Load Charts and Capacity Determination
Domain 2: Load Charts and Capacity Determination
The exam tests whether you can select the correct chart and calculate the allowable load for the actual configuration. Articulating crane capacity is not one number: it changes with outrigger spread, boom extension and articulation, jib use, winch configuration and radius.
Chart selection
- Match the chart to the exact model, counterweight, outrigger configuration (fully extended, mid-extend, retracted), boom sections/manual extensions, jib and hoist. If the configuration is not on the chart, the crane is not rated for that lift.
- Read capacity at the actual operating radius: the horizontal distance from the rotation center to the load's center of gravity. For a jib or below-the-hook device, use the radius definition in the manufacturer's chart.
- Apply all deductions the chart requires: hook block, ball, slings, shackles, spreader beams, jib and auxiliary sheave. Never deduct the boom weight; it is already in the chart.
- The lower of structural capacity and stability capacity governs. The LMI/RCL warns of overload but does not create capacity.
Worked example
A chart for fully extended outriggers lists 2,600 lb at 12 ft radius and 2,300 lb at 14 ft radius. The load weighs 2,050 lb and rigging weighs 150 lb, so the lifted weight is 2,200 lb. At 12 ft, 2,200 < 2,600: acceptable. If the actual radius is 14 ft, 2,200 < 2,300 is still acceptable-but if the radius is between 12 and 14 ft, do not assume 2,600 lb. Use the next lower listed capacity, 2,300 lb, unless the manufacturer permits interpolation. At 15 ft, even 2,300 lb may no longer apply.
Traps
Using boom length instead of radius; measuring to the boom tip rather than the load center; using the fully extended outrigger chart with partial spread; ignoring manual extension pin positions; forgetting rigging deductions; and treating an alarm silence as permission.