Telescopic Boom and a Sagging 12.47 kV Line
A 60-ft telescopic boom lift is positioned on the shoulder of a two-lane road to replace a sign bracket. The adjacent 12.47 kV distribution line is 27 ft above grade at the pole but sags to 24 ft at mid-span. With the platform at 32 ft, the platform edge is 14 ft horizontally from the conductor at one point and 5 ft vertically below the conductor at another. The operator plans to use a 4-ft fiberglass pole from the platform. Traffic is moving at 45 mph, 8 ft from the boom's rear bumper. Wind is 10 mph, and the conductor is swaying slightly. A ground spotter is present but has no radio. The utility has not been notified.
1. Is the position compliant with the minimum approach distance? Show the measurement directions and why.
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The 10-ft minimum approach distance for lines of 50 kV or less applies in every direction: horizontal, vertical, and diagonal, from the conductor to the platform, worker, tool, and any conductive object. At one position the platform is 5 ft below the conductor, so the vertical clearance is 5 ft; that violates the minimum approach distance even though the horizontal distance is 14 ft. The 4-ft tool extends the reach and reduces clearance further. Conductor sag to 24 ft and wind sway make the 5-ft dimension unstable. The correct conclusion is non-compliant; the 14-ft horizontal measurement does not override a 5-ft vertical approach. Also account for boom deflection and platform bounce when the operator moves, and for the line's sag changing with load or temperature. A single favorable measurement does not prove clearance in all positions.
2. What controls would you require before work proceeds, and which controls would you reject as insufficient?
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Required controls: stop work; notify the utility; de-energize and visibly ground the line, or install approved insulating cover or hose rated for 12.47 kV with utility oversight. Re-establish the work zone so the entire platform and tool path stay at least 10 ft away, plus a margin for sway and boom movement. Use a dedicated spotter with a radio and authority to stop the job, and mark the minimum approach distance with a visible limit. Controls to reject: the fiberglass pole is non-conductive (it does not change the minimum approach distance); the boom is insulated (only if rated and tested, and the minimum approach distance still applies); the spotter will warn (reaction time is not a substitute for distance); 14 ft horizontal is enough (vertical is 5 ft). If the line cannot be de-energized or covered, use a different method, such as a ground-based sign installation or a longer-reach lift positioned from the opposite side with verified clearance.
3. How should traffic and spotter control be set up?
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Set up a lane closure with advance warning signs, cones, an arrow board, and a buffer space before the work area; use high-visibility clothing for all crew. Keep the boom's rear bumper and outriggers out of the travel lane, or close the lane if the boom can swing over it. The spotter should stand outside the fall and boom-swing zone with a radio, maintain eye contact with the operator, and control traffic and pedestrians. Do not let the spotter double as a flagger unless staffing and the traffic control plan allow it. Check the utility's requirements and the local road authority. Wind at 10 mph and traffic at 45 mph create gusts and vibration; stop if the platform moves unexpectedly or the conductor sways toward the minimum approach distance. A spotter without a radio cannot reliably stop the operator in an emergency.