a. Single and multi-speed magnetic control of
squirrel cage motors.
b. Alternating current adjustable frequency control
of squirrel cage motors.
c. Direct current variable voltage control of shunt
wound ac motors.
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Electric-hydraulic [bridge] [trolley] brakes shall be dc shunt magnet type
equipped with hydraulic actuators manually-operated with a foot-operated
master control unit in the operator's cab, and electrically released with
the operation of the mainline contactor POWER-OFF pushbutton or power
failure. Remote control bleeders operable by pushbutton and foot pedal
shall be provided except for power-assisted brake systems. Remote control
bleeders shall be complete with pushbutton clearly labeled and located in
operator's cab where the operator can easily depress the pushbutton and
pump the brake simultaneously. In lieu of the combination
electric-hydraulic brakes, separate hydraulic and electric brakes may be
provided. Hydraulic brake system shall be designed to ensure equal
pressure at each brake cylinder.
2.4.5.2
Hoist Brake Time Delay
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NOTE: Delete this paragraph if one brake is
specified.
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One of the hoist holding brakes shall be provided with a time-delay setting
(from 1 to 3 seconds). The time-delay shall be initiated upon releasing
the control pushbutton or returning the master switch to OFF. Operation of
mainline POWER-OFF pushbutton or power failure shall result in each hoist
brake's setting without any time-delay.
2.4.5.3
Automatic Stop System
Electrically-controlled brakes shall be fail-safe spring set when power is
interrupted. Brakes shall be released with a mainline contactor POWER-OFF
pushbutton or a master switch for the associated drive. Brakes shall
automatically stop when there is a power failure. Electric shall be
designed to be mechanically released. Enclosures for electrical-controlled
brake components shall be NEMA ICS 6 Type [_____]. Direct current shunt
magnetic shoe brakes shall be provided with an electrical forcing circuit
for rapid release of brake. Each shunt coil brake shall be circuited for
both conductors to open simultaneously when the brake is de-energized.
2.4.6
Control System
A separate controller shall be provided for each motor; a duplex type for
2-motor bridge drives and a quadraplex type for 4-motor bridge drives on ac
central cranes. When 2-motor bridge drives are furnished and dc magnetic
control is required, dc series-connected motors shall be provided. When
4-motor bridge drives are furnished and dc magnetic control is required, dc
series-parallel connected motors shall be provided. Overload protection
shall be in conformance with requirements of NEMA ICS 2 and NFPA 70. When
contactors are used for starting, stopping and reversing, contactors shall
SECTION 14630A
Page 34
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