IEC 61850-3 is the part of the substation communication series that defines the general requirements that equipment must satisfy in order to be installed in a power utility automation environment. It is an equipment standard rather than a protocol standard: the protocol parts of the series specify how devices exchange information, while this part specifies the physical and environmental conditions in which they must operate reliably. Substation installations combine an unusually harsh electromagnetic environment with continuous duty; switching operations, fault currents, lightning and the high voltages present on the busbars all produce disturbances, while the equipment itself must remain available for decades because it carries protection and control functions. The standard therefore states requirements for the ambient temperature range, humidity, mechanical stress and seismic conditions, and a complete set of electromagnetic compatibility requirements including emission limits and immunity tests with levels derived from those in the basic EMC publications but increased where the substation environment demands it. Power supply requirements, including the tolerance to dips and interruptions on the station battery, are also specified.