Test and inspection
Cable assembly testing: continuity, hipot and insulation resistance
Visual inspection finds what can be seen. Electrical testing finds what cannot: a wire in the wrong cavity, a strand touching a shell, insulation nicked during stripping. Knowing what each test catches tells you what to write on the drawing.
The three core electrical tests
| Test | What it applies | What it finds | What it misses |
|---|---|---|---|
| Continuity | Low voltage and current between points | Opens, shorts, miswires (wire in the wrong pin), missing connections | Damaged insulation that has not yet shorted; marginal crimps that still conduct |
| Insulation resistance (IR) | A DC voltage between isolated conductors, measuring the resulting resistance | Contamination, moisture, degraded insulation, leakage paths | Some defects that only break down at higher voltage |
| Dielectric withstanding voltage (DWV, hipot) | A high AC or DC voltage for a set dwell time | Pinched or nicked insulation, stray strands, insufficient spacing, flashover paths | Wrong wiring, if the miswired circuits are still isolated from each other |
Because each test finds faults the others miss, drawings for critical assemblies commonly require all three. Many automated cable testers can run continuity, IR and hipot in one sequence from one fixture.
Continuity testing
A continuity test checks that every point that should be connected is connected, and that nothing else is. A good test program checks both: the intended connections (a from-to list, or netlist) and isolation between every net. Testing only the intended connections will not find a short between two unrelated circuits.
Continuity testing of 100% of production assemblies is common practice and a reasonable expectation from any cable shop. Things to specify:
- the netlist or wiring table the test program is built from, and its revision;
- a maximum resistance for a connection, if the default of the supplier's tester is not appropriate;
- whether shields, drain wires and backshells are included as test points;
- whether intermittent faults should be checked by flexing the cable during test.
Insulation resistance
An IR test applies a DC voltage between conductors, or between conductors and shield or shell, and measures resistance. The result is compared with a minimum value. Specify:
- test voltage (DC);
- minimum acceptable resistance;
- which points are tested against which (each conductor against all others, and against shield);
- dwell time before the reading is taken.
Dielectric withstanding voltage (hipot)
A hipot test applies a voltage well above normal working voltage, for a set time, and checks that leakage current stays below a limit and that there is no breakdown. It is the test most likely to find insulation damaged during assembly. Specify:
- test voltage and whether it is AC or DC;
- dwell time;
- maximum leakage current, or the tester's trip setting;
- ramp rate, if your components are sensitive to it;
- any components that must be excluded or disconnected, such as filters, diodes or surge protection.
Take the voltage from the component ratings. A hipot voltage above what the connector or wire is rated for can damage good parts. Connector and wire datasheets list their rated and test voltages. Where your customer or an industry specification sets a value, use it.
Other tests you may need
| Test | When it is used |
|---|---|
| Crimp pull test | Set-up and process verification for crimped terminations. See crimp pull testing. |
| Crimp cross-section | First article, tooling qualification, or dispute resolution |
| Contact retention / push-back | Confirming contacts are locked in connector cavities |
| Resistance or 4-wire (Kelvin) measurement | Power circuits and low-resistance requirements |
| Signal integrity (impedance, insertion loss) | Coaxial, high-speed and data cables |
| Seal or leak test | Overmolded or sealed assemblies with an ingress rating |
| Flex, vibration, thermal cycling | Design qualification, usually on samples, not every part |
Writing the test note
A test note that says "test per best practice" or "hipot test" will be interpreted by each supplier differently, and their quotes will differ with it. A usable note names the test, the parameters, the sampling and the record. For example:
100% of assemblies: continuity and isolation per wiring table, max 1 ohm per connection. Insulation resistance at [voltage] DC, min [value] between each conductor and all others and shield. DWV at [voltage] for [time], max leakage [value]. Record results by serial number and supply with each shipment.
Fill in the bracketed values from your design requirements. The one-ohm figure is an illustration, not a recommendation.
Test records worth asking for
A pass/fail stamp is weaker evidence than a record. A useful test record shows the part number and revision, the serial or lot number, the test program and its revision, the fixture used, the test parameters, the result for each test, the date, and who ran it. Ask whether records are kept electronically and how long they are retained. For serialized aerospace or defense parts, many buyers ask for the record to ship with the part.
What to ask a supplier
- What tester do you use, and what is its maximum test voltage and point count?
- Is the test program generated from my wiring table, and how is it checked when the drawing changes?
- How do you prove the fixture itself is working at the start of each shift?
- Can you produce a pass record per serial number?
- How are fixtures and adapters quoted: in the piece price, or as separate tooling?
Common questions
Is hipot testing required by IPC/WHMA-A-620?
The standard covers electrical testing, but which tests apply, and their parameters, should be stated by the buyer. Put them on the drawing rather than relying on a default.
Can hipot testing damage a cable?
A test at an appropriate voltage should not damage a good assembly. Excessive voltage, or repeated testing, can stress insulation, which is why the voltage should come from component ratings.
Should every part be tested, or a sample?
Continuity is normally tested on every part. Hipot and IR are often also 100% for aerospace, defense and power applications. Destructive tests such as pull tests and cross-sections are done on samples.
Related: first article inspection, harness drawing notes, and the RFQ checklist.
Last reviewed 2026-09-17