Insulated aerial cables

Originally, overhead low-voltage (LV) networks, or first category structures, were made of bare copper conductors installed either on supports in rural or urban areas, or on fittings (posts, brackets) fixed to facades or roofs in urban areas. The conductors were insulated from their supports by means of insulators.

It was in 1955 that Électricité de France (EDF), to replace the old bare copper networks laid on façades that were becoming obsolete or inadequate, decided to use aerial twists made of insulated conductors, hence their first name of façades networks. Given the materials available at the time, these first twists had copper conductor cores, insulated with synthetic rubber and protected from the weather by a polychloroprene (Neoprene) sheath.

This method of construction seemed immediately interesting, and research was undertaken jointly by EDF's Distribution and Research departments, cable manufacturers, Aluminium Pechiney and the Syndicat des industries du matériel électrique to improve the technique and extend its application to rural areas. Overhead LV networks with insulated conductors are now widely used in France, where bare conductors are no longer installed.

However, in recent years, EDF's desire to bury more of its networks has led to a reduction in overhead techniques (notably bare networks) in favor of underground networks (particularly in built-up areas).

Given the experience acquired on bare conductor networks, the qualities required by the operator were as follows:

• maximum equipment reliability to ensure the best possible quality of service;

• as low-maintenance as possible;

• easy-to-use equipment;

• a service life similar to that of bare conductor lines;

• an overall cost at most equal to that of the bare-conductor line with the same transport capacity;

• improved safety for both personnel and third parties;

• ease of operation, especially when working under voltage.

This technique has also been developed for overhead medium-voltage (MV) networks, or second-category structures, but these are used on an exceptional basis (60 to 80 km per year) and are therefore not covered in the present dossier.