IEEE C37.20.2-1993 pdf free.IEEE Standard for Metal-Clad and Station-Type Cubicle Switchgear.
IEEE C37.20.2 metal-clad switchgear (MC):Switchgear that is characterized by the following necessary features:
a)The main switching and interrupting device is of the removable (drawout) type arranged with a mechanism for moving it physically between connected and disconnected positions and equipped with self-aligning andself-coupling primary disconnecting devices and disconnectable control wiring connections.
b)Major parts of the primary circuit,that is, the circuit switching or interrupting devices，buses，voltage transformers, and control power transformers, are completely enclosed by grounded metal barriers, that haveno intentional openings between compartments. Specifically included is a metal barrier in front of, or a partof，the circuit interrupting device to ensure that,when in the connected position,no primary circuitcomponents are exposed by the opening of a door.
c) All live parts are enclosed within grounded metal compartments.
d)Automatic shutters that cover primary circuit elements when the removable element is in the disconnected,test, or removed position.
e) Primary bus conductors and connections are covered with insulating material throughout.
f)Mechanical interlocks are provided for proper operating sequence under normal operating conditions.
g) Instruments，meters，relays，secondary control devices and their wiring are isolated by grounded metal barriers from all primary circuit elements with the exception of short lengths of wire such as at instrumenttransformer terminals.
h) The door through which the circuit-interrupting device is inserted into the housing may serve as an instrument or relay panel, and may also provide access to a secondary or control compartment within the housing.
The mechanical ratings of current transformers shall be such that they will successfully withstand the momentarycurrent for which the associated circuit interrupting devices are applied. When the primary circuit is protected bycurrent-limiting fuses, the current transformers shall successfully withstand the maximum let-through current of thefuses.Unless specifically limited to a shorter time by the associated protective equipment, the duration of the shortcircuit shall be considered as being 10 cycles.
The thermal ratings of current transformers shall be such that they will successfully withstand the short-circuit currentfor which the associated circuit interrupting devices are applied. When the primary circuit is protected by fuses, thecurrent transformers shall successfully withstand the maximum ‘t of the fuses.Unless specifically limited to a shortertime by the associated protective equipment, the duration of the short circuit shall be considered as 1 s.IEEE C37.20.2 pdf download.