A change in cable installation practices for Commonwealth Edison (Chicago, Illinois) is yielding a 25% to 30% savings over the traditional buried service cable. Since last fall, linemen have been installing 2/0 service cable in addition to the triplexed 4/0 Al cable (two 4/0 and one 2/0) in the field.

ComEd, which serves about 3.7 million customers across Northern Illinois, worked with Southwire (Carrollton, Georgia), which is ComEd's principle supplier of buried service cable. The vendor indicated that it furnishes a smaller 2/0 Al service cable (two 2/0 and one #1) to other large utilities. The smaller-gauge service cable is comprised of less metal, which ultimately drives the cost per foot.

The cable presents several key benefits to linemen including improved ergonomics, ease of installation and reduced cost.

Research and Development

Before installing the cable in the field, ComEd first collected data on typical new home installations. During the summer of 2008, the distribution standards engineers determined that the typical new single-family home in ComEd's service territory was about 2600 sq ft, and that the typical service length was less than 150 ft (85% of underground services installed in 2006 and 2007).

With these critical parameters, the engineers were able to evaluate the effects of voltage drop and flicker. This evaluation was essential because the Illinois Commerce Commission defines steady-state voltage levels. For residential customers, the maximum allowable voltage is 127 V and the minimum voltage is 113 V (this corresponds to a ±5.8% change on a nominal 120-V base).

Based on typical configurations, distribution standards engineers were able to approve the use of 2/0 service cable for use on 200-A services that are 150 ft or less in length.

Plan of Action

In order to be successful, the conversion required the completion of several steps. To achieve these changes, the engineers in distribution standards partnered with peers in the new business, methods and supply departments.

For example, ComEd had to validate annual cable usage and verify compatibility of the smaller size of cable with the customer information and management system. The utility also evaluated the service cable's thermal capability as well as the cost of the cable.

ComEd also had to revise its construction standards and Engineering Standard Practices prior to installing the new service cable in the field. The utility conveyed these changes to the linemen via field bulletins. That way, the field crews had the correct standards when installing the cable in residential applications.

Cable Installation

In October 2008, ComEd field crews began installing the Underground Residential Distribution (URD) service cables. ComEd's System Services Group (SSG) employees, including B-Techs Alex Aguilar and Anthony Scumaci, were some of the first employees to install the new 2/0 service cable last fall.

ComEd's SSG group focuses on the construction of new residential developments within the ComEd service territory. The field techs have been installing the cable throughout Illinois, and they have discovered many benefits of the smaller cable size.

First of all, the cable is lighter weight and easier to handle. Because the cable is easier to pull and terminate, it inflicts less stress on the worker's body. The new cable is stored on a smaller reel, so it is easier to load on the truck. Since the cable is 35% to 40% lighter than the traditional cable, it also can be installed by one, rather than two, workers in most situations.

The techs especially noticed the benefits in cold weather, when the cable is often hard to bend. When trying to manipulate the stiff cable, the workers can injure their arms and wrists.

The smaller size of the cable allows the techs to more easily install frost loops to help protect the cable in cold temperatures.

Despite its benefits, the smaller size of service cable cannot be installed in every residential application. Instead, it must be used only for new homes that have a single rather than a double-gang meter, and the home must have 200-A service or less. Since it is often difficult to determine what size of cable will be needed on the job, many of the line trucks carry both the 2/0 and 4/0 cable. One of the challenges the crews face in the field is that they must always have enough cable on hand. Many times, the builder may say that the house has a 200-A raceway, but when the techs arrive at the home, they find out that it is actually a 400-A raceway.

Investing in New Tools

When installing the new cable in the field, the techs needed a new tool to accommodate the URD service cable size. ComEd approved a new four-way cable insulation stripping tool to improve worker safety and productivity.

The new Ripley (Cromwell, Connecticut) tool is fitted with cable stripping heads in a 4×4 body style that match the all the common cable sizes used in new URD installations. This tool is fitted with stripping heads for the following service cable sizes: 350, 4/0, 2/0 and #1. This tool helps workers to accommodate the neutral cable and to strip the cable in the field regardless of its size.

In addition, ComEd also invested in a battery-operated crimping tool from Huskie Tools (Glendale Heights, Illinois) that works on both sizes of cables.

By investing in the new tools and changing work practices in the field, ComEd could save about $400,000 per year based on 2008 usage levels. While these are modest savings, they are scalable to cable usage. Due to economic factors, cable usage has been sharply declining since 2005. As the economy rebounds, ComEd can realize additional savings.

Tom Giardina (thomas.giardina@comed.com) is the field supervisor with Commonwealth Edison and has been with the company for 10 years. He is responsible for overseeing the construction crews that install URD mainline and service facilities for the new business department in ComEd's northern territory.

John Hans (john.hans@comed.com), a principal engineer in distribution standards for ComEd, earned his bachelor's degree in electrical engineering from the University of Illinois at Chicago in 1973. He joined ComEd shortly after graduation and has been involved in both distribution and transmission engineering activities. His responsibilities include material specifications, vendor approvals, material failure analysis, new product evaluation and field support.

Patrick O'Connor (patrick.o'connor@comed.com) is senior engineer in distribution standards for ComEd. He earned his bachelor's degree in mechanical engineering from Marquette University in 1970. He has been with the company for seven years and is responsible for material specifications, vendor approvals, material failure analysis, new product evaluation and field support.

Peter Tyschenko (peter.tyschenko@comed.com) is manager of distribution standards at ComEd. He earned his degree in electrical engineering from the University of Illinois at Chicago in 1990. He has been with ComEd for 18 years and is involved in field engineering, work management and reliability engineering.

AN INSIDE LOOK AT URD CONFIGURATIONS

A typical ComEd URD installation involves a compartmental, padmounted transformer serving secondary mains running in multiple directions to above-grade pedestals. The normal installation may include up to four pedestals served from one transformer, with a maximum of four homes served from each pedestal.

ComEd defines the cables running from the transformer to the pedestal as secondary mains. These are normally two 350 kcmil and one 4/0 neutral, or two 4/0 and one 2/0 neutral. The service cable runs from the pedestal to the house.

During the research and development process, ComEd focused on maintaining the existing secondary main sizes and evaluating the size of the service cable.