IPC/WHMA-A-620 Class 1, 2 or 3: Which One Belongs on Your Harness PO

Somewhere between the drawing and the purchase order, most harness buyers type "IPC/WHMA-A-620 Class 3" because Class 3 sounds like the safe choice. It is the most expensive sentence in the document, and on its own it buys almost nothing. A class designation without an inspection plan, a sampling rule and a defined order of precedence is not a quality requirement — it is a phrase that both parties will interpret differently at exactly the moment a container is sitting in a warehouse and somebody needs to decide whether 40 assemblies get shipped or scrapped. Here is what the three classes actually change, what they cost you in the places the cost really lands, and how to write the requirement so that it settles arguments instead of starting them.

What A-620 is, and what it is not

IPC/WHMA-A-620 is the acceptability standard for cable and wire harness assemblies, published jointly by IPC and the Wiring Harness Manufacturer's Association. It is the harness world's counterpart to the board-assembly standard that most electronics buyers already know, and it covers the operations a harness shop actually performs: stripping, crimping, soldering, splicing, ultrasonic welding, connectorisation, over-moulding, marking and labelling, shielding termination, wire-bundle securing, and the finished-assembly checks. Confirm the current revision letter with IPC before you cite one; revisions arrive every few years and the criteria move.

Two things it is not.

It is not a certification a factory holds. A-620 is a document you buy, read and impose. There is a personal certification programme for inspectors and trainers — a credential attached to a named person, on a renewal cycle, not to a building — and there are separate audit programmes some assemblers choose to enter. Neither is implied by a factory quoting "we work to A-620". Ask for evidence at the level the credential actually exists: a certificate with a person's name, a number and an expiry date. CMH's own listing for this Shenzhen harness shop notes that no EU or US market-entry product certificates are on file, and instructs buyers to check the issuing body, holder name and validity date on any document they are shown. Apply the same three checks to a workmanship claim.

It is not self-executing, either. The standard defines an order of precedence, and understanding it is the difference between a spec that works and one that does not: your procurement documentation outranks the master drawing, and the master drawing outranks A-620. Anything your drawing says wins over the standard. That is a feature — it lets you tighten one criterion without rewriting a standard — but it also means a drawing that contradicts the class you specified quietly cancels it.

The three classes, in plain procurement terms

The class does not change every criterion. A great many acceptance criteria in A-620 are identical across all three classes — a missing strand is a missing strand. What changes is the threshold on the criteria where a difference is defensible.

Where the classes actually diverge

Read the standard for the exact numbers; these are the categories where the class you write down changes the accept/reject line:

• Strand damage after stripping. Permitted counts of nicked, scraped or severed strands tighten as the class rises and vary with conductor size. This is the criterion that most often turns into a dispute, because it is invisible once the terminal is crimped.
• Conductor brush and insulation position in the crimp. How much conductor must be visible past the crimp barrel, and how far insulation may intrude, tighten with class.
• Bellmouth and crimp geometry. Front bellmouth expectations, carrier cut-off tab length and burr limits are class-sensitive.
• Splices. Higher classes restrict in-line splices unless they are on the drawing and documented; a shop that splices to recover a mis-cut lead is behaving legitimately at one class and creating a defect at another.
• Solder wetting and wicking. Wick-up beyond a defined point stiffens the wire and creates a stress riser; the tolerance narrows with class.
• Marking and labelling legibility, and shield termination quality. Both carry class-graded criteria.

Note what is not on that list: pull-force values and crimp-height targets. Those come from the terminal manufacturer's specification and your own drawing, not from the class. Writing "Class 3" does not tell a factory what pull force to hit on your terminal — that is the subject of the sibling piece on crimp height, pull force and cross-section, and it needs to be on your drawing regardless of class.

Why "Class 3" without the money produces an argument, not a better harness

A class is an acceptance vocabulary. The quality actually arrives through the process controls that make the acceptance criteria achievable — and those cost real money in real places:

Inspection labour. Class 3 acceptance realistically implies a much higher inspection rate, often 100% visual on defined features, sometimes with magnification specified by the standard. On a 1,000-piece MOQ run of multi-branch looms with twenty terminations each, that is a large number of inspected features. Somebody pays for those minutes.

Retained evidence. Cross-sections consume the part they prove. A retained-cross-section regime at, say, one per applicator setup and one per shift means destroying finished terminations and storing images against your part number. That is cheap per unit and expensive to set up.

Tooling discipline. Crimp-height verification at setup and at defined intervals, applicator maintenance records, and a rule for what happens when a reading drifts. Without this, high-class acceptance criteria simply generate more rejects later.

Rework rules. A-620 treats rework as a controlled operation. At higher classes you generally want a written rule that a rejected termination is cut off and re-terminated rather than adjusted, and that re-terminated leads are re-tested — which consumes wire length and can push a lead below its minimum cut length.

Operator competence. The personal certification programme exists because these criteria need trained eyes. Ask whether the person doing final inspection has a current certificate, ask for the number, and ask when it expires.

If your PO names Class 3 but your price assumed a Class 1 inspection rate, one of two things happens. Either the factory absorbs it once and then quietly reverts on the reorder, or your inspection report comes back with a defect list, the factory argues that the parts function correctly, and you discover that neither side agreed what evidence would settle it. That is the failure mode. It is not dishonesty on either side; it is an unfunded requirement.

