This standard covers metal-enclosed interrupter (MEI) switchgear assemblies where air at ambient pressure is the primary insulating medium. Individual components within the switchgear may use other insulating means. The switchgear includes components such as interrupter switches; selector switches; power fuses; circuit breakers; control, instrumentation and metering devices; and protective equipment. MEI switchgear includes, but is not specifically limited to, equipment for the control and protection of apparatus used for distribution of electrical power. This standard is concerned with enclosed (rather than open), indoor and outdoor switchgear assemblies rated above 1 kV ac up to and including 48.3 kV ac. It includes equipment that is part of primary and secondary unit substations. It does not include gas-insulated substation equipment or switching devices mounted integrally within a transformer enclosure.