Undergrounding is a method of burying utility wires underground rather than running them on poles overhead. It is most often used for wires delivering electrical power, cable television, and telephone signals. Undergrounding protects wires from damage by wind but may make them more susceptible to damage from flooding. It tends to be more expensive than installing the same utility wires above ground. Although undergrounding prevents visual clutter from wires, it may have a greater effect on the environment than above-ground wires.
There are several methods of installing underground cables. The most commonly used are direct burying and deep bore tunnels. To direct bury wires, a trench must be dug that is about 5 feet (1.5 m) wide and 4 feet (1.2 m) deep. Cable is set into the trench and surrounded by tightly packed sand set in concrete. This is the least expensive undergrounding method.
To install cables in deep bore tunnels, tunnels must be dug at least 80 feet (about 24 m) below the surface of the earth. Bolted segments line the walls of the tunnel. This is a more expensive method because it requires careful engineering and specialized equipment. Two other methods, surface trough and cut and cover tunnels, are rarely used but may be an option in some areas.
Some land developers and land owners prefer undergrounding because it hides unsightly wires that might make the landscape less attractive. It also protects the wires against damage from wind and debris during extreme weather. Flooding, however, can threaten underground cables if the water seeps into the trough or tunnel where the cables are housed. All methods of undergrounding require that the cables eventually go above ground to power stations or switch boxes that must remain above ground so that they can be easily accessed by technicians. This means that, while extreme weather does not affect underground wires, it may still knock out services.
Underground cables are also more expensive to install than above-ground cables. Overhead cables are insulated by the air, while underground cables require layers of insulation. The thick insulation causes the cables to retain heat, so underground wires must be thicker than those used above ground to reduce the electrical resistance and heat produced. Digging and engineering costs also add to the overall expense of undergrounding.
The environmental effect of undergrounding should also be considered. Digging trenches creates noise, dust, and vibration that may disturb surrounding wildlife. Trenching methods also disrupt soil and vegetation that must be replaced.