Insulating aerial devices and digger derricks are used to provide a level of protection to their operators and ground personnel who work around energized power lines. Following established safe work procedures is critical, as is testing and maintaining the equipment so that it continues to provide the insulation users expect. You cannot simply look at a unit to determine if it will provide the insulation expected; it must be tested.
There are two types of dielectric tests that must be performed on insulating aerial devices and digger derricks: qualification tests and periodic tests. A qualification test is required to determine the voltage rating of the unit. A periodic test is conducted at intervals to verify that the equipment continues to provide the expected insulation. Knowing who is responsible for these tests and when to perform them is essential to identifying any defects or weaknesses in the insulating capabilities of the equipment. Once the equipment is in use, the responsibility falls on the owners and users.
New insulating bucket trucks or digger derricks are first tested by the OEM according to ANSI A92.2 5.3.2 or A10.31 5.3.2 requirements, respectively. This qualification test at the factory establishes the insulation rating for the equipment. The installer will then perform a dielectric test to confirm the insulation after a unit is finished and operational. A qualification test is also required if the fiberglass boom is replaced. The original qualification test is then no longer valid.
Once insulating equipment is placed in service, maintenance tests – also called periodic tests or annual tests – are required to be performed for a variety of reasons. A maintenance test is required annually for most classifications of machines, or more frequently according to the user’s policy. Maintenance tests are also required after repair or replacement of components in the insulating sections, such as hoses or leveling components. If a problem is suspected, or after unintended contact with energized power lines occurs, a maintenance test will verify the insulation is providing the expected protection and not damaged.
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