Connection of Copper wire for grounding when the neutral wire is of aluminum is allowed and is very much in use and is followed by the people.
Compatibility of Copper and Aluminum
It is all right to employ the copper as an EGC in parallel with aluminum for the hot and the neutral wires.
This is permitted by the NEC as long as the terminations are well done and the right connectors are used.
Connections between aluminum and copper are distinct because the two materials tend to corrode when joined together; for this reason, aluminum and copper connections require specific connectors that will not corrode and fit well in the connection area.
Grounding Conductor Size
Based on NEC Table 250. 122, A 10 AWG copper wire is an acceptable grounding conductor for circuits to 60 amps, which is commonly used for homes.
This means, if you have a copper grounding wire it can ground a circuit that has aluminum as the hot and neutral conductor.
Precautions
To connect copper with aluminum, it is mandatory to connect by the help of connectors that are adequate to copper and aluminum.
It is not recommended to use the ‘simple’ wire nuts; instead, wire connectors for Aluminum/Copper are to be used to prevent overheating and moreover fire risks.
Installation Practices
Tighten all connections as much as possible and use an anti-oxidant to cover up all the exposed aluminum as oxidation usually leads to increased resistance and heating up of the conductor.
Conclusively, it is unlawful to use copper wire as grounding and at the same time utilize aluminum as the neutral; rather, it’s a norm as long as one utilizes the correct procedure and materials.