My house was built in the 70s and originally had all aluminum wiring. New circuits have been added over the years and the house currently has a mix of both aluminum circuits and copper circuits, along with a newer 200A panel. I have owned the house for about the past 5 years. There is currently a #2 aluminum stranded ground wire connecting the panel to my water line where the water line enters my basement. The panel and water line entrance are at opposite corners of the basement. That ground wire runs along the underside of my floor joists instead of passing through holes drilled in the joists. This wire is in the way of where some top plates will be going for walls that i am building to finish the basement, so i want to re-route the ground wire to a new path that is not in the way. The new path will be about 20 feet longer than the current run, so I am planning to buy new wire to make this new run from my panel to the water line. Should i replace the current #2 aluminum wire with a longer #2 aluminum wire, or can/should i go with a copper wire instead? The copper costs more but it is easier to work with and i think i would prefer changing to copper unless there is some reason to keep it aluminum.
I would recommend 4 AWG copper, which is equivalent (in general terms) to 2 AWG aluminum. Smaller, easier to run. More standard. And compatible with the copper pipe you're bonding it to.
But while you're doing that, check your local codes (might be worth a call to the building department or equivalent organization). While almost anything old can be grandfathered, once you are going to this trouble you might as well do whatever current local code requires. Which could be any combination of:
- Copper water pipe
- One ground rod with a test
- One ground rod without a test (normally that's only when you also ground to the water pipe)
- Two ground rods without a test
You're talking about the Grounding Electrode Conductor (GEC), which is how your panel gets a "ground reference" to the actual earth, and keeps neutral and ground near earth voltage (or "keeps earth near neutral and ground voltage" under certain fault conditions). It goes to ground rods, UFER ground built into the reinforcing rod, or in older installations to a water pipe (contingent on the utility not having replaced with a plastic pipe or plastic water meter). *
The GEC must be entirely continuous from the main panel to the first ground rod/Ufer/pipe, with no splices. So yeah, there's no "go to a Polaris connector and splice". One particular irreversible compression splice is allowed but the splice tool costs $1000, so makes no sense for a DIYer.
Aluminum is no longer allowed for GEC. Largely because GECs go places prone to high-corrosion environments, like near water pipes, concrete (Ufer grounds) and outdoors in the dirt for ground rods.
Other than that, aluminum wire is not a problem if you respect and understand it. The problem is, people don't/didn't. Back in the 1960s and under great government pressure owing to a copper shortage, UL underestimated the testing needed to certify a terminal for AL wire. Their "AL-CU" certification for 15-20A switches and receptacles didn't work. They were forced to revise it to "CO-ALR" which is much tougher. And second (this was the thing they never figured out)... modern science has proven that screw torque matters, even on the small stuff. Nobody was using torque screwdrivers back then, and that didn't help aluminum any. For splices, wire nuts don't work (not even the purple ones). However, panel lugs and neutral bars have always been made of aluminum, and that works - so they make splices that are "little neutral bars" wrapped in an insulating jacket - these are "Alumiconn" for up. to 3 ports taking one #14-10 per port; or "ILSCO Mac Block Connector" with 2 ports taking 1-4 #14-6 wires per port. With that knowledge, aluminum is perfectly fine, and legal today.
* And if you wonder why Flint, Michigan is having such trouble replacing old leaded water mains to people's houses, that right there because now another trade must come in.