IPC/WHMA-A-620 Class 1, 2 and 3 — What Heavy Equipment Engineers Need to Know

Who Decides the Class — and When

According to IPC/WHMA-A-620E Section 1.3, use of the standard requires agreement on the class to which the product belongs. The User has the ultimate responsibility for identifying the class. If the User does not establish and document the acceptance class, the Manufacturer may do so.

In practice this means: the class must be defined and documented before production starts — not during inspection and not after a field failure. The inspector cannot select the product class. Documentation specifying the applicable class must be provided to the inspector before the inspection begins.

⚠️

Critical rule: The inspector shall not select the Product Class for the assembly under inspection. This is a [D1D2D3] requirement — a defect condition across all three classes if violated. Documentation must come from engineering, not from the inspection floor.

The Three Classes — Exact Definitions

IPC/WHMA-A-620E defines three product classes. Each reflects a different intended use environment, not a different level of workmanship quality.

Class	Official Name	Definition	Heavy Equipment Examples
Class 1	General Electronic Products	Includes products suitable for applications where the major requirement is the function of the completed assembly.	Interior cab controls, non-critical lighting harnesses, operator comfort systems
Class 2	Dedicated Service Electronic Products	Includes products where continued performance and extended life is required, and for which uninterrupted service is desired but not critical. The end-use environment would not typically cause failures.	Engine control harnesses, transmission control, hydraulic valve harnesses, instrument clusters
Class 3	High Performance / Harsh Environment Electronic Products	Includes products where continued performance or performance-on-demand is critical, equipment downtime cannot be tolerated, end-use environment may be uncommonly harsh, and the equipment must function when required.	Mining vehicle fire suppression, operator safety interlock systems, underground machine controls

📌

Key principle from the standard: A Class 1 harness built to standard is not a poor-quality harness. It is a harness designed for a product where the major requirement is function — not cosmetic perfection or extreme environmental resistance. Applying Class 3 criteria to a Class 1 application adds cost without adding value.

How the Standard Communicates Requirements: The Condition Code System

Once you understand the class system, you need to understand how IPC/WHMA-A-620E communicates requirements throughout the document. The standard uses bracket notation to indicate the condition for each class simultaneously.

Acceptable

This condition maintains the integrity and reliability of the assembly in its service environment. Not necessarily perfect — but acceptable.

Process Indicator

Does not affect form, fit, function, or reliability. Not a defect — but signals a process that needs monitoring. Must not be used as a basis for rejection.

Defect

Fails to meet acceptance criteria or negatively affects form, fit, or function. Must be documented and dispositioned by the Manufacturer.

Not Established

No requirement has been established for this class. The condition is not evaluated for this class level.

Reading the Bracket Notation

Throughout IPC/WHMA-A-620E, every requirement is followed by a bracket code that tells you simultaneously what the condition means for Class 1, Class 2, and Class 3 — in that order.

Bracket Notation Examples — How to Read Them

[A1P2D3] Acceptable for Class 1 | Process Indicator for Class 2 | Defect for Class 3 — The condition passes Class 1 inspection, triggers monitoring in Class 2, and is a reject in Class 3.

[N1D2D3] No requirement for Class 1 | Defect for Class 2 | Defect for Class 3 — Class 1 ignores this condition entirely; Class 2 and 3 must reject it.

[A1A2D3] Acceptable for Class 1 | Acceptable for Class 2 | Defect for Class 3 — Only a high-performance Class 3 product must reject this condition.

[D1D2D3] Defect for all three classes — No class accepts this condition. A universal reject.

[N1N2D3] No requirement for Class 1 and 2 | Defect for Class 3 only — Evaluated exclusively in Class 3 assemblies.

✅

Hierarchy rule: A defect for a Class 2 product is also a defect for Class 3. A defect for Class 1 is also a defect for Classes 2 and 3. The hierarchy goes upward — stricter classes inherit all defects from the less strict classes below them, plus their own additional requirements.

