Aluminium wire

Yes, generally speaking aluminum is going to be one size larger but you should consult table 310.16 in the National Electrical Code.

Don't use aluminum wire. We had a discussion on this here several weeks ago. Go back and read it.

It's still widely used here in Washington State. Not for most of the branch circuits, but for the service entry and large loads like the kitchen stove.

The problem was galvanic corrosion when aluminum wire was used with terminals made of a dissimilar metal or joined with wire nuts to copper wire. This created resistance which would heat up. When it's used today, it needs to be used with hardware designed for aluminum, and should be coated with special grease.

Yes. You need to reduce the gauge number by 2, which increases the cross-section area by a factor of about 1.6, for the aluminum wire to have the same resistance per unit length as the copper wire.

So if a particular circuit requires 12 AWG copper, it will require 10 AWG aluminum. That's a rule of thumb based on the physics of the two metals and the way the gauge scale is set up (where the cross section almost exactly doubles for every decrease of 3 in the gauge number). Regulatory requirements may differ.

Dave

Have you checked the stove and dryer circuits? Our house (near Vancouver BC), we have multi-strand aluminum for the electric stove and the original electric dryer circuit, while all other circuits are copper. I asked the house inspector about it when we were in the process of buying, and he said that the multi-strand aluminum for large appliances was not a problem, while solid aluminum branch circuits would be flagged (and might trigger an increase in insurance premium).

Dave

It wasn't just galvanic corrosion. Aluminum expands more than copper or brass when it warms up and is very malleable. So as it tries to expand under the screw/terminal, it actually deforms itself and changes shape to flattish oval that extrudes out from around the terminal. Then when the aluminum cools it shrinks down and is no longer tightly held by the screw/terminal. This of course creates a loose connection so the next time the circuit is loaded it gets hotter than before, more expansion/deformation, looser connection, more heating etc... etc... etc... FIRE! FIRE! FIRE!

Learning all this, the industry started making equipment with connections/terminals that would remain tight with aluminum wire. The standard now is that such devices must be marked Al-Cu if suitable for Aluminum or copper wiring. If it doesn't say that, do not use it with aluminum wire.

daestrom

The house I just sold (not in SD, but the opposite corner of the country) had multi-strand aluminum wire for the dryer and stove circuits. The house was built in '86. I'm pretty sure it's still in use for these applications.

Aluminum is commonly used for services and may be used for higher amp circuits. Both are reliable as far as I know.

The problems in the US were with 15 and 20A branch circuits. The problem was great enough UL delisted everything (early 1970s) and came up with new standards.

Devices like switches and receptacles (15/20A) for use with aluminum are marked CO/ALR. The aluminum alloy was also changed to reduce expansion. CO/ALR receptacles are not tested with old technology wire (which is most of the 15/20A wire installed).

In addition to the expansion problems with old wire, aluminum is very reactive and very rapidly forms a thin insulating oxide layer on the surface. It is standard practice to use an antioxide paste. The surface may also be abraded to remove the oxide (particularly recommended on

15/20A circuits). Larger terminals deform the aluminum which breaks through the oxide. The screws on 20A receptacles aren't as likely to break through. Wirenuts can also fail because of oxide.

My house was built in '72 and has aluminum wiring in the branch circuits. When I purchased it, I went through and pigtailed the aluminum wire to copper wire and then ran copper wire to the switch/receptacle. I put anti oxidation paste on each of the connections.

Note: I also check the connections once a year to make sure they are still tight. It is also worth noting that after 25 years of neglect I found only one connection where there was evidence of heat being generated i.e. burned insulation.

Don't use AL wire--especially for branch circuits. AL is generally good for temp wiring because it is light and cheaper than copper. Even though legal in FL, I never used SER for service entrances; copper only. Save yourself a future headache.