Erection Adjacent to an Overhead Line
A self-erecting crane is being installed in a yard to service a two-storey building refurbishment. On the second day of erection, the erector notices an 11 kV overhead line running along the boundary, approximately 9 m from the proposed slew centre. The crane's jib is 24 m long and the manufacturer's manual states the crane may be climbed to a free-standing height of 18 m. The site has no formal 'permit to work' system, and the erector is being pressured to finish because the crane hire period started that morning. The weather is dry with light wind. The overhead line is not marked on the site plan, and the distribution network operator has not been contacted.
1. Identify the controls required before erection can continue, and explain why the current separation is inadequate.
Read the worked answer
The 9 m distance is measured to the slew centre, not to the nearest point the jib or load line can reach. With a 24 m jib, the jib tip can pass over or near the line at almost any radius, and the load line and hook can swing or be blown toward the conductors. The relevant separation is from the line to the most adverse position of any part of the crane, the load, and the rigging - not the mast.
Controls required before work continues:
- Stop erection. The line was not identified at planning stage, which means the siting and the lift plan are both invalid.
- Contact the distribution network operator to establish the line voltage, the required safe clearance (which for 11 kV is typically expressed as a minimum distance plus a goalpost/barrier arrangement), and whether the line can be diverted, made dead, or fitted with insulated shrouds.
- Re-site the crane, or restrict the slewing range with a physical slew limit and a banksman, so that no part of the machine or load can approach within the DNO-specified distance.
- Mark the hazard on site, brief all personnel, and record the control in a revised lift plan and method statement.
- Introduce a permit-to-work for the erection and for subsequent lifting near the boundary.
Dry, light-wind weather is irrelevant - flashover can occur without contact at high voltage, and the risk is not weather-dependent in the way the erector appears to assume.
2. The erector proposes to use a 'goalposts and bunting' barrier at ground level and to carry on. Evaluate whether this is sufficient.
Read the worked answer
Not on its own. Ground-level goalposts and bunting are a useful visual and physical cue to keep plant and people from passing under the line, but they do nothing to prevent the crane's jib, hook block, or a suspended load from entering the exclusion zone in the air. The hazard here is a crane whose structure extends upward and outward, so the control must address the three-dimensional envelope of the machine.
The barrier must be combined with:
- A slew restriction or mechanical/electronic limit that physically prevents the jib entering the zone, not just a painted line.
- A defined, briefed operating radius and a competent banksman/slinger who understands the restriction.
- DNO agreement on the clearance distance and any line insulation or diversion.
- A lift plan that shows the restricted zone and the maximum permitted radius, and a permit-to-work controlling who may operate.
If the crane cannot be operated so that the full envelope (including the load and any tag lines) stays outside the DNO's required distance, the crane must be relocated. Bunting is a supplement, never the primary control for an overhead line.