[Shop-talk] Aluminum and copper wiring

[Steve Dillen]

I've played this game.  When I bought my house, those purple nuts didn't 
exist, but I believe the underlying principle I followed was sound and 
periodic reinspection of all junctions in the house have identified no 
faults.  As I remodel sections of the house, the original aluminum goes 
in the scrap heap.

As I understand it, the problem with aluminum wire is the result of 
a)the heat expansion characteristics in comparison to copper and b) the 
oxidation characteristics of aluminum.  As aluminum oxidizes, resistance 
in the electrical connection increases which creates more heat, which 
causes expansion of the alumimum.  The repeated expansion/contraction of 
the alumimum reduces the mechanical joint (I've seen screws backed out 
of outlet terminals) of the connection which increases resistance....and 
the cycle expands.

Theory at the time I went through my house (15 years ago) is that you 
trim back the aluminum wire to get a fresh joint, you apply a wire 
anti-oxidant to the wire, then "wet sand" (with anti-oxidant) the 
exposed inch or so of wire with sandpaper to remove all oxidation.  Then 
twist (with pliers) an extremely tight wrap joint between the aluminum 
and a 3" (or so) copper wire "tail".  Then fill a wire nut with 
anti-oxidant and tightly twist it onto the newly created joint.  This 
gives you a non-oxidized mechanical al/cu joint that is protected from 
air exposure.

The attached tails can be used and wired as normal copper. Ground wires 
are handled the same way, cut back, anti-ox, sand, tight mechanical 
twist to copper tail, anti-ox filled wire nut, copper tail tied to 
junction box.

At the time, there was a specific anti-ox compound I selected which 
wouldn't burn (most acted like a fuel) and  3m scotchlock wire-nuts were 
preferred.  I see that there's a "alumiconn" connector that is now 
available for the pigtailing exercise.

Steve


On 2018-04-23 10:33 AM, Jim Stone wrote:
> Hi guys.  I am currently visiting my sister-in-law and offered to install a light switch for her; she has dusk-to-dawn outdoor lights that were installed by a handyman and wired without a switch.  She’d like to be able to turn them off, which is normally a pretty simple job.  However, her house was built in the early 70’s and has mostly aluminum wiring.  I just opened up the box where the handyman spliced in the circuit for the lights and he used a standard outlet made for copper wiring, not a CO/ALR rated one.  Aluminum going in; copper coming out.  No sign of arcing, fortunately, but I will do it right.  The current outlet has a copper ground wire and an aluminum one connected together to the ground screw.
>
> I know using a CO/ALR outlet allows me to connect the (copper) light circuit to the original (aluminum) circuit, but I am not sure about how to do the ground wires.  I assume it is less critical with a ground wire than a hot one, but still…. I suppose I could simply not ground the lights or the new switch, but I am wondering if there is a better solution.
>
> Thanks,
>
> Jim
> _