From Over to Under

It’s a question invariably asked after severe weather or other disasters knock out electrical power. Of course, much of today’s electrical distribution lines already are underground—power companies have routinely buried services and often feeders in new developments since the 1970s. A study prepared for the Edison Electric Institute (EEI) released last summer reported that electric utilities are placing a significant number of power lines underground and that over the past 13 years, about half the capital expenditures of investor-owned utilities in the United States for transmission and distribution lines have been to place cable underground.

However, in older neighborhoods in most American cities, distribution lines—many long past due for replacement—remain suspended from utility poles, often in areas with many trees, and these are the lines usually most vulnerable to wind and ice storms. Even when aerial lines are replaced because they no longer provide dependable service, they often are again suspended from poles, rather than buried.

Higher costs of underground construction is the primary reason power providers usually give for not putting more electrical cable underground. But in areas that have experienced frequent weather-related outages, consumers and some regulatory agencies are asking at what point it becomes more cost effective to bury more cable, rather than incur costs of repeatedly repairing and replacing the same aerial infrastructure.

In December 2007, an ice storm passed through much of the central Plains and Midwest, causing extensive damage. Worst hit was Oklahoma, where about 620,000 customers were left without electrical service. Another 350,000 homes and businesses suffered outages in Kansas, Missouri, Iowa and Illinois.

Consumers again asked why power companies have not buried more electrical lines. Also wanting to know is the Oklahoma Corporation Commission (OCC), the agency that regulates public utilities in the state. On December 12, the commission announced its intention to undertake a study about the feasibility and costs of moving more aerial power lines underground.

Commission Chairman Jeff Cloud said at the time that the immediate focus obviously was to restore power, but looking ahead, he asked utilities under OCC jurisdiction to work with the commission to investigate the feasibility of moving more lines underground.

“While many new power lines are being run underground,” Cloud said, “there has been only limited movement in regards to moving existing overhead lines.”

A public hearing on the issue was held early in January after power had been restored. A standing-room-only crowd heard utility providers report on storm damage and restoration of service and address the aerial-to-underground issue. Immediately after the hearing, OCC staff began seeking information about costs and benefits of converting aerial power lines to underground in order to realistically assess the feasibility of burying more lines.

Fact-finding process continues

“We have sent questions to other state public utility commissions,” said Matt Skinner, OCC spokesman. “We also are sending extensive data requests to the investor-owned utilities and price-regulated co-ops.” Skinner said a second round of follow-up questions to other state regulators followed receipt of the first responses.

“In the meantime,” he said, “we are meeting with the Oklahoma Climatological Survey to get long-term weather information, contacting equipment manufacturers, and getting economic information from the State Tax Commission and Employment Security Commission.”

Once sufficient data are gathered, the OCC staff will prepare a white paper for the three-member commission. The commission’s investigation will be aided by information it already has about the aerial-to-underground conversion program currently under way by Public Service Co. of Oklahoma (PSO), one of the state’s two largest public power companies. The PSO program is a result of a cooperative process among the utility, its customers, the city of Tulsa and other municipalities involved.

Skinner said the commission also is aware of a program in the Oklahoma City suburb of Edmond where the city-owned power provider (which is not under the jurisdiction of the OCC) has converted two neighborhoods from aerial to underground, a direct result of damages caused by previous ice storms.

Underground program

Public Service Co. of Oklahoma (PSO), a business unit of American Electric Power, provides electricity for metropolitan Tulsa and portions of eastern and southwestern Oklahoma.

As part of a reliability-improvement program, PSO has either completed conversion, or begun construction to convert aerial to underground power lines in 26 neighborhoods, most in the Tulsa metropolitan area, said Stan Whiteford, PSO spokesman.

Whiteford said anecdotal information from the recent storm indicates areas where conversions are complete experienced fewer outages and that, for those where power was lost, it was restored sooner than other neighbors.

The PSO program has two key elements: trimming of trees around power lines on a regular basis and converting aerial cable to underground. The average cost for underground construction is approximately $580,000 per mile, Whiteford said.

Certainly the amount represents a significant expenditure, but it is significantly less than the “up to $1 million per mile” figure often cited by utilities, sometimes as a justification for not undertaking aerial-to-underground projects.

