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The guide provides data in current-temperature and tabulation form for use in evaluating the effect of solar radiation on outdoor switchgear. The guide applies to switchgear as defined by IEEE Std C37.20.1, IEEE Std C37.20.2, IEEE Std C37.20.3 and IEEE Std C37.20.9; control switchboards as defined by IEEE Std C37.21; metal-enclosed bus as defined by IEEE Std C37.23; medium-voltage ac controllers as defined by UL 347; motor control centers as defined by UL 845; switchboards as defined by UL 891; and medium-voltage air-insulated circuit breakers for outdoor application defined by IEEE Std C37.04.


The purpose of this guide is to provide a reference for engineers to use to enable switchgear to perform satisfactorily and have a reasonable life expectancy when operated within the temperature limits established; for example, in the following standards: — IEEE Std C37.20.1™ — IEEE Std C37.20.2™ — IEEE Std C37.20.3™ — IEEE Std C37.20.9™ — IEEE Std C37.21™ — IEEE Std C37.23™ — UL 347 — UL 845 — UL 891 — IEEE Std C37.04™ These standards specify the temperature rise limits above a standard (maximum) ambient temperature of 40 °C. This is satisfactory for indoor applications where the temperature rise is due entirely to heat release (internal losses). 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 switchgear. The magnitude of these factors will vary geographically and from season to season. The time relationship of maximum circuit 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 are made to point out the cumulative effect of these various influences.


Revision Standard - Active - Draft. Information to assist in evaluating the effect of solar radiation on outdoor metal enclosed switchgear including metal-enclosed bus and control switchboards is provided in this guide. Specific data in the form of a continuous current capability factor for specific maximum monthly normal temperatures at the installation location to adjust the continuous current capability of outdoor metal-enclosed switchgear to the solar radiation condition required are given in this guide. Examples of maximum monthly normal temperatures along with sources for data for the US and for Canada are also presented in this guide.