1. The potentials of copper enameled wire and aluminum enameled wire are different. The contact part between copper enameled wire and aluminum enameled wire will accelerate the oxidation of aluminum wire due to galvanic cell reaction, and the contact between copper enameled wire and aluminum enameled wire will be poor over time. If you want to connect them together, you must use copper enameled wire and aluminum enameled wire over clamps or over conduits.
2. This is a chemical problem. The chemical characteristics of metals are relatively active and inactive. For example, gold never rusts. This shows that gold is chemically inactive, iron is easy to rust, and iron is more active than gold. If the two metals are put together, the oxidation of active metals will be accelerated. Aluminum enameled wire is more active than copper enameled wire. The connection of the two cables will accelerate the oxidation of aluminum (i.e. rust) and affect the use.
3. When copper and aluminum conductors are directly connected, the contact surfaces of the two metals are easy to form electrolyte under the action of moisture, carbon dioxide and other impurities in the air, thus forming a galvanic cell with aluminum as the negative electrode and copper as the positive electrode, causing galvanic corrosion of aluminum and increasing the contact resistance at the copper-aluminum junction.
In addition, because the elastic modulus and thermal expansion coefficient of the copper enameled wire and the aluminum enameled wire are very different, after many cold and heat cycles (power on and power off) in operation, a large gap will be generated at the contact point, thus affecting the contact and increasing the contact resistance. When the contact resistance increases, the temperature will rise during operation. Corrosion and oxidation will intensify at high temperature, resulting in a vicious cycle and further deterioration of connection quality, which will lead to high temperature of contact points and even smoke, burning and other accidents.
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