IPC/WHMA-A-620 Class 1, 2, and 3: What the Standard Means

IPC/WHMA-A-620 is the industry's shared standard for how wire harnesses and cable assemblies should be built and inspected. It sorts work into three classes by how much reliability the end product demands, and the class on the print decides where the line sits between a connection that's good enough and one that has to be rejected.

Somewhere right now there's a wire harness inside a defibrillator, and another one inside a flight control system, and a third inside a kid's toy. All three were built from wire, terminals, and crimps. What separates them isn't the parts. It's how much it matters when one fails, and how the people building them agreed to define "good."

That agreement has a name. IPC/WHMA-A-620 is the standard that lets a buyer and a builder a thousand miles apart mean the same thing when they say a harness is acceptable. It's worth understanding, not because you'll ever read all 326 pages of it, but because the class designation buried on your engineering drawing is quietly making decisions about your product's reliability, and it helps to know what those decisions are.

What IPC/WHMA-A-620 Is

IPC/WHMA-A-620 is the only industry-consensus standard for the requirements and acceptance of cable and wire harness assemblies. It's published jointly by IPC, now known as the Global Electronics Association, and WHMA, the Wire Harness Manufacturers Association. In plain terms, it's the rulebook for how a harness should be crimped, soldered, spliced, shielded, molded, marked, and tested, and how an inspector decides whether the finished work passes.

The current version is Revision F, published in October 2025. That matters, because a lot of what you'll find written about this standard still references the older Revision E from 2022. The criteria are stable from one revision to the next, but if you're reading about 620, it's worth knowing which version someone is working from.

One distinction worth clearing up, because it confuses people. IPC/WHMA-A-620 covers wire and cable assemblies. A different standard, IPC-A-610, covers assembled circuit boards. A product that has both a harness and a populated board may call out both standards, but they're separate documents covering separate work. When someone says a shop builds to 620, they're talking specifically about wire and cable.

The Three Classes

The heart of the standard is a simple idea: not every product needs the same level of reliability, so the standard defines three classes, and the requirements tighten as you move up.

Class 1, General Electronic Products.

Work where the main thing that matters is that the finished assembly functions. Think consumer goods and basic electronics, products with a limited life where the cost of building to a higher standard wouldn't be worth it.

Class 2, Dedicated Service Electronic Products.

Work where continued performance and a longer life are expected, where uninterrupted service is wanted but a failure isn't catastrophic. This is the broad middle, industrial equipment, commercial gear, most of the things that need to keep working reliably without a life depending on them. It's where a large share of real-world harness work lives.

Class 3, High Performance and Harsh Environment Products.

Work where performance on demand is critical, where downtime can't be tolerated, where the environment may be punishing, and where the equipment has to function when it's called on. Life-support medical devices, aerospace, defense. The kind of product where a failure isn't an inconvenience, it's a serious problem.

The classes aren't grades of effort, and Class 1 doesn't mean sloppy. They're a match between how the product will be used and how much margin the build needs to carry. A toy built to Class 3 would be a waste of money. A flight system built to Class 1 would be reckless. The point is to build each product to what it needs.

One Crimp, Three Answers

Here's the part that makes the classes concrete, and it's the thing the standard does that most people don't realize.

Take a single crimped connection with a few strands of wire slightly out of place, what's called birdcaging, where the strands spread instead of staying tight. Look at that same condition through the lens of each class, and you get three different answers.

In Class 1, that minor strand separation may be perfectly acceptable. The connection works, and for a general product that's the bar.

In Class 2, the same condition might be flagged as a process indicator. That's the standard's term for "this isn't a defect, but it's a sign something in the process is drifting, and you should pay attention before it becomes one." The part can still pass, but it's telling you something.

In Class 3, that same strand separation can be a defect, full stop. The connection gets rejected and rebuilt, because in a product where performance on demand is critical, the margin that minor flaw eats into is margin you're not allowed to give up.

Same crimp. Same wire. Three different calls, depending entirely on the class the product was assigned. That's the standard working exactly as intended, holding the build to the reliability the end use demands, no more and no less.

What Building to a Class Takes

Understanding the classes is one thing. Building to them, day in and day out, is another, and it's where a shop's seriousness about the standard shows.

