For hot-dip galvanized fireproof cable trays, the standard zinc coating thickness is typically 65 µm or more, while electro-galvanized trays require a minimum of 12 µm.

Zinc Coating Requirements

Hot-Dip Galvanized (HDG) Cable Trays:

• The zinc coating thickness for HDG trays is generally ≥65 µm, corresponding to a coating weight of approximately 460 g/m² per side .
• This thickness ensures long-term corrosion resistance, especially for outdoor or highly corrosive environments .
• HDG provides strong adhesion, compactness, and durability, making it suitable for fireproof cable trays exposed to harsh conditions .

Electro-Galvanized (EG) Cable Trays:

• For electro-galvanized trays, the minimum zinc coating thickness is 12 µm, which is suitable primarily for indoor, dry environments .
• EG coatings have lower corrosion resistance compared to HDG and are generally used where environmental exposure is limited .

Measurement and Inspection

• Local Thickness: Measured at multiple points using a magnetic thickness gauge; all points must meet the minimum requirement .
• Mean Coating Mass: Determined gravimetrically for arbitration purposes, representing the average zinc mass per unit area .
• Adhesion and Corrosion Tests: Include mandrel wrap tests, copper sulfate tests, and visual inspection for defects such as bare spots, blisters, or rough nodules .

Standards and Guidelines

• NEMA VE-1 / IEC Equivalents: Metallic cable trays should comply with NEMA VE-1 or equivalent IEC standards .
• ASTM A123/A123M: Defines hot-dip galvanizing procedures and coating grades .
• GB/T 26941.1-2011: Specifies electro-galvanized tray requirements .
• Project Specifications: Fireproof cable trays must also meet national fire safety and project-specific coating thickness requirements, verified through calibrated measurement devices and adhesion tests .

Practical Considerations

• Outdoor Installations: Always use HDG or anodized aluminum for corrosion protection.
• Repair and Maintenance: Damaged areas of HDG trays should be repaired with compatible materials to maintain coating integrity .
• Fireproof Coating: Ensure that any additional fireproof topcoat is applied uniformly and meets national fire safety standards .

By adhering to these standards, fireproof cable trays achieve both corrosion resistance and fire safety compliance, ensuring long-term reliability in electrical installations.