Harrington Hoists and Cranes (N)ER Load Limiter - ((N)ER1) - Manual (Page 8)

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2.4 Principle of Operation
Refer to Section 5.0 Parts List for diagram and parts names.
When a load is applied between the Plunger and the Casing, the Plunger acts to compress the Belleville
Spring. As the spring compresses, the Adjuster mounted on the Plunger Arm moves toward the Switch. If
the load is great enough, the spring will compress enough for the Adjuster to actuate the Switch. When the
Switch is actuated, it breaks the hoist’s lifting contactor control circuit.
2.5 Electrical Circuit
LL --- Load Limiter Switch
RY11 --- Self-hold relay
MC11 --- Lifting contactor coil
MC12 --- Lowering contactor coil
Note: MC contactors are mechanically
interlocked.
Fig. 2-2
When the load applied to the hoist exceeds the setting of the LL, the LL’s Switch will actuate. When the LL
Switch actuates, its contacts close. This energizes RY11. When RY11 energizes, contact RY11a closes
latching RY11, and RY11b opens disabling MC11. This interrupts the control circuit for the lifting contactor
coil MC11, which prevents any further lifting. The lowering contactor coil is unaffected by this, and lowering
the load is still possible.