The Capacity Chart at Full Reach
You are lifting roof trusses onto a single-storey extension. The trusses are bundled at 900 kg. The pick-up point is 4 m from the machine; the placement point is 9 m from the machine and 6 m high. Your telehandler is fitted with a 1.2 m integrated fork carriage, and the load centre is roughly 600 mm from the fork heel because the bundle is wide. The capacity chart in the cab shows 1,500 kg at 9 m with the boom retracted, but you notice the chart has a separate column for 'load centre 600 mm' that is lower. A colleague says the chart is 'conservative' and that everyone lifts a bit over. The ground is firm compacted hardcore, level, and outriggers are not fitted.
1. Explain how you determine the safe capacity for this lift, and whether the 900 kg bundle is within it.
Read the worked answer
The rated capacity depends on three variables at once: radius, height/boom extension, and load centre. The chart's 1,500 kg figure applies only at the stated load centre (usually 500 mm). Because the bundle sits about 600 mm out, I must read the 600 mm column, which is lower - I cannot use the 1,500 kg figure.
Method:
- Measure the actual radius to the load centre at the placement point, not to the fork heel. At 9 m radius plus a 600 mm load centre, the effective radius is greater than 9 m, so I read the chart at the next radius out (e.g. 9.5 m or 10 m).
- Read the capacity at that radius and height in the correct load-centre column.
- Compare with 900 kg plus the weight of any attachment or slinging gear.
- Confirm the machine is level, on firm ground, and that the chart's conditions (tyres, outriggers, counterweight) match the machine as configured.
If the 600 mm column at the corrected radius gives less than 900 kg, the lift is not permitted. The colleague's 'everyone lifts a bit over' is exactly the attitude that causes overturns; the chart is a limit, not a guide. If capacity is short, the fix is to break the bundle, reposition closer, or use a larger machine - not to exceed the chart.
2. What would change if the ground sloped 3 degrees toward the placement point?
Read the worked answer
A 3-degree slope toward the load reduces stability margin because the machine's centre of gravity moves toward the downhill side as the boom extends. Charts assume a level machine. On a slope:
- The effective capacity is reduced and the chart no longer directly applies.
- The machine should be levelled (using the manufacturer's permitted methods) or repositioned so the boom works across the slope rather than down it.
- The load will tend to swing downhill, increasing radius and shock loading.
I would not proceed on the slope using the level-ground chart. I would reposition to level ground, or if that is impossible, seek the manufacturer's/competent person's guidance on derating. The 3 degrees looks small but at 9 m radius the geometry matters, and an overturn at height is likely to be fatal.