scope:

The general information in this guide is intended to assist in evaluating the effect of solar radiation on outdoor metal-enclosed switchgear and is applicable to outdoor metal-enclosed power switchgear, control switchboards, and metal-enclosed bus. Specific data are given in current-temperature relationship and tabulation form for outdoor metal-enclosed low-voltage power circuit breaker switchgear, outdoor metalclad switchgear, and outdoor metal-enclosed interrupter switchgear.

Purpose

Switchgear will perform satisfactorily and have a reasonable life when operated within the temperature limits established in IEEE Std C37.20.1™-2002, IEEE Std C37.20.2™-1999, IEEE Std C37.20.3™-2001, IEEE Std C37.21™-1985, and IEEE Std C37.23™-1987. 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 capacity of outdoor metal-enclosed 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 will be made to point out the cumulative effect of these various influences.