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IEC TS 62775: Performance of Telecommunication Cables Under Fire Conditions
Technical specification for evaluating the fire performance of telecommunication cables in building installations
IEC TS 62775, published in 2016, provides a comprehensive framework for evaluating the fire performance of telecommunication cables installed in buildings. As telecommunication networks have expanded to every corner of modern buildings — from fibre to the home (FTTH) installations to data centre structured cabling — the fire safety characteristics of these cables have become a critical concern for building designers, fire safety engineers, and code authorities. Unlike power cables, telecommunication cables carry low voltages but are deployed in very large quantities throughout buildings, contributing significantly to the total fire load.
The standard was developed by IEC TC 46 (Cables, wires, waveguides, RF connectors, and accessories for communication and signalling) and addresses the full range of telecommunication cable types including copper twisted-pair cables (Cat 5e, Cat 6, Cat 7, Cat 8), coaxial cables, fibre optic cables, and hybrid cables combining multiple transmission media. The fire performance requirements cover cable installed in various building environments including plenums (air-handling spaces), risers (vertical shafts), general-purpose areas, and outdoor-to-indoor transitions.
Fire Performance Parameters and Test Methods
IEC TS 62775 defines a suite of fire performance parameters that characterise the behaviour of telecommunication cables when exposed to fire conditions. These parameters are assessed using established test methods adapted from the broader cable fire testing standards, with modifications specific to the physical characteristics and installation configurations of telecommunication cables. The standard recognises that telecommunication cables differ from power cables in conductor size, insulation thickness, and typical bundle sizes, requiring adjustments to testing parameters such as exposure time, flame intensity, and sample preparation.
| Parameter | Description | Test Method | Classification Criteria |
|---|---|---|---|
| Flame propagation | Vertical flame spread along a cable bundle | IEC 60332-3 (adapted for telecom cables) | Burning length < 2.5 m |
| Smoke emission | Smoke density during cable burning | IEC 61034 (for small cables, modified) | Light transmission > 60% |
| Heat release rate | Rate of heat energy released during combustion | ISO 5660-1 (cone calorimeter) | Peak HRR < 200 kW/m² |
| Toxicity index | Concentration of toxic gases from combustion | NF X 70-100 or similar | Toxicity index per national regulations |
| Acid gas emission | Halogen acid gas (HCl, HBr) from combustion | IEC 60754 (for telecom cable materials) | pH > 4.0, conductivity < 10 μS/mm |
| Total heat release | Total heat energy released during complete burning | ISO 5660-1 / cone calorimeter | THR < 50 MJ/m² for plenum |
The heat release rate measurement using cone calorimetry is a particularly important parameter introduced for telecommunication cables. Unlike traditional pass/fail flame propagation tests, heat release data provides quantitative information about the fire contribution of cables, enabling fire safety engineers to perform performance-based design calculations. Telecommunication cables with low heat release rates contribute less to fire growth and flashover, providing additional time for building occupants to evacuate and for fire services to respond.
The smoke emission performance of telecommunication cables is a critical safety parameter that is sometimes overlooked in cable selection. In a building fire, smoke is the primary cause of death and injury, and telecommunication cables — deployed in large quantities in ceiling spaces and risers — can generate dense, toxic smoke if not properly specified. IEC TS 62775 requires smoke density testing specifically adapted for telecommunication cable configurations, which often differ significantly from power cable test configurations due to the smaller individual conductor cross-sections and different insulation material formulations.
Cable Classification and Application Categories
The standard establishes a classification system that maps fire performance parameters to application categories, enabling cable specifiers to select appropriate cable types based on the fire safety requirements of the installation environment. The classification scheme considers the critical installation parameters including cable quantity (number of cables in a bundle), installation geometry (horizontal, vertical, in trays, or in conduit), and environmental category (plenum, riser, general purpose, or restricted areas).
