Anti two-blocking devices are electrical sensing devices, the CCR anti two block switch is compatible with most makes of cranes and provide either a 'NO' 'NC' 1Kohm, 4.7Kohm and 300ohm output.
They are installed on the crane to prevent the "headache ball" from hitting the sheave. If such contact causes the line to break, the man basket can tip or fall. The anti two-blocking device consists of a weighted ring around the hoist line; the ring is suspended on a chain from a limit switch that is attached to the boom tip. When the "headache ball" or hook assembly touches the suspended weighted ring, the switch opens and an alarm in the cab warns the operator to stop hoisting.
These anti two-blocking devices should be standard equipment on all cranes that are intended to lift personnel.
Currently, most new mobile hydraulic cranes are equipped with these devices. Employers who use older model cranes should establish which are to be used for lifting personnel platforms, then install an anti two-blocking device. This will help prevent serious man basket-related injuries and meet OSHA requirements. It is important to include this equipment on the operator's daily inspection log as well.