The Law and Requirements:
According to CSA C225-M88 (the applicable standard for dielectric testing in Ontario) a dielectric test must be performed at least once a year on any insulated aerial device. Dielectric testing is the process of applying high voltage to the insulated end of the aerial device and it's components while measuring the amount of current leaking out the part close to ground. In recent years EUSA (Electrical Utility and Safety Assocation) has required all dielectric testing to be completed by certified testing facilities, in 2008 Rocwin became ISO9001:2008 accredited for dielectric testing.
At this time, most facilities in the area not accreditted for dielectric testing
Depending on the aerial device you have; you might require any or all of the following to be tested:
The main boom is often your most reliable source of insulation on an aerial device. These pieces are testing to the highest voltages (100kV AC or 140kV DC) but still must leak no less than any other portion of the aerial device.
While CSA C225-M00 no longer requires the testing of operator platforms the current standard in Ontario does. The lower 12 inches of the bucket must be tested (50kV AC or 70kv DC) for insulation purposes in case of contact with a lower phase or ground.
Bucket liners are tested (35kV AC or 70kV DC) through the thickness of the liner material. The best method for this is to fill both surfaces with water and use the water as a conductor. The combination of the bucket and liner make the platform insulated.
Lower Boom Insert/Chassis Insulation System
The lower boom fibreglass insert is tested (18.3kV/ft AC or 25.3kV/ft DC) to insure that no injuries or shocks happen to ground crew or anyone else passing by. Lower booms often get the worst of road salt and debris and can fail more than other components, most just need a good cleaning.
A fibreglass jib is tested much like a lower boom insert (18.3kV/ft AC or 25.3kV/ft DC) but lacks road debris issue and tend to pass regularly.
Fibre Reinforced Covers
Fibre reinforced plastic covers are surface tested to make sure no pinholes or weak areas exist for power to flow through. All covers are set up on a live electrode and a grounded metal is coated along the outside of the cover. When the correct voltages are chosen for the particular class of cover any defective is clearly visible during testing.
Live line tools
Tools, along with work procedures, are your main protection and insulation from power. Tools are tested the most harshly at 75kV every foot of insulation. These used to be tested to IEEE978-2000 but that standard was recalled due to numerous problems with the wet test method. With the abense of a replacement standard we continue to test IEEE978-1984, which use the same voltages but exclude the water; the method recommended to us by EUSA.
While phase sticks aren't tested for insulation it is important that the voltages they tell you are present are accurate. Our calibrated equipment will allow us to record and point out defective or mis-calibrated meters.