Fire-resistant cable trays must be bent with a radius no smaller than the cable's minimum bending radius, supported on both sides of the bend, and installed to maintain fire integrity and mechanical stability.

Minimum Bending Radius

When routing fire-resistant cables through bends in a tray, the internal radius of the bend should not be less than the cable's minimum bending radius to prevent damage and maintain performance under fire conditions . This applies to both horizontal-to-vertical and vertical-to-horizontal transitions. Using a radius smaller than recommended can compromise the cable insulation, reduce fire resistance, and increase mechanical stress.

Support Requirements

Cables must be supported on either side of the bend to avoid undue mechanical strain. For long vertical runs, strain relief sections should be incorporated, typically by offsetting the cable by at least two cable diameters per relief section . For vertical runs exceeding 100 meters, additional tension-relieving measures, such as short horizontal sections of at least 1 meter, are recommended to prevent straight vertical stress.

Fire Safety Considerations

Fire-resistant cable trays are designed to maintain mechanical integrity and minimize fire spread. Installation must comply with standards such as NEC Article 392, IEC 61537, and EN 50200 / BS 476 . Key practices include:

• Using fire-resistant supports that will not fail in a fire .
• Maintaining proper separation between power, data, and fire alarm cables.
• Including expansion joints for long tray runs to prevent warping or bending.
• Regular inspection for corrosion, loose fasteners, or damage, replacing compromised sections immediately.

Firestopping at Penetrations

Where cable trays pass through walls, slabs, or shafts, openings must be sealed with firestopping materials such as fire-rated boards, mineral wool, or firestop packs . Gaps should not exceed 1 cm², and packing thickness should be at least 24 cm. Proper firestopping ensures that the tray maintains its fire-resistant performance and prevents fire spread through penetrations.

Best Practices

• Always follow manufacturer guidelines for bending and support.
• Avoid sharp bends or unsupported spans that could compromise cable integrity.
• Ensure that all supports and fixings are fire-rated and capable of withstanding high temperatures.
• Plan tray layouts to facilitate maintenance and inspection while maintaining compliance with fire safety codes. By adhering to these guidelines, fire-resistant cable trays will maintain both mechanical stability and fire performance, ensuring safety, regulatory compliance, and long-term reliability .