Overhead distribution wires are supported by large wood, steel, or concrete poles. However, wood is still the most common choice for economic reasons. The higher the voltage of the distribution line, the larger the distance electrical codes require between the wires and ground. There are a number of common construction methods used for distribution lines depending on the utility, the topography of the land, and the amount of right-of-way available for the pole location.
Distribution lines can be run on poles with or without cross-arms. A cross-arm is the smaller horizontal piece of wood attached near the top of the pole. Some styles of insulators require a cross arm to support them while other styles have fittings and hardware that allow the insulator to be supported directly off the main pole.
A common construction method in many utilities is to place a distribution voltage circuit underneath the transmission circuit thereby reducing the number of poles along roadways.. This is known as underbuild because the distribution line is supported underneath the transmission circuit.