1-14. ELECTRICAL SYSTEM (CONT)
Figure 1-21. Material Handling Crane (MHC) System
h. Material Handling Crane (MHC). The primary electrical components of the MHC System are the remote control box
(1, Figure 1-21), junction box (2), overload shutdown box (3), tension load cell (4), left and right side jack cylinder
proximity sensors (5) and several function and lockout solenoids. When the operator selects an MHC function using
the remote control box, electrical current is sent through the junction box and to the appropriate solenoid. When
energized from the remote control box, the function solenoid controls hydraulic pressure to the function selected by the
operator. When the function solenoid is de-energized, hydraulic pressure is removed and the function stops. The
overload shutdown system controls the lockout solenoids. The lockout solenoids prevent operation of certain MHC
functions when an overload condition is sensed. Overload conditions are sensed, in combination, by the tension load
cell and a microprocessor inside the overload shutdown box which monitors boom angle and extension. When an
overload condition is sensed, the boom up/boom down, hoist up, telescope out functions are locked out. The hoist
down and telescope in functions will still operate and allow the operator to safely lower the load to the ground. When
the power switch on the remote control box is used as an emergency shutdown, all crane functions are locked out.
The left and right side jack cylinder proximity sensors prevent operation of the MHC until both jack cylinder outrigger
pads are lowered fully to the ground.