The Process of Installing Underground Cable to Serve Residential and Light Commercial Developments has gone through a tremendous evolution over the past 10 years at Avista Utilities, an Avista Corp. (Spokane, Washington, U.S.) company. Avista Utilities has seen an increase in the volume of new building lots nearly every year since 1998. This is especially true in the Idaho part of its service territory, so new methods of installation were needed to meet the demand. Through the 1990s, Avista also faced the huge task of replacing much of the underground cable that had been installed in the 1970s and early 1980s. The combination of these two situations drove the utility to the process it uses today.

NEGOTIATING WITH OTHER UTILITIES

Throughout the 1990s, Avista experienced a significant number of faults on its then-aging underground system. This prompted the utility to begin an aggressive cable-replacement program. At the same time, the Coeur d'Alene, Idaho, area was experiencing significant population growth. To handle the workload, the utility experimented with crew structure to come up with an efficient and economical method for the installation of conduit for both cable replacement and new development work.

It started with a conventional crew makeup of a foreman, lineman, equipment operator and groundmen, but this structure was expensive and not the best way to use the utility's highly skilled linemen. Avista also was looking at the inefficiencies caused by the scheduling process in coordination with the phone and cable TV companies and their crew availability.

On a job-by-job basis, Avista started negotiating with the other utilities to install their conduit into the utility's ditch on a $1/ft ($3.28/m) basis. The utility determined that it could adjust the crew structure, removing the lineman and adding groundmen as needed.

By having an agreement with the other utilities to install their conduit, and with its own company also delivering natural gas, Avista was able to control the ditch and give land developers and their construction companies one point of contact for the coordination of the installation of all the dry utilities. The efficiency of this process not only saved time during installation, but it also helped reduce the overall construction time needed for developers to complete their projects.

UPDATING AN OUTDATED PROCESS

The historical method of underground installation was to send a crew out with a trailer load of long radius sweeps, couplings and stick conduit in 20-ft (6-m) lengths. The crew would install it in the ditch along with the natural gas, and then wait for the phone and TV utility crews to come in and install their facilities (direct-buried cable). This was sometimes haphazardly thrown over the top of Avista's installation. When they were done, the electric utility would schedule its crew back, and they would set ground sleeves and secondary hand holes. Then, they would have to wait again for the phone and TV utility crews to install their pedestals before it could reschedule to have a setting and terminating crew come in to complete the development.

This process changed with the agreements that were reached with the phone and TV companies. By digging a wider ditch, Avista was able to have the required 1-ft (30-cm) separation between the gas, electric and communication utilities. This made for a more uniform installation in the ditch and at the property line where each utility maintained the same relative position at all locations.

In 2000, a demonstration of a continuous conduit trailer with a 3000-ft (914-m) capacity and a mounted McElroy Line Tamer contributed to the next increase of efficiency. With this device, Avista was able to pull out an entire run of all the utilities' conduit with a backhoe, saving time and effort. The Line Tamer takes the memory out of the coiled conduit, so that it lies straight and flat in the ditch. Once an entire run of conduit is installed, the crew follows and sweeps up the conduit at each facilities' location. While at the location, the crew also may set the electric facilities (ground sleeves and hand holes), eliminating one return visit. Once the developer has installed curbs and sidewalks, an underground line crew can be scheduled to install and terminate wire and transformers.

MULTIPLE BENEFITS REALIZED

In 2001, ARNCO (Knoxville, Tennessee, U.S.) demonstrated cable-placing equipment pushing underground primary cable into conduit. With the Maxx-Trak cable pusher #1, 15-kV jacketed cable can be pushed into a conduit at the rate of approximately 80 ft (27 m) per minute. This is considerably faster than the speed that the capstan can pull. Avista has had success at installing runs well over 1000 ft (305 m) with no signs of damage to the cable.

There are many benefits to using this method. The top two are time and money savings. The crew does not need to blow a string or rope into the duct to pull in a wire, saving time at each skipped step and also reducing the purchase of pulling string or tape. In one situation where Avista was installing a three-phase underground main line, the crew placed more than 30,000 ft (9144 m) of cable in one day.

A third benefit is reduced stress on the cable. The only force exerted on the cable is the mechanical pressure exerted by the belts used to push the cable into the conduit. This eliminates the pulling force that is normally exerted on the end of a cable from the pulling process. On longer or more difficult pulls, this force can cause the cable to continue to grow (elongate from inside the jacket) after the pull is completed. Recently, Avista was working with Southwire, which is developing a pushable 600-V triplexed cable, 4/0 PowerGlide that should reduce time needed for the installation of the secondary feeders.

The fourth benefit is for the men who install the cable, as there is no strenuous physical effort required. Avista's past practice included pushing mostly 4/0 secondary, hand over hand into the conduit, on short cable runs. The physical effort is now limited to attaching the pusher to the conduit system and holding it in place. Using the pusher has forced the utility to improve the quality of its conduit installation by examining each step from design to layout in the field. Avista collaborates with developers in how they stage their jobs, so utility crews can get in and out at times when the developers don't have equipment moving or open water or sewer ditches that interfere with the crews' work. Avista relies on the contractors to provide it with offset staking for elevation and property-line location before its crews set their facilities. These efforts result in an efficient, uniform and orderly ditch and facility location, which aids in reducing the number of conduit sweeps and increases the probability of successful installation of the cable and transformers.

WHAT'S NEXT?

In addition to implementing a pushable triplex wire, Avista is exploring equipment that would allow it to increase cable lengths. By having a completely mechanized method of handling the cable, the utility should be able to use larger reels. An increase from 3500-ft (1067-m) reel lengths of #1 primary to 5200 ft (1585 m) would provide a 30% reduction in handling, waste and disposal costs. The savings would be even larger with the secondary wire. Avista expects the reel size could be increased to accommodate 3000 ft (914 m) of 4/0 UG triplex compared to the 1000 ft (305 m) it currently uses.

It is the people who make the process work. Since this evolution began, Avista has benefited by having better relationships with its developers and communication utilities. The utility has gained from the open-minded attitude of the foremen and linemen who find a way to take new and unproven equipment and develop processes that support an efficient way to get the job done. Financially, Avista has found a process that subsidizes the installation of its own facilities.

The overwhelming majority of new facilities Avista installs each year are underground. The utility is adapting its construction standards and installation methods to reflect this change.

Jim Rosenlund has worked for Avista Utilities for 27 years, most of them in the Coeur d'Alene, Idaho, U.S. construction office. He began his career as an apprentice lineman, then journeyman lineman, and progressed to contract crew inspector, and then line serviceman. He has been general foreman for the past nine years. jim.rosenlund@avistacorp.com