Tilt-up panel lift beside a live 22 kV overhead line
You are operating a 100 t all-terrain slewing mobile crane on a tilt-up warehouse site. The load chart configuration in use is the main boom with 18 t of counterweight, 12 m radius, giving a rated capacity of 9.4 t. The panel to be lifted weighs 7.8 t including the lifting insert frame and rigging. The panel must be landed on a footing 3 m from a 22 kV overhead line that runs parallel to the building face. The line's lowest conductor is 6.8 m above ground. The site has no written powerline exclusion plan and the spotter assigned to the lift is a first-year labourer. Wind is 12 km/h gusting to 20 km/h, and the panel face presents 24 m² of sail area. The crane's boom tip will pass within 2 m horizontally of the conductors during the slew.
1. Evaluate whether this lift can proceed as planned, and identify the controls that must be in place before any lift occurs.
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The lift cannot proceed as planned. Three independent problems exist.
1. Powerline clearance. With a 6.8 m conductor height and a boom tip passing within 2 m horizontally, the required approach distance for a 22 kV line is not being met. The default control is de-energising and proving dead, or isolation with an approved permit. If the line cannot be de-energised, a documented exclusion zone must be established with goal posts, marker balls and a dedicated spotter whose only task is watching the line. A first-year labourer is not adequate for that role; the spotter must be competent, briefed on the specific geometry, and have authority to stop the lift.
2. Capacity margin. 7.8 t against 9.4 t is 83% of rated capacity. That leaves 1.6 t of margin, but the chart value assumes level ground, no wind, no side load and static conditions. With 24 m² of sail area and gusts to 20 km/h, the panel will induce a side load and dynamic amplification that the chart does not cover. A conservative approach is to keep the lift below roughly 75% of rated capacity where wind is a factor, or to reduce radius, add counterweight or reconfigure the boom.
3. Missing plan. No written powerline plan means no documented hazard control, no briefing record and no basis for the spotter's authority. The lift must be stopped, the plan written and signed off, the spotter replaced with a competent person, and the wind monitored against the panel's sail area. Only then should the lift be reassessed.
2. The site supervisor argues that because the panel is only 3 m from the line, the crane can simply be positioned so the boom never crosses the line. How do you respond, and what does the load chart require you to check?
Read the worked answer
Positioning so the boom never crosses the line is a legitimate control in principle, but it must be verified geometrically, not assumed. The supervisor's claim rests on the boom staying on one side of the conductors for the entire slew, including the pick-up, the travel arc and the landing. That requires a scaled plan view showing the crane's slew envelope, the boom's maximum reach at the working radius, and the conductors' actual position and sag. Sag matters: a 22 kV line between spans can drop well below its support height, and the 6.8 m figure may be measured at a pole rather than at the mid-span where the boom passes.
The load chart check is separate. The chart is valid only for the configuration stated: main boom, 18 t counterweight, 12 m radius, outriggers fully extended on ground capable of carrying the outrigger loads. If repositioning changes the radius, the capacity changes and the chart must be re-read at the new radius. The operator must also confirm the outrigger ground bearing pressure is adequate, that the crane is level within the manufacturer's tolerance, and that no part of the boom, hook block or load can enter the exclusion zone even under gust-induced deflection. If any of those cannot be demonstrated on paper, the lift does not proceed.