It is obvious that conducting components within distribution switchgear have a high voltage potential difference both interphase and with respect to earth when in service. These components have to be securely mounted and fixed in position by using materials which are very poor conductors of electricity. These are known as insulating materials and form a range of components that are continually stressed throughout the whole life of the equipment. It is certain, therefore, that latent defects within insulating materials, due to inadequate selection, design or manufacture, will manifest themselves during the life of the equipment. It follows, therefore, that great care must be taken when designing insulation systems that are to be incorporated within distribution switchgear.

Insulating materials are, by definition, very poor conductors of electricity, which is why they are used to cover conductors, give support to busbars and other conductors, and, in a gaseous form, are used to fill compartments to provide both insulation and a dry, clean environment.