This standard applies to post insulators and post insulator units of ceramic material or glass intended for indoor or outdoor service, and to post insulators of organic material intended for indoor service in electrical installations or equipment operating on alternating current systems with a nominal voltage greater than 1 000 V and a frequency not greater than 100 Hz. It may also be regarded as a provisional standard for insulators for use on direct current systems. The insulators covered by this standard are primarily intended for use in isolators (disconnectors) or as bus-bar or fuse supports. This standard covers five types of post insulators: indoor post insulators of ceramic material or glass and with internal metal fittings; indoor post insulators of organic material and with internal metal fittings; outdoor cylindrical post insulators of ceramic material or glass and with internal metal fittings; outdoor cylindrical post insulators of ceramic material or glass and with external metal fittings; outdoor pedestal post insulators of ceramic material or glass. The term “cylindrical insulators?? is intended to cover insulators of the truncated conical form also. The five types of insulators are distinguished by their electrical, mechanical and dimensional characteristics. Figure 1, Figure 2, Figure 3, Figure 4 and Figure 5 illustrate typical examples of each type of insulator. These drawings are only general illustrations and other shapes and constructions are permitted.