This report gives the engineer guidelines for designing a high-quality underground distribution (UD) system. Before starting a design, the engineer must have comprehensive knowledge of the components of a UD system. Next, the engineer must understand how these components can be configured to form different types of UD systems and the special design concerns of each.


The use of underground distribution by electric co-ops continues to grow. The NRECA Strategic Analysis Department has determined that the percentage of co-op-owned distribution lines that are underground has more than tripled in 27 years from 5% in 1980 to 16% in 2007. In addition, the number of co-ops that have at least 50 miles of underground distribution has increased from 58% in 1995 to 79% as of 2007. Underground distribution will continue to rise as a percentage of total co-op distribution lines due to the strong preference for it in many rapidly growing suburban co-ops.


Since their introduction, UD systems have proved generally popular with electric consumers. Although some of this popularity is due to aesthetics—eliminating pole lines, overhead conductors, and the need for tree trimming—greater reliability is the greater attraction. Consumers facing outages due to wildlife, falling tree limbs, and ice storms believe underground systems are more desirable. Unfortunately, many of the present UD systems are less reliable and have more operational problems than overhead distribution systems. To reverse this trend, NRECA has created a comprehensive guide dedicated to designing underground distribution systems.


This 400+ page guide provides a step-by-step methodical approach to designing an underground distribution system. From selecting the cable to designing the conduit system, readers will be walked through each step of the design process. Topics such as ferroresonance, sectionalizing, cathodic protection, and more are covered in great detail. Checklists, sample specifications, and numerous examples help make the guide easy to read and easy to implement.




Engineering, operations, Underground, direct buried cable, conduit, padmount, sectionalizing