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Laying underground cables

Men at work: laying underground cables, c1900

Changing technology : laying cable

Today laying telephone cable underground is still a strenuous job with the methods used surprisingly not changing much from those used in early days.

Originally a channel was dug into the ground along the route of a pre-planned network where a four-inch earthenware pipe would be laid. Depending on the needs of the network, either a wide or thin cable would be pulled through the pipe by rope, leaving some spare space for future use. A large gang of men would have to pull the cable, as it was so heavy.

Spare rope was left in the ducts for future cables, which today are frequently fibre optic. In fact the only differences now are that the gangs can use machinery to help pull the cables through and if rope is missing or broken, automatic duct motors are used to worm through the pipes threading new lengths.

Engineer working in cable tunnel

The underground network : lifting the cover off the manhole

Below the surface of Britain is a complex network of tunnels, pipes and cables, belonging not only to BT but also to all of the other utility companies such as the gas and electricity companies.

Under the pavement of every town and city lie the pipes and ducts that carry the local distribution network. Footways are peppered with small manhole covers that provide access to the system. Deeper down, closer to the phone exchanges, the network tunnels are wider but again can be accessed by manhole covers and usually need a ladder to climb the six feet to the bottom.

Cable going through ducts

Ferrets and other techniques : sometimes the old ways are the best

Blocked cable ducts can be a problem, especially if the blockage is 60 feet away from an opening. The best way to shift the obstruction is to attack the duct like a blocked drain with a very long pole.

A missing or broken draw rope can cause another major headache. In this case a duct motor is used to feed a replacement through. The motor looks like a barbell with two balloons at either end of a short pole. Twine is tied to the pole and the balloons are alternatively inflated inching the mechanism down the duct.

But the motor can take its time, and according to 'cable layers legend', it's said that the more enterprising engineers have tied string around the neck of a ferret and sent it chasing a rat along the duct to speed things up!

If none of these methods work the only answer might be to dig up the duct and start again from scratch.

Engineers laying underground cable, c1900

Digging difficulties : digging your way out of trouble

As soon as you sink a spade into the ground in a busy city centre the chances are it won't be far away from an underground cable and potential danger. The truth is, it's very crowded under the surface. There are cables of all varieties: telephone, electricity, and cable television as well as pipes from the gas and water companies, not forgetting underground walkways, drains, sewers, tunnels and underground trains.

Although all utility companies should have their cables mapped out, not every map is totally accurate, and not everyone checks the maps before they start digging. To try to reduce the impact of broken cables, BT launched a helpline for contractors to ring before they started work, so they could be on site to identify cables in advance, before they could be damaged. Not only was prevention cheaper than cure, but it meant that customers would not have their essential connections interrupted unnecessarily.

Engineer - (dangerous faults) : Alec Bonsall

Alec Bonsall was attracted to telecoms as a schoolboy during the Second World War, when he drove around in his uncle's van, who was a maintenance engineer for the PO Telephones.

His interest was spurred on by his hobby as a radio pirate working on RAF surplus equipment sold off cheaply after the war. He joined the GPO as a Special Faults Investigation Officer during the late 1940s.

He remembers that some of the faults he had to investigate had nothing to do with the phone but were caused by other domestic appliances with some shocking results

audio clip


I can remember being called out on a on a Sunday once and a lady said 'oh I'm so glad you've come'. She said 'Because the telephone bell keeps ringing'. Well unfortunately there was a stray mains current running up the earth and it was going through the bell. I checked it out and sure enough there was about two hundred and thirty volts AC coming up the earth so I informed the lady that she seemed to have got some electrical appliance that was giving trouble and I said 'is there anything specific that you've got on today that you don't normally have on?' As this is has only happened on a Sunday and she said 'well I've got the oven on'. So I said 'well could you just turn it off momentarily?' So she turned it off. It transpired that there was a fault on the electric cooker and at that moment an old gent stuck his head round the door and he said 'is that why I always get a shock when I'm in the bath Sunday mornings?' And I said 'well yes... you should see yourself lucky sir you're still with us'. But I said 'yes' so the lady switched her cooker off, the gentleman finished his bath and her telephone bell stopped buzzing.

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