Process Indicators: What They Are and What to Do With Them

The process indicator is one of the most misunderstood concepts in IPC/WHMA-A-620E. Many inspection operations incorrectly treat process indicators as defects — which creates unnecessary rework, inflates cost, and undermines the credibility of the quality program.

The standard is explicit: a process indicator is not a defect. It identifies a condition that does not affect form, fit, function, or reliability. Affected product should be used as-is. Disposition of individual process indicators is not required.

What the standard does require is that process indicators are monitored as part of the process control system. If the number of process indicators signals an abnormal variation, an undesirable trend, or a process approaching out-of-control, the process must be analyzed and corrective action taken.

⚠️

Common mistake: Rejecting assemblies for process indicator conditions. If your inspection team is writing nonconformance reports for conditions coded [A1P2D3] on a Class 2 assembly, they are over-rejecting. The assembly should pass — the process should be monitored.

Class Selection: The Decision Sequence for Heavy Equipment

Most heavy equipment harness engineers default to Class 2 without analysis. In many cases this is correct — but it should be a documented decision, not an assumption. Use this sequence:

Step 1 — Is harness failure a direct safety risk?

Yes: Class 3 is required. Examples: fire suppression activation circuits, ROPS/FOPS safety interlocks, emergency stop systems in underground mining vehicles.
No: Continue to Step 2.

Step 2 — Is extended service life (5+ years) required with minimal maintenance?

Yes: Class 2 minimum. Heavy equipment operating in Canadian conditions — Quebec winters, mining dust, hydraulic fluid exposure — qualifies.
No: Class 1 may be sufficient. Continue to Step 3.

Step 3 — Is the harness in a high-vibration or wide-temperature environment?

Yes: Class 2 minimum. Mining and construction equipment vibration profiles and -40°C to +85°C temperature swings require dedicated service product criteria.
No: Continue to Step 4.

Step 4 — Is equipment downtime cost extremely high or service access difficult?

Yes: Consider Class 3. Underground or remote-site equipment where a harness failure means costly extraction is a Class 3 argument.
No: Class 1 or Class 2 based on life requirements.

Default answer for most heavy equipment in Quebec and Canada

Class 2 — engine control, transmission, hydraulic valve control, instrument clusters, and most vehicle electrical systems. Document the decision. Reference it on the engineering drawing.

Inspection Methodology: What Changes by Class

The class selection directly determines how the assembly is inspected. IPC/WHMA-A-620E Section 1.12 defines two inspection methods that apply differently across classes.

Visual Inspection

The assembly shall [N1D2D3] be evaluated in accordance with the established process control system. Class 1 assemblies may use statistical sampling. Class 2 and 3 assemblies require evaluation against the process control requirements of Section 1.6 or 100% inspection per Section 1.11.

Magnification Requirements by Wire Size

Magnification power for assembly inspection shall [A1P2D3] be at least the minimum inspection power specified in the tables below. The magnification requirement is based on the gauge of the wire being inspected.

Table 1-1 — Magnification Aid Applications: Wire and Wire Connections

Wire Size	AWG / Diameter	Inspection Range	Maximum Referee
Large wire	Larger than 14 AWG (>1.63 mm)	N/A	1.75X
Medium wire	14 to 22 AWG (1.63 – 0.64 mm)	1.5X – 3X	4X
Fine wire	<22 to 28 AWG (0.64 – 0.32 mm)	3 – 7.5X	10X
Very fine wire	Smaller than 28 AWG (<0.32 mm)	10X	20X

Table 1-2 — Magnification Aid Applications: Other Inspection Types

Inspection Type	Magnification Requirement
Cleanliness (cleaning or no-clean processes)	Not required — Note 1
Encapsulation, Staking	Not required — Notes 1, 2
Component	Not required — Notes 1, 2
Marking	Not required — Note 2

Note 1: Visual inspection may require magnification for very small features to determine if contamination or anomaly affects form, fit, or function. | Note 2: If magnification is used it is limited to 4X maximum.

