UNDERGROUND CONSTRUCTION
CABLE TYPES

There were many types of cables used by the GPO and these are defined by the cable construction and insulation type and number of wires contained.

Many contained copper wires, but some cables feeding between main exchanges also contained Co-Axial wires.  Aluminium wire was used in the early 1970's but this was stopped due to continual breakages when joints were opened or cabinets worked on.

Some main cables also had repeaters (amplifiers) fitted en-route and some of the Co-Axial cables carried up to 130 volts DC power for repeaters.  When powered cables were worked on by jointers the power was deactivated by means of a token or key switch system.

Cables developed over the years that is why there are so many types.  Sheathings, originally Lead, were later made from Polythene  and PVC thus reducing weight, installation time and cost.

The wires inside the cable were also laid in different manners.  Originally the distribution cables had wires in pairs and the two wires were twisted together to prevent crosstalk with adjacent pairs. Multiple twin cables were then produced, mainly for trunk cables, with the two twisted pairs, twisted together to form a two-pair core or quad.

Star quad cable was then introduced and the four wires of each core are twisted together in one operation.  These were then packed together forming a compact cable of good capacity.

The documents below advise on some, but not all cable types used.

CABLE, PAPER-CORED, LEAD COVERED - Lines, Underground F1001
CABLE, PAPER-CORED, LEAD COVERED - CO-AXIAL - Lines, Underground F1005
CABLE, PAPER-CORED, LEAD COVERED - CONSTRUCTION TYPES - Lines, Underground F1020
CABLE, POLYTHENE - Lines, Underground F1058
CABLE, PVC No's 6, 7 and 8 - Lines, Underground F1045
OBSOLETE CABLES - Lines, Underground F1002

Cable Sample - 542/20 PCQT and comparison with co-axial cable

Cable samples 542/20 PCQT (audio), cable 4/370 DT1 x 2/20 PCQ and 16/20 PCT (4 tube coaxial)

Last revised: April 17, 2023