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A well established electrical company is installing a subpanel a significant distance from our main service. They sent two quotes indicating they could use either 3/0 Aluminum or 1/0 Copper feeder and either would be adequate for the requirements. The quote for the Aluminum was significantly cheaper. I asked why anyone would choose copper, and he said that he just "prefers copper", and did not provide any additional details. Before I tell them to go ahead with the aluminum, is there any additional considerations I should be aware of?

Ideas: Maybe aluminum doesn't last as long or breaks down over time, or has long term problems. I see heavy gauge aluminum on telephone poles so I can't imagine this is the case. I would guess that copper would also be more prone to theft.

Maybe I just "prefer saving money" for this project.

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For feeders, aluminum is perfectly acceptable. It got a bad rap when it was used for residential circuits back in the 70s where it might not have been terminated as carefully as it should have. But for large feeders, it's significantly cheaper (aluminum is a lot less expensive than copper), and as long as it's installed by a pro and torqued down properly, there are no concerns/worries about using it.

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    Yes, not only were the outlets and switches improperly certified for aluminum, but back then, nobody understood the importance of setting torques with a torque driver on the small stuff.
    – Harper - Reinstate Monica
    Commented Apr 27, 2023 at 20:29
  • A year ago, when installing a few new breakers, I made an investment in a gunsmith-style torque screwdriver. Wasn't unreasonably expensive.
    – keshlam
    Commented Apr 29, 2023 at 13:33
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    I just picked one up, @keshlam, for all my new electrical installations. It was about $40 and included a ton of driver bits (that are 4th or 5th or 6th of each type that I already own...).
    – FreeMan
    Commented Oct 20, 2023 at 11:38
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Aluminum and copper are equally acceptable as far as code. There are exceptions, largely for historical reasons, in some jurisdictions - anything from "no aluminum for 15A/20A circuits" to "aluminum OK for panel/subpanel feeders but not for any branch circuits" to "no aluminum at all after the meter". But if there was a local limitation then your electrician wouldn't be giving you the option of aluminum.

So that leaves two practical differences:

  • Cost of wire - much lower for aluminum than copper
  • Size of wire - one or two sizes larger for aluminum (depending on a few factors) than copper

If a customer is paying "cost of parts + set labor cost" for the job (i.e., this type of job takes 3 hours on average, so we'll bill you for 3 hours and if takes less time we win and if it takes more time you win) then the electrician may push copper because it doesn't cost them any extra (customer paying the actual wire cost) and copper is a little bit easier because the wires/cables are smaller.

TL;DR Go with whichever wire gives you the lowest total cost, which will almost certainly be aluminum because 3/0 isn't that much harder to work with than 1/0.

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    That's it right there, it's the markup - the electrician gets higher markup on the more expensive wire. Note also that copper is almost 4 times denser than aluminum (which is why they don't make copper airplanes, they'd be unable to take off)... and that makes it stiffer. As such, bending effort is probably a wash. Also, most panel lugs are made of zinc coated aluminum, since the thermal expansion differences work favorably when aluminum is the lug.
    – Harper - Reinstate Monica
    Commented Apr 27, 2023 at 20:29
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    @Harper-ReinstateMonica Denser = stiffer? Huh? Stiffness has no relationship to density.
    – DKNguyen
    Commented Apr 28, 2023 at 2:45
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    @Harper-ReinstateMonica You almost always have great and complete answers, but is this case I gotta disagree with your comment. I have found copper MORE flexible than AL, esp. on a main 200amp feed you can use 3/0 CU vs 4/0 AL . I used it for a very short run between an automatic generator transfer switch and the main panel (just a few feet) bc I didn't want to wrestle with 4/0 AL. CLEARLY CU is super ridiculously expensive now...so for any substantial length feeders , there's nothing wrong with AL, so I agree with most of what you said, I just find CU easier to work with.
    – George Anderson
    Commented Apr 28, 2023 at 11:38
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'Soft' (less stiff than alluminium) copper wire (with smaller diameter) might be easier pull though torturous route with bends etc.

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Slightly cynical answer - maybe your electrician gets more cash back from the recycling of copper offcuts vs aluminium ?

Both have scrap metal value, but copper's is higher than aluminium at $10.50/kg vs $1.45/kg respectively.