📌

Referee magnification: The referee magnification power is used only to verify a product rejected at the inspection magnification. It is not used for initial inspection. For mixed wire size assemblies, the greater magnification may be used for the entire assembly. The tolerance for magnification aids is ±15% of the selected magnification power.

Lighting Requirements

Illumination at the surface of workstations during inspection shall be at least 1,000 lux (approximately 93 foot-candles). Supplemental lighting may be necessary to assist visual inspection. Light sources should be selected to prevent shadows on the item being inspected — except shadows caused by the item itself.

The color temperature of the light source is an important consideration. Light ranging from 3,000–5,000 K enables inspectors to distinguish various metal and plating features and contaminants with increased clarity.

Summary: What to Document Before Production Starts

The class selection must appear on the engineering drawing before any harness enters production. At minimum, the following must be documented:

Product Class: Class 1, 2, or 3 — referenced on the drawing title block
Applicable Standard: IPC/WHMA-A-620E (include the revision letter)
Inspection Method: Statistical process control or 100% visual inspection
Magnification Requirements: Based on the minimum wire gauge in the assembly
Class Justification: Brief documentation of why this class was selected — protects against scope creep during supplier audits

✅

LoomWire standard practice: Every engineering package we produce includes the class designation, standard revision, and inspection methodology on the drawing title block. When we receive a harness from a certified manufacturer, we verify that the inspection documentation references the correct class before accepting delivery.

IPC/WHMA-A-620E Class 1 Class 2 Class 3 Acceptance Criteria Heavy Equipment Harness Design Standards Quebec Canada

Qui décide de la classe — et quand

Selon la section 1.3 de l'IPC/WHMA-A-620E, l'utilisation de la norme exige un accord sur la classe à laquelle appartient le produit. L'utilisateur a la responsabilité ultime d'identifier la classe. Si l'utilisateur n'établit pas et ne documente pas la classe d'acceptation, le fabricant peut le faire.

En pratique, cela signifie que la classe doit être définie et documentée avant le début de la production — pas pendant l'inspection et pas après une défaillance terrain. L'inspecteur ne peut pas sélectionner la classe du produit. La documentation spécifiant la classe applicable doit être fournie à l'inspecteur avant le début de l'inspection.

⚠️

Règle critique : L'inspecteur ne doit pas sélectionner la classe du produit pour l'assemblage sous inspection. Il s'agit d'une exigence [D1D2D3] — une condition de défaut pour les trois classes si elle est violée. La documentation doit provenir de l'ingénierie, pas du plancher d'inspection.

Les trois classes — définitions exactes

L'IPC/WHMA-A-620E définit trois classes de produits. Chacune reflète un environnement d'utilisation prévu différent, et non un niveau différent de qualité d'exécution.

Classe	Nom officiel	Définition	Exemples équipements lourds
Classe 1	Produits électroniques généraux	Inclut les produits adaptés aux applications où la principale exigence est la fonction de l'assemblage terminé.	Commandes de cabine intérieure, faisceaux d'éclairage non critiques, systèmes de confort opérateur
Classe 2	Produits électroniques à service dédié	Inclut les produits où une performance continue et une longue durée de vie sont requises, et pour lesquels un service ininterrompu est souhaité mais pas critique.	Faisceaux de contrôle moteur, transmission, vannes hydrauliques, tableaux de bord
Classe 3	Produits haute performance / environnement sévère	Inclut les produits où la performance continue est critique, les arrêts sont inacceptables, l'environnement peut être exceptionnellement sévère, et l'équipement doit fonctionner quand requis.	Suppression d'incendie sur véhicules miniers, systèmes de sécurité opérateur, commandes de machines souterraines

Le système de codes de condition

L'IPC/WHMA-A-620E utilise une notation entre crochets pour indiquer simultanément la condition pour chaque classe.

Acceptable

Cette condition maintient l'intégrité et la fiabilité de l'assemblage dans son environnement de service.

Indicateur de processus

N'affecte pas la forme, l'aptitude à l'emploi ou la fonction. Pas un défaut — mais signale un processus à surveiller.

