220 wiring, alluminum to copper??

mattdinkc10June 8, 2010

helping my parents with a project, and will hire an electrician, but I want to understand.... house has alluminum wiring. They are replacing a wall oven/M-w single unit with 2 sepreate appliances. I need to add a new dediacted 110 for the MW, can I run new copper in the old panel? what is the solution? the oven is hard wired, can I join old 220 alluminum to new copper (using proper purple caps)? Thanks in advance

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Depends on what "old 220 aluminum" is. "220" is no indication of wire or circuit size.

Sure, you can run any new circuit you want to an older panel. The panel does not care. In fact, the only restrictions would be for aluminum. Some terminations are not rated for AL.

    Bookmark   June 8, 2010 at 9:39PM
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Thanks. I was making assumption that the original oven was hard wired with alluminum since the entire house has al. wiring. I will be tearing out the old oven next weekend to confirm what is back there.

    Bookmark   June 8, 2010 at 10:18PM
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There is no problem or issue with larger size stranded aluminum wiring.

The problem is with solid aluminum wire for 15 A and 20 A branch circuits.

The softness (lack of temper) required to make the wire flexible for installation makes it soft enough to deform under connections when it heats up (even a little) and this makes the connections become loose.

This creates more heat, deformation, and can lead to arcing and fires.

    Bookmark   June 9, 2010 at 9:24AM
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Thanks brick, always appreciate your feedback thru out the forum. as in allum to copper on 15 amp circuit, is it done the same way with purple caps and inhibitor on larger sizes?

    Bookmark   June 9, 2010 at 5:26PM
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The Copalum crimp connections are much more reliable than the corrosion inhibitor filled purple caps.

The purple caps are better than standard wire nuts.
The problem appears to be that to function the spring in the purple wire nut becomes a part of the current path and is simply not sized for that function.

If the Al conductors are well cleaned to bare aluminum and the purple nuts installed immediately (Aluminum oxide starts forming instantly on the clean surface) with solid contact between the conductors the inhibitor does slow the oxide growth, but it does not last forever.

The Copalum crimps require training before the manufacturers will sell them to anyone.

The problem does not occur with larger stranded aluminum conductors since they are suitable tempered. The bend radius is already large, based on the total conductor size, so the flexibility needed for single solid wires is not required.

    Bookmark   June 10, 2010 at 9:18AM
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Thanks. screw it, not messin' with the alluminum, going to pull new copper and try to talk my folks in to re wiring the entire house

    Bookmark   June 10, 2010 at 1:00PM
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Replacing all the smaller general purpise branch circuits is a good idea.

It is the larger ones (central air, electric heat, water heaters, stoves, dryers. etc.) that should be fine if they are stranded aluminum.

Just as in the past large size copper wire is painfully expensive compared to (even larger for the same ampacity) stranded aluminum.

    Bookmark   June 10, 2010 at 3:55PM
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