Section 6.6 of SAE J1128 specifies the spark test (insulation faults test) for primary wire. A 2kV AC voltage is applied to detect faults, pinholes, or thin spots in the insulation during or after manufacturing.
The spark test is a critical production quality test that identifies insulation defects that could lead to electrical failure in service. Any breakdown detected during the test indicates an insulation defect requiring rejection.