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depth description of Overhead Plant
In the early days of the telephone all cabling, once it had left the subscribers premises, went overhead back to the exchange. Originally this would have gone straight back to the exchange but as telephone numbers grew, so did the number of wires. Each line consisted of two wires and these were run to poles and tied to insulators.
The wires became a spiders nest on top of the exchange buildings and was unsightly. Poles in towns soon became over laden and wires could come into contact with trolley bus wires. So the wiring from the exchange to a local or distant distribution point went underground. Helped by technology the wires were reduced in size and underground cables became cheaper and more reliable.
Today the overhead distribution is generally fed from a local pole to a building. Pole routes are a thing of the past in most places, but where the route is long it may still be cost beneficial to run the wires overhead. Open copper/cadmium wires are no longer used as a twin wire cable called dropwire took over. This was replaced in the 1980's with a 4 wire cable that also consisted of steel strengthening wires.
Smallish wire derrick on the roof of an Exchange
Large wire derrick on the roof of Avenue Exchange, Lime
Street, London (1909)
Another roof top wire derrick - what a mess!
Pole top distribution - picture probably dated early 1960's as
this pole is well loaded
Mid 1960's with the older style ring but with new type drop wire
The above is two core overhead cable - called Dropwire
No.1 and No. 2 were
Dropwire was supported by clamps. The curly No. 3
is all you will see today.
Ring type distribution (2 rings in situ) on a pole that once had wooden
arms (note cut outs in pole).
Late 1960's ring type pole distribution with drop wire
Last revised: March 21, 2021