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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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  • Aluminium wire on telephone poles, repurposed for high frequency internet usage has a VERY bad reputation.
    – Jeremy Boden
    Apr 29 at 20:26

4 Answers 4

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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
    Apr 27 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
    Apr 29 at 13:33
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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
    Apr 27 at 20:29
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    @Harper-ReinstateMonica Denser = stiffer? Huh? Stiffness has no relationship to density.
    – DKNguyen
    Apr 28 at 2:45
  • For fun: "Cost of wire - much lower for aluminum than copper" --> aluminum used to be very expensive
    – chux - Reinstate Monica
    Apr 28 at 11:03
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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
    Apr 28 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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