When connecting copper and aluminum conductors, which should be placed on top?

When connecting copper and aluminum conductors, placing aluminum over copper is considered the correct practice. This approach is rooted in the differences in the properties of the two metals, particularly in terms of their corrosion behavior and conductivity.

Aluminum has a higher tendency to expand and contract with temperature changes compared to copper. Placing aluminum on top allows for better handling of these thermal dynamics, as the copper conductor, which has a lower coefficient of thermal expansion, will maintain a tighter connection over time. Furthermore, this configuration minimizes the risk of galvanic corrosion, which can occur when two dissimilar metals are in contact. Galvanic corrosion happens because electrical potential differences can lead to the deterioration of one of the metals when they are paired.

In addition, the use of an appropriate connector designed for a copper-aluminum connection is crucial, as it typically has specific features that accommodate the differences in metal characteristics and ensure a secure, safe connection.

The other options do not account for the best practices in terms of metallurgy, thermal expansion, and corrosion resistance that are essential when connecting these two types of conductors.