NCCCO Anti-Two-Block Devices and Safety Systems 5

Question 1

Which of the following is a recognized method for manually testing an A2B device without risking actual two-blocking?

Accepted Answer

Manually lift the bob-weight or actuating device by hand to simulate contact

Answer

Manually lifting the bob-weight simulates the hook block making contact with the boom tip and verifies the switch cuts out the controlled functions safely.

Question 2

A crane operator notices the A2B indicator light is on but the crane is not near two-block condition. The MOST likely cause is:

Accepted Answer

A damaged or shorted wire in the A2B circuit

Answer

A constant A2B warning when the hook is well below the boom tip usually indicates a wiring fault, damaged switch, or short circuit in the A2B system.

Question 3

What is the primary reason crane manufacturers require A2B devices to cut out BOOM UP as well as HOIST UP?

Accepted Answer

Raising the boom reduces the vertical distance between the hook block and boom tip

Answer

As the boom angle increases, the geometry of the crane shortens the effective distance between the hook block and the boom tip, potentially causing two-blocking.

Question 4

During a pre-shift inspection, the operator finds the A2B bob-weight is missing from the load block. The correct action is:

Accepted Answer

Remove the crane from service until the A2B device is restored

Answer

A missing or non-functional A2B component renders the safety system inoperable; the crane must be taken out of service until the device is repaired.

Question 5

In a luffing jib crane configuration, two-blocking risk is GREATEST when:

Accepted Answer

The luffing jib is at its lowest angle and the hook is being raised

Answer

At low luffing jib angles, the tip sheave is close to the hook block's maximum reach, making two-blocking easier to trigger when hoisting.

NCCCO (National Commission for the Certification of Crane Operators) Practice Test

NCCCO (National Commission for the Certification of Crane Operators) Practice Test

NCCCO Anti-Two-Block Devices and Safety Systems 5