IPC/WHMA-A-620 is the main inspection and acceptance standard for cable and wire harness assemblies. If you source wire harnesses from China, put this standard at the center of your factory audit, supplier qualification, and First Article Inspection (FAI).
A good audit should not only check whether the supplier can assemble wires, terminals, and connectors. It should verify whether the factory can control crimping, soldering, routing, labeling, testing, documentation, and compliance before volume production begins. This guide maps that audit onto the wire harness manufacturing process, from pre-production controls to final inspection.
Key Takeaways
- IPC/WHMA-A-620 is the benchmark standard for cable and wire harness assembly acceptance.
- A proper Chinese wire harness factory audit should cover pre-production controls, in-line inspection, and First Article Inspection.
- The most important harness-specific checks include crimp height, pull-force testing, wire stripping quality, connector seating, continuity testing, insulation resistance, and wire-routing verification.
- IPC/WHMA-A-620 certification usually applies to individual staff, not the factory as a whole.
- Underwriters Laboratories (UL) requirements are separate from IPC/WHMA-A-620 and matter when the harness is used in regulated, safety-related, or US-market applications.
- Major red flags include missing crimp tool calibration records, no pull-force data, wire substitution, unverified UL components, and vague inspection reports.
What is IPC/WHMA-A-620?
IPC/WHMA-A-620, formally titled Requirements and Acceptance for Cable and Wire Harness Assemblies, is the main workmanship standard for wire harness manufacturing. It is published jointly by IPC and the Wire Harness Manufacturers Association, usually shortened to WHMA.
The standard covers the acceptability of cable and wire harness assemblies. That includes crimped, soldered, mechanically secured, and insulation displacement connections, plus splices, shielding, marking, routing, protective coverings, and finished assembly inspection.
IPC/WHMA-A-620 separates assemblies into three product classes:
| Class | Typical use | What it means |
|---|---|---|
| Class 1 | General electronic products | Basic function is the main requirement |
| Class 2 | Dedicated service electronic products | Continued performance and longer life are expected |
| Class 3 | High-performance or harsh-environment products | Performance-on-demand is required, and downtime is not acceptable |
For many industrial, commercial, and electronics applications, Class 2 is the normal baseline. For aerospace, defense, medical, automotive safety systems, electric vehicle (EV) power systems, and harsh-environment applications, Class 3 may be required.
Why is IPC/WHMA-A-620 the benchmark for wire harness quality?
For buyers, IPC/WHMA-A-620 matters because it gives both sides a common inspection language. Instead of saying a crimp “looks good” or a wire route “seems acceptable,” you can specify the exact product class. You can also define the inspection criteria and test evidence required.
The key point is simple: do not ask for “IPC quality” in a vague way. Specify the full standard, revision, and class in your drawings, purchase orders, and inspection plans.
IPC/WHMA-A-620 Certification vs. Training | What to Ask Your Supplier
One common mistake is asking whether a factory is “IPC/WHMA-A-620 certified.” In practice, IPC/WHMA-A-620 certification usually applies to people, not the factory itself.
A wire harness factory may have employees trained or certified as Certified IPC Specialists, often shortened to CIS. Some facilities may also have Certified IPC Trainers, or CITs, who can train internal staff. These credentials show that specific people have been trained to understand and apply the standard.
That is useful, but it is not the same as proving that every production line follows IPC/WHMA-A-620 during real manufacturing.
When auditing a Chinese wire harness supplier, ask for:
- IPC/WHMA-A-620 training records for operators, inspectors, and quality staff
- CIS or CIT certificates where available
- Training expiry dates
- Internal training logs
- Work instructions that reference IPC/WHMA-A-620
- Inspection reports showing actual acceptance decisions
- Nonconformance records and corrective actions
- Crimp validation records
- Pull-force test results
- Tool calibration records
- First-off and First Article Inspection reports
The best suppliers can connect training to production evidence. They should show that trained staff work on relevant lines, use controlled work instructions, record inspection results, and reject nonconforming assemblies.
Phase 1: Pre-Production Audit: Before Assembly Begins
A pre-production audit checks whether the supplier is ready to build the harness correctly before volume production starts. This stage should confirm that the factory has trained operators, controlled documents, verified materials, and calibrated tooling. It should also show a clear inspection process before the first production run.