Your locale will have different values, but likely a similar ratio of about 7 to 1.

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I wouldn't allow aluminum wire to be used in my house--or at least not at any point after the electric meter.

Yes, the electrical code allows aluminum wire in some cases, and if installed correctly it is supposed to be safe.

From what i understand, nicking aluminum wire, failing to use antioxidant paste on the connections, or torquing it incorrectly may all cause it to oxidize and start a fire.

If you're only going to own the house for 10 or 20 years and don't care what happens to the next owner, then it's probably fine. If you're in it for the long haul, then it seems like a foolish economy.

Recent amendments to the California electrical code require copper wire (i.e. ban Al wire) for most residential purposes:

Article 310.2(b) is hereby amended by the addition of a second paragraph to read as follows:

Copper wire shall be used for wiring No. six (6) and smaller in all installations. Consideration for use of aluminum wiring can be made by the Building Official for feeder lines only on an individual basis were adequate safety measures can be ensured.

But if you really, really want to use Al wire there does seem to be an exception:

310.106 Continuous inspection of aluminum wiring.

Aluminum conductors of No. six (6) or smaller used for branch circuits shall require continuous inspection by an independent testing agency approved by the Building Official for proper torqueing of connections at their termination point.

I don't know what "continuous inspection" means, but it sounds expensive.

Also, Farmers Insurance recently cancelled the fire insurance on our 3 unit building in San Francisco (built in 1908--just after the Earthquake). Our insurance agent said that most insurers in California will not insure a building that has aluminum wiring, knob and tube wiring (which we have), fuses, or circuit breaker panels made by Federal Pacific, Zinsco, Challenger, or Sylvania GTE. We had to pay $$$ to get insurance from a one of the two companies willing to insure a building with knob & tube, and we also had to have it inspected by a licensed electrician.

A good web page provided by the state of California for those unfortunate enough to have Al wiring in their homes:

https://www.connectcalifornia.com/utilities/aluminum-wiring-home-buyers

References for the electrical code (admittedly, these are references to the electrical code for two cities in California, not California as a whole, but they are both titled CALIFORNIA ELECTRICAL CODE

https://www.codepublishing.com/CA/LakeElsinore/html/LakeElsinore15/LakeElsinore1538.html

https://library.municode.com/ca/san_marcos/codes/code_of_ordinances?nodeId=TIT17BUCOREAC_CH17.12CAELCO_17.12.010AD#:~:text=Article%20310.3(B)%20is%20amended,oxidation%20of%20the%20aluminum%20wire.

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    – Community Bot
    Commented Oct 20, 2023 at 7:23
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    You'd best call the power company, then, and ask them to replace the drop from the power pole to your meter with copper. While they're doing that, take advantage of the power out situation to go around to every single electrical connection in your whole house (panels, switches, receptacles, fixtures) to ensure the screws are properly torqued on the copper wires because improperly torqued connections on copper wires can fail and start fires, too. Oh, and all those backstab connections DIYers use? Yeah, get rid of them, too...
    – FreeMan
    Commented Oct 20, 2023 at 11:37
  • i'm sorry you didn't like my answer. i agree with some, but not all, of your points -- i don't trust backstab connections either, or those new wire nuts that use backstab style connections. i asked the electricians to not use them in their work. perhaps the most interesting point is that Farmers Insurance has decided they don't want to insure our building any more (a 3 unit building in San Francisco built in 1908). We're hunting for new insurance and have been told that most other insurers won't cover a building with aluminum wiring or knob & tube wiring.
    – craigster0
    Commented Oct 24, 2023 at 7:54
  • @craigster0 -- most insurers & HIs are only concerned about 12-10AWG solid Al, especially the old EC/AA-1350 stuff; stranded AA-8000 series aluminum (as found in SE cables and outdoor runs) isn't a concern for them
    – ThreePhaseEel
    Commented Feb 19 at 12:41
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    Note also that 310.2(b) bans AL for wire sizes 6 and smaller, while the OP is installing 3/0 AL wire which is considerably larger than a #6. Additionally, the OP may not be located in the People's Republik of Californistan.
    – FreeMan
    Commented Feb 19 at 13:30

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