My electrician made reference to a splice from aluminum to copper which
is safe, I did a little internet search and came up with this:
The crimp connector repair consists of attaching a piece of copper wire
to the existing aluminum wire branch circuit with a specially designed
metal sleeve and powered crimping tool. The metal sleeve is called a
COPALUM parallel splice connector and is manufactured only by AMP
Incorporated. This special connector can be properly installed only
with the matching AMP tool. This tool makes a permanent connection
that is, in effect a cold weld. An insulating sleeve is placed around
the crimp connector to complete the repair.

Source: http://www.heimer.com/information/aluminum_wiring.html