Allowable deviation in thickness of fiberglass cable trays

The allowable deviation in thickness of fiberglass cable trays is generally governed by standards such as UL 568 and IEC 61537, with typical tolerances ranging from ±5% to ±10% depending on the manufacturing process and material type.

Material and Manufacturing Considerations

Fiberglass cable trays are typically made using pultrusion, compression molding, or resin transfer molding, with a glass fiber-to-resin content maintained between 45–65% by weight for pultruded components and 25–45% for molded components. The thickness of these trays is influenced by the resin system, fiber content, and surfacing veils used for UV and chemical protection . Variations in thickness can occur due to the pultrusion or molding process, and manufacturers usually specify tolerances in their technical documentation.

Standards Governing Thickness Tolerances

• UL 568: Covers performance requirements for fiberglass cable trays, including structural integrity and safe application. While it does not prescribe a single numeric tolerance, it requires that trays meet load and deflection criteria under specified conditions .
• IEC 61537: Specifies requirements for cable tray systems, including nonmetallic trays, and mandates that manufacturers declare safe working loads and ensure consistent material properties, which implicitly includes thickness control .
• NEMA FG-1: Provides manufacturing requirements for nonmetallic cable trays, including fiberglass, and ensures that deviations in dimensions, including thickness, do not compromise structural performance .

Typical Industry Practice

In practice, fiberglass cable tray manufacturers maintain thickness deviations within ±5% to ±10% of the nominal value, depending on the tray type and production method. Pultruded trays tend to have tighter tolerances (closer to ±5%) due to the continuous fiber reinforcement, while molded components may allow slightly higher deviations (up to ±10%) because of resin flow and mold variability . These tolerances ensure that the trays meet load-bearing, fire retardancy, and UV resistance requirements.

Recommendations

• Always refer to the manufacturer's datasheet for specific allowable deviations, as they may vary by product line and resin system.
• Ensure that installation and load calculations account for the minimum thickness within the tolerance range to maintain safety and compliance.
• Verify that trays meet UL 568, IEC 61537, and NEMA FG-1 standards for structural and fire performance. By adhering to these guidelines, fiberglass cable trays can maintain their mechanical integrity and safety performance even with minor thickness deviations.