What is the purpose of anti-two-block devices on cranes?

• A. Limit hoist rope travel
• B. Improve radio range
• C. Increase hoist speed
• D. Change load weight

Answer: (A)

Anti-two-block devices are safety interlocks that stop hoist motion when the hook block gets too close to the upper block. Their job is to limit how far the hoist rope can travel so the hook block cannot reach the upper block, which would cause two-blocking. When two-blocking happens, the rope can become crushed or jammed, the hoist can stall or overload, and the load can shift or drop, potentially causing equipment damage or injury. By sensing rope position or proximity and stopping hoist movement, these devices prevent that dangerous condition and keep crane operation safe. They don’t affect radio range, hoist speed, or load weight.