NCCER Crane Load Charts & Rigging Principles 3 — Questions and Answers
Question 1: What is the significance of the 'tipping line' in crane stability calculations?
- The point on the rope where it should be cut
- The fulcrum axis over which a crane would rotate if it tipped (Correct answer)
- The maximum rated line pull of the hoist
- The line drawn on the ground to mark the swing radius
Correct answer: The fulcrum axis over which a crane would rotate if it tipped
The tipping line is the axis (typically the outer edge of the outriggers or rear axle) over which the crane would rotate if it were overloaded and began to tip.
Question 2: Wire rope used for rigging should be removed from service if it has how many randomly distributed broken wires in one rope lay?
- 3 or more
- 6 or more (Correct answer)
- 12 or more
- 20 or more
Correct answer: 6 or more
ASME B30.9 specifies that wire rope slings with 6 or more randomly distributed broken wires in one rope lay must be removed from service.
Question 3: What effect does a choker hitch have on a sling's rated capacity compared to a vertical hitch?
- Increases capacity by 25%
- Reduces capacity to approximately 75–80% of vertical rating (Correct answer)
- Has no effect on capacity
- Doubles the capacity
Correct answer: Reduces capacity to approximately 75–80% of vertical rating
A choker hitch reduces a sling's working load limit to approximately 75–80% of its vertical hitch rating because of the bend and friction at the choke point.
Question 4: In crane load charts, 'structural' rated capacity is limited by:
- The crane's stability on outriggers
- The strength of the crane's boom, structure, and components (Correct answer)
- The wire rope's breaking strength
- The hydraulic pressure of the hoisting system
Correct answer: The strength of the crane's boom, structure, and components
Structural capacity is the maximum load the crane's structural components—boom, luffing mechanism, pins—can handle before failure, independent of tipping.
Question 5: When rigging a load with a four-leg bridle sling, ASME standards assume how many legs are considered load-bearing for rating purposes?
- All four legs equally
- Three legs, to account for the possibility that one leg may not be taut (Correct answer)
- Two legs only
- All four legs at half capacity each
Correct answer: Three legs, to account for the possibility that one leg may not be taut
ASME B30.9 conservatively assumes only three of four legs share the load, because minor load imbalances can result in one leg carrying little to no tension.
Question 6: What is 'fleet angle' in crane rigging, and why does it matter?
- The angle of the sling legs from vertical, affecting load distribution
- The angle between the wire rope and the drum centerline, affecting rope wear and piling (Correct answer)
- The angle of the boom relative to horizontal
- The angle of the load relative to the hook
Correct answer: The angle between the wire rope and the drum centerline, affecting rope wear and piling
Fleet angle is the angle between the wire rope and the centerline of the drum; excessive fleet angle causes uneven rope spooling, wear, and crushing on the drum.
Question 7: A crane's load chart specifies capacities for specific boom lengths. If an operator uses a boom length between two chart values, what should they do?
- Use the higher capacity listed for the longer boom
- Interpolate between the two values or use the more conservative (lower) capacity (Correct answer)
- Use the same capacity regardless of actual boom length
- Add 10% to the shorter boom's rated capacity
Correct answer: Interpolate between the two values or use the more conservative (lower) capacity
When the actual boom length falls between charted values, operators should interpolate or use the conservative lower value to ensure safe operation.
NCCER Crane Load Charts & Rigging Principles 3
What is the significance of the 'tipping line' in crane stability calculations?