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• Fire Resistance of Cable

  Written by Administrator

  6/4/2009

  Materials are commonly classified in flammable, slow-burning, self-extinguishing, intrinsically non-flammable. Within the wire and cable field only mineral insulated cables are intrinsically non-flammable. Halogenated polymer ( FEP, PVC) exhibit the best fire behaviour but additives are often required to meet various technical requirements (flexibility for instance) and these additives increase the polymer combustibility. Polymer combustibility or flame resistance is commonly measured by the highest Limiting Oxygen Index (LOI), the amount of oxygen needed to support combustion. The higher the LOI value, the more flame-resistant the material. Nevertheless, required fire behaviour can generally be achieved by introduction of other additives named flame retardants (chemicals that inhibit sustained combustion).
  
  

  Some fire behaviour tests

  • Test on flammability (of single cables or of cable bundles). For a single cable, the test is regarded as passed if the sample does not burnt, or if the flames self-extinguish, and if the damage to the cable does not exceed a certain length.
  • Test on smoke density : measurement of the levels of light transmission in a close chamber.
  • Test on corrosive gas emission : small quantities of halogens can be detected by measurement of pH-value and conductivity of a solution where the gas are dissolved.
  • Test on insulation integrity : during certain duration and temperature, the conductor (electrical current or light) must remain a conductor.