Verify IPC/WHMA-A-620 training and inspection competence
Start with the people who will build and inspect the harness. Operators and inspectors should understand IPC/WHMA-A-620 requirements for wire stripping, strand damage, terminal seating, insulation clearance, crimp acceptability, soldering, routing, shielding, and labeling.
Do not only check certificates. Ask line staff to explain what makes a crimp acceptable, what a nicked conductor looks like, and when a connector contact should be rejected. A supplier that cannot explain its own acceptance criteria is not ready for controlled production.
Review crimp tooling and calibration records
Crimping is one of the high-risk wire harness processes. A terminal can look acceptable while still failing electrically or mechanically if the crimp height, tooling, compression, or conductor position is wrong.
Ask for current calibration records for presses, applicators, dies, pull testers, and measuring tools. The supplier should also show crimp height records by wire gauge, terminal, and production lot. Missing calibration logs or crimp setup records should be treated as a serious warning sign.
Verify wire gauge, insulation, and material specifications
The approved Bill of Materials (BOM) should match the actual wire, connectors, terminals, insulation, sleeving, shielding, labels, and other components on the production floor. Pay close attention to wire gauge, insulation rating, voltage rating, color coding, approved part numbers, and UL style where required.
Wire substitution is a common sourcing risk. A supplier may replace the specified conductor with a smaller wire, lower-rated insulation, or non-approved brand to reduce cost. For American Wire Gauge (AWG) wire, remember that a higher AWG number means a smaller conductor.
Check UL-rated components where required
IPC/WHMA-A-620 does not replace UL compliance. If the harness is used in a US-market product, industrial control panel, flexible cord application, power equipment, or safety-related device, UL requirements may apply.
Before production begins, confirm whether the harness needs UL-rated wire, connectors, terminals, sleeving, heat shrink, labels, insulation materials, or strain relief components. The exact requirement depends on the final product, application, current, voltage, temperature, installation environment, and market.
Review work instructions, routing diagrams, and master samples
Wire harness manufacturing depends heavily on process discipline. The same BOM can produce different results if routing, bend radius, breakout lengths, labeling, and connector orientation are not controlled.
Before production begins, the supplier should have approved drawings, a controlled BOM, wire cut list, crimp specification, connector pinout, and routing diagram. It should also hold the harness board layout, labeling instructions, test requirements, packaging instructions, and an engineering change control process. The master sample can help control production consistency, but it should support the approved drawing rather than replace it.
Special Offer: Get $100 off your order!
Email sales@ourpcb.net to get started!
Phase 2: In-Line Inspection: Monitoring Crimp Quality and Wire Routing
In-line inspection checks whether the factory can maintain quality after the first setup has been approved. This stage should focus on actual production behavior, especially crimp quality, wire stripping, connector seating, routing, and electrical continuity.
Crimp height monitoring
Crimp height is one of the most important controls in wire harness production. It confirms whether the terminal barrel has been compressed correctly for the wire, terminal, and tooling combination.
The factory should record the terminal part number, wire gauge, target crimp height, measured crimp height, tool ID, operator, lot number, and inspector approval. Crimp height should be measured with calibrated tools, and high-risk builds may require cross-section analysis during setup or validation.
Pull-force test sampling
Pull-force testing checks the mechanical strength of a crimped termination by pulling the wire and terminal under controlled conditions. The supplier should test against the applicable IPC/WHMA-A-620 minimum pull-force value for the wire size and termination type.
The results should be recorded with the test frequency, wire gauge, terminal type, actual pull-force value, pass/fail decision, and corrective action for failures. A supplier that refuses to share pull-force data should not be approved without further review.
Wire stripping inspection
Wire stripping defects are easy to miss but can cause long-term reliability problems. Inspectors should check for conductor nicks, cut strands, broken strands, pulled insulation, ring cuts, incorrect strip length, and insulation damage.
Repeated stripping defects at the same machine or station may indicate worn blades, poor machine setup, incorrect wire settings, or weak operator training.
Connector insertion and seating verification
Connector seating problems can create intermittent electrical faults that are difficult to diagnose later. During in-line inspection, contacts should be fully inserted, locked, correctly oriented, and placed in the correct connector cavity.
Inspectors should also check for backed-out pins, bent contacts, missing sealing plugs, incorrect wire colors or circuit IDs, and damaged connector housings. For high-reliability builds, tug checks or retention verification may also be required.
Routing and continuity checks against the master sample
Wire routing is not cosmetic. Poor routing can cause abrasion, excess tension, connector strain, bend radius violations, heat exposure, electromagnetic interference (EMI) issues, or installation problems.
