2.3.7.2
Hoist Control Brake
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NOTE: Mechanical load brake shall be allowed only
in MHI CMAA Class "A", "B" or "C" applications with
less than 6 m (20 foot) maximum lift height.
Mechanical load brakes provide poor control
characteristics under light loads relative to rated
load. Electrically controlled system breaking will
be used in MHI CMAA Class "D" and "E" applications.
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[Each hoist shall be equipped with an integral mechanical load brake of the
"Weston" type or multiple-disc type. Multiple disc-type brake shall be
provided with external adjustment for wear.] [Each hoist shall be provided
with electrically-controlled braking system to prevent overspeeding.]
2.3.7.3
Trolley Brake
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NOTE: 1. Coordinate selection of motor type with
selection of control type.
2.
Select applicable ac or dc control system.
3. Include micro-drive motors if micro-drive motors
are specified; otherwise delete.
4. If micro-drive is specified include clutches;
otherwise delete.
5. If dc control system specified, include sentence
concerning control rectifiers.
6. Include thyristors if dc variable specified;
otherwise delete.
7. Delete requirement for rectifier bridge if ac
control systems are used.
8. Select protective enclosure type. Enclosures
containing devices that produce excessive heat
(resistors) or ozone or devices that require cooling
for proper operation may require ventilation. Types
1, 2 and 3R may be ventilated or non-ventilated.
Type 12 enclosures are non-ventilated, but may
include sections and compartments that are
ventilated. Type 1 enclosures are normally
specified for indoor cranes. Type 3R enclosures are
normally specified for outdoor cranes. Type 12
enclosures are specified for exceptionally dirty
environments.
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[Trolley braking system shall be provided with spring-applied and
electrically-released shoe, disc, or conical brakes.] [Trolley braking
system shall be provided with electrically-operated and
hydraulically-operated shoe, disc, or conical brakes. Hydraulic portion of
braking system shall be designed so that the shoes will become disengaged
SECTION 14630A
Page 24
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