Why copper wires and aluminum wires cannot be directly connected？
The difference between the main characteristics of copper wires and aluminum core cables
1. Low resistivity: the resistivity of aluminum core cables is about 1.68 times higher than that of copper wires;
2. Good ductility: the ductility rate of copper alloy is 20~40%, the ductility rate of electrical copper is more than 30%, while that of aluminum alloy is only 18%;
3. Good stability and corrosion resistance: copper core cables are resistant to oxidation and corrosion, while aluminum core cables are more susceptible to oxidation and corrosion;
4. Low voltage loss: Due to the low resistivity of the copper wires, the voltage drop of the copper wires is small when the same current flows through the same cross section. The same power transmission distance can guarantee higher voltage quality; under the condition of allowable voltage drop, copper wires power transmission can reach a longer distance, that is, the power supply coverage area is large, which is conducive to network planning and reduces the number of power supply points. .
5. Low heat generation temperature: Under the same current, the heat generation of copper core cables with the same cross section is much smaller than that of aluminum core cables, making the operation safer.
6. Anti-oxidation and corrosion resistance: The connectors of copper core cables have stable performance and will not cause accidents due to oxidation. When the joint of the aluminum core cable is unstable, the contact resistance will increase due to oxidation, and accidents will occur due to heat generation.
7. Low energy consumption: Due to the low resistivity of copper, it is obvious that copper cables have lower power loss compared to aluminum cables. This is conducive to improving the utilization rate of power generation and protecting the environment.
Copper core wires and aluminum core wires and cables can be connected together in some way. The materials of copper core wire and cable and aluminum core wire and cable are different, so the characteristics are also different. To connect them together, special handling is required. Then why can't copper core wires and cables and aluminum core wires and cables be directly connected?
First, the resistivity of aluminum wires is different from that of copper wires.
Second, and this is the most important point, the aluminum wire is easily oxidized in the air, forming a layer of oxide on its surface. In addition, the hardness of aluminum is less than that of copper, which will greatly increase the contact resistance of the connection between aluminum wire and copper wire. When current flows through this connection, the contact resistance heats up. If it is a large current, the heat will be severe and the connection will be burned.
Third, according to safe operation regulations, aluminum wires cannot be connected with copper wires.
Copper and aluminum cannot be directly connected together, and copper and aluminum wires must be transitionally connected:
(1) For the connection of a single small-section copper-aluminum wire, the copper wire should be tinned first, and then connected to the aluminum wire.
(2) When connecting multiple strands of large cross-section copper-aluminum conductors, copper-aluminum transition tubes or copper-aluminum transition clamps should be used.
(3) If the aluminum wire is connected to the copper terminal of the switch, a copper-aluminum transition nose should be used.
Consequences of direct connection of copper and aluminum wires:
When the copper and aluminum conductors are directly connected, the contact surface of the two metals will easily form an electrolyte under the action of impurities such as moisture and carbon dioxide in the air, thus forming a primary battery with aluminum as the negative electrode and copper as the positive electrode, resulting in aluminum Electrochemical corrosion increases the contact resistance at the copper-aluminum junction.
Due to the large difference in the elastic modulus and thermal expansion coefficient of copper and aluminum, after multiple cooling and heating cycles (power on and off) during operation, a large gap will be generated at the contact point, which will affect the contact and increase the contact resistance. As the contact resistance increases, the temperature increases during operation. At high temperatures, corrosion and oxidation will intensify, forming a vicious circle, further deteriorating the quality of the connection, and eventually leading to excessively high temperature at the contact point, and even accidents such as smoke and burns.
Precautions for connecting copper core wires and aluminum core wires:
In dry rooms, copper conductor wires should be tinned. Or indoors where the relative humidity of the outdoor air is close to 100%, a copper-aluminum transition plate should be used, and the copper end should be tinned.
In addition, copper-aluminum connecting tubes can be used when copper cables are connected to aluminum cables, and copper-aluminum terminals can be used when copper cables are connected to aluminum wires, and the copper terminals should be tinned.