Causes of fire caused by the hottest wires and cab

Causes of fire caused by wires and cables

1 the causes of fire caused by wires and cables are mainly due to overload, short circuit, excessive contact resistance and the effect of external heat sources. Although necking has continued to develop since then, under the fault state of short circuit, local overheating and other humidity that will weaken the grinding mark effect of polishing, and the effect of external heat, the insulation resistance of insulating materials will decline, lose insulation capacity, and even burn, leading to fire. The main characteristics of wires and cables in fire are as follows: (1) the fire temperature is generally 800 ℃ ~ 1000 ℃. In case of fire, wires and cables will soon lose their insulation capacity, which will lead to secondary electrical accidents such as short circuit, causing greater losses; (2) The conductor and cable have large overload capacity under the specified allowable current carrying capacity; (3) Under the short-circuit condition, the conductor and cable will instantly cause the insulation material to melt and burn, and ignite the surrounding combustibles

2 analysis of fire protection performance of wires and cables

2.1 analysis of fire protection mechanism

2.1.1 flame retardant mechanism

(1) under the thermal action of combustion reaction, the flame retardant in the condensed phase decomposes and absorbs heat, slowing down the temperature rise in the condensed phase and delaying the thermal decomposition rate of the material; 2) After thermal decomposition of the flame retardant, it releases a chain reaction free radical blocker, which interrupts the branches of the flame and chain reaction, and slows down the gas phase reaction speed; 3) The formation of coking layer or foam layer enhances the role of these layered hard shells in hindering heat transfer; 4) Under the action of heat, the flame retardant appears endothermic phase transition, which physically prevents the temperature rise in the condensed phase

2.1.2 fire resistance mechanism

(1) add some additives to the insulation and sheath materials of wires and cables to reduce the heat generated by the polymer, prevent the polymer from decomposing or promote the carbonization of insulation and sheath materials to form a protective layer; 2) A layer of inorganic insulating materials such as mica glass ribbon is added at the core. After the insulation and sheath layers are burned by fire, the mica fire-resistant tape wrapped on the conductor is protected and continues to be energized, so as to maintain normal operation for a certain period of time in case of fire

2.1.3 mechanism of mineral insulated cable

use the absorption effect of metal hydrate to make the cable flame retardant. For example, with Al (OH) 3 and Mg, the price often fluctuates (OH): as a flame retardant, Under high temperature operation, Al (OH) 3 is "we plan to affirm one theme in each session in the future, 34.6%, Mg (OH) Z is 31% (see reaction formula 1 and reaction formula 2), and the reaction decomposes into endothermic reaction, which can inhibit the combustion of polymers. 2ai (OH) 3--*alz03+3hkj (1) Mg (OH) 2-- ～ MgO +h.3kj (2)

2.2 classification and standard test of combustion characteristics of wires and cables

wires and cables can be divided into ordinary wires and cables, flame-retardant wires and cables, fire-resistant wires and cables, halogen-free low smoke wires and cables and mineral insulated cables according to their own combustion characteristics

(1) flame retardant wires and cables refer to wires and cables that are difficult to catch fire and have the ability to prevent or delay the spread of flame. The commonly used standard test is GB/t18380.3 (equivalent to IEC); (2) Fire resistant wire and cable refers to the wire and cable that can still maintain the integrity of the line under the flame combustion at the specified temperature and time. The commonly used standard test is GB/t12666.6 (equivalent to IEC); (3) Halogen free low smoke wires and cables are divided into flame-retardant and flame-retardant and fire-resistant types. Flame retardant refers to wires and cables that contain no halogen, produce less smoke and dust when burning, and prevent or delay the spread of flame. The commonly used standard tests include GB/t17650.2 (equivalent to IEC), GB/t17651.2 (equivalent to IEC) and GB/t18380.3 (equivalent to EC). On the basis of the above, the flame-retardant and fire-resistant type also needs to meet the requirements of maintaining the integrity of the line. At the same time, GB/t12666.6 (equivalent to iec60331) is added to the commonly used standard test; (4) Mineral insulated cables are non combustible, smoke-free and non-toxic in flames, and they will not cause fire due to short circuit. In addition to GB/t12666.6 fire resistance test, the commonly used standard test should also refer to the standard requirements of British BS standard for the test of cables with the ability to resist sprinkler water and mechanical impact (heavy object falling). At the same time, refer to the national standard mineral insulated cables and terminals with rated voltage of 750V and below (GBL)