NCCCO Boom Angle and Radius Calculations 2

Question 1

A crane's load chart shows a rated capacity of 18 tons at a 30-foot radius. If the operator extends the boom to increase the radius to 45 feet, what will happen to the rated capacity?

Accepted Answer

It will decrease because the load moment increases

Answer

As the working radius increases, the load moment (load x radius) increases, which reduces the crane's rated capacity per the load chart. Longer radius means less lifting capacity.

Question 2

If a crane has a 100-foot boom at a 45-degree angle, what is the approximate working radius from the crane's center pin to the load?

Accepted Answer

70.7 feet

Answer

At a 45-degree boom angle, the working radius equals the boom length times cosine(45 degrees) = 100 x 0.707 = 70.7 feet. This horizontal distance is used for load chart lookups.

Question 3

When a crane operator lowers the boom angle from 75 degrees to 55 degrees while keeping the same boom length, what happens to the working radius?

Accepted Answer

Working radius increases

Answer

Lowering the boom angle increases the working radius because the boom reaches farther horizontally. Lower boom angle equals longer horizontal reach equals larger radius equals lower load capacity.

Question 4

What instrument on a crane helps the operator verify the current boom angle during a lift?

Accepted Answer

Boom angle indicator (inclinometer)

Answer

A boom angle indicator (inclinometer) directly measures and displays the current boom angle, allowing the operator to verify the angle matches the load chart being used. It is a critical safety device for capacity verification.

Question 5

If a crane's load chart only shows capacities at 20-foot and 30-foot radii, and the operator needs to lift at a 25-foot radius, what should the operator do?

Accepted Answer

Interpolate between the two chart values and use the lower (more conservative) result

Answer

When the actual radius falls between chart values, the operator should interpolate between the two nearest values and use the more conservative (lower) capacity to ensure safety within the actual working conditions.

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

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

NCCCO Boom Angle and Radius Calculations 2