Snapped wire in 60s light switch

Hi all,

I've got a bit of a problem and i'm hoping someone's got some ideas which doesn't involve re-chasing out the wall

Whilst replacing the dodgy light switch in my lounge i noticed that the core of one of the wires was just hanging in the insulation as the copper core had snapped (which would explain why it was dodgy)

I removed the insulation of the wire to see where it had snapped with the aim of doing a repair.

As you can see (from the picture below) there's a tiny bit (1-2mm) of the wire remaining this side of what looks like a cap. I know from around the rest of the flat that the lighting circuits are run through metal conduit which is earthed. The cap seems to be holding the wires in very tightly and there appears to be no way of removing it.

* Does anyone know what this cap is and how to remove it? Is there a set of connectors on the other side which i could use to replace it or put a repair in?

If i could remove it i think this would allow me to pull through maybe another ~3-4mm which would mean i could get a chocolate box on there and bridge it.

If that doesn't work I was also thinking about soldering another wire on to the tiny bit which is left and insulating it but as there's a lack of a real earth wire and i'm not behind an RCD this scares me a bit.

* Do any of you have any clever ideas on how to fix it or come across something like this before?

Thanks in advance (It's getting pretty dark in the flat )

D

That cable is mineral insulated cable.

Do not remove the cap. The mineral insulation will get damp, and cause a short between the bare wires inside. Magnesium acts as an insulator.

You will NOT be able to pull any slack on this cable.

To alter this existing cable you will require an experienced electrician who has experience with this cable. There WILL be damage to the walls.

Alternatively, trace where this cable goes and replace with regular twin and earth PVC cable.

Is there by any chance a light switch back to back with this one?

Do you know if the broken wire is the permanent live or the switch live?
Only find out if you can test for this SAFELY.

Do you have access above the light?

Sorry, but that's Pyro cable, not conduit. You'll need to find an electrician to put a new pot on the end of the cable.

Thats MI... if you've snapped the stub off at the pot then the only thing that can be done is to chase out the wall to gain enough on the cable to strip back and re-pot it.

You wont gain anything by pulling at whats left of the stub, and you dont want to take the pot off... its sealing the end of the cable, the mineral inside will readily absorb moisure from the air and fail without it

You need an electrician who has the tools to work on MI (and hopefully various different sizes of pots to try as it is quite likely to be imperial).

Its possible to do it with minimal tools, but if you have never touched the stuff before then I can't see it being possible to be able to do it without behind shown

That looks like MICC (aka pyro) to me, which means you don't stand a chance of DIYing it, look up micc in the wiki to see what you are up against.

Before we do anything, are you certain the wire has snapped/going to snap?

Remember, the black sleeve just slides over the bare wire.

RF Lighting said:

//www.diynot.com/wiki/electrics:micc

Click to expand...

Never got on with those joiststripper things, might be something to do with the one I was lent had a dull blade. I must be one of the few people under 30 who gets on better with the bit of angled bar with a slot in the end...

Hi all thanks for your quick replies! - If you could make them good news next time that would be ace heheheh

Doh!

Ok...

I get the feeling this is going to get a bit messy! I presume all this stuff was used before plastic was cheap and nice and flexy?!

So it's a copper pipe filled with 3 wires (I think there's another hidden rose under the plastered ceiling somewhere) which then had magnesium oxide used as an insulator... Nice... Good job i didn't remove the cap then!
(The reason you can only see 2 is the 3rd one is the one that's snapped - I removed the insulation once the copper core had fallen out)

This is going to make a bit of a mess i think as the ceilings are solid concrete and therefore we don't have any access to the wiring up there.

I guess if it's the permanent live i could just run another live to it... So i hope it's not the switched live. Can i test if it is with the power off? The permanent live i guess should have pretty much no resistance to a plug socket live (When the main power is off but the circuit breakers are on)

Unfortunately there's not another switch on the other side. But the CU is about 50cm away which i guess is pretty much the same...

Do these cables have junctions on them or is it going to be one of these from there to the ceiling rose?

The cable had three wires going to the switch?

Is this a 2 way switch (ie another switch at the other end of the room controlling the same light)?

It wasn't a case of MI being used before pvc multicore was invented... before PVC, we had vulcanised rubber (1950's, early 60's) and before that we had rubber insulation with lead outer sheath... 1940's.

No MI was (and still is) used where its properties make it desireble... bare copper looks good in historic buildings etc, and its also completely fire proof, so is often used for fire alarm systems.

In the past though (when labour was cheaper) it did find its way into more installations than it does these days, no one would wire a school's socket outlets and lights in it these days, but years ago it was often done to provide a 'high spec' install

Its probably embedded straight into the ceiling and this will be why its been used on your installation. If you take your ceiling light down you will hopefully find a BESA box behind it that the cables are made off into.

Not sure why theres (was) 3 cores though, is this just a single light controlled by a single swith or is there more to it than that?