Atmospheric pollution can be a serious problem for the insulators of outdoor e.h.v. substations, especially when situated near the coast, as it can lead to flashovers due to wet salt deposited as a result of storms. A method of maintaining such insulators in a condition to provide the required degree of security is the provision of automatic spray washing. Special attention to the design of insulator-washing installations is necessary to avoid creating the conditions for flashover when pollution deposits are wetted during washing, and also to keep capital and revenue costs to a reasonable minimum, to avoid creating difficulties of access for maintenance and to avoid increasing the area of the substation. This paper describes the basis of the CEGB design of automatic fixed washing installation and gives details. These include the measurement of pollution deposit, the effect of pollution and different types of insulator. The relationships between washing time, spray configuration and pressure, wash grouping, water storage, water conductivity, control facilities etc. are described. Operational experience is examined, and of particular interest is a graphical presentation of weather conditions and the automatic responses of a washing installation over a period of several days of severe storms.