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Classification of flame-retardant cables and flame-retardant grades A, B, and C
1. Definition and background
Due to the frequent occurrence of electrical fires, people have put forward higher requirements for the safety of wires and cables. Flame-retardant cables refer to cables that can spread the flame within a certain range and have the function of self-extinguishing when an electrical fire occurs.
The combustion of the cable is caused by the external heating to produce flammable gas. To realize the flame retardant of the cable, the three elements that cause the combustion must be suppressed: flammable gas, heat and oxygen. The traditional method is to add halogen-containing halides and metal oxides to the sheath material. This limits the spread of fire to a certain extent. However, because these materials contain halide, they release a large amount of smoke and hydrogen halide gas when burned. The visibility during fire is low, which brings great impact to the safety of personnel evacuation and fire fighting. obstacle. In recent years, with the continuous improvement of the level of science and technology, the flame retardant problem has been further developed from the halogen flame retardant in the past to the low halogen, halogen-free flame retardant.
2. Flame retardant grade
The determination of flame-retardant cable grade usually adopts the vertical burning test method of bundled wires and cables. The test divides wires and cables into flame-retardant A, B, and C three categories. That is to say, multiple wires or cables with a length of 3.5m (the total number is different due to the flame retardant category and the non-metallic materials contained in each meter of the wire and cable) are installed in bundles on the sample ladder and placed vertically in the test box In the medium, a gas burner with an intensity of 20.6kW is used to supply fire to the wires and cables vertically.
Class A and B flame-retardant wires and cables provide fire time for 40 minutes; Class C fire time for 20 minutes. After the test, if the carbonization height of the wire and cable does not exceed 2.5m, it will be passed. Specific grades of non-metallic materials per meter of wire and cable are as follows: A type 7 liters/meter; B type 3.5 liters/meter; C type 1.5 liters/meter.
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