Hot Report: Undergrounding Electric Lines

OLR Report 2011-R-0338, written after Irene hit Connecticut, answers questions about putting power lines underground.

The report summarizes recent reports on undergrounding electric distribution lines prepared by public utility commissions in several states and a national study prepared by the Edison Electric Institute (EEI), the trade group of investor-owned electric utilities.

The primary benefits of placing new or existing distribution lines underground are that it reduces:

• the frequency of outages, particularly those caused by storms;
• the costs of post-storm restoration of the electric system;
• revenue losses for electric utilities resulting from these outages;
• the costs of tree trimming and other vegetation management and damages to electric facilities caused by vehicle crashes;
• the risk of the public coming in contact with live wires; and
• visual clutter.

The report points out that undergrounding is expensive. According to EEI, building a new overhead distribution line costs between $136,000 and $197,000 per mile, depending on several factors including population density of the area served (urban areas being the most expensive). The cost of new underground lines ranges between $409,000 and $559,000 per mile. The Virginia commission estimated the cost of new underground lines to be four to six times more expensive than new overhead lines. Undergrounding existing overhead facilities is even more expensive.

The Virginia commission found that “the relocation of currently existing overhead lines would result in tremendous costs and significant disruptions… [and] could take decades to complete.” It estimated that the cost of placing all existing electric distribution lines in the state underground would be about $83 billion or about $3,000 per customer per year. Undergrounding telecommunications lines statewide would cost an additional $11 billion. The Florida, Oklahoma, and North Carolina commissions made similar findings.

Several disadvantages to undergrounding besides costs are brought to light by the report. While underground lines experience fewer outages than overhead lines, it is more difficult to find faults on them than overhead lines and they take longer to repair. Underground lines are less capable of dealing with overloads and are more complicated to upgrade or modify.

Undergrounding in urban areas has several additional barriers. Underground lines need boxes for switches and other equipment. These boxes, which are located above ground, are typically six feet long, eight feet wide, and four feet high. In densely populated urban areas, there may be insufficient room in the existing utility easement for the boxes.

For more information, read the full report.