Cable manufacturers reveal why aluminum wire is more prone to fire than copper wire in electrical lines?

All natural things are for human enjoyment, so many metal materials each metal material has its own characteristics, copper wire and aluminum wire as the most commonly used metal in the power system has its own uses, but also has its own advantages and disadvantages. As an electrician, we must understand the characteristics of these two metal wires to be used. Only by understanding the advantages and disadvantages and characteristics of both of them can we make appropriate use of materials and make the best use of them. Otherwise, it is easy to cause improper use, light line damage, heavy cause fire, the following cable manufacturers on the two different metal materials to explain to you, in the construction of the time should be how to choose the right material of wire and cable.



First of all, we must understand the following points, that is, the advantages and disadvantages of copper and aluminum:

1, load power: the same cross-sectional area of copper wire and aluminum wire two kinds of wire, copper wire load power is greater than aluminum wire.

2, flexibility: copper wire flexibility is better, easy to bend, strong fatigue resistance. Aluminum wire is relatively easy to break when bent.

3, stability: aluminum wire is very easy to oxidize, so that the resistance becomes larger, reduce the wire load, prone to safety problems. But the copper core is extremely stable.

4, resistivity: the resistivity of copper wire is small, compared with the resistivity of aluminum wire is less than 1.68 times, resulting in the power loss of aluminum wire is relatively large, heat is more serious, affecting the utilization rate of electricity.

5, price: The price of aluminum wire is much cheaper than copper wire, copper wire price is generally many times that of aluminum wire, copper wire is also heavier than aluminum wire.

We all know that the danger of aluminum wire fire is much greater than that of copper wire, and the fire of aluminum wire is not in the aluminum wire itself but in the connection of aluminum wire. Compared with copper wire, aluminum wire connection fire risk is greater for the following reasons:

1, the surface of aluminum wire is easy to oxidize in the air

Film resistance exists more or less on the surface of all conductors. If the film resistance causes the connection to overheat, and the overheating increases the film resistance, the electrical conductivity will deteriorate, and this type of overheating is particularly serious in the aluminum wire connection. This is because even if the surface of the aluminum wire is scraped clean, it only needs to be exposed to the air for a few seconds to be oxidized and immediately form a layer of alumina film. Although its thickness is only a few microns, it has a high resistivity, resulting in a large film resistance. Therefore, when connecting aluminum wire construction, conductive paste should be applied immediately after scraping the surface of the aluminum wire to cut off the contact between the aluminum wire connection surface and the air, otherwise the contact resistance will be increased.

2. High expansion coefficient

The expansion coefficient of aluminum is as high as 23*10-6/ C, which is 39% larger than copper and 97% larger than iron. When the aluminum wire is connected to these two metal conductors and passes an electric current, the connection point heats up due to the presence of contact resistance. All three conductors expand, but aluminum expands more than copper and iron, causing the aluminum wire to be squeezed. After the line is powered off and cooled, the aluminum wire is slightly flattened and cannot be fully restored, so that there is a gap at the connection and it is loosened, and an alumina film is formed due to the entry of air, which increases the contact resistance.

The heat will intensify when the next power is on, making the situation worse, and in serious cases, it may ignite a fire due to abnormal high temperature or generating sparks. For this reason, transition joints should be configured when aluminum conductors with large cross-sectional areas are connected with copper and iron conductors. The connection of small cross-sectional area (not more than 6mm²) aluminum wire should use a spring crimping cap, so that no matter whether the connection is energized or not, there is no heat, the connecting contact surface is under the pressure of the spring, so that the air and moisture have no gap to enter, so as to maintain the good conduction of the connection.

3, easy to appear electrolytic corrosion

If there is an acidic or alkaline liquid between the two metals with different potentials, the two metals will form a local battery. Aluminum has a potential of -0.78V and copper is -0.17V, and this local battery is formed when there is salty water between the aluminum conductor and the copper conductor. The ionization will cause the low potential aluminum conductor to be corroded and increase the contact resistance.

4, easy to be corroded by hydrogen chloride

Another problem may arise with PVC insulated aluminum core wires and cables. In order to prevent PVC insulation from decomposition of hydrogen chloride gas, PVC insulation is added to prevent the decomposition of hydrogen chloride stabilizer. However, when the line temperature exceeds 75 ° C, such as when the line is overloaded or the connection temperature is too high for 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.

Qingdao Tianxing Cable Co., Ltd. specializes in the production of customized wire and cable manufacturers, exports to more than 40 countries and regions around the world, the annual production capacity of 1 billion yuan. 6000 square meters of storage, standing hundreds of millions of inventory, order demand for rapid distribution and delivery, large prices more favorable. Hotline: 16678668090/ 16678668098