During in-line inspection, compare production units against the approved drawing and master sample. Run continuity tests as defined in the test plan to catch wrong pinouts, missed wires, open circuits, and misrouted circuits before final inspection.
Phase 3: First Article Inspection: Validating the First Production Run
FAI confirms that the first production build matches the approved drawing, BOM, process requirements, and IPC/WHMA-A-620 acceptance class. For wire harnesses, FAI should go beyond a basic visual check and include dimensional, electrical, material, and workmanship verification.
Dimensional verification
Dimensional FAI confirms that the harness physically matches the approved drawing. The inspector should check overall length, branch lengths, breakout locations, connector orientation, label location, protective covering length, and tolerance requirements.
This matters because a harness can pass continuity testing and still fail during installation if the dimensions are wrong.
Point-to-point continuity test
A point-to-point continuity test confirms that each circuit connects to the correct terminal, pin, or connector cavity. The results should be checked against the approved wiring diagram or net list.
This test helps identify open circuits, miswires, crossed wires, missing circuits, and incorrect cavity assignments. For complex harnesses, automated test fixtures are preferred because manual probing increases the risk of human error.
Insulation resistance and dielectric withstand testing
Insulation resistance (IR) testing checks whether conductors are properly isolated. Dielectric withstand testing, also known as hi-pot testing, checks whether insulation can withstand a specified voltage without breakdown.
These tests may apply to power harnesses, high-voltage assemblies, industrial or medical equipment, EV systems, safety-related wiring, or harnesses exposed to moisture and contamination. The test voltage, dwell time, leakage limit, and acceptance criteria should be defined before production begins.
Full visual inspection to IPC/WHMA-A-620 criteria
The FAI should include a full visual inspection to the required IPC/WHMA-A-620 class. This should cover wire stripping, crimping, soldering, splices, connectorization, labeling, shielding, routing, protective coverings, and finished assembly condition.
Inspectors should not treat visual inspection as a quick cosmetic review. They should verify whether the assembly meets the required acceptance class.
Wire gauge and color coding verification
The FAI should confirm that actual production materials match the approved BOM. This includes wire gauge, insulation color, conductor type, shielding, connector type, terminal part number, label content, sleeving, heat shrink, and UL-rated materials where required.
This step protects against material substitution, one of the most expensive problems to discover after volume production.
Third-Party Inspection Firms for Wire Harness Audits
Some buyers use third-party inspection firms to audit Chinese wire harness factories before production or before shipment. Common options include SGS, TÜV Rheinland, Bureau Veritas, and Intertek.
Third-party inspection can be useful when you cannot visit the factory yourself. However, the inspection scope must be specific. A generic factory audit is not enough for a wire harness program.
The audit request should mention IPC/WHMA-A-620, the required class, crimp height records, pull-force testing, wire gauge verification, routing inspection, test reports, and FAI requirements.
| Inspection type | Typical cost range | Turnaround | Best for |
|---|---|---|---|
| Basic factory audit | $300–$700 | 2–5 business days | Supplier legitimacy, capacity, general quality system |
| Pre-production wire harness audit | $600–$1,200 | 3–7 business days | Tooling, materials, documentation, training, UL component checks |
| In-line inspection | $400–$900 per man-day | Same day to 3 days | Crimping, routing, stripping, connector seating, process control |
| First Article Inspection | $700–$1,500 | 3–7 business days | Dimensional checks, continuity, IR, hi-pot, full visual inspection |
| Pre-shipment inspection | $300–$800 | 1–3 business days | Final quantity, packaging, visual defects, sample testing |
| Full technical audit with test witnessing | $1,200–$2,500+ | 5–10 business days | High-risk Class 3, UL-related, automotive, aerospace, or industrial builds |
Wire harness audits may cost more than PCB inspections because harness inspection is labor-intensive. Each unit may require manual routing verification, connector cavity checks, label checks, dimensional measurement, and electrical testing.
UL Requirements for Wire Harnesses Manufactured in China
UL requirements are separate from IPC/WHMA-A-620. A harness can be well-built to IPC/WHMA-A-620 and still fail to meet UL-related requirements if the materials, ratings, or final product application are wrong.
UL matters when the harness will be used in a product that needs US safety compliance, customer approval, or regulatory acceptance. This often includes industrial control equipment, power equipment, appliances, flexible cord assemblies, EV-related equipment, and safety-related electronics.
