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Discuss Bi metal connections in the Electrical Wiring, Theories and Regulations area at ElectrciansForums.co.uk.

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  1. nunojpg
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    nunojpg New EF Member

    I have a lot of doubts about Aluminium and Copper connections.

    I understand the galvanic corrosion principle, but its still confusing how that applies to the connections.

    1 - Is is possible to have a connector that can take both Aluminium or Copper? Let's take a electricity meter or a Circuit breaker, they usually take Aluminium conductors, it means they can't take copper?
    2 - A solar panel can be grounded with a copper lug and wire because it is anodized?
    3 - If I use aluminium wire to ground a anodized aluminium structure, I must always use aluminium lugs?
     
  2. hermetic
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    hermetic Regular EF Member

    Location:
    East Yorkshire
    galvanic corrosion takes place in the presence of moisture. We used to dip the end of the cable in Denso grease before making the connection to exclude damp from the joint, if you can use the same metal throughout, do it.Aluminium cables in brass connections will eventually fail as the galvanic action will turn the Alu into oxide. Denso or similar compounds help to prevent this, but are not perfect.
     
  3. needasparks
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    needasparks Electrician's Arms

    Location:
    Essex
    Good tip fella, your prob talking japanesse to some but worth remembering. I had a similar problem with this at the not so new st pancras station when we fitted all the large fire security doors all being aluminium. This was what we used.
     
  4. Engineer54
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    Engineer54 Guest

    You can purchase purpose made connectors and lugs, to virtually eliminate the galvanic oxidation reaction between copper/aluminium...
     
  5. Knobhead
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    Knobhead Guest

  6. nunojpg
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    nunojpg New EF Member

    Thanks to all for the answers.

    Actually I'm just interested in the theoretical part, precisely the answer to the 3 questions I placed.

    Grease will surely help, but I don't see the electrical company using that for connecting the grid to the meter, and it's aluminium...
     
  7. hermetic
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    hermetic Regular EF Member

    Location:
    East Yorkshire
    1. electricity meters and circuit breakers in my experience do not take aluminium cables unless the brass or copper is heavily tinned, and then the long term survival of the electical connection is not good. You must not connect aluminium to bare (unplated)copper or brass connections.

    2. Yes it can, provided the hole for the bolt securing the lug was drilled prior to anodising, otherwise galvanic corrosion will take place between the bolt securing the lug and the aluminium.

    3. Yes
     
  8. hermetic
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    hermetic Regular EF Member

    Location:
    East Yorkshire
    "Grease will surely help, but I don't see the electrical company using that for connecting the grid to the meter, and it's aluminium..."

    No, you won't see it, it is very rare that anything is done properly today,especially concerning the new cash cow which is solar panels, It's the new double glazing!
     
  9. nunojpg
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    nunojpg New EF Member

    ITRON ACE300 datasheet (random meter found on the web):
    The terminals are suitable for copper and aluminium cables

    This can be because they are tined like you said? Tin will not corrode Aluminium and will not be corroded with Copper?

    About the the aluminium frame being anodized and drilled after. I imagine it will corrode inside , but that doesn't affect the electrical contact or the frame longevity...right?

     
  10. hermetic
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    hermetic Regular EF Member

    Location:
    East Yorkshire
    It is difficult to be definite about this! ALL disimilar metals will cause galvanic action when connected together in the presence of even a little damp air. The idea of the Densogrease is to exclude the air and the moisture. tinning or plating the terminals with less reactive metals can slow the process down dramatically, but it will still happen. If you can exclude air and moisture, then the joint will be stable untill moisture gets in, then corrosion will begin, and the time clock to joint failure starts ticking. the complete answer is not to use disimilar metals, especially aluminium. If you are in a situation where you need definitive answers for an exam, you must ask your trainers, because unfortunately, whilst the answer they will give you will pass the exam, it may not be the whole truth, and in practice, may be useless rhetoric. I have seen 6mm zinc plated steel bolts corrode through in 5 years when installed into aluminium in and exposed installation, that is if densogrease, or any other silicon based grease was not used.
     
  11. nunojpg
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    nunojpg New EF Member

    Ok. I think I have a slightly better understanding now. Thanks!
     
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