Please ID my cable!

[John]

Thank you sir, very kind of you :o)

The biggest cable size we use is 4,800-pair (so 9,600 individual conductors) but that's usually only on the exchange Main Distribution Frame (MDF) and it's usually jointed in the exchange cable chamber. As the cables leave there they are filled with compressed air at 9psi until the reach the green jointing cabinets that you see on street corners etc.

The reason for that is that once a cable is pressurized there should be no air flow (in theory at least). If there is a flow, it trips an alarm and pressure transducers along the cable route can then give a location of the air leak and, as the air leaks out it stops water from getting into the cable - and there can be a few feet of water in a manhole, I can tell you.

These cabinets can hold anywhere from 100-pairs in a rural location to about

1000-1500 in city centres and it's here that the E-side (exchange side) cables meet the D-side (distribution side) cables. D-side cables are filled with petroleum jelly to stop water ingress and can range in size from (IIRC) about 400-pairs down to a 20-pair going to the top of a telegraph pole or a 5-pair "garden leader" if your house is fed directly from underground.

Here's a couple of photos of a job I got called out on at about 6.00am after local vandals had set a cabinet alight:

Where would BT be likely to have used the aluminium cable? closer to me

Impossible to say I'm afraid mate

Unfortunately there's nothing you can do to get BT to change the cables, they'll just be changed when necessary - but rest assured it's in BTs interest in getting rid of all the ali cables.

John.

[RobertL]

cable:

> The cable doesn't seem to have any connection to the property per se,

My house also has a thick cable 9with 12 cores) coming up like that behind a metal cover. it splits into three at the top and one goes to my house and the other two went on along the ends of the rafters, just like you say, to my neighbours. . It is the current (active) BT cable!

Robert

[Andy Hall]

Ah, so that's still done. I can recall visiting our local exchange when I was a kid - must have been in about 1970 or just before. They had an open day with guided tours. It was still Strowger equipment and I can remember the hot oily smell where the equipment was. One of the engineers told me that he could pretty much pinpoint a selector that was going faulty or needed a tweak by wandering around and listening. Then they had a cabinet with a large mercury arc rectifier and a separate room with a large number of lead acid batteries that smelled distinctly unpleasant. Not long after that, diesel generators arrived, probably coincident with the miners strikes. I do remember them saying that they pressurised the cables, though.

fix this one?

However, be pleased that you don't work for Telkom in Johannesburg. They have a big problem in this regard. The main game is to get a pickup truck or to steal a tow truck with a hook on the back; then to go to a suitable manhole cover in the street. Hook goes on cable and drive off. Usually about 50m of cable follows. This is then taken to a suitable place and burned. Result is a respectable amount of copper which can be sold. They had hoped that the problem would tend to go away with the increasing use of fibre. Apparently not but nobody seems to know what the market would be. The best theory I heard was that the fibres could be used in lamps to be sold at the roadside.

Greater incidence of faults?

[John]

Hmm..... IIRC it took about 3 days to restore temporary service and about 2 weeks in total for the complete job, start to finish - but it was a few years ago so I may well be wrong :o)

I am, indeed, very glad I don't work there :o)

Yes - and, of course, broadband doesn't work as well with ali so they really are doing all they can to get rid of it. It just takes time 'cos there's still a fair bit of it underground yet.

John

[Andy Hall]

OK.

is there anyone that one can ask as to what the plans are in a given area?

[John]

Not that I know of Andy. It used to be so much easier when each area was under the control of the Telephone Manager, but hey, that's progress. I can only suggest the planning dept but how you'd go about contacting them I haven't got a clue. Sorry.

John

[Andy Hall]

I'll give it a go. I do have a few contacts in BT.

[Harry Bloomfield]

Andy Hall laid this down on his screen :

Yes...

It has been a while, but from memory they were identified by the way they are colour coded and the way the cores were served with a thin tape.

In the street boxes they were ID'ed by a number on a terminal block. Probably much easier now it is all electronic.

[Harry Bloomfield]

Yes and no....

Any cable will act in a similar manner to a transformer, in that they will pick up some voltage from their surroundings and it will show up on an high impedance digital voltmeter. So a better thing to use would be an analogue one on both AC and DC ranges.

[Harry Bloomfield]

The size was more a matter of being sufficiently robust, rather than its absolute current carrying capacity. As you probably know, alu is much more brittle than Cu. In current carrying capacity terms, the cable needed to be one size up on the copper to achieve the same capacity.

Aside from it oxidising, plus the poor connections, if the alu is larger diameter I would expect more crosstalk between the cores.

[Harry Bloomfield]

[e-mail] explained :

I would guess they would have to use a larger wire size, simply to make it sufficiently robust.

[Richard Conway]

In the street boxes they were ID'ed by a number on a terminal block.