Main buses shall be three-phase [three-wire] [four-wire] with a continuous
current rating of [_____] amperes rms. [The neutral bus shall be rated for
[_____] amperes, continuous.] Switchgear ratings at 60 Hz shall be in
accordance with ANSI C37.06 and as follows:
Maximum voltage..................................[_____]
Nominal voltage class............................[_____]
BIL..............................................[_____]
Maximum symmetrical interrupting current.........[_____]
3-second short-time current......................[_____]
Continuous current...............................[_____] [as shown]
2.7.2
Circuit Breakers
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NOTE: Cell-mounted switches are seldom needed.
Circuits protected by vacuum and SF6 circuit
breakers are susceptible to multiple arc
re-ignitions and high transient recovery voltages
under certain conditions. The designer shall
evaluate the distribution system and provide surge
suppressors or other means recommended by the
manufacturer to minimize or eliminate these effects.
(Surge suppressors are normally added on the load
side of the switch.)
**************************************************************************
Circuit breakers shall comply with IEEE C37.04 and ANSI C37.06 and shall
consist of items listed for such units in NEMA SG 6. Where indicated, bus
or lug connections to mount field-installed, slip-on, medium-voltage cable
terminations for cable entering from below [and a flanged throat for direct
connection to the associated transformer] [and a bus throat for connection
to the associated metal-enclosed bus] [and roof bushings for aerial line
connections] shall be provided. [Roof bushings shall [have the same BIL
as] [be one BIL higher than] the associated switchgear and shall conform to
IEEE C57.19.00 and IEEE C57.19.01.] Circuit breakers shall be of the
[vacuum] [sulfur hexafluoride (SF6)] drawout type having electrically
charged, stored-energy mechanisms which are mechanically and electrically
trip free. A means for manual charging of each trip mechanism shall be
provided. Circuit breakers of the same ampere rating shall be
interchangeable, both mechanically and electrically. [Each circuit breaker
shall have a cell-mounted switch assembly for control and interlocking.]
[Cell switches may be connected either in parallel or in series with
control contacts that are used for interlocking, but either connection
shall permit operation of a circuit breaker when it is in a test position.]
In addition to any contacts used or shown, each circuit breaker shall be
provided with four spare auxiliary [and cell contacts], two normally open
and two normally closed, wired to interconnection terminals. If auxiliary
relays are used to provide additional contacts, such relays shall not be of
the latching type. Interconnection terminal blocks shall be wired to
permit remote open and close operations of each circuit breaker and for
other required exterior connections or connections between switchgear
sections.
SECTION 16311A
Page 41
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