I want to know about bad phone wiring!

[dom]

First off - I reckon there is no better place than this to get honest descriptions of what kind of poor-quality phone wiring installations there are around the country than asking about it here!

Second off - I need to be upfront and say this is about my day job - and not diy phone wiring.

Basically, I'm going to be testing some prototype high speed (200Mbps) modems, and as well as test rigs that match up to standard modern practice - I also want to build a rig that reflects poor but all-too- common wiring too.

I'm particularly thinking about Victorian blocks of flats (like London tenements) that were never built with wiring in mind. So the phone wiring to the flats might be drop wires bunched together, with more and more of them added ad-hoc as more phones were connected.

Even more so if the ad-hoc wiring happens to be crammed together with mains wiring (although wiring regs says in shouldn't be!)

If you can spare a couple of minutes to tell me about it (particularly if you know the wiring layout around the building) - I'm really interested!

The only other way I can find out is to peer around blocks of flats, tracing wiring, making sketches and getting arrested. I'd be very grateful if you told me about it instead!

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Explanation for those that want to know what's going on:

FYI - these are high speed modems that use the existing copper wire from your house/flat to the pole (or whatever - the place known as the CN - convergence node), where there's another box - followed by bonding of lines back to exchange/central office).

Hence the wiring length in original copper is usually less than 100m, hence it can support much greater speeds - provided that it doesn't pick up masses of electrical noise.

For those not familiar with how this stuff works - phone drop wires consist of a number of twisted pairs - i.e. two insulated wires twisted around each other into a spiral, before being laid next to the others and the outer cable jacket applied. This improves the noise immunity of the wiring because each of the wires in the pair should be affected equally. Twisted pair wiring is then used with differential signalling i.e. the signal is the voltage difference between the two wires in the twisted pair. This works to a degree - if the source of interference is too close or too big, the signal can still be excessively affected.

[Frank Erskine]

Newer dropwire is like that, but the earlier stuff, much of which is still in use, is figure-of-eight single pair construction, often of copper-coated steel wires. It was supposedly run from pole to house with a few twists - to prevent it from whipping in the wind, rather than to reduce interference.

HTH -

[dom]

Most interesting - thanks.

I'll have a google about and see if I can find more info about that.

If anyone has links to material on that, please post them up!

[Peter Crosland]

You would better off asking in uk.telcom or uk.telecom.broadband.

Peter Crosland

[Tabby]

I would think you'd encounter all you've described, plus a great deal of untwisted pair, plus bad connections, plus long extensions with their capacitance and a few old fashioned inductive bells and wiring run next to bell circuits.

I hope you're including plenty of fallback modes, reduction in throughput is far less likely to cause contract end or dispute. Failure to implement such fallback modes is a real headache for some people, and ties up a lot of manhours and creates ill will.

NT

[Peter Parry]

As has been mentioned - Some BT dropwire is figure of 8 and nailed to walls which can get very wet so at RF the characteristics are very variable.. The most common wiring problem though is not found just in old houses but equally in new ones and it is where the electrician has been given the task of doing the internal phone wiring as well as the alarm wiring. Quite frequently they simply use alarm cable for both the alarm system and the telephone wiring. Alarm cable isn't twisted pair and unused cores (it is usually 6 or 8 core) are usually simply left to act as aerials. I've seen a set of 20 new flats with telephones wired with alarm cable.

Very long extension cables made of flat parallel laid cable are also common -often used because they can hide under carpets. The spare cable will be wound in a neat coil at one end!

[dom]

Good idea - I'll post there too.

Though I do also want to appeal to a large sample of people with a "man in the street" type opinion - and it is diy'ers that seem to uncover a lot of the OMG's!

[dom]

These boxes would be installed as a replacement master socket (similar to an ISDN line termination) - so at least the downstream effects of improvised phone-extension isn't something I have to reckon with in testing (it provides a POTS outlet, so what the consumer does with that is their own business).

Yes there are lots of lower-rate modes, although at this high bandwidth, mode changes involve quite a bit of adaptive jiggery-pokery and best avoided.

[dom]

Wow - thanks for that - I knew I would get some high-quality intelligence out of this group.

That possibility simply hadn't crossed the radar at all yet.

[MuddyMike]

Watch out for these.

?sort=0My phone line came into the house through this when we moved here 6 years ago, and I wondered why the broadband was a bit slow until I found this box and had the incoming cable re rerouted so as not to use this and the associated old cloth covered cable.

I left it in situ in the cupboard under the stairs as a novelty.

Mike

[dom]

Arrgh - I think I remember you posting this one a few months back!

You mean it isn't good for 400MHz+?

[Skipweasel]

I found some lead covered wiring leading to ceramic sockets at a friend's house. We left that for the same reasons, though it was in a loft she didn't know she had until we asked where the hatch went.

[MuddyMike]

I left a few of these in situ for the same reason. Must take a picture of ones I have cleaned up.

[Andy Champ]

Watch out for aluminium wiring too. Our entire estate (1980s?) is done with it. It has worse electrical properties, and is prone to joint corrosion.

Andy

[dom]

_MASK_i?a63jfAD$z_ [e-mail]...

I remember those as a kid in Rochdale!

[dom]

Yeah - might be worth seeing if I can get hold of an old spool of the stuff on ebay or something.

[Tabby]

the problem normally only shows up after years of service in applications where the cable heats up (and contracts). As it expands in the connector it squashes (deforms), so when it contracts its no longer gas tight. Aluminium loves to oxidise, and then you have a somewhat insulating oxide layer in the connection. Heating should never happen with phone wiring, so it should behave itself. Probably you could replicate the fault by heating the cable then clamping to it quite gently, but I'm not convinced there's a need.

NT

[dom]

Thanks to all for your replies on this one - very valuable feedback, and much appreciated.

[Dave Liquorice]

If you want to do the pikey thing I know where there is a few miles of 20 pair that could be "borrowed". Trouble is it's direct buried so would not be easy to pull out, might get BT to replace it with nice new copper though. B-)

[Dave Liquorice]

And it becomes brittle. The ali wire in the "jelly bean" can fracture at the IDC causing an open circuit but the insulation holds the wire in the bean so it looks OK. The fracture can happen with very little movement and stops POTS working, ADSL being RF can "leap the gap" but at much reduced speed.