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I am a lineman for the power company and constantly making electrical connections between copper and aluminum. There is a theory at my job that aluminum must go on top of copper. Is this true? And if so why? What is the difference between being above or below. I looked up galvanic corrosion and understand the process in which the anode ( copper I believe) breaks down to the cathode ( aluminum) with a presence of an electrolyte. But what I am unable to find is the reason for them having to be in a certain order. Thank you very much for your help I look forward to reading your response.
- Dan (age 21)
By "on top" I'm assuming you mean actually higher up, not farther from some support structure. I can't think of any simple reason why that would matter, since the gravitational forces involved are very weak compared to the local electrical and chemical effects. I can think of one reason why it might conceivably matter. More water will accumulate on the lower piece. Maybe for some reason having more aluminum wet is worse than having more copper wet. Do your colleagues have any account of why it should matter?
Although that wasn't much help, perhaps having this posted will draw some more knowledgeable comments from other readers.
(published on 10/31/11)
Follow-Up #1: copper/aluminum corrosion
They say that the connection breaks down significanty faster if the copper is ok top. example on a wye system there is a neutral wire running from pole to pole for which we use aluminum. When making a ground attachment we have copper. So the tail of the copper wire can either be bonded above or below the aluminum neutral. I cannot research any hard evidence as to why is matters .
- Dan (age 21)
Whoops- In the first answer, I had the two metals switched- fixed now. Since the Al is the one that is forming ions more readily, maybe it's particularly bad to have more of it wet.
Any electrochemists out there who can help?
(published on 11/03/11)
Follow-up on this answer.