3.1 Continuity, Hipot & Resistance
Electrical harnesses are the nervous system of any electronic system, and testing them is about proving both functionality and safety. From simple continuity checks to high-voltage stress tests, each method is a safeguard against defects that could cause failures in the field or hazards to operators. Running these tests in a logical sequence not only prevents costly mistakes but also builds trust that every harness is solid, traceable, and ready for service.
3.1.1 The plan (order matters)
Run tests in this sequence so you find cheap problems first and keep operators safe:
- Continuity & shorts (low-voltage net check).
- End-to-end resistance (does the metal match the math?).
- Insulation Resistance (IR) (DC at high voltage).
- Hipot (high-voltage stress with ramp, dwell, discharge).
If a step fails, stop and contain—don’t “see what happens” at higher stress.
3.1.2 Continuity & shorts (the fast netlist truth)
Goal: verify opens, shorts, and miswires against your From–To table (19.2).
Method
- Use a bed-of-nails harness tester or mating connector box; load the netlist by PN/Variant (scan to select).
- Stimulus: 5–20 V current-limited (≤20 mA is plenty).
- Continuity threshold (starter): ≤ 3 Ω or (R_calc + margin), whichever is higher (see 21.1.3).
- Shorts threshold (starter): ≥ 1 MΩ between unrelated nets.
Tips
- Treat shields/chassis as their own nets.
- Use guided probe mode for debug (lights show where the miswire is).
- For multi-branch looms, test submodules before final loom-up to isolate faults fast.
3.1.3 End-to-end resistance (does the number make sense?)
Measure each conductor’s DC resistance; compare to a smart limit.
Quick math
R_expected = (Ω/m from gauge) × length_along_centerline
Add contact allowance: ~20–50 mΩ per mated contact (two ends → 40–100 mΩ).
Starter limits
- Pass if R_measured ≤ (R_expected × 1.5) + contact_allowance.
- Flag asymmetry: matching-length mates should be within 10% of each other.
Low-ohm conductors (power, <100 mΩ): use 4-wire (Kelvin) measurement to avoid lead error.
3.1.4 Insulation Resistance (IR)
What: DC voltage applied between conductors (and to shield/chassis) to measure MΩ/GΩ.
Why before Hipot: finds moisture/contamination gently.
Starter setup
- Test voltage: 500 VDC (typical low-voltage harness). Use 250 VDC for sensitive electronics or per spec; 1000 VDC for heavy-duty looms if required.
- Dwell: 60 s (or 30 s + 5 s/m of cable length for very long runs).
- Limits (defaults—tighten per customer):
- Indoor/benign: ≥ 100 MΩ.
- Harsh/automotive: ≥ 10 MΩ minimum, ≥ 100 MΩ preferred.
- High-reliability boxes: ≥ 1 GΩ.
Notes
- Temperature/humidity affect IR. If borderline, retest in spec environment (5.2).
3.1.5 Hipot (with respect, not fear)
What: apply high voltage to prove no breakdown under stress.
DC vs AC
- DC Hipot (most harnesses): cleaner leakage reading; easier on capacitive loads.
- AC Hipot (some specs): stresses alternately; leakage limit is in mA RMS.
Starter DC setup (follow customer spec if given)
- Voltage: 500–1000 VDC for low-voltage harnesses.
- Ramp: 1–2 s up to setpoint.
- Dwell: 2–3 s + 0.3 s/m of harness length (capacitance driven).
- Trip/leakage: set 0.5–2.0 mA depending on length/capacitance; use the lowest value that avoids nuisance trips.
- Discharge: active discharge to <30 V before PASS/FAIL clears or the door unlocks.
Pairs to test
- Every signal net ↔ all others commoned.
- Power rails ↔ shield/chassis.
- Shield ↔ cores (if single-ended bond strategy, still Hipot for breakdown).
3.1.6 Fixtures & variants (ban pin damage and mix-ups)
- Prefer mating connectors or guided pogo blocks; no raw pin stabbing.
- Keyed plates and pin-1 triangles on fixtures; color bands per variant.
- Test program chosen by scanning the harness SN or cart; the tester blocks start on mismatch.
3.1.7 Safety (non-negotiables for Hipot/IR)
- Interlocked enclosure with door switch; two-hand or guarded start.
Red beacon and HV signage during test. - Bleed-down with indicator; door stays locked until safe.
- Guarded HV leads, rated probes; no alligator clips on bare metal.
- One-hand rule training; ESD strap OFF during Hipot.
- Emergency stop within reach; daily functional check.
3.1.8 Recording & traceability (make it audit-proof)
Each unit record (SN or lot) should store:
- Program ID / limits, operator, fixture ID.
- Continuity/shorts: pass, failing nets if any.
- Resistance: measured values or max per family.
- IR/Hipot: voltage, dwell, max leakage, result; timestamp.
- Photos (ends vs golden) if your flow requires them.
Tie this to 20.5 genealogy automatically—no screenshots living on laptops.
3.1.9 Typical limit starters (tune to your product)
Use customer/standard limits when specified. These are starting points to get you safely productive.
3.1.10 Common traps → smallest reliable fix
3.1.11 Pocket checklists
Before test
- Program/limits loaded by scan (PN–Rev–Variant)
- Fixture ID & orientation OK; connectors seated
- Visual: TPA/CPA locked, labels readable, boots cooled
Continuity/Resistance
- Continuity pass; no shorts
- Power lines 4-wire measured; results logged
IR/Hipot
- Door closed; beacon on; ESD strap off
- Ramp/dwell set; trip current appropriate for length
- PASS; discharge complete; door unlocks
Closeout
- Results attached to SN/lot in MES
- Fails to NG-QUAR with netlist of defects
- Fixture condition check; pins undamaged