Standard Requirements for Welding of Level 3 Distribution Boxes

Level 3 distribution boxes require continuous, defect-free welding that meets ISO 3834 and EN ISO 5817 standards to ensure structural integrity, sealing, and corrosion resistance.

Welding Quality Standards

Level 3 distribution boxes must comply with ISO 3834, which defines quality requirements for fusion welding of metallic materials, covering personnel qualifications, welding procedures, and documentation such as Welding Procedure Specifications (WPS) and Welder Qualification Records (WPQR) to ensure consistent quality . Additionally, EN ISO 5817 specifies acceptable defect levels in welds, with Level B or C quality typically required depending on structural importance and fatigue considerations . For structural steel enclosures, EN 1090-2 links execution classes (EXC) to weld quality, ensuring that critical parts meet higher standards.

Welding Process Requirements

• Continuous Welding: All seams should be continuously welded rather than spot-welded to maintain sealing performance and prevent moisture ingress, which is critical for achieving IP54, IP65, or higher protection ratings .
• Seam Finish: Welds must be uniform, bright, and clean, free from defects such as porosity, cracks, or undercuts. Grinding should produce a flush surface with consistent texture, avoiding welding slag .
• Structural Strength: Continuous welds enhance the box's ability to withstand vibration, impact, and transportation stresses, meeting IEC 60068-2-6 vibration and IK-level shock tests .

Corrosion and Protection Measures

• Anti-Corrosion Treatment: Steel plates and sections must be degreased, derusted, and phosphatized before coating. Welded areas should be treated to prevent crevice corrosion, as welds are often the first points of failure .
• Inspection: Welds should be visually inspected and, if necessary, tested using non-destructive methods to ensure defect-free joints.

Operational and Safety Considerations

• Internal and Opening Edges: Must be flat and smooth without burrs or cracks to allow safe installation and maintenance .
• Hinges and Locks: Doors should open at least 90 degrees, with hinges and locks rated for repeated use without deformation or failure .
• Insulation: All internal insulation must be self-extinguishing, and the box should maintain operation under three-level pollution conditions (IP3X minimum), .

Documentation and Compliance

Manufacturers must maintain WPS, WPQR, and personnel qualification records to demonstrate compliance with ISO 3834 and related standards. Execution classes and weld quality levels should be documented according to EN 1090 and EN ISO 5817 to ensure traceability and regulatory compliance . By adhering to these standards, Level 3 distribution boxes achieve high structural integrity, environmental protection, and long-term reliability, meeting both European and international requirements.