Dead wire, leave in wall? Ask questions and find answers to many subjects relating to electrics and electrical work

[CompetentDIYer]

Hi all, I'm new to these forums, bear with, sorry for the long post. I'm not an electrician, but have good engineering knowledge and understanding of what I'm doing. Nonetheless, nothing like some advice from who knows their stuff. I'm also not British, but have grown adept of the rules around electrical installations in this country, it's all quite clear when it's done by the book, but unfortunately, it means the cowboy solutions baffle me to how crap they are.

So, to keep it simple, moved in to new house, redoing the kitchen. Previous owner moved boiler from the kitchen to upstairs. Whoever did the job was quite "creative", leaving pipes sticking out of the ceiling (sorted), a live gas pipe capped off sticking out of the wall (what?! sorted now) and the electrics were complicated, so they just shaved the wire leading to the boiler at the wall and plaster over it (not joking).

Now, current situation. Above the counter and below the former boiler location, I have 3 boxes (from right to left): a fused switch to the dishwasher and washing machine socket (standard, all good), right next to this we had another fused switch operating the boiler and then further out to the left a mysterious cover plate.

Undoing the boiler ones, it became clear that the fused switch to the boiler has 2 cables coming from the ceiling (I'm guessing each making the left and right of the associated ring?) and the switch then powers another smaller gauge cable which goes up towards the ceiling (possibly). The box to the left (cover plate only) has the return of the powered smaller gauge cable and from this box is where there was a creative white sheath cable that snaked up the wall, out of it through the plaster ~50cm up and presumably into the old boiler.

In this cover plate box, there's also another low gauge cable coming in (I can't seem to understand where it leads to) and a 3+earth cable (I suspect this was originally installed as a 2-way switch to the lighting in the kitchen). The "configuration" I found this setup coming into this home was: switch off and behind the cover plate, all cables simply taped together (yes, seriously)

I've checked for continuity and also for voltage relative to nominal pairs as well as voltage to a powered mains neutral and live, and nothing's hot. I've also checked all sockets and light fixtures in the wall behind (conservatory) as well as bedrooms above, and nothing seems to be affected by having any of these cable ends floating or together. With this in hand, I am pretty sure these cables are neither live nor connected to anything else.

Question, as I want to avoid an irrelevant cover plate, can I simply heatshrink each of the conductor ends, leave it all as is, and tile over the leftmost box, leaving the pattress and those mystery cables in place?

Also, can I replace the old boiler switch to a socket block ( a bit more functional than just a cover plate, this will always have to be present given the live wire behind it), given it's ~150mm from the edge of the sink drainer side, or is the 300mm supposed to be a guide? The actual sink and tap are a good half meter to the right (1m wide sink, drainer on the left).

[ericmark]

I had a potential extremely dangerous situation with what I was told were redundant cables, which were only live when a remote plant was running.

So I am now very wary with seeming dead cables, thermostats and timers can mean cables which seem dead are not, so unless one can ring out the cable and find out where it goes, safest method is to cover with a blanking plate so you can return latter if you find what it seems may be other end.

I also use a non contact voltage tester, in my case built into the multi-meter, and I know it can give misleading results. Remember both line and neutral are considered live, but the neutral wire is unlikely to trigger a non contact voltage tester.

I have not traced all circuits in my own home, however my whole home is protected by 14 RCBO's so if some thing is un-towards then likely a RCBO will trip before I find out the hard way, it's not 100% you can still get a nasty shock, but where there is some uncertainty it makes sense to have all circuits RCD protected.