What do continuity, insulation resistance and hipot tests check on a cable harness?

Continuity testing confirms that every intended connection exists at low resistance, catching an open circuit or a missed crimp. Insulation resistance testing measures leakage current at a set DC voltage between conductors that should be isolated, catching gradual insulation degradation rather than a broken connection. Both are run on the same harness because they check opposite failure modes: missing connection versus unwanted leakage.

Where the customer drawing or specification does not set its own value, IPC/WHMA-A-620's default hipot, or dielectric withstanding voltage, test is 1000 V DC for a Class 2 assembly with a 0.1 second dwell, and 1500 V DC for a Class 3 assembly with a 1 second dwell. Wire and connector voltage ratings are checked first, since testing above a component's rating can damage sound insulation.

The minimum acceptance value depends on the assembly: 100 megohms or more for an assembly of three metres or less, 10 megohms or more for a longer assembly, and 500 megohms or more for coaxial cable. These are the standard's default values where the customer drawing does not specify its own minimum for the particular harness.

IPC/WHMA-A-620 does not require a separate shorts, or isolation, test once dielectric withstanding voltage or insulation resistance testing has been performed, since either of those tests would also reveal an unintended short between conductors. Many test houses run a quick shorts check anyway, before the higher-voltage tests, because it catches a basic wiring error faster and more cheaply.

Class 1 covers general products where basic function is the main requirement. Class 2 covers dedicated service products needing extended performance where uninterrupted service is desirable but not critical. Class 3 covers high performance, harsh-environment products, including defence and aerospace work, where failure cannot be tolerated, and it carries the tightest acceptance criteria and the highest default hipot voltage of the three.

An automated harness tester connects to every connector through dedicated adapters and checks the wiring against a learned or programmed netlist, finding opens, shorts and miswires far faster than a manual check. Higher-end testers add hipot and insulation resistance testing to the same cycle and log every result against the harness's serial number, giving a traceable test record rather than a signed card with no data behind it.