5.1 Reading the Manufacturer Load Chart
Key Takeaways
- The load chart is the legal authority on lifting capacity; the operator must use the manufacturer chart matching the exact crane model, serial range, and configuration in use
- Capacity is read at the intersection of operating radius (horizontal distance from center of rotation to load center) and boom length, not by boom angle alone
- The range diagram and the capacity chart are separate tools: the range diagram shows where the load can physically reach, while the capacity chart shows how much can be lifted there
- On-outrigger ratings are higher than on-rubber (on-tire) ratings, and 360-degree ratings are usually lower than over-front or over-rear ratings
- Chart notes and footnotes are part of the rating: they define deductions, minimum boom angles, parts of line, and quadrant of operation, and a lift is not legal if a note is violated
Why Load Charts Dominate the Exam
The Load Charts domain is the single largest section of the National Commission for the Certification of Crane Operators (NCCCO) Mobile Crane Operator core written exam at 27% of scored content. It is also the most computational domain on the test. Every other domain describes hazards and procedures; load charts ask you to prove with numbers that a planned lift is within the crane's rated capacity.
The load chart is not a guideline. Under the operating practices the exam tests, the manufacturer load chart is the controlling authority for how much the crane can lift in a given configuration. The operator is responsible for confirming the chart matches the exact crane.
Match the Chart to the Crane First
Before reading a single number, verify the chart matches the machine. A capacity chart is valid only for a specific:
- Crane make, model, and serial-number range
- Counterweight configuration (amount of counterweight installed)
- Outrigger state (fully extended, intermediate/mid, or fully retracted)
- Boom and attachment configuration (main boom, boom extension/jib, offset)
- Quadrant of operation (over-front, over-rear, over-side, or 360-degree)
Using the wrong chart, or a chart for a different counterweight, is one of the most dangerous chart-reading errors because the displayed capacity can be far higher than the crane can actually lift safely.
How the Capacity Chart Is Organized
A typical mobile crane capacity chart is a grid. One axis lists operating radius and the other lists boom length. The number at the intersection is the gross rated capacity for that radius and boom length in that configuration.
Key definitions you must keep straight:
- Operating radius: the horizontal distance, measured along the ground, from the crane's center of rotation (the centerline of the rotating superstructure) to the vertical centerline of the suspended load. Radius increases as the boom is lowered or extended.
- Boom length: the length of the boom from the boom foot pin to the boom point sheave, set by telescoping (on a telescopic boom) or by inserting sections (on a lattice boom).
- Boom angle: the angle of the boom above horizontal. It is related to radius but is not the value used to enter most capacity grids; radius is.
The table below shows an illustrative capacity layout (not any real manufacturer's chart). All values are invented for teaching only.
| Operating radius (ft) | Boom 40 ft (lb) | Boom 60 ft (lb) | Boom 80 ft (lb) |
|---|---|---|---|
| 12 | 64,000 | 58,000 | 50,000 |
| 20 | 38,000 | 34,000 | 30,000 |
| 30 | 22,000 | 20,500 | 18,000 |
| 40 | — | 13,500 | 12,000 |
| 50 | — | 9,200 | 8,400 |
Notice two patterns that hold on real charts and are tested constantly:
- Capacity falls as radius increases. Reaching farther out reduces how much you can lift, because leverage works against the crane.
- A dash means no rating. A blank or dash at a radius/boom combination means the crane is not rated to lift there at all. It does not mean "a small amount." It means do not lift.
Range Diagram vs Capacity Chart
Candidates confuse these two tools. They answer different questions:
| Tool | Question it answers | What it shows |
|---|---|---|
| Range diagram | Can the load physically get there? | Boom length, boom angle, radius, and the resulting tip height / lift height the load can reach |
| Capacity chart | How much can I lift there? | Rated weight at each radius and boom length for the chosen configuration |
Workflow on the exam: use the range diagram to confirm the load can be placed where it needs to go (height and reach), then use the capacity chart to confirm the crane is rated to lift that weight at the resulting radius. Both must pass.
Lift Area and Work Area
The lift area (sometimes called the working area or work area) is the arc, defined by quadrant diagrams, in which a given rated capacity applies. Charts often divide the area around the crane into quadrants:
- Over-front (or over the front, between the front outriggers): often the strongest direction on a truck-mounted telescopic crane because the chassis and outrigger spread support the load best there.
- Over-rear: strength varies by machine; some carry deck cranes are strongest over the rear.
- Over-side / 360-degree: typically the least favorable and lowest rating, because the crane can be least stable when swinging over the side or rotating fully.
When a chart shows different capacities by area, you must rate the lift for the least favorable area the load will pass through, not just the area where it starts.
On Outriggers vs On Rubber (On Tires)
Mobile cranes usually publish separate charts:
- On outriggers (fully extended): the crane is leveled and supported on outrigger floats with tires off the ground or unloaded. Capacities are highest.
- On outriggers (intermediate / mid extension): a reduced chart for partially extended outriggers.
- On rubber / on tires: the crane lifts while supported on its tires, with no outriggers deployed. Capacities are dramatically lower and carry extra restrictions (tire pressure, creep speed, pick-and-carry rules, very small radius).
Never read an on-outrigger number and then lift on rubber. They are different charts with different numbers.
Notes and Footnotes Are Part of the Rating
The small print is not optional reading. Chart notes and footnotes commonly:
- State that listed capacities do not include the weight of the hook block, headache ball, slings, or boom extensions, and must be deducted (covered in 5.2).
- Define minimum boom angle or maximum boom length for an attachment.
- Specify parts of line required and the maximum line pull per part.
- State whether ratings are limited by structural strength or by stability (often a bold line or asterisk on the chart separates these).
- Require specific counterweight, outrigger extension, or tire conditions.
A lift that violates any applicable note is an overload even if the raw grid number looks adequate. On the exam, if a footnote condition is not met, the correct answer is that the configuration is not permitted.
Using the illustrative capacity chart in this section, what is the gross rated capacity at a 20 ft operating radius with a 60 ft boom?
A capacity chart shows a dash (—) at a 40 ft radius with a 40 ft boom. What does that dash mean?
Which tool tells you whether the load can physically reach the required height and distance, as opposed to how much weight can be lifted there?