Bunging up a hole!

[vicky whitworth]

Hello, I have had a light switch and a plug socket removed however the electrics are still behind the metal boxes which have been removed. They have been capped but it has left two holes in my lime plaster inside which are the cables. There is a reason why the cables haven't been taken away but I need to plaster over. My electrician says chuck some lime plaster in the holes and make good. Do you think this will be OK? I was planning on buying a small bag of haired lime plaster but somehow this doesn't seem right. Thank you. V

 

[MikeG]

I would be cautious of trying to build plaster up to that sort of depth, and would be looking for something to push into the hole prior to plastering such that the depth of plaster isn't greatly different from that of the surrounding wall. If you've ever taken an old building apart, you'll know that anything from lumps of straw through a bundle of rags to crumpled newspaper has been used for this task in the past, but an off-cut of wood-wool board would probably be favourite these days if you happen to have any lying around.

 

[Flyfisher]

How have the wires been left? Joined with a terminal block and wrapped in insulating tape? Crimped then insulated? Small junction box? I'm not sure what the regulations say but I've seen all those examples over the years. I believe junction boxes are frowned upon these days unless they are readily accessible, because of possible maintenance issues I suppose, but as you've discovered it's not always practical to remove such joined wiring and replace with a new un-jointed length of cable.

I'd be inclined to follow your electrician's advice, as long as the cables are secure and unlikely to need attention in the coming decades. I'd probably put a layer of plastic or similar over the cables while filling the hole though (and switch off that circuit while doing the work - wet stuff and electricity is generally best avoided).

I agree with MikeG above about the depth of the hole and possible problems, though if the hole is to be covered with wallpaper or similar, I'd probably just go with something like 'polyfilla', which would be less prone to cracks - and easy to fix with more filler if it does. Otherwise I'd try to match the existing wall material and texture as closely as possible.

 

[malcolm]

I don't think there would be any benefit in using haired lime plaster. Haired plaster is good when you are plastering over cracks as it adds a little strength, but no benefit for filling a hole. It makes sense to reduce the depth of the hole as MikeG mentioned. About 15-20mm short of the surface would be good. Then fill with just about any plaster to about 5mm shy of the final surface and leave to dry for a couple of weeks. That first coat will shrink and crack around the edges but the second coat should be OK once the first coat has settled.

 

[MikeG]

How have the wires been left? Joined with a terminal block and wrapped in insulating tape? Crimped then insulated? Small junction box? .......

I assumed these wires were dead (ie disconnected at the other end as well). There is no way on this planet that anyone should be plastering disused but still live wires into a wall in the circumstances described, no matter what is done with the ends. Disconnected/ dead wires might be left in a wall because of the disruption caused by trying to remove them.

 

[Flyfisher]

Could be, though I assumed the wires were left in place as the socket could have been on a ring main so the cables needed to remain connected, which I've seen done before (albeit behind a blanking plate). Live wires within a wall are clearly not a problem, per se. I'd agree the ideal thing would be to isolate the cables and rewire the circuit, but in the real world this would likely entail a lot more disruption so I can imagine it not always being done.

Perhaps Vicky could confirm about the cables, one way or the other?

 

[MikeG]

.....Live wires within a wall are clearly not a problem, per se.........

Indeed, but live wires not connected to a socket or switch very much are a problem, as there is no visual clue to their existence. No one in their right mind drills into a wall directly above a socket or switch, but you'd feel pretty unlucky to wake up in accident and emergency after drilling into a blank bit of wall.

 

[Flyfisher]

I think you'd be unlucky to end up in A&E in such circumstances. I've drilled into a live cable and the only shock was the bang, and that was in an installation without an RCD, which I'd expect to take all the drama out of such a thing.

But I take your point that it's not ideal. Fortunately, live cable detectors are readily and cheaply available these days.

I wonder what the regulations say about such things?

 

[Hobden]

I think you'd be unlucky to end up in A&E in such circumstances. I've drilled into a live cable and the only shock was the bang, and that was in an installation without an RCD, which I'd expect to take all the drama out of such a thing.

But I take your point that it's not ideal. Fortunately, live cable detectors are readily and cheaply available these days.

I wonder what the regulations say about such things?

Last time I heard anything about it, they said that if cables were buried in a wall they had to be at least 4 inches deep, unless the circuit was RCD protected (and you're not allowed to put the cables in the 4" deep cavity of a cavity wall either!) Only applies to installations put in after the regs changed of course.

