A load chart answers one question: how much can this crane lift in this exact setup? Getting the right answer means reading it in the right order. This is the method we teach in class, and it is the same reasoning the NCCCO specialty exams test.
Start with the configuration, not the number
Every chart is printed for a specific setup, and a capacity from the wrong page is just a wrong number. Before you look at any capacity, confirm:
- Support: on outriggers fully extended, outriggers at an intermediate setting, or on rubber.
- Counterweight: how much is installed. Many cranes have several charts for different counterweight packages.
- Working area: 360 degrees, over the rear, or over the front. Some cranes lose a lot of capacity over the front.
- Attachments: main boom only, or with a jib or extension erected or stowed.
Write the configuration at the top of your lift worksheet. If anything changes during the job, you are on a different chart.
Find radius and boom length, then read the cell
Radius is the horizontal distance from the center of rotation to the center of the hook, with the load suspended. It is not the distance from the outrigger or the edge of the crane. Boom length is the length of the main boom, read from the boom length indicator on a telescopic crane.
Find the row for your radius and the column for your boom length. If your exact values are not listed, the safe practice is to use the next larger radius and the next longer boom length shown (unless the chart's notes allow something else). Never interpolate between two capacities to squeeze out a few hundred extra pounds.
Remember that radius grows once the load comes off the ground. Boom deflection on a telescopic crane pushes the hook outward, so measure or estimate with that in mind.
Know which part of the chart you are in
Most mobile crane charts have two kinds of ratings. At short radius, capacity is limited by the strength of the boom and other components. At longer radius, it is limited by stability: how much load would tip the crane. Many manufacturers mark the boundary with shading or a bold line.
The difference matters because of how failure happens. In the strength area, an overload can damage the boom before the crane shows any sign of tipping. Operators who rely on feeling the crane get light will not get a warning there. ASME B30.5 sets stability ratings as a percentage of the tipping load, which is why the stability numbers are lower than what would actually tip the machine. That margin is not extra capacity.
Subtract everything that hangs from the boom
The number in the chart is gross capacity. To get what is left for the load, subtract the weight of everything below the boom tip that is not the load itself:
- The hook block or overhaul ball
- Slings, shackles, spreader bars and other rigging
- A stowed or erected jib or extension, as the chart's deduction table specifies
- On some cranes, a portion of the load line
Then compare the net capacity with the load weight. On the exam, a missed deduction is the most common reason a candidate picks the wrong answer. On the job, it is how a lift that "was fine on paper" ends up overloaded.
Read the notes and the range diagram
The notes pages carry rules that override the table: the parts of line needed for a given load, wind limits, when the capacities assume a level crane, and which boom extension mode the numbers are based on. Read them every time you use an unfamiliar crane.
The range diagram, the drawing of boom angles and lengths, helps you check whether the boom tip will clear a building or obstruction and what height you will reach at a given radius. Pair it with the load chart for lifts over walls or into tight spaces.
Practicing charts before the exam
Load charts are a large part of the NCCCO specialty exams, and the only way to get fast at them is repetition with feedback. In our courses, students work real manufacturer charts in the classroom with an instructor, then set up the same configurations in the yard so the numbers connect to what the crane is doing. The Mobile Crane Operations Fixed/Swing Cab 40 Hours course is a good fit for operators whose main gap is the chart work. New operators get more practice time in Mobile Crane Operations Fixed/Swing Cab 120 Hours. If you want to set up a crane yourself and check your numbers against the indicator, you can also book hourly practice time in our yard.
Load chart questions
Is the load moment indicator a substitute for reading the chart?
No. The indicator depends on the operator entering the correct configuration, and it does not know what rigging you have hung. Work the chart first and use the indicator as a check.
What does it mean when a load chart cell is blank?
A blank cell usually means the crane cannot work at that radius with that boom length, often because the boom angle would be outside its allowed range. Do not lift there.
Why do capacities over the front sometimes differ from 360 degrees?
Stability depends on how the crane is supported in each direction. Many cranes are less stable over the front, so the manufacturer publishes lower capacities, or none, for that area.