The classification system draws from and aligns with the European Construction Products Regulation (CPR) classification for power, control, and communication cables, which defines Euroclasses B2ca, Cca, Dca, Eca, and Fca based on fire performance. IEC TS 62775 provides the technical basis for assigning telecommunication cables to these Euroclasses, including the specific test configurations and acceptance criteria applicable to the physical characteristics of telecom cables.
For building designers, the practical value of IEC TS 62775 lies in its cable classification framework. A Cat 6A data cable certified to Euroclass B2ca according to IEC TS 62775 methodology provides quantified assurance that the cable will not contribute significantly to fire propagation, will generate limited smoke, and will not release halogenic acid gases that can corrode electronic equipment and building structures. This enables fire safety engineers to specify cables with confidence, knowing the fire performance has been evaluated using test methods appropriate for telecommunication cable construction.
Engineering Design Insights for Fire-Safe Cable Selection
From a practical engineering perspective, selecting telecommunication cables with appropriate fire performance requires consideration of several factors beyond the basic classification. First, the installation environment is the primary determinant of required fire performance. Cables installed in plenum spaces (used for air circulation in HVAC systems) require the highest level of fire performance because smoke and flames can spread rapidly through the air handling system. Riser cables installed in vertical shafts require good flame propagation resistance to prevent fire spread between floors. General-purpose cables installed in cable trays in open areas have less stringent requirements but must still meet minimum fire safety standards.
Second, the cable construction materials significantly influence fire performance. Low Smoke Zero Halogen (LSZH) compounds for cable jackets and insulation provide the best fire performance for telecommunication cables, with reduced smoke emission, no halogen acid gas release, and limited flame propagation. However, LSZH materials typically have different mechanical properties than standard PVC compounds, including reduced flexibility and different installation characteristics. Engineers must balance fire performance with installation requirements, particularly in tight bend radius applications and outdoor installations where UV resistance and water ingress protection are also important.
Third, the trend toward higher data rates (Category 8 cabling for 25/40GBASE-T, beyond) is driving changes in cable construction that affect fire performance. Higher-performance cables often use physically larger conductors (AWG 22 vs. AWG 24 for standard cables) and additional shielding layers, increasing the combustible material content per metre of cable. Designers of data centres and other high-density cabling environments must account for this increased fire load when specifying cable fire performance requirements, potentially requiring higher Euroclass ratings for the same installation configuration than would be needed for standard Category 6 cables.
| Installation Environment | Required Euroclass | Key Fire Parameters | Typical Cable Types |
|---|---|---|---|
| Plenum (air-handling spaces) | B2ca or better | Low flame spread, low smoke, low HRR | LSZH Cat 6A/7/8, OFNP fibre |
| Riser (vertical shafts) | Cca | Vertical flame propagation resistance | LSZH or FR-PVC riser rated |
| General purpose (trays, conduit) | Dca or Eca | Basic flame retardance | PVC or LSZH general purpose |
| Outdoor-to-indoor transition | Dca | Flame retardance + UV + water resistance | UV-stabilised LSZH or PE jacket |
| Data centre (high-density) | B2ca or Cca | Low HRR, low smoke, acid gas free | LSZH Cat 6A/7/8, OM4/OM5 fibre |
Fourth, fibre optic cables present unique fire performance characteristics that differ from copper cables. The small glass fibres themselves do not burn, but the cable jacket, strength members (aramid yarn), and any water-blocking materials contribute to fire load. All-dielectric fibre cables have a lower fire load than copper cables of similar diameter, but hybrid cables combining copper conductors for remote powering (power-over-fibre applications) with optical fibres require evaluation of the combined fire performance. The standard provides specific guidance for testing and classifying hybrid telecommunication cables.
