Utility pole

Utility pole

A utility pole, telegraph pole, telephone pole, power (electricity) pole, or telegraph post is a pole used to support overhead electrical wires, cables, and optical fiber and associated equipment. They may carry both wires to distribute electric power for an electric utility, and communication cables for telecommunications networks. Electric power wires are routed overhead as a cheap way to keep them insulated from the ground, and out of contact with the public. Utility poles were first used in the mid-1800s with telegraph systems. They are used for lower voltage power distribution; higher voltage power transmission lines are suspended from metal towers called pylons.

History

Telegraph poles first became commonplace in the middle 19th century, carrying at first one steel wire, then in urban areas many. Most utility poles are made of wood pressure-treated with some type of preservative to keep away woodpeckers, insects, fungi, and fires. Many different types of trees can be used to make utility poles, including Douglas fir, Jack Pine, Lodgepole Pine, and Pacific Silver Fir. Western Red Cedar is also popular for its natural insecticidal properties and durability, though its higher price deters many utility companies. Despite the preservatives wood poles decay and have a life of approximately 25-50 years in UK conditions and therefore need regular inspections. Other common utility pole materials are steel and concrete, with composites (fibreglass) also becoming more prevalent. In some countries, for example the UK, telegraph poles have sets of brackets arranged in a standard pattern up the pole to act as hand and foot holds for those working on the equipment or connections atop the pole. In the USA such steps are usually provided only for the upper part of the pole; the lineman or other worker often uses climbing spikes to reach them. In the UK boots fitted with steel loops that go around the pole (known as “Scandinavian Climbers”) are also used for climbing poles.

The appearance of telecommunication poles has changed with technology through the 20th century, with for example the loss of the stereotypical but now redundant crossbeam used to mount rows of insulators for open wire telephone circuits. These more traditional poles can sometimes be seen unaltered beside non-electrified railways, or where no effort has been made to remove crossbeams not in use.

However in the countries of Eastern Europe, in Russia and in countries of the third world, there are still many utility poles carrying bare wires mounted on insulators not only along railway lines, but also along roads and sometimes even in urban areas. Errant traffic being uncommon on railways, their poles are usually less tall.

In the UK, much of the rural electricity distribution system is carried on wood poles. These normally carry electricity at 11 or 33kV (three phases) from 132kV substations supplied from super pylons to distribution substations or pole mounted transformers. The conductors on these are bare metal connected to the posts by insulators. Wood poles can also be used for LV distribution to customers.

Today utility poles may hold much more than the uninsulated thin copper wire that they originally supported. Thicker cables holding many twisted pair lines or coaxial cable or even fibre-optics may be carried. Simple analogue repeaters or other outside plant equipment have long been mounted against poles, and often new digital equipment for multiplexing/demultiplexing or digital repeaters may now be seen. In many places, as seen in the illustration, providers of electricity, television, telephone, street lighting, traffic signals and other services share poles, either in joint ownership or by renting space to each other. Such poles provide a safe gap between power lines on top and signal wires below.

Wooden utility poles and railroad ties are almost always treated with creosote to slow decomposition. This is also the most common way of preserving wood in the United States.

Throwing poles similar to utility poles is a traditional Scottish sport known as the caber toss.

British Telecom telegraph post markings

British Telecom posts are usually marked with the following information:

  • 'BT' - to mark it as a British Telecom UK Post
  • a horizontal line marking 3 metres from the bottom of the post
  • the pole length and size (eg. 9L implies a 9 metres long, light post)

The date on the pole is put on by the manufacturer and refers to the date the pole was "preserved" (treated to withstand the elements usually by using creosote).

Coordinates on pole labels

In some areas, utility pole name plates may provide valuable coordinate information: a poor man's GPS.

In other especially rural areas, even their simple sequential numbering still excels the local house numbering system in providing a means of communicating location information: "Turn left at Williams Main Line #43. My house is at pole #43-Left-7."

In East Anglia, EDF Energy Networks often add the Ordnance Survey Grid Reference coordinates of the pole or substation to the name sign.

Pole route

A pole route refers to a telephone link or electrical power line between two or more locations by way of an overhead cable suspended on wooden utility poles. This method of link is common especially in rural areas where burying the cables would be expensive. Another situation in which pole routes were extensively used were on the railways to link signal boxes. Traditionally (prior to around 1965) pole routes were built with open wires; this necessitated insulation when the wire passed over the pole, thus preventing the signal from becoming attenuated. To do this, cables were separated using spars with insulators spaced along them; in general four insulators were used per spar. Two such pole routes still exist on the UK rail network, one in the highlands of Scotland, and the other between Wymondham, Norfolk and Brandon in Suffolk, the latter being due for replacement in 2009.

Notes

See also

External links

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