Load Charts and Capacity Calculations Flashcards
6 cards from real NCCCO practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Load Charts and Capacity Calculations flashcards as text
When reading a mobile crane load chart, what two primary variables determine the rated lifting capacity?
Answer: Working radius and boom length/angle
Load charts are organized by working radius (horizontal distance from center of rotation to the load) and boom length or angle configuration. These two variables intersect to give the maximum rated load.
A mobile crane load chart shows a capacity of 40,000 lb at a 30-foot radius. The rigger plans to lift a 38,000-lb load plus 800 lb of rigging hardware. What is the total suspended load?
Answer: 38,800 lb — rigging hardware weight must be added to the load weight
Total suspended load includes the load weight plus all below-the-hook rigging hardware (shackles, slings, spreader bars, hooks). Here: 38,000 + 800 = 38,800 lb total.
What does the deduction column on some load charts represent?
Answer: The weight of the hook block and ball that must be subtracted from the rated capacity to get net load capacity
The deduction column lists the weight of the crane's own hook block/ball assembly. This weight counts as part of the lifted load and must be deducted from the rated capacity to determine the actual net weight you can attach to the hook.
A crane is rated for 20 tons at a 40-foot radius on fully extended outriggers. The operator is setting up on a slope of 2%. What is required before using the rated capacities?
Answer: Re-level the crane to within manufacturer tolerances — off-level operation voids the load chart
Load charts are developed for level operation (within manufacturer-specified tolerance, typically ±1%). Operating off-level shifts the center of gravity and reduces tipping stability — the crane must be leveled before using rated capacities.
Which of the following correctly describes 'working radius' as used in crane load charts?
Answer: Horizontal distance from the center of the crane's rotation to the center of the suspended load
Working radius is the horizontal distance — not the boom length — from the center of rotation (turntable center pin) to the plumb line of the suspended load. It determines the overturning moment.
A crane load chart note states 'Capacities are based on structural strength and do not exceed 75% of tipping load.' What does this note indicate?
Answer: The published capacities already include the ASME-required stability derating, so no further reduction is needed for normal lifts
ASME B30.5 requires mobile crane manufacturers to rate capacities at no more than 75% of the actual tipping load (on outriggers). The load chart already incorporates this derating — operators use the published values directly.