hard-drawn copper, aluminum, or aluminum-alloy. Shop splices and tap
connections shall be brazed, pressure-welded or bolted. All splices
for field assembly shall be bolted. Where bolted connections are used,
contact surfaces shall be silver-plated except that contact surfaces
for aluminum-alloy may be tin-plated and shall be equipped with
provisions for adequate clamping. The buses shall be mounted on
insulating supports of wet process porcelain, glass polyester, or
suitable molded material. All primary connections including the power
connections to the line side of the circuit breakers shall be by bus
bar.
b. The standard phasing within equipment housing for AC power circuits
shall be A-B-C from left to right when facing the front of the
equipment, A-B-C from top to bottom, and A-B-C from front to back.
Nonstandard phasing in any compartment will be permitted only upon
approval and providing each phase is identified and a warning sign,
"Nonstandard Phasing," is incorporated within such a compartment.
c. Blank compartments without buses and small spare compartments with
buses and complete provisions for installing future feeder circuit
breakers shall be provided where shown.
2.5.4
Power Circuit Breakers
2.5.4.1
General
The power supply, bus tie, and feeder air circuit breakers shall be 3-pole,
dead-front, drawout type rated 600 volts AC, conforming to the requirements
of NEMA SG 6; IEEE C37.13; ANSI C37.16; and IEEE C37.17. All circuit
breakers of the same frame size and type of operation (electrical or
manual) shall be interchangeable. Suitable means shall be provided for
removing and handling the drawout circuit breakers. These means may
include support from the top of the switchgear enclosure without
interference with incoming or outgoing wiring. The Government reserves the
right to change the indicated current ratings, within frame limits, of the
tripping devices at the time the shop drawings are submitted for approval.
Overcurrent trip alarm contacts, with means for manual reset, shall be
furnished as indicated. Covers shall be provided over readily accessible
energized portions to prevent hazards to personnel when withdrawing or
inserting the breakers.
2.5.4.2
Power Supply and Bus Tie Circuit Breakers
The 2 power supply circuit breakers and the bus tie circuit breaker shall
be electrically-operated drawout type with the closing mechanism designed
for operation on 125 volts DC. The circuit breakers shall be rated 600
volts AC, [600] [1,600] [3,000] ampere frame size, [22,000] [42,000]
[65,000] amperes symmetrical interrupting capacity at 600 volts AC, with
continuous current ratings as indicated. Each circuit breaker shall be
provided with functional components in accordance with Table 1 of IEEE
C37.13, including means for manual emergency tripping and manual closing
for maintenance operation. Each power supply breaker and the bus tie
circuit breaker shall be provided with a solid-state direct-acting
over-current tripping device consisting of long-time-delay and
short-time-delay elements. The bus tie circuit breaker shall be furnished
without an overcurrent trip device but shall be provided with a 125-volt DC
shunt trip device. Long-time and short-time-delay operation bands shall be
selected to provide maximum selectivity between the primary supply
protective relays, power supply breakers, bus tie breaker, feeder breakers
SECTION 16404A
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