Only posting what is considered reliable technical source data.
Copy from referenced T.O.:
a- High potential voltage or insulation breakdown testing of aircraft electrical wiring and cabling will be conducted as a last resort after all previous methods of detecting faulty cabling have been accomplished. These methods shall consist of continuity, visual inspection, common voltmeter and ohmmeter checks, and other methods not involving high potential voltage tests.
WARNING
Potential explosive hazards may exist. Equipment operators shall become thoroughly
familiar with operational characteristics of the testers prior to use.
b- The following procedures will apply where tests, employing high potential testers, are made to check aircraft electrical cabling and wiring involving those areas where fuels, fumes, or explosive vapors may possibly be present.
(1) Providing fumes or vapors can be removed by isolating fuel from the areas involved by means of shut-off or bypass
valves, only that portion of the fuel system which is isolated must be drained, purged, and maintained at less than 20% LEL (Lower Explosive Limit).
(2) Providing adequate isolation cannot be accomplished, the entire fuel system will be drained, purged, and maintained at less than 20% LEL (Lower Explosive Limit).
