The effects causing the burning of plastic coatings of fire-resistant cables and its consequences

摘要

Electric wiring is part of the fire protection systems; therefore, it must work reliably for a given period of time. Cable is in the first place among the cause of fire. Fires are always triggered by unsafe and nonstandard conditions, so we can approach safety if we know the properties of cables we want to use. We recommend adding standard ratings (PH, EP) with overload and combustion in increased/higher oxygen ratio. A plastic-coated cable does not burn in normal air, but, in a higher oxygen ratio, it shows specific burning phenomena. Cable fires may have two starting points: One is the heat reaching the plastic insulation of cables, due to the fire created by burning; the other one may be due to the fire generated by the overvoltage in the inappropriately sized cables when the outer plastic coating begins to burn. The basic condition of fire retardancy is that wire breaks or short circuits may not occur in a cable system. During this research, both effects are tested on fire-retardant cables. On the one hand, we exposed wires of various plastic sheaths to flame and to heat, as well as tested at which actual oxygen content they start combustion and flame propagation. In addition, we have investigated how fire-resistant cables react to a possible overvoltage when auto-ignition occurs. The goal was to see how conventional tests reflect requirements caused by a real fire and what the actual fire resistance of cables is, as well as examining whether the cables that have been certified as fire-resistant meet the requirements under real fire. The limited oxygen index (LOI) parameter seemed to be the most appropriate for real fire resistance. Our results have shown that factory certifications are not enough to provide complete fire safety. For example, the PH 180, E90 best rated plastic gave the weakest LOI value. PH 30 and PH 120 has proved correct the flammability. Due to the complex layers their investigation their testing is complex to, requiring a variety of tests to give a complete burn behavior. The most important exothermic peaks of diagraphs give the expected LOI values. The first and second decomposition is only indicative of damage and smoke, that is only by the tests with overload to see.