IEEE/AIEE 955-1962

The general information in this Guide is applicable to all forms of outdoor metal-enclosed switchgear. Specific data are given in Figure 2 for outdoor metal-clad switchgear.* The many combinations of sizes and ratings in similar housings make it impractical to provide equivalent information for outdoor low-voltage metal-enclosed air circuit breaker switchgear. Data are not yet available for specific recommendations on outdoor cubicle-type switchgear, isolated phase bus, outdoor power circuit breakers and other switchgear equipment or components

Switchgear will perform satisfactorily and have a reasonable life when operated within the temperature limits established in American Standard C37.20-1955. In outdoor applications, the limiting temperatures result from the net effect of internal losses and external influences, principally the sun, wind, and local ambient temperatures. All of these must be considered in determining the current-carrying capability of outdoor metal-clad switchgear. when the gear is located outdoors, several additional factors require consideration. The effect of sun, wind, ventilation, ambient temperature, etc. on internal temperatures will be considered in this Guide. The magnitude of these factors will vary geographically and from season to season. The time relationship of maximum breaker loads with respect to maximum ambient temperature is important. IT IS NOT PRACTICAL TO DESIGN SWITCHGEAR ON THE BASIS THAT ALL ADVERSE FACTORS REACH THEIR MAXIMA COINCIDENT WITH MAXIMUM LOADS. IF THIS DOES NOT OCCUR, FULL CURRENT RATINGS MAY BE REALIZED. Recommendations will be made to point out the cumulative effect of these various influences.

Revision Standard - Inactive-Withdrawn. 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.