A utility pole is a pole used to support overhead power lines and various other public utilities, such as cable, fibre optic cable, and related equipment such as transformers and street lights. It can be referred to as a transmission pole, telephone pole, telecommunication pole, power pole, hydro pole,1 telegraph pole, or telegraph post, depending on its application. A stobie pole is a multi-purpose pole made of two steel joists held apart by a slab of concrete in the middle, generally found in South Australia. Electrical cable is routed overhead as an inexpensive way to keep it insulated from the ground and out of the way of people and vehicles. Utility poles can be made of wood, metal, concrete, or composites like fiberglass, and are used for distribution and transmission voltages.
(video) Three aerial work platform trucks work together on utility poles, in Bunkyo, Japan.
Utility poles were first used in the mid-19th century with telegraph systems, starting with Samuel Morse who attempted to bury a line between Baltimore and Washington, D.C., but moved it aboveground when this system proved faulty.
In 1844, the United States Congress granted Samuel Morse $30,000 to build a 40-mile telegraph line between Baltimore, Maryland and Washington, D.C. Morse began by having a lead-sheathed cable made. After laying seven miles underground, he tested it. He found so many faults with this system that he dug up his cable, stripped off its sheath, bought poles and strung his wires overhead. On February 7, 1844, Morse inserted the following advertisement in the Washington newspaper: “Sealed proposals will be received by the undersigned for furnishing 700 straight and sound chestnut posts with the bark on and of the following dimensions to wit: ‘Each post must not be less than eight inches in diameter at the butt and tapering to five or six inches at the top. Six hundred and eighty of said posts to be 24 feet in length, and 20 of them 30 feet in length.’” One of the early Bell System lines was the Washington DC-Norfolk line which was for the most part, square sawn tapered poles of yellow pine probably treated to refusal with creosote. “Treated to refusal” means that the manufacturer forces preservatives into the wood, until it refuses to accept more, but performance is not guaranteed.8 Some of these were still in service after 80 years.9
However, in Eastern Europe, Russia, and third world countries, many utility poles still carry 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 United States electricity is predominately carried on unshielded aluminum conductors wound around a solid steel core and affixed to rated insulators made from glass, ceramic, or poly. Telephone, CATV and Fiber Optic cables are generally attached directly to the pole without insulators.
In the United Kingdom, much of the rural electricity distribution system is carried on wood poles. These normally carry electricity at 11 or 33 kV (three phases) from 132 kV substations supplied from 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 low voltage distribution to customers.Read more