NCCCO - National Commission for the Certification of Crane Operators Load Moment Indicators and Safety Devices 1

Question 1

What is the primary function of an anti-two-block (ATB) device, and which crane movements does it typically arrest when activated?

Accepted Answer

It prevents the hook block from contacting the boom tip sheaves by automatically stopping hoist-up and boom-down movements

Answer

An ATB device uses a weight-and-switch assembly hung near the boom tip. When the rising hook block lifts the ATB weight, the circuit triggers and stops hoist-up and boom-down movements — the two motions that would drive the block further into the sheaves and cause catastrophic structural damage.

Question 2

How does operating a crane on an out-of-level surface most directly affect the accuracy of an LMI system?

Accepted Answer

It shifts the crane's center of gravity, increasing actual radius and causing the LMI to underestimate the load moment

Answer

Load moment is calculated as weight × horizontal radius. When a crane is not level, the true horizontal radius to the load increases beyond what a perfectly level setup would show, meaning the actual load moment is greater than the LMI may indicate — a direct safety hazard.

Question 3

When an LMI's audible alarm and warning light activate while a lift is in progress, the operator's FIRST required action is to:

Accepted Answer

Stop all crane motion immediately and assess the situation before any further movement

Answer

Stopping all crane motion is the mandatory first response to an LMI alarm. Any continued movement — even lowering — can change the load moment unpredictably. The operator must assess what triggered the alarm before deciding on a safe next action.

Question 4

In the load moment formula used by LMI systems, the load moment is the product of:

Accepted Answer

The gross load weight multiplied by the horizontal radius from the crane centerline to the load

Answer

Load moment = weight × horizontal radius. This is why radius is the dominant variable in crane stability calculations — doubling the radius doubles the overturning moment even if the load weight stays the same, which is why rated capacity decreases as radius increases on all load charts.

Question 5

When calculating the total suspended load for comparison against an LMI reading, the operator must include:

Accepted Answer

The cargo weight plus the combined weight of the hook block, ball, shackles, slings, and all other below-the-hook hardware

Answer

Rated capacity must not be exceeded by the total suspended load, which includes every item hanging from the boom tip: hook block, swivel, shackles, wire rope slings, spreader bars, and the load itself. Omitting rigging weight is a common cause of unintentional overloading.

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

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

NCCCO - National Commission for the Certification of Crane Operators Load Moment Indicators and Safety Devices 1