Défaut

Ne satisfait pas aux critères d'acceptation ou affecte négativement la forme, l'aptitude à l'emploi ou la fonction. Doit être documenté et dispositionné.

Non établi

Aucune exigence n'a été établie pour cette classe. La condition n'est pas évaluée pour ce niveau de classe.

Exemples de notation entre crochets

[A1P2D3]Acceptable Classe 1 | Indicateur de processus Classe 2 | Défaut Classe 3

[N1D2D3]Non établi Classe 1 | Défaut Classes 2 et 3

[D1D2D3]Défaut pour les trois classes — rejet universel

Sélection de la classe pour les équipements lourds

Étape 1 — La défaillance du faisceau représente-t-elle un risque direct pour la sécurité ?

Oui : Classe 3 requise. Exemples : circuits d'activation de suppression d'incendie, verrouillages de sécurité ROPS/FOPS, systèmes d'arrêt d'urgence en mines souterraines.
Non : Continuer à l'étape 2.

Étape 2 — Une longue durée de vie (5+ ans) avec maintenance minimale est-elle requise ?

Oui : Classe 2 minimum. Les équipements opérant dans les conditions canadiennes — hivers québécois, poussière minière, exposition aux fluides hydrauliques — sont concernés.
Non : La Classe 1 peut suffire. Continuer à l'étape 3.

Étape 3 — Le faisceau est-il dans un environnement à haute vibration ou à large plage de température ?

Oui : Classe 2 minimum. Les profils de vibration des équipements miniers et de construction et les variations de -40°C à +85°C l'exigent.
Non : Continuer à l'étape 4.

Réponse par défaut pour la majorité des équipements lourds au Québec et au Canada

Classe 2 — contrôle moteur, transmission, commande de vannes hydrauliques, tableaux de bord et la plupart des systèmes électriques de véhicules. Documenter la décision et la référencer sur le dessin d'ingénierie.

Méthodologie d'inspection

Tableau 1-1 — Aides à la grossissement : fils et connexions

Calibre du fil	Diamètre	Plage d'inspection	Arbitre maximum
Gros fil	Plus grand que 14 AWG (>1,63 mm)	N/A	1,75X
Fil moyen	14 à 22 AWG (1,63 – 0,64 mm)	1,5X – 3X	4X
Fil fin	<22 à 28 AWG (0,64 – 0,32 mm)	3 – 7,5X	10X
Fil très fin	Plus petit que 28 AWG (<0,32 mm)	10X	20X

L'éclairage à la surface des postes de travail lors de l'inspection doit être d'au moins 1 000 lux (environ 93 bougies-pied). La température de couleur recommandée se situe entre 3 000 et 5 000 K pour distinguer les caractéristiques métalliques et les contaminants.

Résumé : Ce qu'il faut documenter avant la production

Classe du produit : Classe 1, 2 ou 3 — référencée dans le cartouche du dessin
Norme applicable : IPC/WHMA-A-620E (inclure la lettre de révision)
Méthode d'inspection : Contrôle statistique de processus ou inspection visuelle à 100%
Exigences de grossissement : Basées sur le calibre de fil minimum dans l'assemblage
Justification de la classe : Documentation brève de la raison du choix de cette classe

IPC/WHMA-A-620E Classe 1 Classe 2 Classe 3 Critères d'acceptation Équipements lourds Conception de faisceaux Normes Québec Canada

Need a harness designed to IPC/WHMA-A-620E? Besoin d'un faisceau conçu selon IPC/WHMA-A-620E ?

LoomWire produces complete EPLAN engineering packages with the acceptance class, standard revision, and inspection methodology referenced on every drawing. Get a preliminary quote within one business day. LoomWire produit des packages d'ingénierie EPLAN complets avec la classe d'acceptation, la révision de la norme et la méthodologie d'inspection référencées sur chaque dessin. Obtenez un devis préliminaire en un jour ouvrable.

Request a Quote Demander un devis Browse More Articles Voir plus d'articles