As we all know, the fire risk of aluminum wire is far greater than that of copper wire. The fire of aluminum wire is not caused by the aluminum wire itself but by the connection of aluminum wire. Compared with copper wire, the fire risk of aluminum wire connection is higher for the following reasons:

　　1. The surface of aluminum wire is easily oxidized in air

　　Film resistance exists more or less on the surface of all conductors. If the film resistance causes the connection to overheat, the overheat will increase the film resistance, and the conductivity will be worse, especially in the aluminum wire connection. This is because even if the surface of the aluminum wire is scratched and clean, it can be oxidized after being exposed to the air for a few seconds to form a layer of aluminum oxide film immediately. Although its thickness is only a few microns, it has a very high resistivity, thus presenting a large film resistance. Therefore, during the construction and connection of aluminum wire, conductive paste shall be applied immediately after the surface of aluminum wire is scraped to cut off the contact between the connecting surface of aluminum wire and air, otherwise the contact resistance will be increased.

　　2. High expansion coefficient

　　The expansion coefficient of aluminum is as high as 23 * 10-6 / ℃, 39% higher than that of copper and 97% higher than that of iron. When the aluminum wire is connected to these two metal conductors and passes current, the connection point generates heat due to contact resistance. These three kinds of conductors expand, but aluminum expands more than copper and iron, which causes the aluminum wire to be squeezed. After the line is cut off and cooled, the aluminum wire is slightly flattened and cannot be completely restored to its original state, so that there is a gap at the connection and it becomes loose, and the aluminum oxide film is formed due to the air, which increases the contact resistance.

　　The heat generation will be intensified during the next power on, which will worsen the situation. In serious cases, the fire may be ignited due to abnormal high temperature or power generation sparks. Therefore, transition joints shall be provided when aluminum conductors with large cross-sectional area are connected with copper and iron conductors. Small sectional area (not more than 6mm ²) Spring crimping cap shall be used for the connection of aluminum wire, so that the connection contact surface is under the pressure of spring no matter whether the connection is electrified or heated, so that air and moisture can enter without gap, so as to maintain good conductivity of the connection.

　　3. It is prone to electrolytic corrosion

　　If there is acidic or alkaline liquid between two metals with different potentials, the two metals will form a local battery. The potential of aluminum is -0.78v and that of copper is -0.17v. When there is water containing salt between the aluminum conductor and the copper conductor, such a local battery is formed. The ionization will cause the aluminum conductor with low potential to be corroded and increase the contact resistance.

　　4. Easily corroded by hydrogen chloride

　　For PVC insulated aluminum core wires and cables, another problem may occur. In order to prevent the decomposition of hydrogen chloride gas from PVC insulation, a stabilizer to prevent the decomposition of hydrogen chloride is added in the PVC insulation. However, when the line temperature exceeds 75 ℃, for example, when the line is overloaded or the connection temperature is too high due to other reasons, the stabilizer can no longer prevent the formation of hydrogen chloride, and hydrogen chloride will corrode aluminum, which will also increase the contact resistance and fire risk.