Ring main joint - pyro to normal

Hi,
I have just had some new sockets inserted into my ring-main - or rather not. The decorator who did it turns out to have made a bit of a hash of it. The problem is that at one end the join to the old ring can be made in the outlet socket - no problem. Because of the way the old cable was removed though the new join has to happen in the middle of nowhere. To compound matters the old cable is pyro, so needs special connectors etc.
I'm getting an electrician to sort it, but want to get an idea of what to tell him and what to expect. Is the following correct:
I can join the cables in a junction box This junction box can be recessed into the wall and plastered over AS LONG AS the cables are soldered or crimped together If they are only screwed into terminals, they must be accessible
How big a job would it be for someone to chisel out space for a junction box and make the above joint, then presumably test the ring for continuity etc. Ring mains seem deadly - they still work if they are split, but you're fuse is twice what it should be. I wouldn't know anything was wrong unless I'd happened to notice an unusual wire...
Cheers,
Ben
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It happens that Ben formulated :

It doesn't just need special connectors, it needs a specialised method to terminate the cable itself. The insulation absorbs moisture from the air, so it needs to be sealed up air tight with a proper termination.
Modern metric ones are difficult to get hold of, but imperial ones might be impossible. Also you need to make sure the electrician is familiar with terminating Pyro' - that is the old name for the type of cable BTW.
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Regards,
Harry (M1BYT) (L)
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wrote:

Ah -ok. This could be bad... The wire will have been open to the atmosphere for a few days by the time it gets sealed - if I can find the stuff. If I can't, I'm a bit stuffed. I currently have a radial rather than a ring, with a live bit of Pyro poking through the wall...
I haven't got any callipers, but the external diameter seems to be 5.5mm or 7/32". Do either of those sound like standard sizes (they don't sound it...) Ooo err. This is not good. I WISH he hadn't cut the cable!
Cheers,
Ben
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I have a section of the cut cable in front of me. What dimensions other than OD are used to identify it - it is 2 core, conductors look about 1mm...
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It is probably imperial equiv of 2L1.5 pyro. Good luck finding someone who can and has the tools to work on it. We do and are based in Portsmouth if that helps.
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Stephen Dawson
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Turn it off, turn it off now. Don't stop to anything on the way, just turn it off.

Depends, the OD varies amongst old and new and also throught the different grades and imperfections.
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Stuart.
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After a bit of detective work with the meter I have managed to isolate the exposed piece of cable so it is no longer live or in danger of shorting out. I have to watch the loading on the now radial circuits, since they are still fused as a ring, but someone is coming to look at it soon and will give their expert opinion. I'm certainly not using more than 20A at the moment anyway.
Cheers,
Ben
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Ben submitted this idea :

For a ring, I think it should be 1.5mm if metric. Could you perhaps compare the size directly against a known cable?
Even then it still leaves you guessing about imperial or metric as they were so close in Pyro. If it is of any help I have the tools you need for the job here in W. Yorks and the nack of making the ends off, but not the materials needed.
Check the plastic sleeving, they sometimes stamp the core size it fits on that.
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Regards,
Harry (M1BYT) (L)
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If you can find a terminated end the "pot" should also have the size embossed on it, like 2L1.5 for two core 1.5mm (If it's metric).
Alternatively replace that whole bit of pyro with twin and earth if it's suitable.
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Clive Mitchell
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Ben pretended :

Look at the brass cable gland or seal, on both should be stamped a number which you will be able to quote to an electrical wholesaler. From memory the old imperial sizes had a number based on the diameter in thousands of an inch. The metric ones used a number based on the number and size of the cores.
All is not lost, even if moisture has got in. It penetrates quite slowly, perhaps a fraction of an inch per day. The fix is to heat up the Pyro to a dull red heat, at a point beyond the damp and gradually move the heated point towards the open end - this drives the moisture out. Obviously if you don't start far enough back, or move to fast, it will make the problem even worse.
Once dried out, the end can be sealed temporarily with a blob of the sealing compound, as used it the seal or 'pot'.
To make the end off, you will need 2x glands, 2x pots, 2x plastic ends to suit the number of cores, sealing compound - then the special tools. Crimper, ringer and a stripper.
TBH, what with all the faffing about and cost, it might be cheaper/quicker to simply replace the cable with new. FP cable does much of what the Pyro cables were once used for and you don't need any special tools or skills to be able to use it.
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Regards,
Harry (M1BYT) (L)
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Did he actually cut the pyro? So has he torn the copper back and just connected onto the wires where they come out of the chalk?
If so he really shouldn't be doing electrical work.
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Clive Mitchell
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Do you know when the 'pyro' was installed? It doesn't need special connectors as such but has to be properly terminated. This involves fitting a special seal to the end. If you look inside a socket etc you'll see what I mean.
If it's old imperial stuff - roughly pre '70 or so - I dunno where you'll find a termination kit. And even the modern stuff might be tricky, depending on your location. Few wholesalers stock MICC these days. For reference if it's the current metric cable it will almost certainly be 2L1.5 for a final ring circuit.
And you may have a problem finding an electrician who can work this stuff - it's not much used these days, and ideally needs special tools to make the termination.
I do have a small stock of terminations for the common sizes but am unwilling to sell them except to someone who knows what they're doing.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Pyro is still widely used in modern buildings for alarm systems despite the availability of other fire rated cables. It's also used in fuel stations and some entertainment venues.
Pyro is an abbreviation of Pyrotenax.
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Clive Mitchell
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Indeed - however your average jobbing domestic sparks ain't going to work in such places.

Of course the Pyrotenax company no longer exists - they merged with BICC some 40 years ago. But the name tends to be generic - like hoover.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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I think the original problem was this:
The plan was to remove the pyro between two outlets and replace it with modern cable. But the old cable was removed before it was all exposed. It turns out that just before it reaches the second socket, it diverts to the next floor up, loops the bedroom, and then comes back down again - all in the horizontal space of a few cm. So when he had removed the cable he all of a sudden found it didn't go to an easily accesible socket, and the problems started. However, not new cable/pyro cable have been made yet (which would reform the ring) due to the lack of an electrician and of the neccesary bits. I've found someone, but he's busy this week, so fingers crossed for next.
Ben
Ben
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I obtained a pack of pot seals and a pack of glands for 2L1.5 from Newey and Eyre this week. The brand name Pyrotenax boldly displayrd on the packs!
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That's interesting - last ones I bought were 2L1 about a couple of years ago (for lighting wiring in an oak beamed room) and they were just marked BICC.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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I'll have a look when I get back for the type of cable it is. Last time I looked, I could see the two copper wires, which had been sheathed with black plastic. They disappeared into a larger diameter black circular pipe that was filled with some sort of resin. I can't really see the other side of the pots, as they are behind plaster. Whereabouts should I be looking for the designation (is it, in fact, on the outside edge of the box - if needs be I can always remove a bit of plaster to have a peek, since that section of wall hasn't been finished properly yet anyway)
I have definitely learnt a lesson from this whole episode!
Cheers,
Ben
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If your electrician can't identify the size of cable you can send a sample to one of the manufacturers. They are usually helpful. I have done this with a bit of old imperial size. They sent me a pair of pot seals almost by return. (about 7 years ago now)
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The material inside the pot seal is rather like putty - except that it doesn't set. It's normal to either clamp the seal in a special back box to provide the earth, or to use a compression gland which fits a standard 3/4 cutout and is fixed by a backing ring. Although I've a feeling neither of these methods is now considered satisfactory for an ECC.

It's a very tactile material to work with when the cable is exposed. Rather like plumbing in many ways.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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