Mix and match might work for some things. However, it does not make for a pretty or safe sight when working with electrical wiring when circuits include both copper and solid-strand aluminum wiring. The panel below has both -- mix and match. The terminal on the left clearly has a solid aluminum wire on the top breaker. The ones below that are copper. Solid-strand aluminum branch wiring, used for a relatively brief period into the early 1970's, has a history of safety problems. I have seen estimates that a home could be as much as 50 times more likely to have a fire when such wiring is present.

The photo to the right is the same panel, viewing it from farther away, and at that location some odd work was done. They cut many of the aluminum wires off, and then they used wire nuts to splice copper pigtails onto the aluminum. The copper went to the breakers so, in glancing at the breakers, one saw mainly copper but looking at the grounds or neutrals one saw solid-strand aluminum in abundance.

This makes it all more confusing but it does not resolve the issue with the solid-strand aluminum wiring. And it makes each connection at each wire nut suspect -- dis-similar metals in contact.  They do make wire nuts, that they say are designed for this purpose of joining the two different materials together but, even those are suspect as far as any long-term repair. In almost all cases, the recommended cleanup procedure is eliminating the solid-strand aluminum wiring. Sometimes, an electrician might use special pig-tails but for those to be done right it is not cheap. Also, the problem does not exist only in the panel. Those aluminum wires attach to switches, outlets, lights and often, when viewing those locations, corrosion will be apparent. A home inspector, when confronted with this issue, directs the client to consult a licensed electrician for repairs and further evaluation.

Steven L. Smith

Bellingham WA Home Inspections