Fire Resistance Rating Classification of Flame-Retardant Cable Trays

Flame-retardant cable trays are classified based on their ability to limit flame spread, smoke, and toxic gas emissions, while fire-resistant trays are rated for maintaining circuit integrity under fire conditions.

Flame-Retardant Cable Trays

Flame-retardant cable trays are designed to limit the propagation of fire along the tray and its cables. Their performance is primarily determined by the sheath and insulation materials, which form a carbonized barrier under heat to slow combustion and reduce heat transfer. Flame-retardant classifications often follow IEC 60332 standards, which include:

• Single-cable tests (Parts 1 & 2): Evaluate vertical flame propagation on individual cables.
• Bunched-cable tests (Part 3): Simulate real installations with multiple cables on trays or ladders, assessing flame spread and char height under controlled burner conditions (20–40 kW) for categories A–D . In addition, GB/T 19666 and GB 31247 standards classify flame-retardant cables based on bundled installation tests and combustion characteristics, including heat release, smoke, and toxicity . Flame-retardant trays are typically used to buy evacuation time by slowing fire spread without necessarily maintaining electrical circuit operation.

Fire-Resistant Cable Trays

Fire-resistant cable trays are rated for their ability to maintain circuit integrity during fire exposure, typically for up to 90 minutes. Testing methods include:

• DIN 4102-12 and BS EN standards: Evaluate the tray's ability to contain fire and protect cables from heat, ensuring continued operation of critical systems .
• Fire resistance tests: Measure burn duration, flame spread, smoke, and toxic gas emissions. Trays are exposed to direct flames, and performance is assessed by how long they prevent ignition or maintain structural integrity . Fire-resistant trays are essential for critical systems such as emergency lighting, fire alarms, and communication networks, acting as a “lifeline” during fire events .

Key Classification Considerations

1. Flame Spread: How far flames travel along the tray and cables.
2. Smoke and Toxicity: Amount of smoke and corrosive gases produced.
3. Circuit Integrity: Duration the tray maintains electrical operation under fire.
4. Installation Conditions: Bundled vs. single-cable setups, mechanical stress, and environmental exposure.
5. Standards Compliance: IEC 60332, GB/T 19666, GB 31247, DIN 4102-12, and BS EN standards provide internationally recognized testing and classification frameworks .

Practical Implications

• Flame-retardant trays are suitable for general fire prevention and slowing flame spread.
• Fire-resistant trays are required where maintaining electrical operation is critical.
• Selection should consider building type, installation environment, cable type, and required fire duration to ensure safety and compliance. By understanding these classifications, engineers and designers can choose the appropriate cable tray system to meet both fire safety and operational requirements.