Try a full lesson: Load chart fundamentals

What this module covers

Load charts are their own domain on the Core written exam. You will be handed a chart and asked to read it, do some simple arithmetic and pick the right answer. There is no calculator on the Core exam, so the arithmetic has to be done in your head or on whatever the test site allows.

This module covers five things. The words a chart uses. Arithmetic tricks for subtracting deductions quickly. How to pick the right table for the way the crane is set up. The three kinds of chart you will meet. And how parts of line and boom angle notes can limit a lift even when the capacity table says yes.

Real exams hand out real manufacturer charts. On the job and on the exam, always follow the chart and the notes for the machine in front of you. Every chart in this course is invented for practice, and each one is labeled that way.

Load chart vocabulary: gross, net, radius, deductions

• Rated capacity is the most the crane may lift in a given configuration. Charts list it by boom length and radius.
• Gross capacity is the number printed in the table. It is not what the load may weigh. It has to cover the load and everything hanging below the boom tip.
• Deductions are what you subtract from gross: the hook block or overhaul ball, all rigging (slings, shackles, spreader bars, below-the-hook devices) and any attachment deduction the notes list, such as a stowed or erected jib or boom extension.
• Net capacity is what is left for the load itself: gross minus every deduction.
• Radius is the horizontal distance from the crane's center of rotation to the center of the hook with the load hanging. It is not the boom length, and it grows a little as the boom deflects under load. Use the loaded radius.

Two conventions run through every chart in this course:

1. Never interpolate. If your radius falls between two rows, use the next longer radius. If your boom length falls between two columns, use the next longer boom. The longer one always gives the lower, safer capacity.
2. Capacity falls as radius grows and as boom length grows. If an answer goes the other way, check your row.

Arithmetic without a calculator

Most chart questions are a lookup followed by a few subtractions. Three habits keep you fast and accurate.

• Add the deductions first, then subtract once. One subtraction is easier than four.
• Round and adjust. To take 1,800 off a number, take off 2,000 and add 200 back.
• Work in hundreds. Chart values usually end in 00. Drop the last two zeros, do the arithmetic, then put them back: 245 - 19 = 226, so 24,500 - 1,900 = 22,600.

Worked calculation: net capacity from a practice chart

Here is an excerpt of practice Chart PC-1 (fictional, invented for this course, not any manufacturer's chart). Telescopic crane on fully extended outriggers, 360 degrees, gross capacities in lb.

The boom is at 60 ft and the loaded radius is 23 ft. The PC-1 hook block weighs 750 lb, slings and shackles 250 lb, and a spreader bar 900 lb.

Step 1: find the row. 23 ft is between 20 and 25 ft. Use the next longer radius, 25 ft. Gross capacity is 24,500 lb.

Step 2: add the deductions. 750 + 250 = 1,000. 1,000 + 900 = 1,900 lb.

Step 3: subtract once. 24,500 - 1,900. Round and adjust: 24,500 - 2,000 = 22,500, then add back 100 to get 22,600 lb.

Check it another way. 24,500 - 750 = 23,750. 23,750 - 250 = 23,500. 23,500 - 900 = 22,600. Same answer, so the load may weigh up to 22,600 lb.

The common wrong answers are 24,500 (no deductions), 31,000 (the shorter radius) and anything between the two rows (interpolating).

Picking the right chart for the setup

A chart book holds many tables. Only one matches the crane as it sits. Before you read a number, match every one of these to the setup:

• Support: outriggers fully extended, mid extension, retracted, or on rubber. A crane on mid-extended outriggers uses the mid-extension table, never the full-extension one.
• Counterweight: the amount actually installed.
• Area of operation: 360 degrees, over the rear, over the side or over the front.
• Boom configuration: main boom only, or with an extension or jib stowed or erected. Practice Chart TC-4 (fictional) shows a 1,900 lb deduction at 16,200 lb gross (70 ft boom, 35 ft radius) just for having the extension stowed on the boom.
• On rubber: stationary or pick and carry. Practice Chart RT-3 (fictional) lists different figures at 20 ft for stationary 360 degrees (7,800 lb) and for pick and carry over the front (9,600 lb). The pick and carry figure only applies when the boom is centered over the front.

If no table matches the setup, there is no rating for that lift.

Rated capacity chart, range diagram and work area chart

• The rated capacity chart is the table of gross capacities by boom length and radius.
• The range diagram is a side-view drawing of boom lengths and angles against radius and height. Use it to check that the boom can reach the radius and give enough tip height to clear obstacles. It shows geometry, not capacity.
• The work area chart is a top view showing which capacity table applies in each zone around the crane (front, sides, rear). If the load swings through more than one zone, the lowest capacity of every zone the load passes through governs.

Parts of line, boom angle limits and choosing the best configuration

Parts of line

Each line running between the boom tip and the hook block is a part of line. The chart's hoist information gives a load allowed per part. The total hoisted weight (load plus block plus rigging) divided by that allowance, rounded up, gives the fewest parts needed.

Worked calculation: parts of line needed for a load

Practice Chart PC-1 allows 7,000 lb per part of line. The load is 24,000 lb, the PC-1 block 750 lb and the rigging 250 lb.

Step 1: total hoisted weight. 750 + 250 = 1,000. 24,000 + 1,000 = 25,000 lb.

Step 2: count up in sevens. Without a calculator, multiply instead of dividing. 7,000 × 3 = 21,000, short of 25,000. 7,000 × 4 = 28,000, enough. So 4 parts.

Step 3: check the chart too. The reeving only proves the rope can hold the weight. On the 60 ft boom, 25,000 lb needs at least that much gross capacity. At 25 ft the chart gives 24,500, which is not enough. At 20 ft it gives 31,000, which is. So this lift needs 4 parts and a radius of no more than 20 ft.

Boom angle limits

Chart notes may set a minimum boom angle for a boom length, or leave cells blank. A blank cell or an angle below the minimum means no rating. Do not borrow a figure from a nearby row.

Choosing the best configuration

When more than one boom length reaches the radius and height, the shortest boom that does the job usually gives the most capacity. On PC-1 at 40 ft, the 60 ft boom gives 13,000 lb and the 80 ft boom 12,000 lb.

Check yourself

In the course, three check questions close this lesson: what gross capacity includes, a net capacity lookup between chart rows, and parts of line checked against the chart. The free 10-question check has more load chart questions like them.

Where to look in your own books

• ASME B30.5, Section 5-1.1 (load ratings) and the load rating chart provisions that follow it
• OSHA 29 CFR 1926.1417 (operation, including staying within rated capacity) and 1926.1416 (operational aids)
• IHSA Mobile Crane Manual, the load chart chapters
• AEM mobile crane safety manual, the load chart sections
• The crane's operator manual and the notes printed with its load chart