Choosing the class honestly

Work from the consequence of a field failure, not from ambition:

1. What happens when one assembly fails in service? A charging lead that stops charging is an RMA. A battery lead that opens under load in an e-scooter is a different category of event. Write the class that matches the consequence.
2. Who else is imposing a class on you? If you are selling into an automotive or medical tier, the class is usually dictated upstream. Take it from the customer document rather than inventing it.
3. Is the difference achievable on this product at all? Some constructions — heavy over-moulds, dense breakouts — make certain higher-class visual criteria impossible to verify after assembly. If a criterion cannot be inspected in the finished part, it must be inspected in process, and that has to be written down.
4. Does your drawing agree with your class? Because the drawing outranks the standard, a drawing that permits something the class forbids will win. Reconcile them before release.

For a great deal of industrial, appliance and light e-mobility work, Class 2 with a properly specified inspection plan produces a better outcome than Class 3 with none. Most machine builders and energy-storage integrators land there.

Do not rely on a default

Some houses treat an order with no class stated as Class 2. Do not depend on it — confirm what the revision in force says, and then name the class explicitly in the PO anyway. An unstated class is the cheapest ambiguity to remove.

Writing the requirement so it is enforceable

A workmanship clause that holds up has six parts. Put all six on the PO or in the quality agreement it references:

1. Standard, revision and class. "IPC/WHMA-A-620, revision [x], Class 2" — with the revision letter, because criteria change between revisions.
2. Order of precedence, restated. Name your drawing number and state that the drawing governs where it conflicts with the standard, so nobody has to argue about it later.
3. Inspection plan. 100% on named features, sampling on the rest, with the sampling scheme and acceptable quality limit named (a published attribute sampling scheme, referenced by name and level, rather than "spot check").
4. Electrical test coverage. Continuity and mis-wire testing on 100% of assemblies is normal and cheap; insulation resistance and withstand-voltage testing on a stated basis if your application needs it. Say which, and say whether records are delivered per lot. The reading of those reports is covered in continuity, hipot and insulation resistance testing.
5. Records and retention. Which records travel with the shipment (test log, cross-section images, crimp-height log), in which format, and how long the factory keeps them.
6. Disposition rules. What happens to a lot that fails: rework allowed or not, re-inspection basis, who pays for third-party re-inspection, and whether a deviation can be granted in writing.

That sixth item is the one buyers skip and then need. Agree it while everyone is friendly.

What the factory side of this looks like

The equipment that makes class-graded acceptance verifiable is not exotic, and it is worth checking against a supplier's published roster before you argue about class at all. The Shenzhen shop profiled on CMH lists automatic cut-strip-crimp machines, servo crimping presses and benchtop crimpers on the production side, and on the QC side a terminal cross-section analyser, tensile and insertion-force testers, withstand-voltage and insulation testers, a salt-spray chamber and cable-continuity testers. That bench covers the physical checks A-620-style verification leans on.

What a roster cannot tell you is frequency and record-keeping — how often a cross-section is taken, whether crimp height is logged at setup, whether the continuity tester's results are captured per assembly or just used as a pass/fail gate at the bench. Those are questions, and they are answerable on a video call: ask the supplier to point the camera at the cross-section analyser and open the last month of images, then at the crimp-height log at a press. On a shop stating sample dispatch in 7–10 days and volume lead of 15–25 days to warehouse, the sample stage is your chance to agree what a lot record looks like before the schedule is under pressure.

Buyers who have run IPC class 3 automotive board assembly programmes will recognise the pattern: the class is the easy part, and the evidence regime is the whole job. The general framework in quality control in Chinese manufacturing and pre-shipment product inspection applies here, with one harness-specific twist — a third-party inspector who does not have your crimp specification and your class in hand will inspect for cosmetics and count cartons. Send them the drawing.

Common questions

Can a third-party inspector verify A-620 class compliance at pre-shipment?

Partially. A trained inspector with your drawing can check visual criteria, labelling, and finished-assembly features, and can witness electrical testing. What they cannot do at the warehouse is verify process history — crimp-height logs, applicator maintenance, cross-sections taken during the run. If those matter to you, require them as delivered records rather than expecting an inspector to reconstruct them.

Is a harness shop allowed to say it is "A-620 compliant"?

A supplier can reasonably say it builds to A-620 criteria at a stated class, and that claim is testable against your inspection. Treat any stronger phrasing as a claim to verify rather than a fact: ask what document supports it, who issued that document, in whose name, and until when.

Does specifying Class 3 improve reliability if my design is the weak point?

No. Workmanship class governs how the assembly is built and judged, not whether the conductor is sized correctly, the wire style suits the temperature, or the connector is rated for your current. Fix the specification first — the wire side of that is covered in the sibling article on AWM style numbers on a harness spec.

How do I keep the class from disappearing on the reorder?

Put it in a standing quality agreement referenced by every PO, not in the body of one PO, and require that any change of terminal, applicator, wire supplier or subcontracted operation triggers a new first article. Reorders drift because nothing forced a re-approval.

What to ask your supplier next

• Which A-620 revision do you work from, and can you show me the copy on your shop floor?
• At Class 2, what is your standard inspection rate, and what changes at Class 3 — in inspection minutes, not adjectives?
• Are crimp heights logged at setup and at intervals, and will those logs ship with the lot?
• How often is a cross-section taken — per lot, per shift, or per applicator change — and are the images retained against my part number?
• Does anyone doing final inspection hold a current personal A-620 certificate? Name, number, expiry.
• What is your written rule for a rejected termination: cut back and re-terminate, or adjust?
• Which electrical tests run at 100%, and can the results be issued per lot against my part number?

Send those questions with your drawing rather than after the quote — the answers change the price, and you want the price that reflects the real requirement. A compact Shenzhen builder like Huisheng Electronics, working across industrial, automotive and energy-storage harnesses laid out to buyer drawings, is the size of supplier where a clearly written class and inspection plan tends to be the difference between a smooth reorder and a negotiation.