7.1 Scope

The next two chapters look at conductors the workhorse of the overhead line. Chapter 8 looks at the electrical choice for conductors and how to calculate what is required. This chapter, however, continues with the mechanical theme of chapter 6. The conductor that goes up must maintain its statutory clearance to ground for the next 40 or 50 years, whether cold or up to its maximum allowable operating temperature (normally 50 C but now often higher). Mechanical and metallurgical creep cause a conductor to stretch and so slacken off between the poles and this must be allowed for.

Conductors also take wind and ice loads and, within reason, should not break or be strained beyond their elastic limit under severe weather conditions. There is, therefore, a need to make further allowances e.g. use factors of safety.

Finally, not all lines are on level ground. Hills are always present and sag/tension calculations must take account of the fact that an intermediate pole may be on top of a hill or deep in a gully. This chapter therefore seeks to cover the most general aspects of conductor sag and tension calculations, including the weather loads and uneven ground and compares manual methods of line design with computer software design packages.

7.2 Conductor loadings