Anyone can fix an MICC cable leading to a light switch in my house (London, N6)?

[Deleted member 148954]

Hello, I am looking for an electrician who has an expertise in dealing with MICC (mineral-insulated copper-clad) cables. It is a domestic job in my house (I live in Highgate, London; postcode is N6). When I was replacing a light switch in my living room, 2 out of 6 wires coming out of 2 MICC cables (which come through the wall; each cable has 3 wires) broke off. I am attaching two photos of the light switch in question (the 2 wires that have snapped are behind the switch). Please contact me if you can do the job and provide a quote. (If you need any further info, please let me know). Thanks, Eugene

 

[buzzlightyear]

The wifey was cleaning the garage came
Across the old pyro gear, she says you can chuck this lot out me to her throw that out you has well throw the washing machine out has well.

 

[cireland]

Wasn't the older stuff imperial?

 

[Lucien Nunes]

A lot of the flush MICC installs I've come across/dealt with have been imperial sized cables which can add another little bit of complexity to the situation.

Agreed, the cables looks large relative to the seals. Are they 5/8" seals on 0.0015 sq ins. cable? Hopefully an inside view of the seals and sleeves will resolve that question. Although I expect the OP is simply looking for a contractor to do the work, rather than chat about it on here, eliciting any complications might help the said contractor prepare for the job and not arrive without the necessary bits.

It looks like there is just about enough cable there to make the ends off again and have an inch beyond the disc to put a Wago on. But has anybody ever jointed a conductor within a pot and sealed it up again? I think one would have to be very careful to avoid soldering flux wicking into the insulant and deflux thoroughly before filling with compound. But it might be possible, especially if one is prepared to go to the trouble of making a scarf joint in the conductor. Then again, not much room in a 5/8" seal if that is what they are.

I wonder how they came to break in the first place? Perhaps the conductors were nicked with the stripping tool and weakened. It would take a lot of mauling to break an otherwise completely intact conductor.

 

[Deleted member 148954]

Home - Eastway Electrical

www.eastwayelectrical.com

Thanks for your reply. I'll contact you shortly.

Not sure if any member is close to you, but we will soon find out.

MICC is a fairly specialist area now. Not used so much nowadays as a new install.
If the core snapped right at the pot (I still know the lingo!) it’s going to need replaced.

Looks like it’s buried in plaster on a brick wall.

What do the switches control? If they’re all in the same room, likely solution is to have only one switch, controlling all lights and taking that length of cable out of circuit.
Or remake the end of both cables, bringing the switch up the wall a bit.
Or remake the cables high up on the wall, fitting in a box to use as a joint box with a blank plate… then extend in regular t&e cable back down to switch.


Have never know MICC to be used domestically except as a sub main up a tenement building in Edinburgh.
Was my brothers flat, and all the sub mains were bare copper MICC clipped surface up the stairwell. Amazing neat job.


Edit. Just saw Dusty’s reply….. Is that the celeb spark, Delroy? Love to see him work on MICC on YouTube… lol

Thanks for your reply. Very helpful input.

 

[Deleted member 148954]

Can you post a picture of what's left inside the switch?

Is there any writing on the black insulation of the conductors inside the switch? Hopefully it will have the cable size written on it to help identify what size fittings will be required for repairing it.

A lot of the flush MICC installs I've come across/dealt with have been imperial sized cables which can add another little bit of complexity to the situation.

Thank you for your reply. There is no writing of any kind on the black insulation of the conductors. I'll post a picture of what's left inside the switch tomorrow morning. In the meantime, here are the pictures of the conductors that have snapped. Are these the imperial size in your estimation (don't know if it is possible to determine from the pictures). Thanks.

 

[davesparks]

looks like there is just about enough cable there to make the ends off again and have an inch beyond the disc to put a Wago on. But has anybody ever jointed a conductor within a pot and sealed it up again? I think one would have to be very careful to avoid soldering flux wicking into the insulant and deflux thoroughly before filling with compound.

That's exactly what I was thinking when I asked for a pic inside the switch. dig the old compound out, solder some extensions on and re-seal. I'd be game for giving it a go if I had time.

It would take a lot of mauling to break an otherwise completely intact conductor.

I don't know what the size is but the smallest imperial size MICC I've worked with is pretty tiny and easily snappable

 

[freddo]

But has anybody ever jointed a conductor within a pot and sealed it up again? I think one would have to be very careful to avoid soldering flux wicking into the insulant and deflux thoroughly before filling with compound. But it might be possible, especially if one is prepared to go to the trouble of making a scarf joint in the conductor. Then again, not much room in a 5/8" seal if that is what they are.

Yes I have, I just took my time. Prepared the ends of the conductors with a needle file, the scarf was not much of an angle, and I'm sure if I did it again I'd get away with a butt joint as described in the handbook. I was also able to remove the pot for better access. The cable was coming down the wall so that helped with keeping flux away, I did also use a flux cleaner, mostly to prevent the flux causing future corrosion. I used a fairly powerful micro jet type torch to silver solder the joint and a small oxy/mapp torch to preheat the end of the cable to prevent it sinking all the heat away, roughly following the Pyrotenax cable handbook instructions for jointing cable ends. I also used one of those helping hands things to hold the ends during soldering, I was able to fix that to the wall using one of the switch box wall fixing holes. The repaired cable passed the insulation tests off the scale of the meter. I did unclip a fair section of the cable from the wood panelling to prevent the risk of hot cable burning the wood.

