A
utility pole, alternately referred to as a
power pole,
telephone pole,
telegraph pole or
telegraph post, is a (usually wooden)
pole used to support overhead
wire,
cable,
fiber optic cable, and related equipment such as
transformers and
street lights. A single pole is often used to support both
electric power distribution lines and
telecommunications cables, as well as their associated equipment. Wire and cable are routed overhead as a relatively inexpensive way to keep them
insulated from the ground and each other, and out of contact with pedestrians or vehicles. Utility poles were first used in the mid-1800s with
telegraph systems.
Utility poles are commonly used to carry two types of electric power lines,[1] distribution lines (or "feeders") and subtransmission lines. Distribution lines carry power from local substations to customers. They generally carry voltages from 4.6 to 33 kilovolts (kV) for distances up to thirty miles, and include transformers to step the voltage down from the "primary" voltage of the lines to the lower "secondary" voltage used by the customer. Service drops carry this lower voltage to customers' premises. Subtransmission lines carry higher voltage power from regional substations to local substations. They usually carry 46 kV, 69 kV, or 115 kV for distances up to 60 miles. Higher voltage transmission lines are usually not supported by poles, but by metal pylons. For economic or practical reasons, such as to save space in urban areas, a distribution line is often carried on the same poles as a subtransmission line, but mounted under the higher voltage lines, a practice called "underbuild". Telecommunication cables are usually supported by the same poles that support the power lines, but may have their own dedicated poles.
Different length poles, up to 120 feet (36.6 m) or more, are used to satisfy clearance requirements, but the standard utility pole in the US is about 40 feet (12.2 m) long and is buried about 6 feet (1.8 m) in the ground, for a height above ground of about 34 feet (10.4 m).[2] They are spaced about 125 feet (38 m) apart. Joint use poles are usually owned by one utility, which leases space on it for other cables. In the USA the National Electrical Safety Code, published by the IEEE, sets the standards for construction and maintenance of utility poles and their equipment.
Most utility poles are made of wood, pressure-treated with some type of preservative for protection against rot, fungi and insects. Southern Yellow Pine is the most widely used species in the United States, however many species of long straight trees are used to make utility poles, including Douglas fir, Jack Pine, Lodgepole Pine, Western Red Cedar and Pacific Silver Fir. Traditionally the preservative used was creosote, but due to environmental concerns, alternatives such as pentachlorophenol, copper naphthenate and borates are becoming widespread in the US. For over 100 years the American Wood Protection Association (AWPA) has developed the standards for preserving wood utility poles. Despite the preservatives, wood poles decay and have a life of approximately 25-50 years, depending on climate and soil conditions, therefore requiring regular inspection and remedial preservative treatments.[3][4][5] Other common utility pole materials are steel and concrete, with composites (fibreglass) also becoming more prevalent.
