02. Class 1, 2 and 3 Defined: How to Select the Right Acceptance Class for Heavy Equipment 02. Classe 1, 2 et 3 : Comment sélectionner la bonne classe d'acceptation pour les équipements lourds

Why the Class Decision Comes Before Everything Else

The acceptance class is not a quality level. It is not a pass/fail threshold. It is the intended use category of the product — and it determines every subsequent decision in your harness engineering package: which connector seal materials are acceptable, what conductor fill percentage is required, how many nicked strands trigger a reject, what crimp bellmouth dimensions must be present.

Getting the class wrong at the start means your inspection criteria are wrong, your supplier qualification is wrong, and your drawing callout is wrong. These errors compound. A Class 2 harness inspected to Class 1 criteria will pass inspection with conditions that would cause field failures in a demanding mining or construction environment.

The Three Classes: Exact Definitions from §1.3

IPC/WHMA-A-620E defines three product classes based on end-use requirements. The definitions are precise and should be applied literally when making the selection decision.

Step-by-Step Class Selection Framework

Use this sequence for every harness you design. Work through it in order — the first "Yes" answer determines the class. Document your answers and keep them with the engineering package.

Requirements Flowdown: How the Class Applies to Subassemblies and Suppliers (§1.9)

Once the class is established for a product, it flows down through the supply chain. Section 1.9 defines this precisely — and it has direct implications for how you write purchase orders and subcontract agreements.

When this standard is contractually required, the applicable requirements including the Product Class shall [D1D2D3] be imposed on all applicable subcontracts, engineering documentation, and purchase orders.

The flowdown rule also addresses unclear boundaries. When it is unclear where flowdown should stop, the flowdown shall [D1D2D3] be established between the Manufacturer and the User. This requires a documented agreement — not an assumption. If you are subcontracting harness fabrication to a shop in Quebec, the class must be stated on your purchase order and confirmed in writing.

Acceptance Requirements (§1.11)

Section 1.11 is short but absolute. All products shall [D1D2D3] meet the requirements of:

• The contracts — whatever your purchase order and quality agreement specify
• Engineering documentation — your EPLAN drawings, BOM, and assembly specifications
• Applicable standards — IPC/WHMA-A-620E and any referenced standards
• The requirements for the applicable Product Class — Class 1, 2, or 3 as documented

All four must be satisfied simultaneously. A harness that passes visual inspection to Class 2 criteria but was manufactured from a non-conforming BOM material is still a nonconformance. The standard does not allow partial compliance.

Facility Requirements That Change by Class (§1.13)

Class selection also has implications for the assembly environment. Section 1.13 defines what the workspace must look like — and one of these requirements changes based on whether field assembly is involved.

Documenting the Class Decision

The class selection must be documented in the engineering package before production begins. Here is the minimum documentation required:

Summary: The Class Selection Rules in Plain Language

• Safety-critical function → Class 3, no exception
• Extreme downtime cost or inaccessible service → Class 3
• Extended life, harsh environment, heavy equipment → Class 2
• Quebec winter operation alone → Class 2 minimum
• Short lifecycle, mild environment, non-critical function → Class 1 acceptable
• COTS assemblies → requirements do not flow down automatically
• Field assembly at Class 2 or 3 → documented precautions mandatory
• Never leave the class off the drawing → incomplete callout is a nonconformance

Pourquoi la décision de classe vient avant tout le reste

La classe d'acceptation n'est pas un niveau de qualité. C'est la catégorie d'utilisation prévue du produit — et elle détermine chaque décision ultérieure dans votre package d'ingénierie de faisceau : quels matériaux de joint de connecteur sont acceptables, quel pourcentage de remplissage du conducteur est requis, combien de torons entaillés déclenchent un rejet.

Les trois classes : définitions exactes du §1.3

Cadre de sélection de classe — étape par étape

Transmission des exigences aux sous-traitants (§1.9)

Lorsque cette norme est contractuellement requise, les exigences applicables incluant la Classe de Produit shall [D1D2D3] doivent être imposées à tous les sous-contrats, la documentation d'ingénierie et les bons de commande applicables.

Exigences d'installations (§1.13)

Résumé : Les règles de sélection de classe en langage clair

• Fonction critique de sécurité → Classe 3, sans exception
• Coût d'arrêt extrême ou service inaccessible → Classe 3
• Longue durée de vie, environnement sévère, équipements lourds → Classe 2
• Opération hivernale au Québec → Classe 2 minimum
• Courte durée de vie, environnement doux, fonction non critique → Classe 1 acceptable
• Assemblages COTS → les exigences ne se transmettent pas automatiquement
• Assemblage terrain en Classe 2 ou 3 → précautions documentées obligatoires
• Ne jamais omettre la classe sur le dessin → appel incomplet = non-conformité