applications. The clutch housing is required to be of a type having convenient
access for visual inspection and designed to dissipate heat readily. Clutch
housings of hoist drives are required to be steel or ductile cast iron.
Electrical Criteria for Clutches. Power is not to be permitted to be
applied to a micro-drive unless the clutch is fully and positively engaged. If
the clutch should, for any reason, disengage during operation of the micro-drive,
main line contacts are required to be opened and all non-time delayed brakes to be
set. Application of power to the main motor is required to be prevented with the
Means are required to be provided to allow transfer to and from the
micro-speed mode of operation only when the master switch is/pushbuttons are in
the OFF position and all brakes have been set for not less than five seconds.
Transfer is then required to occur by energizing (or de-energizing) the clutch and
transferring master switch/pushbutton, electric brakes, and limit switch functions
to the control system associated with the selected mode.
A current sensing relay, is required to be utilized in series with the
clutch coil to verify energization/de-energization. The current sensing relay's
contacts are also required to be used to energize a (green) CLUTCH
ENGAGED pilot light in the operator's cab/on the pushbutton station when the
clutch is energized.
In addition, a speed responsive switch is required to be provided on the
main motor shaft to sense an overspeed condition of approximately 150 percent of
its speed in the micro-speed mode. The overspeed switch is required to be of a
design that is not damaged by normal operating speed of the main motor. The
overspeed switch is required to be utilized to energize a (green) MICRO SPEED
NORMAL pilot light in the operator's cab/on the pushbutton station. The light is
required to be illuminated whenever the drive speed is less than 150 percent of
the micro-speed mode speed in either normal or micro-speed mode. The overspeed
switch is required to cause the opening of the main line contact and the setting
of all non-time delayed brakes when an overspeed condition is sensed.
Gearmotors. Gearmotors are commercial off-the-shelf units with the motor
and gear reducer packaged into a single unit. The gear motor's overall rating is
American National Standards ANSI/AGMA 6019, American National Standard
for Gearmotors Using Spur, Helical, Herringbone, Straight Bevel, and Spiral Bevel
Gears, and ANSI/AGMA 6034, American National Standard, Practice for Enclosed
Cylindrical Worm Speed Reducers and Gearmotors, establish industry standard for
gearmotors with various types of gearing spur, helical, herringbone, straight
bevel, spiral bevel, and cylindrical worm.
Electrical. The National Electrical Code (NEC), crane industry standards
CMAA Specification Numbers 70 and 74, and ANSI/ASME HST-4M prescribe the criteria
that apply to virtually all electrical components of cranes. Some elements of
those design criteria are recommendations ("should" statements), but NCC policy is
to consider them mandatory. Design criteria are established for the following
electrical components of cranes: