Lift Near a 25 kV Overhead Line
A service truck crane must set a 1,800 lb motor on a pad inside an industrial yard. The only practical setup puts the boom tip about 11 ft from a confirmed 25 kV overhead line at its closest point. The line crosses diagonally, and sag at midspan is not known. The operator plans a 15-ft boom extension with a 12-ft radius pick, then a slow swing. A dedicated spotter is available, but the operator says that because 25 kV requires only 10 ft, an 11-ft clearance is acceptable and no further controls are needed. Wind is 12 mph gusting to 18 mph. The load has a 20-ft tag line, and a ground helper will hold it. The utility has not been asked to de-energize. The lift is scheduled for 30 minutes.
1. Evaluate the proposed 11-ft clearance. What is the minimum table distance for 25 kV, and why is 11 ft not a reliable plan?
Read the worked answer
- For a 25 kV line, the Table A minimum clearance for crane equipment is 10 ft for lines of 50 kV or less. So 11 ft is only 1 ft beyond the table minimum.
- That is not a reliable plan: the 11 ft is an estimate, line sag at midspan is unknown, boom deflection and swing can reduce clearance, 12–18 mph wind can move the load and tag line, and the operator's attention is divided.
- A table minimum is a line not to cross; it is not a target. Without confirming sag and controlling movement, 11 ft should be rejected.
2. List the controls you would require before allowing the lift, including spotter duties and tag line handling.
Read the worked answer
- Stop the lift until the utility confirms voltage and sag or de-energizes and grounds the line.
- If work continues near an energized line, use a dedicated, qualified spotter whose only job is to watch the line and who has stop authority, in continuous communication with the operator.
- Establish a marked warning boundary at a safe distance from the line, brief the crew, limit boom and swing speed, and prohibit tag lines or materials that can contact the line. Use non-conductive tag lines and keep them clear.
- Re-evaluate wind; stop if gusts cause load swing. Do not allow the helper to stand under the load.
3. If the line cannot be de-energized, what alternatives would you consider?
Read the worked answer
Alternatives include repositioning the crane so the boom and load path stay well outside the minimum distance; using a different lift method or a machine with a shorter boom; having the utility de-energize and ground the line for the lift; or postponing the work. Do not use the 11-ft estimate as the sole control, and do not rely on a spotter to make an inadequate clearance acceptable.