Minimum Approach Distance to an Unearthed 11 kV Line
A 60 t slew crane is lifting formwork panels onto a second-storey slab. An 11 kV overhead line on wooden poles runs along the site boundary. The line is not earthed and the pole stays are visible. The crane's maximum boom height at the planned radius would place the boom tip approximately 2.5 m from the conductors at the closest point. The client says the line is 'only 11 kV' and that the last crane worked closer without incident. The spotter is positioned on the far side of the crane and cannot see the boom tip. Work is scheduled for early morning when the line is lightly loaded.
1. Assess the clearance against the applicable minimum approach distance and state whether the lift can proceed as planned.
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The lift cannot proceed as planned. For an unearthed 11 kV overhead line, the minimum approach distance for a crane and its load is 3.0 m under the relevant state guidance, and some jurisdictions require more. The planned 2.5 m is inside that distance, and the minimum approach distance is a hard limit, not a target.
The fact that the line is lightly loaded in the early morning is irrelevant to the electrical hazard; the line is still live at 11 kV. The previous crane's closer approach is not evidence of safety, it is evidence of a prior unsafe act.
Options: relocate the crane so the entire boom and load path stays outside the minimum approach distance plus a margin; have the line de-energised and earthed by the network operator with written confirmation; or install physical barriers and a limit system that prevents the boom entering the exclusion zone. Only after one of these is in place, and the spotter is repositioned to see the boom tip, can the lift be replanned.
2. What controls would you require if the lift must go ahead near the line?
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First preference is to have the line de-energised and earthed by the network operator, with a written confirmation and an isolation certificate before work starts. If that is not possible, relocate the crane so the minimum approach distance is maintained with margin for boom deflection and load swing.
Where proximity is unavoidable, use a dedicated spotter whose only task is to watch the boom tip and load against the line, positioned so both are visible, with a agreed radio protocol and a positive stop signal. Fit a boom limit or proximity warning device where available. Mark the exclusion zone on the ground with barriers and signage so no person or plant enters it.
Brief all personnel on the hazard and the stop-work authority. The operator must know the maximum permitted boom angle and slew arc. If the spotter loses sight, or the boom approaches the limit, work stops. The client's assurance does not override these controls.
3. What would you do if the spotter reports the load has contacted the line while you are operating?
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Assume the line is live and the crane is energised. Do not touch the crane, the load, or any part of the machine. Stay in the cab if you are the operator and warn others by radio or horn to stay clear and not approach.
If it is safe to do so and the machine is not on fire, slew or lower the load away from the line slowly, following the network operator's or emergency services' advice. If the crane is on fire or you must leave, jump clear with feet together and shuffle away without touching the crane and ground at the same time, to avoid step and touch potentials.
Call emergency services and the network operator immediately. Nobody approaches until the line is confirmed de-energised and earthed. The incident is reported and the lift plan is suspended pending investigation.