Originally Posted by Newmarket
In house that is at least 40 years old, changing the switches and receptacles makes sense anyway. And more importantly, you don't introduce added connection points. And even more important than that you don't overcrowd the boxes or put extra strain on the existing and perhaps fragile AL wiring insulation in order to add those additional connection points. Old aluminum wire tends to form cracks in the surface, which, if flexed - as you will be doing when you pigtail them - can open up - creating a fire hazard. What's more, some of the boxes for sure will be out of code with the pigtailing which will require the installation of new boxes as well. Also, pigtailing copper to aluminum is always problematic not just because of the expansion and contraction differences, but because of the oxidation that forms between dissimilar metals. That means in addition to the pigtailing, one must use paste and a special cap on all those pigtails in Canada, or in the US, one must use the special COPALUM crimping system - which isn't cheap to buy.
Simply changing the old switch and outlet devices to new CO/ALR devices is the cleaner and safer solution. I know at Home Depot, a CO/ALR receptacle is $4.95.
The US UL and Canadian CSA both approve AL to copper pigtails using special twist on connectors and paste (according to what I've read so far). Hard to say if it's fact or fiction there's so much out there.
Also the US Consumer Product Safety Commision are the ones who do not advocate the use of pigtails with twist on connectors... they say use one of the following methods for dealing with AL branch circuits:
1) Complete Replacement of Copper
2) COPALUM Method of Repair
3) AlumiConn Connector
BUT NO TWIST ON CONNECTORS... here's the link if you're curious...
Replacing the receptacles/switches/fixtures with AL compatible sounds like the best way however the aluminum wire in the one receptacle box I checked in my house is so fragile with very short wire... if it breaks off while removing or installing the new receptacle I think I'm screwed... there's not enough slack.
Aluminum wire is not "re-useable" it appears... it's just to brittle. That's ok if there's plenty of slack in the wire so you can trim some more off... but if there isn't I don't see how replacing them can be done. May as well just rip it all out.