This guide provides information regarding the planning, selection, specification, and life cycle management (installation, commissioning, operation, maintenance, decommissioning) of metal-enclosed gas insulated substations equipment (typically indoor) rated 1 kV to 52 kV. This guide is intended to supplement the information found in IEEE Std. C37.20.9TM and provide information for other medium voltage equipment or apparatus contained in the substation by providing guidance to users, specifiers, and purchasers. This guide does not cover outdoor substation equipment covered by other guides or standards such as outdoor circuit breakers, outdoor switches, or reclosers.