Why should aluminum wiring never be directly connected to copper wiring?

Aluminum wiring should never be directly connected to copper wiring due to the risk of galvanic corrosion and differences in thermal expansion rates. Galvanic corrosion occurs when two dissimilar metals are in contact in the presence of an electrolyte (moisture). Aluminum is more reactive than copper, so it acts as the anode and corrodes preferentially. This corrosion creates an insulating layer at the connection, increasing resistance and potentially leading to overheating and failure. The rate of galvanic corrosion is accelerated by the presence of moisture and contaminants. Aluminum and copper also have different coefficients of thermal expansion. This means that they expand and contract at different rates with changes in temperature. Over time, this differential expansion and contraction can loosen the connection, further increasing resistance and the risk of overheating. The increased resistance generates heat, which accelerates the corrosion process and further loosens the connection, creating a positive feedback loop. To safely connect aluminum and copper wiring, special connectors and techniques must be used. These connectors are designed to prevent direct contact between the two metals and to provide a gas-tight seal to prevent moisture from entering the connection. Anti-oxidant compounds are also used to prevent corrosion. For example, in older agricultural buildings, aluminum wiring was sometimes used. Directly connecting this to copper wiring in new equipment without proper connectors creates a fire hazard due to corrosion and overheating.