Repairing Fixed Wiring

[Flyfisher]

On the other hand, it didn't find two mains cables that were at the back of a 50mm cavity behind the plaster board. Good job I didn't trust it . . .

This quote from another thread reminded me about something I've been meaning to get around to for many years now, as well as reminding me why I bought my metal/stud detector in the first place

Yes, I drilled right through a 2.5mm2 cable. The bang was most spectacular and the 1/4 inch masonery bit was burned right through.

I effected a temporary repair by channelling out about 6 inches either side of the hole to expose the broken cable. I then used two junction boxes and a short length of new cable to re-make the circuit. because this 'temporary repair' is neatly hidded behind some curtains (I was fixing a tie-back hook at the time!) it has, of course, been more or less forgotten for a number of years.

My question is, what is the approved method of repairing such a break in the cable? There is no slack in either cable so I can't pull them together enough to join them, so I'll need to insert a new, short bit of cable. But what is the approced method of making the new joints? I don't really want to have to bury two large junction boxes in the wall but I don't know of a suitable, smaller, way of making the joints. I though of using one of those plastic terminal strips and wrapping it in insulating tape before embedding it in the wall and re-plastering, but it smacks of a bodge to me - or am I being too cautious? Any ideas?

 

[NT]

What youve done's good, but youre not supposed to use screw connections when something is plastered over. In those situations regs require crimping or soldering. If its not plastered over its compliant as is.


NT

 

[MdB]

As NT says, you aren't allowed to plaster over junction boxes (or put them anywhere you can't get access to). You either need to replace the entire wire, take it back to points where you can put a junction box in an accessible space or use one of the methods NT mentions (which I didn't know you were allowed to do).

The soldering method is interesting as this is something you are not allowed to inside of electrical goods when connecting earthing wires, they need to be crimped. Such is the wonder of non consistent regulations....

NT, do you have details of how you are allowed to make crimped and soldered connections to mains cables. I would assume there would be all sorts of regs regarding the way that you have to insulate the connections after they have been made.

 

[NT]

Unfortuately no. You can ask on uk.d-i-y, theyre good at this sort of thing.

NT

 

[Flyfisher]

I was in a bookshop earlier today and had a browse through some electrical books as well as the 16th edition wiring regs, specifically to find out about joining cables.

All the books I read mentioned soldering and crimping as being acceptable but were very short on detail, apart from saying that wires should be twisted before soldering and then covered with insulating tape. It is acceptable to then cover up such joints, i.e. re-plaster the wall in my case.

Screw-terminals and junction boxes etc must never be covered as they are required to be always accessible for inspection. So, it seems that burying my existing junction box repair is not acceptable, even if I wanted to go to the bother of chiselling out large chunks of the wall.

I've used crimp connectors many times for low-voltage wiring but have always used the correct tool. My understanding is that crimps create a 'cold weld', but only if properly done. I assume it would be the same with crimping 2.5mm2 wiring but I hardly think it's worth buying the correct tool for just a couple of joints. Hire might be an option I suppose?

So, I think I'll make a solder repair and use self-amalgamating tape to insulate the joints. I'm OK with doing that and it seems to be acceptable practice.

 

[NT]

> I've used crimp connectors many times for low-voltage wiring but have always used the correct tool. My understanding is that crimps create a 'cold weld', but only if properly done. I assume it would be the same with crimping 2.5mm2 wiring but I hardly think it's worth buying the correct tool for just a couple of joints.

Dont crimp without using a proper tool, the £1 tools create bad joints that will be a fire risk.


NT

 

[Flyfisher]

I entirely agree, although I've never seen a £1 crimp tool . . . . unless you mean a pair of pliers :wink:

 

[MdB]

I don't like the idea of crimping mains wire and the twist, solder, insulate doesn't sound much better. I would be happy with the joint (if you used a correctly rated soldering iron that is) but I really wouldn't be happy with a bit of tape for insulation, it screams of bodge and removes the double insulation principle. Heat shrink would be better but I'm not sure that would be thick enough.

If anybody does have a go at making joints like this (not recommended by me) then I would suggest that offset the joins, i.e. cut the cable so that the blue is longer than the earth which is longer than the brown. Do the opposite on the other connecting piece. This way, when the cable is put back in the wall, the joints are not next to each other and so there is less chance of a short between them. Still don't like it though.

 

[Flyfisher]

I agree with all that. I'm not entirely happy with the sound of it all, which is probably why I've stayed with my junction box solution for so many years (OK, that's stretching credibility and denying my own out-of-sight-behind-the-curtains mentality), but it does seem to be the officially recommended method for such repairs.

Unless anyone else has any other information?

 

[MdB]

I entirely agree, although I've never seen a £1 crimp tool . . .

Not quite £1 but close - click

 

[Flyfisher]

Ahh, I've got one of those but I don't remember it being that cheap. I was actually thinking about those ratchety crimp tools that ensure you apply enough, but not too much pressure.

 

[tony]

Crimps are perfectly ok, use inline crimps for 2.5mm2 cable use the blue straight connectors, with a proper ratchet crimper, you wont be able to pull them apart, you also need to install a enclosure over these crimps to protect the cables.

