The differences between overhead and underground power lines
There are two methods of installing the power lines that carry electricity to your home, overhead and underground. Our members sometimes ask why we use one versus the other, or more to the point, why all power lines are not installed using the underground construction method. Isn’t one method better than the other? These are great questions, and the answer is that each method has its place.
Overhead line construction starts with the setting of utility poles. Poles can be set in nearly any type of terrain, even rocky areas. In the case of heavy rock, special equipment is used to augur out the hole. If placement occurs in boggy or wet terrain, many techniques are available to set poles securely. Once the poles are in place, wires can be strung and then equipment –– like transformers, fuses and reclosers –– are installed. Power can now flow.
Underground line construction requires digging a trench that is deep enough to keep the lines well away from surface activities. Where the terrain is extremely rocky, underground lines may not be an option. Next, wires are laid in the trench directly or placed in conduits for protection. The trench is filled in, and the surface is restored to its original condition. Padmount transformers and additional equipment are installed as needed, now the system is ready to deliver electricity.
Let’s take a look at some the advantages and disadvantages of each construction method, beginning with overhead.
• Lower cost, quicker construction, easier to spot damage and faults, less expensive to repair and upgrade, can be built anywhere, any voltage can be placed overhead.
• Susceptible to wind, ice and snow; more vulnerable to damage from trees and vegetation, which requires right of way trimming; vulnerable to blinks when animals and branches contact lines; susceptible to damage from vehicle collisions; less attractive.
• Not vulnerable to damage from tree branches; no right of way trimming required; less susceptible to damage from vehicle collisions; not impacted by wind, ice and snow; less vulnerable to blinks when animals and branches contact lines.
• More expensive to build; susceptible to flooding; difficult to locate faults; expensive to repair; fed by overhead lines at some point, making the lines vulnerable to outages and interruptions; limitations on voltages that can be buried underground; can be vulnerable to dig-ins.
Determining if power lines should be overhead or underground boils down to what is best for the situation. Underground lines might be ideal in situations where there is a desire to keep the poles and wires out of sight, such as a residential neighborhood, park or historical area. There are many cities and towns that construct only underground lines for a variety of reasons.
Overhead systems work well when appearance is not a major concern. Examples include extremely long line distances across country, where the voltages are higher than the limitations set for underground lines.
The ultimate mix of underground and overhead construction used by your electric co-op provides you, our members, with the highest possible quality of service at the lowest possible price. Cost, appearance, reliability, maintenance and future upgrades will drive which is the better approach, overhead or underground.