Thickness of zinc coating on galvanized cable trays

Hot-dip galvanized cable trays typically require a zinc coating thickness of 55–85 µm depending on steel thickness, while electro-galvanized trays require a minimum of 12 µm.

Hot-Dip Galvanized (HDG) Cable Trays

HDG is the preferred method for cable trays exposed to harsh environments such as outdoors, coastal areas, or industrial settings. The process involves submerging steel components in molten zinc, forming a thick zinc-iron alloy layer with excellent adhesion and corrosion resistance . Typical zinc coating thickness based on steel thickness:

• 1.5–3 mm steel sheets: minimum 55 µm (mean coating mass ~325 g/m²)
• >3 mm components (brackets, supports): minimum 70–85 µm
• Maximum practical thickness: 85 µm for steel ≥6 mm to avoid brittleness and cracking Standards governing HDG cable trays include GB/T 13912-2020, ASTM A123/A123M, and ISO 1461, which specify both local thickness (minimum at any point) and mean coating mass (average over the entire surface), .

Electro-Galvanized Cable Trays

Electro-galvanizing deposits a thin, uniform zinc layer via electrolysis. While it provides a bright finish, its corrosion resistance is limited compared to HDG. The minimum zinc coating thickness for electro-galvanized trays is 12 µm, as per GB/T 26941.1-2011 . This method is suitable for indoor or less corrosive environments.

Measurement and Quality Considerations

• 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.
• Surface quality: coating should be continuous, uniform, and smooth; minor dull areas are acceptable, but bare spots, blisters, or excessive zinc dross are not permitted .

Summary Table

Ensuring the correct zinc coating thickness is critical for long-term corrosion protection, structural integrity, and compliance with international standards .