13.8 kV Beside the Panel Set
Precast panel and rebar work on a commercial site. A 13.8 kV overhead distribution line runs parallel to the north property line; the utility confirmed the voltage in writing and refused to de-energize during the pour. A 22-ton rough-terrain crane is setting 3,000-lb precast wall panels, and the boom's closest approach to the line is estimated at 12 ft when the crane swings to the north rack. The operator takes hand signals from the mason foreman, who stands behind the crane's counterweight. On the ground, a 120 V extension cord runs from a panel with no GFCI receptacle to a mortar mixer sitting in a puddle; the cord's grounding pin has been cut off and the jacket is taped over a nick. The crew wears leather work boots and hard hats.
1. Is 12 ft acceptable clearance for this lift? Show how you determine the required distance and what the alternatives are.
Read the worked answer
Determine the table value first. For cranes near power lines, clearance is set by the voltage tier in Table A of 1926.1408. For lines rated up to 50 kV, the minimum is 10 ft; the requirement climbs in steps as voltage rises. With 13.8 kV confirmed in writing by the utility, the floor is 10 ft - and the written confirmation is itself a requirement: the employer must establish the voltage, not guess it.
Then attack the '12 ft' number. It was estimated, and it is the closest approach as the operator intends to swing today. The table distance must hold for every movement of the equipment, the boom, the load, the rigging, and the tag line, including wind drift, boom deflection under load, and a startled operator. A 2-ft margin on an estimate is not a margin. Ways to make 12 ft real:
- A dedicated spotter whose only job is watching the line, in continuous contact with the operator.
- A range limiting device or proximity alarm set inside the 10-ft envelope.
- Barricades or a marked swing limit so the boom physically cannot reach the encroachment zone.
- De-energize and visibly ground - refused here, so it drops out.
- Relocate the panel rack so the swing never approaches the line.
The part people miss: the 10-ft table protects the equipment. Workers on the ground holding tag lines and guiding panels are not inside a crane cab and have no such protection. Ground crew must stay clear of the zone the load and rigging could reach if anything lets go.
2. The superintendent says 'GFCI or not, the mixer is on a rubber-tired cart.' Evaluate the electrical hazards at the mixer and state what must happen before it runs again.
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The rubber tires are irrelevant. Tires insulate the cart, not the worker. The fault path is: ungrounded tool or damaged cord energizes the mixer frame, the worker touches the frame while standing in a puddle with wet boots, and current crosses the chest to earth. Wet boots and leather are not insulation.
Three separate defects, each independently serious:
- Grounding pin removed. The equipment grounding conductor is what gives fault current a low-impedance path back to trip the breaker. Cutting the pin removes the only protection the tool has.
- No GFCI. Where 120 V temporary receptacles are used, the employer must provide either GFCI protection or an assured equipment grounding conductor program - a written program with daily visual inspection of cords and equipment, continuity testing of the grounding conductor at intervals not exceeding 3 months, and records of those tests. Nothing here suggests either exists.
- Damaged cord jacket in a puddle. Flexible cords must be protected from damage and may not be used with damaged insulation; a taped-over nick is a splice waiting to fail.
Before the mixer runs: de-energize and lock out, take the damaged cord out of service and destroy it, repair or replace the receptacle with GFCI protection (or stand up a documented AEGCP), route cords overhead or off the ground and out of standing water, inspect all cords on the site, and train the crew that a missing grounding pin is a stop-work condition. Rubber-tired or not, no one touches that mixer until the fault path is eliminated.
3. Who is responsible for the overhead-line hazard, and what should the signaling arrangement be?
Read the worked answer
Responsibility is layered, not delegated to the operator.
- The employer must confirm the line voltage with the utility owner (done here), ensure the required clearance is maintained, and implement encroachment prevention - spotter, range limiter, or physical barriers.
- The controlling entity on site must identify the hazard to subcontractors and coordinate the swing limits and the rack location.
- The operator must stop when the load, boom, or machine approaches the limit, and must stop for a stop signal from anyone.
- The rigging crew must stay out of the zone and control the panel with tag lines.
The signal arrangement is wrong as described. A signal person standing behind the counterweight cannot see the load, the boom tip, or the line - he is looking at the wrong end of the machine. The signal person must be positioned to see both the load and the operator (or use radio), must be qualified for the signals being used, and must be the only one giving signals. The mason foreman is doubling as a working foreman and a signal person while standing in a blind spot, which is exactly how a boom contact happens. Fix: a qualified signal person with a clear view and radio contact, one voice on the channel, and anyone on site authorized to give a stop signal.