Thickness of zinc coating on outdoor galvanized cable trays

The zinc coating on galvanized cable trays typically ranges from 18–55 microns for electro-galvanized trays and 45–85 microns for hot-dip galvanized trays, depending on steel thickness and environmental exposure.Galvanizing Methods and Thickness

1. Electro-galvanized (EG) cable trays:

• Zinc is deposited via electrolysis, producing a thin, bright, and uniform layer.
• Typical thickness: 18–20 µm (corresponding to a coating mass of ~275 g/m² for Z275 steel) for standard tray sheets .
• Provides moderate corrosion resistance, suitable for indoor or less aggressive environments . 2. Hot-dip galvanized (HDG) cable trays:
• Steel is submerged in molten zinc, forming a zinc-iron alloy layer and a pure zinc layer.
• Local thickness for tray sheets (1.5–3 mm thick): ≥45 µm (coating mass ≥325 g/m²).
• Heavier components like brackets or supports (>3 mm) require ≥55 µm .
• Offers superior corrosion resistance, ideal for outdoor, coastal, or industrial environments .

Standards and Compliance

• GB/T 13912-2020: Specifies hot-dip galvanized coatings on fabricated steel articles, including local thickness and mean coating mass .
• GB/T 26941.1-2011: Defines requirements for electro-galvanized cable trays .
• ISO 1461 / UNI EN ISO 1461: International standard for hot-dip galvanizing, recommending ≥85 µm for steel thicker than 6 mm and providing measurement methods .
• IEC 61537: Defines performance classes for cable trays; HDG products are typically Class 6, while high-resistance coatings can reach Class 8 .

Measurement Methods

• Magnetic thickness gauges: Non-destructive, measure at multiple points to ensure local thickness compliance .
• Gravimetric (stripping and weighing): Determines mean coating mass for arbitration .
• Optical microscopy: Cross-sectional measurement of zinc layer .

Practical Considerations

• The coating should be continuous, uniform, and smooth; minor dull or light grey areas are acceptable, but defects like bare spots, blisters, or excessive zinc dross are not .
• Zinc protects steel both as a physical barrier and via sacrificial corrosion, forming a protective zinc carbonate layer over time .
• Thicker coatings extend service life, especially in aggressive environments, while thinner coatings are sufficient for indoor or low-corrosion areas . In summary, hot-dip galvanized cable trays require a minimum zinc thickness of 45–55 µm depending on component thickness, while electro-galvanized trays typically have 18–20 µm, with all measurements guided by relevant standards to ensure corrosion protection and durability.