What are the reasons for the fire of low voltage cable?

What is the cause of the fire of the low voltage cable?

The main causes of low-voltage cable fires are overload, short circuit, excessive contact resistance, insulation damage and high temperature baking.

(1) Overload refers to the power or current of electrical equipment or wires exceeding its rated value. The main hazard of overload is that the conductor can convert electrical energy into heat energy under overload conditions, causing the conductor and its insulation to overheat locally. When the necessary temperature is reached, it can ignite nearby combustibles and form a fire.

(2) Short circuit. When the electrical circuit is short-circuited, the branch load of the electrical circuit will be cut off. The current is inversely proportional to the change of the load impedance. When the impedance becomes very small, the current is often very large, so the heat generated is very large. At this time, If the insurance cannot be disconnected instantly, the conductor will catch fire, causing a fire.

(3) Contact resistance. When the electrical lines overlap, the contacts are loose, and the voltage between the contacts is sufficient to break down the air in the gap and form air conduction. If the gap between the contacts is slightly larger and it happens to be the peak value of the power supply voltage fluctuation, an arc will be pulled out in the air, igniting nearby combustibles to form a fire.

(4) The design load is small, and the electrical circuit is in or on the verge of overloading for a long time, which not only causes the electrical circuit to overheat, but also the contact resistance effect at the electrical circuit connection is prominent, resulting in the electrical circuit of the building always transiting in concealment.

(5) Improper selection of conductor materials. In the fire prevention inspection or fire cause investigation, it is found that the power distribution trunk of some large-scale building electrical circuits adopts copper wire, and the end adopts aluminum wire. The connection mode is copper-aluminum direct connection. Under the action of air, copper-aluminum contact galvanic corrosion occurs at the connection. Long-term adapter joints naturally loosen under the action of galvanic corrosion, resulting in large contact resistance. The results are as follows: local heat release or ignition, discharge will ignite the surrounding combustibles and cause a fire.

(6) caused by the fire, the daily life of electric welding, blowtorch, alcohol furnace, electric furnace, a large number of use, directly or indirectly threaten the insulation of low voltage cable.

(7) caused by heat sources, such as various high-temperature steam pipelines in power plants and chemical plants; slag from power plant boilers, when chemical plant production equipment sprays high-temperature combustible raw materials; hot molten steel in steel plants, etc.

Fundamentally speaking, low-voltage cable fires are mainly caused by the aging and flammability of insulating materials.

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