The higher the class, the more the standard asks for beyond the part itself. Class 3 work requires a documented process-control system, a real discipline around how tools are calibrated, how operators are verified as proficient, how materials are kitted and tracked. That's not paperwork for its own sake. It's the difference between a shop that happened to build a good harness once and a shop that can prove it builds good harnesses every time, and can show the records to back it up.

Inspection rigor climbs with the class too. The same crimp gets looked at harder, under the right magnification, against tighter acceptance criteria, with more of the lot checked rather than sampled. And when something needs to be reworked, the higher classes require that the rework be documented and, in many cases, that the customer sign off on how a nonconformance was handled.

None of this is exotic. It's the ordinary, unglamorous discipline of a shop that treats the standard as the way it works rather than a box to check at the end. A shop that has been building to these criteria for years doesn't experience 620 as a burden. It experiences it as the shared language it uses with every customer.

Who Decides the Class, and What That Means for You

Here's a point that trips up some buyers: you usually don't pick the class, and neither does your contract manufacturer. The class is set by the engineer who designs the product, and it shows up as a callout on the engineering drawing or in the purchase documentation. By the time a print reaches a shop like ours, the class is almost always already specified, because the engineer knows what the product has to survive.

What a good manufacturer does is build and inspect to whatever class the print specifies, and flag it when something doesn't add up. If a drawing comes in silent on the class, the standard does allow the manufacturer to establish it, but the better move is to ask, because guessing at the reliability a product needs is exactly the kind of assumption that causes problems later. A shop that knows the standard cold is a shop that catches the missing callout and confirms it with you, rather than quietly building to whatever's easiest.

At Metro Assemblies, we build and inspect to IPC/WHMA-A-620 and IPC-A-610 workmanship standards. We don't decide what class your product needs. Your engineers do that, on the print, where it belongs. What we do is build to it faithfully, inspect to it without cutting corners, and treat the standard as what it's meant to be: the shared definition of good that lets you trust the harness in your product without having to stand over the bench yourself.

Ready to Build to Your Spec?

Send us the drawings, bill of materials, and quantities for your assembly, with whatever class your engineers have specified, and we'll turn around a quote in 24 to 72 hours and build to exactly the standard your product calls for.

If you want to see what we build before you send a print over, our capabilities page covers the wire and cable work we take on.

Frequently Asked Questions

What is IPC/WHMA-A-620?

It's the industry-consensus standard for the requirements and acceptance of cable and wire harness assemblies, published jointly by IPC (now the Global Electronics Association) and WHMA, the Wire Harness Manufacturers Association. It defines how harnesses should be crimped, soldered, spliced, shielded, molded, marked, and tested, and how an inspector decides whether the work passes. The current version is Revision F, published October 2025.

What's the difference between IPC-620 Class 1, 2, and 3?

The classes match the build to how much reliability the end product needs. Class 1 (general products) is for work where the main requirement is that the assembly functions. Class 2 (dedicated service) is for products that need continued, reliable performance over a longer life. Class 3 (high performance and harsh environment) is for products where performance on demand is critical and failure isn't tolerable, like life-support medical, aerospace, and defense.

Who decides which IPC-620 class my product needs?

The engineer who designs the product decides, and the class is specified on the engineering drawing or in the purchase documentation. The contract manufacturer builds to whatever class the print calls for. If a drawing is silent on class, the standard allows the manufacturer to establish it, but a good shop will confirm the intended class with the customer rather than guess.

What does the same defect look like across the three classes?

A minor flaw can get three different calls. Take a slightly birdcaged crimp, where wire strands spread. In Class 1 it may be acceptable. In Class 2 it may be a process indicator, a sign the process is drifting, though the part can still pass. In Class 3 it may be a defect that has to be rejected and rebuilt. The same condition is judged against the reliability the product's class demands.

Is IPC-A-620 the same as IPC-A-610?

No. IPC/WHMA-A-620 covers cable and wire harness assemblies. IPC-A-610 covers assembled printed circuit boards. A product with both a harness and a populated board may reference both standards, but they're separate documents covering separate work.

What does it mean for a shop to "build to" IPC/WHMA-A-620?

It means the shop manufactures and inspects to the standard's acceptance criteria for the specified class. Worth knowing, IPC certifies individuals, not companies, so building to the standard is about conforming to its criteria and having proficient people, which is separate from any individual holding an IPC certification. A shop can build and inspect to 620 as its normal way of working.