Incident Prevention Magazine

Joe Cisneros

When Insulating Booms Fail Dielectric Testing

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Insulating boom aerial devices and insulating boom digger derricks are designed to provide secondary protection to help prevent workers from being electrocuted. Maintenance and dielectric testing are critical and required by law to verify that the insulating portion of the machine is functioning as designed.

A new boom is dielectrically tested at the factory following ANSI requirements for a qualification test to verify the insulating rating. Additional tests are performed to confirm the insulating value after units are finished and operational. Once insulating equipment is placed in service, maintenance tests are required to be performed for a variety of reasons. Periodic testing in accordance with the ANSI A92.2 or A10.31 standard is required. If the equipment has not had a dielectric test performed within the last 12 months, as required by ANSI and OSHA, it cannot be considered insulating. Dielectric testing also should take place after repairs or replacement of components in the insulating sections, when a problem is suspected or after incidents of contact with energized power lines.

Environmental factors can affect the results of a dielectric test. The environment of use, exposure to sunlight, surface condition, damage, and cleanliness of the boom and internal components could lead to dielectric test failure. Following are some of the procedures a boom test technician performs when booms don’t pass a periodic test. Periodic testing usually is conducted annually, but many owners perform tests more frequently when weather or harsh conditions warrant them.

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