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

Reply to
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.

Reply to
Harry Bloomfield

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

Reply to
Ben

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...

Reply to
Ben

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.

Reply to
Stephen Dawson

On 17 Apr 2007 12:58:05 -0700, Ben mused:

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.

Reply to
Lurch

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

Reply to
Ben

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.

Reply to
Harry Bloomfield

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.

Reply to
Harry Bloomfield

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.

Reply to
Dave Plowman (News)

In message , Harry Bloomfield writes

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.

Reply to
Clive Mitchell

In message , "Dave Plowman (News)" writes

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.

Reply to
Clive Mitchell

In message , Ben writes

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.

Reply to
Clive Mitchell

If he really was a decorator what did you expect? ;-)

Follow the cable back to the next accessory in line, and replace it with T&E from there.

Half hour tops, with normal T&E, crimps, heatshrink etc and a SDS drill

- perhaps longer if including a MICC pot as well.

When you analyse the most likely faults that can happen, ring circuits are a pretty good compromise all things considered (much harder for one poor joint to leave the bulk of a circuit unearthed, or the full design current passing through one high resistance point). Not to mention the current carrying capacity[1] for 1.5mm^2 MICC in plaster is not far of the circuit breaker rating anyway at 28A. So you would have to try quite hard to cause damage to that during normal usage.

[1] Table 4J2A in BS7671
Reply to
John Rumm

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.

Reply to
Dave Plowman (News)

Hi - Thanks for the reply. I have got an electrician coming around who has worked with pyro cable before, but the cable is bare unmarked brass so he'll need to work out what type it is. We then need to discuss the practicalities of joining vs rerunning (rerunning would be an arse). He also suggested just derating, but I really want to avoid that if I can!

If he is able to identify the cable but unable to find the bits, perhaps I could contact you again? He can't make it around for about a week - I have isolated the offending cable, but how much of a problem will atmospheric moisture be? Should I temporarily tryt to seal it off with a blob of glue or similar?

Cheers,

Ben

Reply to
Ben

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

Reply to
Ben

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!

Reply to
cynic

A termination 'pot' should have the details on it, so a look inside the socket feeding the cable should do it. And the cable outer is copper - not brass.

That's a bit of a worry. Assuming there is about 12" of the MICC get attable, it should be possible to fit a new termination.

Yes. But only after he's certain he can't order them from his wholesaler - as I say I keep them for my own emergencies. ;-)

Tape it over with PVC tape.

Reply to
Dave Plowman (News)

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.

Reply to
Dave Plowman (News)

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