NCCCO Load Charts & Capacity Calculations 4 — Questions and Answers
Question 1: When a load chart lists capacity at '360°' rotation, what does this indicate?
- Capacity applies only when rotating 360 degrees per minute
- Capacity is the same regardless of which direction the boom is pointed (Correct answer)
- The crane must complete a full rotation before lifting
- Capacity decreases by 360 pounds for each degree of rotation
Correct answer: Capacity is the same regardless of which direction the boom is pointed
A '360°' designation means the rated capacity is uniform in all directions around the crane's slewing circle.
Question 2: A crane load chart shows a capacity of 18,000 lbs at 40 ft radius. If the actual load weighs 15,000 lbs and rigging weighs 800 lbs, what is the total load on the hook?
- 15,000 lbs
- 15,800 lbs (Correct answer)
- 18,000 lbs
- 14,200 lbs
Correct answer: 15,800 lbs
The total load on the hook includes the weight of the load plus all rigging hardware, so 15,000 + 800 = 15,800 lbs.
Question 3: What is the purpose of the 'structural' capacity line on a crane load chart?
- It shows the maximum load the crane structure can withstand before tipping (Correct answer)
- It indicates the minimum load needed to keep the crane stable
- It represents the capacity of the crane's electrical system
- It lists the weight of the crane's structural components
Correct answer: It shows the maximum load the crane structure can withstand before tipping
The structural capacity line represents the maximum load the crane's structural components (boom, hook block, wire rope) can handle before failure.
Question 4: On a telescoping boom crane, why do load charts typically show reduced capacities as the boom is extended?
- Extended booms weigh less and reduce counterbalance
- Longer booms create greater bending moments and stress on structural components (Correct answer)
- Extended booms increase the center of gravity of the crane
- The hydraulic pressure drops when the boom extends
Correct answer: Longer booms create greater bending moments and stress on structural components
As the boom extends, the lever arm increases, creating greater bending moments and structural stress that reduce the safe rated capacity.
Question 5: A load chart footnote states 'capacities based on freely suspended loads.' What does this mean for a crane operator?
- The load must be swinging freely before lifting
- The load must hang vertically with no side pull on the hoist line (Correct answer)
- Only loads suspended by wire rope chains are covered
- The load must be lifted and lowered freely without pausing
Correct answer: The load must hang vertically with no side pull on the hoist line
Freely suspended loads hang vertically; side pulls or dragging loads create additional forces not accounted for in the rated capacities.
Question 6: When interpolating between two radius values on a load chart, what is the safest approach?
- Average the two capacity values
- Use the higher capacity value
- Use the lower capacity value or interpolate conservatively (Correct answer)
- Add 10% to the closer capacity value
Correct answer: Use the lower capacity value or interpolate conservatively
When interpolating between chart values, always use the lower capacity or interpolate conservatively to maintain a safety margin.
Question 7: A crane is rated at 20,000 lbs at 30 ft radius on outriggers fully extended. If the outriggers are only 50% extended, what capacity should be used?
- 20,000 lbs — outrigger extension doesn't affect ratings
- 10,000 lbs — exactly half the rated capacity
- The operator must consult the manufacturer's chart for that specific outrigger position (Correct answer)
- 15,000 lbs — 75% of rated capacity
Correct answer: The operator must consult the manufacturer's chart for that specific outrigger position
ASME B30.5 requires operators to use the manufacturer's load chart specific to the actual outrigger extension percentage; guessing or extrapolating is not permitted.
NCCCO Load Charts & Capacity Calculations 4
When a load chart lists capacity at '360°' rotation, what does this indicate?