Over the past several years, outdoor metal-clad switchgear has reached a position of widespread application comparable to that of indoor gear. Its satisfactory record for many years in cold, temperate, and hot climates has contributed to this increased usage. However, there are conditions affecting its application which are different from those for indoor gear and warrant special consideration.
This was realized and a study of the situation was undertaken by the AIEE Switchgear Assemblies Subcommittee. It was first determined that temperature data were not available on fully loaded units in the field. Outdoor laboratory and field testing was then tried, and it became evident, due to uncontrollable conditions, that accurate and complete data suitable for establishing the current-carrying capability of outdoor metal-clad switchgear could not be obtained. Next, indoor testing simulating outdoor conditions was resorted to. Further valuable data were accumulated, but there is still no absolute relationship between results obtained indoors and conditions existing outdoors. However, based on these investigations, sufficient data are now available for the preparation of a Guide for using outdoor metal-clad switchgear in various climates.