don't follow the rules, seems unlikely they are going to take anyone to court for doing the same as they do.
