From other posts it seems clear I need to update my transformer to 16V 30 VA in order to handle my wired Google Nest doorbell when the weather turns cold. My existing transformer is wired directly to the aluminum wiring in my house - I can't tell if it's a copper or aluminum transformer. I bought a new transformer already which I assume is copper (it doesn't actually provide any specs on this). For any other new switches that are copper I've pigtailed to the aluminum using the appropriate marrettes and the anti-oxidant compound. Am I right that I need to do the same with the transformer?

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    Usually stuff will have CU-AL if they are rated for aluminum wire.
    – crip659
    Commented Feb 7 at 21:34
  • RED FLAG: "it doesn't actually provide any specs on this"! This is likely an indicator that it is not UL/ETL approved for use in the US. How about a brand/model or (better) a link to where you bought this transformer without specs.
    – FreeMan
    Commented Feb 8 at 13:27
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    @FreeMan yes, from reading other posts I am sure it's not UL approved and I've become very skeptical about it and have now returned it. I'll pay a little more and get a good one
    – Alex
    Commented Feb 10 at 16:47
  • Probably a good call. Whatever extra you spend on buying UL approved electrical devices now will be more than made up for by not having to rebuild your house (even with insurance) in the future. ;)
    – FreeMan
    Commented Feb 10 at 16:52

1 Answer 1


If the transformer has the simple screw contacts, and it does not state copper or aluminum, I doubt it is rated for aluminum. So pigtail with marrettes and antioxidant paste as you would any connection.

If the transformer has stranded wire leads, you could connect the solid aluminum directly to the stranded leads with marrettes and antioxidant paste.

In both cases it is best to abrade the solid aluminum with emery cloth before connecting. First coat the aluminum conductor with antioxidant paste then in a twisting motion abrade through the paste (in the presence of the paste). Then join the aluminum and the copper conductors with a marrette filled with paste (or with a generous dab in it).

  • Thanks Jim. It has stranded wire leads and I realized after my post that pigtails were likely unnecessary in this case but it's great to have that confirmed!
    – Alex
    Commented Feb 10 at 16:49
  • Proper procedure in that case is to "accept" the answer. Commented Feb 10 at 23:22

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