MIL-HDBK-1038
sources of power. Timer type switches are used to limit the length of time
current is being drawn from the batteries.
4.5.24.2 Hook Load. Spotlights, trainable from within the operator's cab, are
provided on portal and floating cranes. The operator can use the spotlights to
illuminate the load under the hook.
4.5.24.3 Work Area. On portal and floating cranes, floodlights are mounted along
the boom to illuminate the work area beneath it. Mounting brackets for the
floodlights are designed to permit the floodlights to hang plumb at any boom
angle. The floodlights are switched from the operator's cab. Floodlights are
also mounted around the portal base or tub to illuminate the area about the crane.
These floodlights are also switched from the operator's cab.
On bridge cranes, floodlights are mounted along the bridge to illuminate
the floor area beneath the crane. The floodlights are spaced to match the
building's lighting fixture arrangement so as to compensate for the shadow cast by
the crane.
4.5.24.4 Aircraft Warning. If the highest location on a crane is more than 200
feet above the ground, aircraft warning lights must be installed there. If that
location is the tip of the boom, the control circuit for the warning lights is
designed to ensure that they are energized when the boom tip is 200 feet or more
above the ground and de-energized when it isn't. Local civil aviation authorities
may have more stringent rules if an airfield is located nearby. These lights
should be fed from the dedicated panelboard for equipment heater and battery
charger circuits.
4.5.25
Operator's Controls. Master switches or pendent station pushbuttons are
used to enable the crane operator to control the motors. In stepped control
systems, contacts in the master switch or pushbutton are configured to be closed
in various speed points to establish circuits energizing specific combinations of
relays and contactors to obtain designed motor performance. In infinitely
variable control systems, encoders, inductors, or rheostats provide the reference
signal for motor speed.
4.5.25.1 Pendent Pushbutton Stations. Pendent pushbutton stations are suspended
from bridge cranes for use by the operator. In addition to the pushbuttons needed
to control the speed and direction of each crane drive, POWER ON and POWER OFF
pushbuttons are provided to control the main line contactor. The drive control
pushbuttons are spring returned to the OFF position. A white POWER AVAILABLE and
a blue POWER ON indicating light, to indicate that there is power on the line and
load sides of the main line contactor, respectively, are also provided on the
station. A red MOTOR OVERTEMPERATURE indicating light may be there, also. There
is also a toggle switch to turn on the floodlights.
Pendent pushbutton station enclosures may be fabricated from plastic,
hard rubber, aluminum, or stainless steel and selected based upon the environment
in which they are used. All metal parts on the pendent pushbutton station must be
grounded.
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