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BT MULTI PAIR PAPER INSULATED TELEPHONE CABLE, 1970's
Telephone cable usually laid in sealed ducts, containing hundreds of wires all identified by a colour code system, the only insulation being paper.
Once installed all joints were made with molten lead wiped with a cloth similar to old lead plumbing, the cable itself had to be kept dry, and the ducts were pumped full of air to check for leaks regularly.
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- Your example, is of a local cable ( i.e. Exchange to Cabinet ).
Assuming there are four units in the 1st layer, this cable is either 1200/6 1/2lb.( 8 units second layer ),or 1400/4lb. ( 10 units second layer ) Paper Core Unit Twin ( PCUT ), lead sheeted. Most likely made by WT Henley London.
This type of sheeting was replaced by Polythene sheeting in 1964, so your example it probably of 1950 early 1960's vintage.
Confusingly the polythene sheeted cable was also designated PCUT Polythene Sheeted Paper-Core Unit Twin.
With regard to your other posters, the use of CO2 to pressurise cables was discontinued and replaced with desiccated air due to the danger of a fatal concentration of the gas building up in chambers in the event of a leak from the cable.
.......... annon, Ireland, 1st of May 2015
- All trunk and major cables were kept pressurized by a compressor and dryer at each exchange. If the pressure dropped an alarm would sound automatically. The location of a leak would be detected by taking pressure readings along the cable with a manometer and a graph drawn. Where the graph was lowest was approx where the leak would be.
There were only a few pairs that were colour coded, the rest were identified by their physical location within the cable.
.......... Bob Foudy, Cape Town RSA, 15th of November 2013
- Perhaps some was replaced with plastic, but my local distribution cabinet is still (2013) served by paper-insulated, lead-sheathed cables.
Unsurprisingly the quality of the lines is poor and attempting to run modern *DSL services on them is fraught with problems.
Anecdotally there is a lot of this stuff still in service nationwide.
.......... Alan Brown, Leatherhead UK, 10th of March 2013
- During the 1960's these lead sheathed paper covered cables were rapidly being replaced by TW plastic covered wires and TW plastic outer sheaths. All joints were pressure tested. Nevertheless we still had to go to a GPO Telephone Engineers school and learn 'plumbing' that was the same technique a plumber would use on water or sewer pipes. The hazards of working in GPO manholes were many, such as gas leaks from adjoining gas transmission pipes. Electrical cable and telephone cable were almost indistinguishable and the gas used to pressurize cable was not air but CO2.
.......... David Lisle, Birmingham, 1st of June 2011