The main reason for repairing rather than replacing was because I got to use a blowtorch the bare cable was very neatly run with 2 others from the same switch, the cable run was very visible so a joint box wouldn't look good and accessing the other half of the cable for replacement would be impractical as it would damage the ornate plaster covings etc.

I'm not sure why the conductor broke, was called out because the light was flickering and when the switch was unscrewed from the backbox the conductor pulled out of the sleeve, broken at the tip of the stub cap. No sign of damage or corrosion, must have been weakened during installation. I did have the benefit of this cable being metric though so it was easy to find a replacement pot. I'm not too good at opening old pots carefully to be able to reclose them. The pot was fitted a little past the gland too so I could remove a bit of the sheath for a tight fit for the new pot.

Not a quick job, I don't get many chances to improve my skills with this sort of work to be able to do it faster. I wish I'd taken some photos.

 

[Dustydazzler]

Thanks for your reply. I'll contact you shortly.

Thanks for your reply. Very helpful input.

Just fir the record contrary to popular folk law I am not Delroy from Eastway

He is a good old sparks who happens to work in London area

 

[Lucien Nunes]

the scarf was not much of an angle, and I'm sure if I did it again I'd get away with a butt joint as described in the handbook. I was also able to remove the pot for better access. The cable was coming down the wall so that helped with keeping flux away, I did also use a flux cleaner, mostly to prevent the flux causing future corrosion. I used a fairly powerful micro jet type torch to silver solder the joint and a small oxy/mapp torch to preheat the end of the cable to prevent it sinking all the heat away,

I was thinking that a plain scarf would be best silver-soldered, but a soft-soldered joint might be equally satisfactory if bound with some 32SWG TC wire first. I'd probably want to support the conductor to file it, e.g. drill the right diameter hole in a small block of material e.g. hardwood and cut the angle on one end. Feed the conductor through the hole and file it flush with the block. If it had to be done in situ in the pot, one could do something similar with a little piece of tubing.

Perhaps one of those mini spot-welders for putting the inter-cell links on battery packs would make a good weld of this size? Would avoid the flux issues and make a very quick job of it.

Many decades ago, one of my mentors did some very crafty jointing to the leadouts of a valuable prewar CRT that had been in someone's garden for years and the leads had corroded off at the welds. There were tiny, weak stubs remaining in the pinch but he managed to get inside with some 26SWG and make successful joints, and the tube turned out to be a corker.

There is no writing of any kind on the black insulation of the conductors.

The fact that it is not emblazoned with 'STUB SLV' etc. hints at it being imperial

 

[Sparky5473]

The micc on the right hand side looks like it has some cuts to the outer copper sheath before it goes through the wall so I would think that the insulation resistance could be low

 

[Lucien Nunes]

I also wondered at first whether there were dings in it, but now I'm more inclined to think it's an artefact of the pic.

 

[davesparks]

I also wondered at first whether there were dings in it, but now I'm more inclined to think it's an artefact of the pic.

I reckon it's had an intimate encounter with the chisel used to dig the hole in the wall.

 

[Deleted member 148954]

That's exactly what I was thinking when I asked for a pic inside the switch. dig the old compound out, solder some extensions on and re-seal. I'd be game for giving it a go if I had time.


I don't know what the size is but the smallest imperial size MICC I've worked with is pretty tiny and easily snappable

Here are the pics of what's behind this switch. Hopefully they help figure out what could be done here. Thanks again for your help.

 

[Lucien Nunes]

It's a pity we can't see the seal discs clearly or exactly where within them the conductors have snapped. But scaling the size off the pic compared to the box and cable, I am increasingly convinced that they are 5/8" seals on imperial cable. If the existing seals can't be salvaged and re-used, metric pots can be fitted; it may be necessary to drill out the cable entry and solder to the sheath, according to the specific cable diameter.

@Eugene: Do you know what year the property was built / wired? Is the circuit protected by an RCD or RCBO? Could you tolerate the box being moved 5cm up the wall?

Slightly odd setup there, with two cores from one cable and one from the other going to each gang of the dimmer, but there are a number of reasons why that might have come about. Clearly some previous convictions with those bits of terminal block.

 

[Deleted member 148954]

It's a pity we can't see the seal discs clearly or exactly where within them the conductors have snapped. But scaling the size off the pic compared to the box and cable, I am increasingly convinced that they are 5/8" seals on imperial cable. If the existing seals can't be salvaged and re-used, metric pots can be fitted; it may be necessary to drill out the cable entry and solder to the sheath, according to the specific cable diameter.

@Eugene: Do you know what year the property was built / wired? Is the circuit protected by an RCD or RCBO? Could you tolerate the box being moved 5cm up the wall?

Slightly odd setup there, with two cores from one cable and one from the other going to each gang of the dimmer, but there are a number of reasons why that might have come about. Clearly some previous convictions with those bits of terminal block.

Thanks. The house was built sometime in the 1960s. Don't know about RCD or RCBO - there is a fuse box of course but that's all I know. Yes, the box can be moved 5cm up the wall.