NCCER Crane Load Charts & Rigging Principles 4

Question 1

What is the primary reason crane manufacturers provide separate load charts for different counterweight configurations?

Accepted Answer

Counterweight mass directly affects the crane's stability and therefore its rated lifting capacity

Answer

Counterweight provides the righting moment that balances the lifted load; more counterweight generally increases stability and allows higher rated capacities at greater radii.

Question 2

When a load must be rigged using a spreader bar, what is the primary advantage over a standard multi-leg sling bridle?

Accepted Answer

A spreader bar eliminates inward compressive forces on the load from inclined sling legs

Answer

A spreader bar keeps sling legs vertical, eliminating the horizontal compressive force that inclined sling legs would otherwise exert on the sides of a load.

Question 3

On a lattice boom crawler crane load chart, why are capacities typically higher over the rear than over the side?

Accepted Answer

The rear counterweight provides greater stability when lifting over the rear

Answer

The counterweight is mounted at the rear of the crane, providing the greatest stabilizing moment when the boom swings over the rear, resulting in higher rated capacities in that direction.

Question 4

What is the correct formula to determine the horizontal leg tension in a two-leg bridle sling where the sling angle from horizontal is 30 degrees?

Accepted Answer

Load ÷ (2 × sin 30°)

Answer

Tension in each leg = Load ÷ (number of legs × sin θ), where θ is the angle from horizontal, so T = Load ÷ (2 × sin 30°).

Question 5

A load chart shows crane capacity drops significantly between 40-ft and 50-ft radii. This drop most likely indicates a transition from:

Accepted Answer

Structural capacity to stability-limited capacity

Answer

At shorter radii, capacity is often limited by structural strength of components; as radius increases, the load moment can exceed the crane's stability margin, making stability the governing limit.

(NCCER Crane) National Center for Construction Education and Research Crane Certification Practice Test

(NCCER Crane) National Center for Construction Education and Research Crane Certification Practice Test

NCCER Crane Load Charts & Rigging Principles 4