 

[fernicarry]

No one in their right mind drills into a wall directly above a socket or switch

Cables should only be run in 'safe zones' so that any future works can anticipate their potential location. This is horizontally or vertically from the location of an accessory (socket, switch etc.) as well as in the corner of the room. As you say places where someone with half a clue would think twice before drilling/nailing.

http://electrical.theiet.org/wiring-matters/54/cables-in-walls/index.cfm

If you really don't need the accessory any more but aren't able to reroute the cables then you should really leave the old back box and fit a blanking plate -- assuming cables left behind are indeed still live and if the socket was on a ring then they must be otherwise you have problems of a different and possibly quite serious kind.

When I moved my fuse box I also moved a socket over by a couple of feet to make a new safe zone for the new cable runs. Must remember to fill up the hole in the wall from the old socket location sometime...

If this was done by a registered spark then he can deviate from the rules but he has to justify why he has done so.

I think you'd be unlucky to end up in A&E in such circumstances. I've drilled into a live cable and the only shock was the bang, and that was in an installation without an RCD, which I'd expect to take all the drama out of such a thing.

Provided your installation is in good condition then yes even without an RCD chances are there will just be a flash and a bang and the lights will go out. But there's also a chance that you only hit the live conductor so that your body now forms the path for the fault current to flow to earth. Without an RCD its unlikely anything would disconnect automatically. Even RCD's can fail to work correctly, that's why they have a test button (which of course we all remember to press monthly, blacking out the whole house in the process...)

I'm not a sparky, so no axe to grind, but I do quite a lot of fiddling around with electricity and have made a point of swotting up on it.

-Alan

 

[Hobden]

Even RCD's can fail to work correctly, that's why they have a test button (which of course we all remember to press monthly, blacking out the whole house in the process...)

Use RCBOs, a combined RCD and MCB. That way you only black-out one part of the house at a time! And nusiance tripping only affects a small number of appliances.

 

[Flyfisher]

Provided your installation is in good condition then yes even without an RCD chances are there will just be a flash and a bang and the lights will go out. But there's also a chance that you only hit the live conductor so that your body now forms the path for the fault current to flow to earth.

Wouldn't the drill bit be earthed and the drill itself be double-insulated? I was using a mains-powered drill, which I think accounted for the large bang as the earthed drill bit hit the live conductor, but there was no shock to me. Of course, today's prevalence of cordless drills means the metal parts of the drill will not be earthed, though the housing is still plastic and therefore a good insulator.

However, while I certainly take your basic point that a severe shock is a possibility, there are other ways to mitigate or even eliminate the risk of drilling through a cable, and given that we are mainly interested in period properties here, I would dare to suggest that any reliance on 'safe zones' in such old properties is quite a large risk in itself! Indeed, the unthinking reliance on someone else's invisible cable routing has never seemed a particularly good idea to me. Live cable detector 'pens' are cheaply available and should, I'd say, be part of every serious DIYers tool kit. Even without such a detector, the next best thing would be to switch off the power at the consumer unit.

I'm not trying to make light of such things. Electricity can indeed be dangerous and even fatal, so should be treated with due care and attention. But I do think that sometimes the risks are overstated, except of course there's no defence against 'the regulations' - even though the vast majority of installations throughout the country do not actually meet the latest regulations. Does that mean the vast majority of installations are not 'safe'?

 

[Flyfisher]

Even RCD's can fail to work correctly, that's why they have a test button (which of course we all remember to press monthly, blacking out the whole house in the process...)

Use RCBOs, a combined RCD and MCB. That way you only black-out one part of the house at a time! And nusiance tripping only affects a small number of appliances.

Agreed, or a split CU with more than one RCD. I don't know if this is part of 'the regulations' but the two new CUs we've had installed are both split so that nuisance trips don't shut off all power.

 

[malcolm]

Regulations are very well meaning and the electrical ones seem well thought out. Building regs required a couple of fire doors here and they were fitted today. I'm big on safety and have given everyone strict instructions to close them in the event of a fire.

 

[paulc]

Wouldn't the drill bit be earthed and the drill itself be double-insulated? I was using a mains-powered drill, which I think accounted for the large bang as the earthed drill bit hit the live conductor, but there was no shock to me.

Unless things have changed in recent years, the chuck on a pistol drill won't be earthed... Whan PAT testing became mandatory, the guy nominated to do the testing where I worked was failing all the pistol drills and grinders because they were not passing the earth bonding test. Because the tools were double insulated, the metal parts weren't earthed.

