As I see that you have gotten an electrician involved, you probably
don't need this info. But I thought that I would post in case there
are others out there with the same or a similar situation.
The concept of pigtailing is a recommended strategy for all connections
behind devices. IE. black to black with a short length to the device
connected with a wire nut. Same for whites and grounds.
NOTE: There are different configurations for connections behind
switches and light fixture boxes.
When dealing with aluminum wiring "AL" the manufacturers have designed
receptacles, switches, etc. to properly handle connections without
oxidizing. Oxidization looks like a powdery substance on the surface
of the wire (much like rust on a metal object). Electricity doesn't
flow through this oxidization well, and causes heat.
To avoid this, always use devices rated for AL wire and when connecting
the wires with wire nuts use wirenuts rated for aluminum.
If you are pigtailing, you can use Copper Wire for the pigtail (which
allows you to connect to devices rated for copper only). However, the
connections at the pigtail need to be protected by a product call
anti-oxidant - Penetrox and No-Alox or the 2 most popular in my area.
This is available at most hardware stores and should be at all
Remember, that when making these splices, use wirenuts rated for
aluminum "AL" wiring only. Fill the wirenut about 3/4 full with
anti-oxidant paste and then put onto wire being connected. If after
the wirenut is installed, there are any bits of exposed wire visible
not covered in anti-oxidant then put more into the cap to cover.
For those without much experience with wiring, consult with a qualified
electrician to ensure that this is being done in a safe manner. The
big box stores usually have a couple on staff to answer questions, so
don't be afraid to ask, they are there to help.
Remember Also, always turn off the breaker prior to working on
electrical circuits and test to make sure that the power has indeed
been turned off before proceeding with any such work.
I hope this information helps and if anyone has questions, please
forward me an email, and I can try to help.