Proponents for burying more power cable point out that one problem with using the $1 million-a-mile estimate or citing other “average” costs is not specifying what is included in the estimate. Every project is different, and actual costs are influenced by many factors, including what lines actually go underground.

PSO conversions leave feeder lines on poles and replace back-lot aerial laterals and service lines with new underground cable at the front of the property. Most underground cable is buried primarily by horizontal directional drilling, which limits the amount of excavation required and reduces surface restoration needed after cable is in the ground.

“Because feeders usually are on poles along street right-of-way and are easy to access, they are not buried,” Whiteford said. “The problems in areas we convert relate directly to heavy tree growth and difficulty accessing rear lots.”

Laterals are buried in front right-of-way, usually within 8 feet of the curb.

“We place a 2-by-2-by-3-foot, pad-mount transformer every three or four houses,” Whiteford said. “We directionally drill services to each house and replace existing meters with RF meters, which are read from the street. When a neighborhood is complete, we never have to go in the back yard again. All future repairs can be made in the front. Whether the access service point is a transformer or flush-mount pedestal, repairs are much quicker with less impact to the homeowner. No worry about downed lines. No locked gates. No dog bites.”

During planning stages of the reliability-enhancement program, PSO evaluated neighborhoods to identify the best candidates for replacing aerial lines underground.

“Most of those selected,” he said, “are older neighborhoods, usually with many old, large trees. In looking at the process we identified between 700 and 800 miles of overhead distribution cable that converting to underground would have a significant impact to improving reliability.”

Criteria considered when targeting areas were the following:

• Accessibility: Without alleys in the city, back yards can be difficult to access for repairs.

• Terrain: Is it conducive to directional drilling? Planners wanted to use this technique and avoid trenching.

• History of reliability

“For the first underground conversion,” Whiteford said, “we selected an area that was reasonably representative of the city—one where trees were causing problems, but not one of the worst areas in terms of reliability problems. It was a good starting point.”

Considering all factors, Whiteford said PSO is pleased with progress.

“We have converted roughly 65 miles of aerial cable to underground,” he said. “And we believe we are getting better at it as we proceed. Engineering is more nailed down. Contractor crews are more efficient.”

PSO currently uses three contractors for underground conversions, all working on a turnkey basis. In some instances, contractors make connections and perform other tasks in addition to burying cable.

“Much of the time is spent coordinating with other utilities and the city,” Whiteford said. “Existing utilities must be located and marked. Typically natural gas lines are in the back yards, so they are not an issue for work we do in the front. Soil conditions are suitable to directional drilling. We have encountered rock in a few areas, but for the most part, drilling is not difficult.”

The OCC has provided PSO a mechanism for the expenditure of $20 million per year for the capital investment in the underground program.

Whiteford said costs are submitted to the commission quarterly and must be reviewed and approved before customers are billed. The cost for the overall reliability program, including tree trimming on a four-year cycle and conversions to underground, is about $2 per month with less than half that amount going to underground costs.

Whiteford said reaction feedback to PSO is that most residents are pleased with the underground conversions.

“We had complaints in two neighborhoods where the objection was placing boxes in the front yard,” he said. “In one area, property owners mounted a ‘Stop the Box’ campaign, urging the boxes be placed in back yards.”

Plans for converting both areas to underground were dropped.

As planned, PSO’s conversion program will take 25 years to complete. However, company representatives have advised the commission that the time could be reduced by approximately half if a proposed accelerated program is approved. The additional cost to accomplish that would be initially adding 25 cents to monthly bills.

The state’s other major power provider, Oklahoma Gas and Electric Co. (OG&E), serving metropolitan Oklahoma City and parts of central and western Oklahoma, has no active program to convert aerial power lines to underground.

In a statement issued following the January OCC hearing, OG&E spokesman Brian Alford said OG&E supports the commission’s decision to investigate converting aerial power cable to underground and wants to be involved.

OG&E did not respond to an invitation to provide information for this report.

GRIFFIN, a construction and tools writer from Oklahoma City, can be reached at 405.748.5256 or


About the Author

Jeff Griffin

Construction Journalist

Jeff Griffin, a construction and tools writer from Oklahoma City, can be reached at

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