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switchgear is usually painted a light gray, ANSI Std. 70, using lacquer or enamel. Outdoor
switchgear is usually painted the same color inside, but the outside is painted a dark gray, ANSI
Std. 24. Epoxy paints may be necessary where corrosive atmospheres exist and special
protection is required. Outdoor switchgear is mounted on sill channels and the structure is
undercoated with a heavy coat of an asphalt material to prevent rusting.
(b) Metal-clad switchgear may be obtained for use indoors or in weatherproof
structures for outdoor use. The same comments that apply to outdoor metal-enclosed switchgear
(paragraph (a) above) apply to outdoor metal-clad switchgear. Outdoor switchgear may be used
to serve indoor loads when indoor space is limited, when corrosive or explosive atmospheres are
present inside the building, or when the indoor atmosphere is excessively dusty. Metal-clad
switchgear structures differ from the standard low-voltage switchgear structures in several
respects. By definition of metal-clad switchgear the circuit breakers must be of the removable
type. Circuit breakers must be enclosed, as in low-voltage switchgear, but buses, potential
transformers, control power transformers and cable terminals must also be enclosed in separate
metal compartments. All metal barriers must be grounded. Shutters must be provided, which
close automatically when a breaker is withdrawn, to prevent operators from contacting the
primary contacts or the bus which may be energized. Interlocks must also be provided to prevent
moving the breaker into or out of the connected position when it is closed and to prevent closing
the breaker when in an intermediate position. Instruments and relays may be mounted on the
door through which the breaker is inserted into the cubicle, but when this is done, a barrier must
be provided between the instruments and the breaker. Circuit breakers may be moved into the
connected position in metal-clad switchgear by either the horizontal-draw-out or the vertical-lift
method. When the horizontal-draw-out method is used, the breaker is moved horizontally into
position in the cubicle; then a racking mechanism is provided to force the breaker into the
operate position where the primary contacts are fully engaged. The secondary contacts for
control of the breaker must also be in contact. A test position is also provided where the
secondary contacts are separated from the primary contacts by a safe distance. Vertical-lift
breakers are moved into the cubicle beneath the stationary primary contacts, then raised with
either a manually or electrically operated hoist until the primary and secondary contacts are fully
engaged. To connect a breaker located outside the cubicle, a plug-jumper (replacing a test
position) is provided to control circuits in the switchgear for test breaker electrical operation. Mechanism. The mechanism of a circuit breaker is the complete assembly of
levers and other parts that actuates the moving contacts. The mechanism consists of two parts,
the tripping mechanism and the closing mechanism.
(a) The tripping mechanism is an electrically or mechanically operated device that
releases the contacts with a mousetrap like spring-driven snap action. The tripping mechanism
consists of an electromagnet (trip coil) acting as a trigger that releases a latch permitting the
breaker to open. The opening energy is normally supplied by accelerating springs that are
charged (compressed) when the breaker is closed. All circuit breakers are equipped with a


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