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Question for Strowager!


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Hi there!

With your telecoms experience from the past, I'm wondering whether you might be able to identify an old cable type we have come across on a site. I'm not sure how old the cable is but suspect 20 years or thereabouts.

The cable is steel wire armoured covered in black PVC and internally a heavy PVC inner reveals 5 pairs of cables wrapped in clear cellophane or similar. The conductors are solid, not stranded and the diameter is about 1mm. The cable is marked as follows:-






It's not a "wet" cable and I'm looking to fit 300 metres of it or similar to re-route a section of the existing run as the current route runs through buildings that are going to be demolished. The colour code seems to follow a similar convention and the cable is currently running bi-directional RS422 via line drivers and Network Video Technologies composite video baluns quite happily.

Your advice would be much appreciated!

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Memory lane.... :)

Yes Cable, Armoured, Polythene.

Colour code was exactly what you've said, and you also have the colours in the right sequence, as they rotate around "the butt". - Blue - Orange - Green - Brown - Slate , with the accompanying twisted "b" leg in black.

99% of it was copper core, although they did try aluminium briefly, which was a disaster, reliability-wise.

All telecomms fixed cable, (as distinct from instrument cord flex), was solid core single strand.

Black sheathed cable was suitable for running undergound and also above ground, unlike the "natural" clear polythene type, which degraded in sunlight and could only therefore be used underground.

Advising on the transmission qualities for modern high frequency usage is very difficult, when I was designing with it, we only had to contend with analogue voice audio, up to about 20 khz. The fastest data use was "modemmed" into analogue, up to 9600 bps , back in the Prestel days.

Cables came in different weights, (pounds per mile of a single conductor), and we had to calculate the resistance drop from the exchange and use heavier weight conductor to compensate for excess distance. It's been over 40 years now, so I can't relate what poundage 1 mm diameter would be !

So, in summary, probably not as informative as you'd hoped, I can verify those physical qualities of the cable, but not how well 300 metres of it will perform conductively and capacitivly with that sort of signal use.

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Thanks very much Strowie!

I've certainly got all our cable suppliers in a whirl trying to find a modern day equivalent and the best responses go like "derrr, whaaat, never heard of it or anything like it"

To be honest, I think re-routing it with a Belden equivalent should work fine as some time ago, the original CCTV supplier re-routed another section using internal alarm wire (cable used to wire PIR's back to the panel) :o and currently, it works fine.

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I'm not surprised that cable suppliers have no knowledge of it !

Back in those days, the "GPO" had the monopoly on Public telephone service supply, so all of the cables were made exclusively for them by Plessey, STC etc..

The multi core cables were divided up into two basic groups, Internal and External. Your armoured cable with the black outer sheath was external, for burying direct in the ground or running exposed on walls.

The internal cable had a thinner, white or cream outer sheath and the same colour code and ranged from 2 pair up to "Cable, Equipment" sizes of hundreds of pairs, normally found in exchanges and large buildings with private exchanges.

As you say, modern internal alarm multi core cable is virtually identical electrically to internal phone wiring cable, with single core conductors of about the same weight, differing only in the colour code. It's only drawback is the relative fragility of the outer sheath.

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  • 2 years later...

I installed cables a bit like that in early nineties for MS Dos computer systems. I bet there are drums of it somewhere collecting dust. Happy hunting.


cheers Iain.


I'd hope that Jim had already been successful with his hunting Iain. :)


John exhumed that post from 2012 !


.....what a boring anorak I am on such topics !

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we use a similar type of cable as pilot cables to run alongside 22kV and 33kV cable routes to provide the intertripping of the protection for each end of the cable routes, these come with a number of twisted pairs in a steel wire armoured PVC cable. (generally though we default on 19 pair).


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