Inspecting aerial devices after electrical contact

Responding is Joe Cisneros, national services technician, Terex Utilities, Watertown, SD.

Insulated aerial devices are used in the utility industry to work on or near energized power lines. They’re designed to help protect workers – who follow proper work practices – from electrocution.

If an inadvertent electrical contact does occur, causing an arc or damage, the aerial device should be removed from service for inspection. Before a qualified inspector examines the machine, he or she should consider interviewing the operator to gather information to assist the inspection. If an injury occurred because of the electrical contact, notify the proper authorities and the aerial device manufacturer.

The qualified inspector should document all findings. The inspection should start with a determination of the entrance and exit points of the electrical current. There will always be at least two contact areas. Inspect the boom, tower, subframe and chassis before operating. Take pictures of the contact points and any carbon tracking on the boom, if present. Clean soot from the fiberglass boom and perform a dielectric test. If the boom fails the test, it may need to be replaced.

If metal portions of the boom have arc marks, photograph them and note the location, size and depth of erosion.

It’s important to inspect the inside of the boom in case a flashover occurred. A flashover could cause other components to be damaged and may be evident by discolored paint. Note the size and location of the symptoms of a flashover. (Note: All components between all points of contact will need to be inspected for arc marks and damage in the path between the points. This includes, but isn’t limited to, cylinders and boom pivot points.)

If both the entrance and exit points of contact can’t be identified, all components from the point of contact to the ground level need to be inspected for arc marks. These items may include rotation bearing and fasteners, the leveling system, outriggers and cylinders, gearboxes, and electric and hydraulic swivel joints, as well as the vehicle. Be careful during inspections, as escaping fluid under pressure can penetrate skin, causing serious injury.

Finally, once all information has been gathered, contact the manufacturer to determine whether additional steps should be taken. Repairs can be made in-house or by a third party, but must be done according to the manufacturer’s recommendations.

Testing required to return the unit to service is determined by the location of damage and the extent of repairs. Testing must be performed according to the manufacturer’s recommendations and ANSI guidelines. Although there’s no set limit on the number of electrical contacts an insulated aerial device can sustain, the unit must pass a structural inspection and dielectric test after every contact. Any insulating portion of the aerial device that is damaged and can’t pass a dielectric test must be replaced and retested before returning the aerial device to service.

Editor's note: This article represents the independent views of the author and should not be construed as a National Safety Council endorsement.