NCCCO Anti-Two-Block Devices and Safety Systems 4

Question 1

On a crane with multiple part-of-line configurations, the A2B device must be:

Accepted Answer

Capable of functioning correctly regardless of the number of parts of line

Answer

The A2B system must protect against two-blocking in all reeving configurations used on that crane.

Question 2

What immediate danger does two-blocking create for the wire rope?

Accepted Answer

The rope can be pulled over the sheave causing catastrophic failure

Answer

When two-blocking occurs, continued hoisting pulls the rope over or through the sheave, causing sudden rope failure and uncontrolled load drop.

Question 3

An A2B device must interrupt which crane functions when activated?

Accepted Answer

At minimum, hoist up and boom up and telescope out functions

Answer

ASME B30.5 requires A2B devices to interrupt hoist-up, boom-up, and boom-extension functions since each of these can worsen a two-block condition.

Question 4

Which condition can DEFEAT a weight-actuated A2B switch even when it is mechanically intact?

Accepted Answer

Wind blowing the hanging bob-weight sideways causing it to contact the boom

Answer

Strong wind can deflect the hanging bob-weight into contact with the boom structure, falsely triggering the A2B switch and halting operations.

Question 5

When a crane is equipped with a fly jib (boom extension), the A2B device must:

Accepted Answer

Protect both the main boom tip and the fly jib tip sheaves

Answer

Separate A2B protection is required at the fly jib tip because the hook block can two-block against the fly jib sheaves independently of the main boom.

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 4