Crimps are designed for this use, soldering I wouldnt do and have never seen done on repairing mains cables,

the last joint i did was a 400 volt 200 amp underground cable and we used crimps!.

was there a socket above below your drilling point, if not the cables are not really routed in a safe zone, but theres no point in hacking it out as this seems a bit pointless but for new installations cables should follow a route as laid down in the regs, to prevent this sort of thing in the future
I was in B&Q a while ago and they sell a crimping tool in a box with a good selection of crimps for about £20, cant vouch for the quality, as I use mine most days it cost over £100 5 years ago but i do it for a living.

regards

tony

 

[Flyfisher]

Crimps are perfectly ok, use inline crimps for 2.5mm2 cable use the blue straight connectors, with a proper ratchet crimper, you wont be able to pull them apart, you also need to install a enclosure over these crimps to protect the cables.

My 'guide to the regs' book didn't mention any need for an enclosure to protect the cables. I was thinking of just covering the joint with some plastic trunking to match the existing and then plaster over it all again.

Crimps are designed for this use, soldering I wouldnt do and have never seen done on repairing mains cables,

the last joint i did was a 400 volt 200 amp underground cable and we used crimps!.

I do take your point on this. Crimping seems so much more professional somehow, but I'm wary about making a good crimp, hence the need for the proper tool.

I've seen the red, yellow and blue in-line crimps you mentioned but didn't think of them as being suitable for solid 2.5mm2 wiring. Maybe I'll get some and try some practice joints.

Coincidentally, I was changing some wall-lights earlier today and behind one of them were two wires joined together by being twised and then pushed into a porcelain 'thimble-like' thing. Or maybe the straight wires are pushed in first and then the thimble thing is twisted? Anyway, I doubt this meets current standards, but it does support the idea that soldering is not the normally done thing.

was there a socket above below your drilling point, if not the cables are not really routed in a safe zone, but theres no point in hacking it out as this seems a bit pointless but for new installations cables should follow a route as laid down in the regs, to prevent this sort of thing in the future

Yes, I was drilling about 30 inches above a twin socket but it didn't register at the time - no excuses really, my own stupid fault!

I was in B&Q a while ago and they sell a crimping tool in a box with a good selection of crimps for about £20, cant vouch for the quality, as I use mine most days it cost over £100 5 years ago but i do it for a living.

Can you remember if the crimp tool was one of those ratchety ones, or like the one in the link that MdB posted earlier?

 

[NT]

Coincidentally, I was changing some wall-lights earlier today and behind one of them were two wires joined together by being twised and then pushed into a porcelain 'thimble-like' thing. Or maybe the straight wires are pushed in first and then the thimble thing is twisted? Anyway, I doubt this meets current standards, but it does support the idea that soldering is not the normally done thing.

Ohh, you've got wire nuts Banned long ago in UK, these are one of the main causes of fires in US homes. I think they were banned when the 14th edn came out, 1966?, anyway its one more reason to suggest you've got historic wiring still on the loose.


NT

 

[Flyfisher]

The more I dig around the worse it seems to get !

 

[NT]

The more I dig around the worse it seems to get !

Well, if that pre-war fusebox is still connected its going to get a lot worse than wirenuts.


NT

 

[Penners]

Flyfisher - thanks for this thread. I haven't yet done what you did, but it's a dead cert one day!

At least now I'll know what the solution is.

 

[tony]

Yes the B&Q crimp kit is a ratchet crimp, look quite good.

What i meant was the crimped joint has to be in a enclosure, you cant just tape it up and plaster it, put it in a box first and then plaster over it, you can only do this with a crimped joint, a normal joint box with screwed terminals requires access for maintenance.

Plastic trunking is not a suitable housing for this joint.

A cheap one that are easy to use are called choc block enclosurers.

for example if you were connecting up a few spot lights that were wired loop in and out, you would use connector block for the joint and the wrap the enclosure around it., the standard joint box is more fiddly and time consuming.

If you dont have sufficent depth, chase out the wall a little more to get the required depth, fix the enclosure to the wall and then plaster over.

regards

tony

regards

tony

 

[Flyfisher]

Flyfisher - thanks for this thread. I haven't yet done what you did, but it's a dead cert one day!

It'll certainly make you jump if it ever happens! One thing I would add is that the fuse in the consumer unit didn't actually blow, even though the tip of the masonry bit was completely burned through - so if it ever does happen, don't just assume the fuse must have blown and be sure to isolate the circuit before poking around to examine the damage.


Tony, thanks for the pointer to the B&Q crimp kit. I'll have a look at the weekend,

Just one point about an enclosure for the crimps though, I can understand it's probably a good thing to not plaster over them directly, but why would covering them in trunking not be suitable (after wrapping them in self-amalgamating tape as well)? After all, the rest of the cable is protected in this way and I'd prefer not to chisel two deep holes just to bury enclosure boxes.

 

[Flyfisher]

I checked out the crimps & tools in B&Q today and I think this is definitely the solution for my repair. The blue crimps are specifically stated to be for 2.5mm cable.

The correct ratchety crimp tool was £20 or £25 in a kit containing loads of different crimps. The tool has holes for the red, blue and yellow crimps.

I only bought a pack of 10 blue 'butt' crimps (43p) because I have a number of rachety crimp tools somewhere and I suspect one of them might be suitable. If not I'll probably buy the kit.

I couldn't see any 'choc box enclosures' though, so my question about the suitability of using standard trunking to protect the crimps remains. It's all going to be plastered over anyway . . .