When UL applies, check whether the supplier is using UL-recognized materials and components. Ask for documentation for wires, cords, connectors, terminals, insulation, labels, heat shrink, sleeving, and other safety-related materials.
The audit should verify:
- UL file numbers where applicable
- Correct component ratings
- Correct voltage and temperature ratings
- Approved wire style or cord type
- Material traceability
- Supplier certificates
- Component markings
- BOM match
- No unauthorized substitution
Do not assume that a Chinese factory using “UL equivalent” parts is acceptable. If UL compliance is required, the exact component approval and application must be confirmed.
Red Flags in Chinese Wire Harness Factories
A good factory should be able to show evidence. A weak factory will often rely on verbal promises, sample quality, or vague statements about experience. Watch for these red flags:
| Red flag | Why it matters |
|---|---|
| No crimp tooling calibration logs | Crimp quality may be uncontrolled |
| No pull-force test data | Mechanical termination strength is not verified |
| Refusal to share inspection records | Quality claims cannot be validated |
| Wire gauge substitution | Smaller conductors can create overheating and performance risks |
| No UL-rated components on UL-required builds | Product compliance may fail |
| No IPC/WHMA-A-620 training records | Inspectors may not understand acceptance criteria |
| No controlled work instructions | Production may vary by operator |
| No first-off approval process | Defects may enter volume production immediately |
| No golden sample control | Operators may copy outdated or incorrect samples |
| Poor connector cavity checks | Miswires and intermittent faults may escape |
| Manual continuity testing without records | Failures may be missed or undocumented |
| Unclear rework process | Repaired assemblies may create hidden reliability risks |
The biggest warning sign is inconsistency. If the sample looks good but the process records are weak, volume production may not match the approved sample.
How OurPCB Approaches Wire Harness Quality
At OurPCB, we treat wire harness quality as a process control issue, not only a final inspection task. A finished harness must match the drawing, BOM, electrical requirements, mechanical layout, labeling requirements, and customer acceptance class. For projects that need controlled sourcing and production, OurPCB provides custom wire harness manufacturing for prototype and production builds.
If your project includes both board-level electronics and harness connections, OurPCB can support custom cable assembly manufacturing alongside PCB fabrication and assembly. For PCB supplier checks, read our guide on how to verify a Chinese PCB manufacturer.
To discuss a controlled wire harness, cable assembly, or PCB assembly build, request a quote from OurPCB and share your drawings, BOM, target volume, IPC/WHMA-A-620 class, and test requirements.
FAQs on IPC/WHMA-A-620
What is IPC/WHMA-A-620?
IPC/WHMA-A-620 is the main acceptance standard for cable and wire harness assemblies. It defines workmanship and inspection criteria for wire preparation, crimping, soldering, connectorization, splices, routing, labeling, shielding, protective coverings, and final testing.
How do I verify a factory is IPC/WHMA-A-620 compliant?
Ask for staff training records, CIS or CIT certificates where available, controlled work instructions, and crimp height records. Also request pull-force test data, calibration records, inspection reports, FAI reports, and nonconformance records. Do not rely only on a supplier’s claim that it “follows IPC standards.”
What is a pull-force test in wire harness inspection?
A pull-force test measures the mechanical strength of a crimped termination. A technician pulls the wire and terminal under controlled conditions. This confirms that the crimp meets the required minimum strength for the wire size and termination type. It helps verify that the crimping process is mechanically sound.
Do I need UL certification for wire harnesses made in China?
You may need UL-recognized or UL-listed components when the harness is used in a US-market product. Examples include an industrial control system, power application, flexible cord assembly, or safety-related device. UL requirements depend on the final product and application. IPC/WHMA-A-620 does not replace UL compliance.
What is the difference between IPC/WHMA-A-620 Class 2 and Class 3?
Class 2 applies to products that require continued performance and extended service life, but where downtime is not usually life-threatening or mission-ending. Class 3 applies to high-performance or harsh-environment products where performance is required on demand and failure cannot be tolerated. Class 3 has stricter acceptance expectations and is often used for aerospace, defense, medical, automotive safety, and other high-reliability applications.
Back to Top : IPC/WHMA-A-620: The Complete Wire Harness Audit Guide for Chinese Factories
Special Offer: Get $100 off your order!
Email sales@ourpcb.net to get started!
