Which mechanism is commonly used to prevent anti-two-blocking in a crane system?

• A. Wind speed sensor.
• B. Limit switches, sensors, or mechanical limits.
• C. Visual inspection.
• D. Load cell.

Answer: (B)

Preventing anti-two-blocking relies on detecting the position of the blocks and stopping hoist movement before the blocks can come together. Limit switches, sensors, or mechanical limits provide that position-detection and a built-in stop signal, so the hoist (and sometimes the trolley) is halted to keep the upper and lower blocks from contacting each other. This is a dedicated safety feature designed to automatically intervene based on travel limits.

Wind speed sensors relate to weather-related operating limits, not block separation. Visual inspection is a manual check and cannot reliably prevent a two-block condition in real time. A load cell measures weight on the hook but does not control the relative position of the blocks to prevent two-blocking.