• • • DATA CENTRE MANAGEMENT • • •


conduit is exposed to a 1kW burner and must extinguish within 30 seconds of the removal of the flame with no flaming droplets. To assess how flame retardant a material is, the


normal test method is to measure the Limiting Oxygen Index (LOI) according to BS EN ISO 4589-2. This determines the percentage of oxygen that needs to be present to support combustion. The higher the LOI percentage, the greater the flame retardancy of the material. Another method is to use a glow wire test, BS


EN IEC 60695-2, which applies a glow wire to a plaque of material at 7500C, 8500C or 9600C.


Low smoke emission If the conduit is involved in a fire, the smoke generated may obscure the vision of people trying to escape, or the firefighters trying to extinguish the flames. There are a number of fire tests, where a


specified sample of material is burnt under controlled conditions in a given size smoke chamber and the smoke obscuration of a defined beam of light is measured.


Low toxicity To test for toxicity, a specified sample of material is burnt under controlled conditions in a given size smoke chamber and the fumes are analysed for various gases. The concentration of each gas is then multiplied by its toxic potency to give a toxicity index.


22 ELECTRICAL ENGINEERING • JUNE 2022


If halogens, sulphur or phosphorus are


present in a material, it is unlikely to pass the low toxicity tests.


Halogen free Typical halogens are fluorine, chlorine, bromine and iodine. Chlorine is the most common in PVC, fluorine is present in fluoro-polymers and bromine appears in flame retardants. All of them produce highly toxic fumes and thick smoke if exposed to a naked flame; another reason why operators may have tended to rate this area of performance above other fire hazard properties.


Specification first While fire performance is of prime concern, it is worth noting that specifying cable protection based on one property alone can be a costly mistake and the full range of environmental factors should be considered. These can include exposure to extremes of temperature, UV radiation, harsh chemicals, compression strength, abrasion resistance and the likelihood of water or dust ingress. While many products may look the same,


performance properties can vary greatly so customers should always check suitability and compatibility for their application and consider the installation as a complete end-to-end system. Polypropylene, NFR (Non-flame retardant) is a commonly used material for data centre cable


protection as it is halogen, sulphur and phosphorous free, so will not aid acid formation, but is highly flammable, and flame propagating. In contrast, PA6 (nylon) is self-extinguishing,


halogen, sulphur and phosphorous free. As a standard nylon, Flexicon’s FPAS, is highly flame retardant and low fire hazard. A modified PA6 conduit, FPR, has even higher flame retardancy and is extra low fire hazard, as are Flexicon’s injection moulded PA66 fittings. The specifier should look for independent test


results to back up the supplier’s claims rather than relying on un-substantiated jargon.


Bespoke-designed cable


protection For more complex application requirements, customers should speak to their supplier to discuss bespoke options. These could include conduit supplied in


non-standard or pre-cut lengths, in larger or smaller diameters or with different thread termination or fitting options. 45- and 90-degree elbows can also be used to help maintain bend radius. Additionally, more complex requirements,


such as altering performance characteristics to meet a certain temperature requirement, compression strength or abrasion resistance or to achieve a greater fatigue life may also be considered.


electricalengineeringmagazine.co.uk


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