A common mistake in building cable specification is assuming that all cables from a given manufacturer with the same jacket material have the same fire performance. Fire performance depends on the complete cable construction — conductor size, insulation type and thickness, shield materials, jacket compound formulation, and overall cable geometry — not just the jacket material. Two Cat 6 cables from different manufacturers, both labelled PVC, may have dramatically different fire performance characteristics. IEC TS 62775 provides the framework for verifying fire performance through standardised testing rather than relying on material declarations alone.
Q1: What is the difference between IEC TS 62775 and IEC 60332 for cable fire testing?
A: IEC 60332 series specifies the test methods for flame propagation on single cables (Part 1) and cable bundles (Part 3). IEC TS 62775 provides a comprehensive framework that combines flame propagation testing with smoke emission, heat release rate, and toxicity assessment parameters specifically adapted for telecommunication cables. It also provides the classification framework that maps test results to application categories, which IEC 60332 alone does not provide.
A: IEC 60332 series specifies the test methods for flame propagation on single cables (Part 1) and cable bundles (Part 3). IEC TS 62775 provides a comprehensive framework that combines flame propagation testing with smoke emission, heat release rate, and toxicity assessment parameters specifically adapted for telecommunication cables. It also provides the classification framework that maps test results to application categories, which IEC 60332 alone does not provide.
Q2: Are halogen-free cables always required for building installations?
A: Not always, but they are strongly recommended for occupied spaces, enclosed areas, and critical infrastructure. Halogen-free (LSZH) cables prevent the release of corrosive acid gases that can damage electronic equipment and harm building occupants. In plenum spaces and data centres, LSZH cables are typically required by building codes. For outdoor or industrial environments where mechanical robustness is the primary concern, halogenated compounds (PVC, FEP) may sometimes be more appropriate, though halogen-free alternatives with equivalent mechanical properties are increasingly available.
A: Not always, but they are strongly recommended for occupied spaces, enclosed areas, and critical infrastructure. Halogen-free (LSZH) cables prevent the release of corrosive acid gases that can damage electronic equipment and harm building occupants. In plenum spaces and data centres, LSZH cables are typically required by building codes. For outdoor or industrial environments where mechanical robustness is the primary concern, halogenated compounds (PVC, FEP) may sometimes be more appropriate, though halogen-free alternatives with equivalent mechanical properties are increasingly available.
Q3: How does cable bundling affect fire performance?
A: Cable bundling significantly affects fire performance because closely packed cables provide less surface area for heat dissipation and can support flame propagation along the bundle length. A single cable that passes the flame propagation test may fail when installed in a dense bundle of 50 or more cables. IEC TS 62775 requires fire testing at bundle sizes representative of the intended installation, and the classification system accounts for different bundle density scenarios to ensure safe installation.
A: Cable bundling significantly affects fire performance because closely packed cables provide less surface area for heat dissipation and can support flame propagation along the bundle length. A single cable that passes the flame propagation test may fail when installed in a dense bundle of 50 or more cables. IEC TS 62775 requires fire testing at bundle sizes representative of the intended installation, and the classification system accounts for different bundle density scenarios to ensure safe installation.
Q4: How is the heat release rate of telecommunication cables measured?
A: Heat release rate is measured using a cone calorimeter per ISO 5660-1, with sample preparation and test conditions adapted for telecommunication cable construction per the standard’s guidelines. The cable sample is exposed to a controlled radiant heat flux (typically 50 kW/m² for telecom cables) in a horizontal orientation, and the oxygen consumption calorimetry principle is used to calculate the heat release rate. The peak heat release rate (PHRR) and total heat release (THR) are the key metrics reported.
A: Heat release rate is measured using a cone calorimeter per ISO 5660-1, with sample preparation and test conditions adapted for telecommunication cable construction per the standard’s guidelines. The cable sample is exposed to a controlled radiant heat flux (typically 50 kW/m² for telecom cables) in a horizontal orientation, and the oxygen consumption calorimetry principle is used to calculate the heat release rate. The peak heat release rate (PHRR) and total heat release (THR) are the key metrics reported.
