The other thing I have seen muppets do is drill the joists in the wrong places, when you do an apprenticeship with a properly trained mentor you will learn about simple things like how and where to drill Joists, how far from the corners of partition walls cables can run etc, how to chase walls straight, how to clip cables through lofts, the standard of works these days is pretty poor, cables slung over ceilings. holes drilled anywhere, cables in the same slots as central heating pipes, theres a lot more to designing and installing a Domestic Installation than a ring main, for instance how many do you put in? thats one decision, I have seen one only on a new build and thats the truth, I also Remember one so called spark who was green and had no experience actually wire the whole house on one ring and he did it in 1.5mm2 6243Y by mistake, when I asked why he installed one ring he said "whats the problem" he assumed there was no load and it wouldn't be an issue, when I explained we just don't do that due to our sparks standards and I wanted him to install a ring in the kitchen and up as well as down he thought I was mad, he was a DIYer who bluffed his way into a job and the gaffer who we worked for at that time fell for it, as the foreman on the site at the time it didn't take long to sus him out, a nice guy but a DIYer.I also had a guy who flattened some metal capping with an hammer an then tape it to cables in the wall, he said he had never used capping before and didn't realise the lip was there to go around the cables, he thought the capping had to be flattened, I also had one guy install a burglar alarm and there was 2 key pads on it, one at the front door and one in the master bedroom so the owner could alarm the downstairs from his bedroom at night, he phoned me one day saying Mike can you come to site I'm stressed, well I said okay calm down I'm on my way, so after making sure the other guys on the Job I was on were busy and happy I left site to see him. Once there I asked him what the problem was, he said the alarm wouldn't set and the key pad kept saying tamper fault, he said he checked everything and couldn't work it out and was going home as he had had a guts full. I went around the system and saw the key pad in the en-suite was not on properly, pushed it on and the fault went, he went mad and started throwing his kit around in anger as I was there 10 seconds and found the fault, he said after he had calmed down that he had forgotten he wired the second Key pad, astonishing, I am running out of thread now but you wouldn't believe what he did in the boiler room, the house was a biggy, the system for the heating was not the usual, haha, it turned out he was a telecommunications engineer who bluffed his way into the job, just like the other one I mentioned, More to domestic work than a ring main.