Load Charts 101 — Reading the Chart and the Notes

Core · Domain 4: Load Charts & Capacity · ~25 min · OSHA 1926 Subpart CC + ASME B30.5-2025 (Authored & cited — pending SME review.)

1. What the chart is — two limits, one number

Every capacity cell is the lesser of two independent limits:

1. Structural strength — how much the boom, jib, cylinders, and components can carry before something yields. Dominates at short radii / steep boom angles.
2. Stability — how much before the crane starts to tip about the tipping fulcrum. Set as a percentage of the tipping load (85% on outriggers, 75% on tires). Dominates at long radii.

The chart prints whichever is smaller. That distinction matters because counterweight helps only the stability-governed side. Above the bold stability line, you're structure-limited; adding counterweight does nothing.

Cited: ASME B30.5-2025 §5-1.1 (Load Ratings); §5-1.2 (Backward Stability). OSHA 29 CFR 1926.1417(b)–(c): do not operate above rated capacity.

2. Terms you must own exactly

• Operating radius — horizontal distance from the center of rotation to the center of the hook/load line. Not boom length. Not distance from the cab.
• Loaded radius — radius with the load applied. The boom deflects and the machine settles under load, pushing the hook outward. Charts are read at the loaded radius — always larger than the empty-hook radius you measured.
• Gross capacity — the raw number in the chart cell.
• Net (available) capacity — gross minus all load-handling devices.
• Rated capacity — manufacturer's maximum at a configuration = the charted value.
• Quadrant / area of operation — the zone the load is over (over-rear, over-side, over-front). A 360° chart gives one value for all directions — the most conservative case.
• Parts of line — number of hoist-rope segments supporting the load block.

Test trap: loading radius vs. unloaded radius. Candidates read the chart at the empty-hook radius and think they're fine. The loaded radius is always larger; use it.

3. Reading the chart — the six steps

1. Verify the setup matches the chart's stated configuration — outriggers fully extended, 360°, firm level ground, level within 1% (§5-3.4.7). On partial outriggers or rubber: use the matching chart for that configuration.
2. Establish the loaded radius and boom length.
3. Read gross at that row/column.
4. Subtract all deductions (Section 4) → net capacity.
5. Check reeving limit — confirm rope/parts-of-line capacity ≥ the load (Section 5).
6. Compare: (load + rigging) ≤ governing limit.

4. Gross → net: deductions (where points and cranes are lost)

The chart capacity is for a bare hook line. Everything you hang to make the lift counts as load and comes out of capacity:

The last two are the classic exam traps because they apply even when you're not using them.

Erected-jib trap: 100 ft boom, 40 ft radius = 27,000 lb gross. Load = 25,500 lb. An offsettable jib is erected but stowed (not used). Lookup says fine — but the jib costs 2,000 lb → net 25,000 lb. 25,500 > 25,000 → NO LIFT. The note flips it.

Aux-sheave trap: 80 ft boom, 50 ft radius = 22,500 lb. Aux tip sheave installed + hook block. Net = 22,500 − 150 − 1,000 = 21,350 lb. The 150 lb sheave deduction is easy to miss.

Jib + reeved-block trap: lifting on the jib, you must also deduct main-boom devices left reeved (e.g., the hook block) from the jib capacity.

Cited: ASME B30.5-2025 §5-1.1.1(c) — blocks, hooks, and slings count as part of the load. §5-1.1.1(e) — erected-jib deduction applies whether the jib is used or not.

5. The second limit: wire rope and parts of line

The reeving capacity = (rope's rated single-line pull) × (number of parts). If the charted capacity exceeds what the current reeving can carry, reeving governs — you add parts of line or you cannot lift the charted number.

Example: rope rated 12,000 lb/line, reeved with 4 parts → 48,000 lb hook capacity. Chart shows 60,000 lb at your config → you are rope-limited to 48,000 lb.

Always confirm the chart's wire-rope / parts-of-line reference, not just the capacity grid.

Cited: ASME B30.5-2025 §5-1.7 (Ropes and Reeving Accessories).

6. Structural vs. stability — and when counterweight helps

• Above the bold line → structural limit. Adding counterweight does nothing — counterweight fights tipping, not steel stress.
• Below the bold line → stability limit. Here counterweight, outrigger setup, and staying level protect you.

Never reason "throw on more counterweight to pick more" at a short-radius, structure-limited pick. It signals a dangerous misunderstanding of what the chart is doing.

7. Configuration factors that change everything

• Outrigger extension — fully extended, intermediate, and retracted each have their own chart. Never interpolate. Partial extension requires manufacturer charts for that position.
• On rubber (on tires) — much lower capacities, separate chart, often with creep/pick-and-carry rules.
• Quadrant — over-the-side is usually weakest; 360° charts already assume the worst direction.
• Wind and dynamics — charts assume freely suspended loads with no wind and smooth control. Wind on the load or boom, swinging, and sudden stops all add effective load.
• Level — within 1%; out-of-level rapidly erodes capacity.

8. Worked lift

Plan: pick a 19,000 lb load at a 50 ft radius. Rigging: hook block 1,000 + slings 1,000 (total 2,000 lb devices). No jib, no aux sheave. Outriggers full.

1. Total to lift = 19,000 + 2,000 = 21,000 lb must be ≤ net.
2. 100 ft boom, 50 ft radius → 20,500 gross. Net = 20,500 − 2,000 = 18,500. 21,000 > 18,500 → won't work.
3. 80 ft boom, 50 ft radius → 22,500 gross. Net = 20,500. 21,000 > 20,500 → still short.
4. 80 ft boom, 40 ft radius → 31,000 gross. Net = 29,000 → comfortably OK if the geometry allows setup at 40 ft. Decision: reduce radius to 40 ft (reposition the crane).

That sequence — total load including devices, find net, check reeving, adjust radius or boom — is exactly the judgment the exam wants.

Common traps

• Reading the unloaded radius instead of the loaded radius.
• Treating gross as net.
• Ignoring an erected-but-unused jib or an installed aux sheave.
• Using the fully-extended chart on partial outriggers or rubber.
• Assuming counterweight raises a structure-limited capacity.
• Forgetting the parts-of-line limit can be lower than the chart.

Quick check

1. 60 ft boom, 25 ft radius (gross 61,000). Block 1,000 + slings 800. Max load? → 59,200 lb.
2. Jib erected but not used — does it affect main-boom capacity? → Yes, deduct it.
3. Chart shows 60,000; rope 4 parts at 12,000/line. Governing limit? → 48,000 lb (reeving).
4. Pick is above the bold line. Will adding counterweight raise capacity? → No (structural limit).

Now test yourself

→ Practice: Load Charts & Capacity — lookups, net-capacity, note-traps, jib charts, go/no-go, max-radius questions on the Academy chart.