The jacket flaws test (spark test, insulation-continuity proof test, or insulation faults test) aims to identify any defects in a wire/ cable’s outer insulation that would allow an amount of leakage current. Testing is performed in an enclosure filled with conductive metal beads/ balls. The beads are electrified and connected to a continuity detection circuit along with the conductor of the sample under test. The sample is fed through the enclosure such that it is constantly surrounded by the electrified metallic beads.
A quality insulator/ jacket will prevent continuity between the sample conductor and the electrified beads. If continuity is detected in the circuit twice in the same location along the length of the sample, it is considered a failure. The total number of failures (if any) are reported.