Use RCBOs, a combined RCD and MCB. That way you only black-out one part of the house at a time! And nusiance tripping only affects a small number of appliances.

If your consumer unit has enough room for an RCBO, then they are worth installing on most circuits. RCBOs are quite tall, and not all CUs have the space.

 

[Flyfisher]

Wouldn't the drill bit be earthed and the drill itself be double-insulated? I was using a mains-powered drill, which I think accounted for the large bang as the earthed drill bit hit the live conductor, but there was no shock to me.

Unless things have changed in recent years, the chuck on a pistol drill won't be earthed... Whan PAT testing became mandatory, the guy nominated to do the testing where I worked was failing all the pistol drills and grinders because they were not passing the earth bonding test. Because the tools were double insulated, the metal parts weren't earthed.

That's interesting. I wonder how the design of such drills protects against an internal fault that might cause exposed metal parts (eg the chuck) from becoming live?

 

[fernicarry]

would dare to suggest that any reliance on 'safe zones' in such old properties is quite a large risk in itself

I agree, I know my wiring was in a shocking state (almost literally!) before I started sorting it out.

For the benefit of the OP, the way its supposed to work is that whenever you touch an existing installation you leave the bit you touched fully up to standard.

I actually find cable pulling in traditional buildings an awful lot easier than modern ones. You can get under suspended floors, lift floor boards for access and the wall studs aren't stuffed full of insulation.

Use RCBOs, a combined RCD and MCB. That way you only black-out one part of the house at a time! And nusiance tripping only affects a small number of appliances

This gets debated at length on electricians boards. If you put each circuit onto its own RCBO then potentially something can be tripped for a long time before you notice and by then the smoke alarms are dead and the freezer has defrosted...

Some electricians don't like RCBO's as they are nearly always single pole devices (us being cheapskates in the UK again) so don't disconnect the neutral. I believe an all RCBO set up is also frowned upon for TT installs (where you have an earth spike in the garden rather than an earth from the supply network) for the same reason.

Convenience versus risk, its very much swings and roundabouts...

 

[fernicarry]

An anecdote on nuisance tripping.

This was before our rewire. I used to work away from home for months at a time and one day my wife called up to say that the power was off. We narrowed it down to the downstairs sockets and she went around unplugging everything one by one but it stayed off. It seemed like it must be a fault in the fixed wiring and I suspected it was due to water ingress as I knew some of the sockets on the outside wall were quite damp. Her temporary 'fix' was to buy a selection of extension leads to run the TV and computer off of the kitchen sockets (DONT do this with large loads like space heaters or hair dryers).

When I came home I went round checking everything on the downstairs sockets, isolating each socket one by one but still it kept tripping. It wasn't until I took the DB apart that I found an extra circuit spurred off the back of the breaker, removing that restored service on the sockets! This circuit turned out to be the immersion heater, which we never used, but was faulty. For some reason my wife had decided to turn it on and didn't link that with the fact that everything stopped working shortly thereafter! (Her logic for turning it on was even more flawed, it wasn't because the water was cold, it was because the bedroom next to the airing cupboard was cold...)

The true state of how haphazard the install was emerged when we took the kitchen out. Missing earths, under-rated and damaged cables, dozens of junction boxes where things had been modified over the years, sockets spurred off of others in surprising ways...

 

[Hobden]

If your consumer unit has enough room for an RCBO, then they are worth installing on most circuits. RCBOs are quite tall, and not all CUs have the space.

Interesting, didn't know that. We've just bought a house and I was planning on having RCBOs installed. Let's hope there's enough height for them, else maybe a new CU! Still, we're chucking money around like water at the moment so a few bob more won't be noticed :lol:

 

[Hobden]

The true state of how haphazard the install was emerged when we took the kitchen out. Missing earths, under-rated and damaged cables, dozens of junction boxes where things had been modified over the years, sockets spurred off of others in surprising ways...

This is all horribly familiar to me. Unearthed metal light fitings in the kitchen. Crumbling cable insulation (1950s probably). 13-amp sockets spurred off the lighting circuit! And more junction boxes than you could shake a stick at, and some of them (heaven knows why) mostly minus their bases, just a big hole underneath, right where you'd put your fingers to lift one up. Having found a couple of those after I first moved in I made sure I always wore gloves whenever investigating the wiring in the loft! I think it was Billy-the-Kid's younger brother who'd wired the place ...