What is the key technology for connecting aluminum?

You wire brush the aluminum conductors to remove the aluminum oxide and then apply a paste (nolox) to prevent formation of new oxide. So, I would guess, you're correct, no significant intervening aluminum oxide. Also, the CuAl connectors prevent the unequal expansion and contraction problem.
j

To avoid problems with aluminum oxide, you use a special paste on the aluminum. The paste contains some kind of air-excluding grease plus fine metal particals. You apply it to the wire, then work it in with a wire brush. The wire brush breaks up the existing surface oxide, and the grease keeps air away so new oxide doesn't form. The metal particles help penetrate the surface of the aluminum too.
Also, aluminum has a problem flowing away from areas of high applied pressure. The old screw wire clamps with a point that digs into the copper wire are a problem with aluminum. Devices designed for aluminum use have a large contact area with less pressure per unit area.
Apparently, much of the problem with aluminum with with the "backstab" connection points on cheap devices. They typically have a single sharp piece of metal that bites into the side of the wire - somewhat iffy with copper but a failure waiting to happen with aluminum.
Dave

Those ought to be outlawed for any sort of wire. I've seen receptacles on multiple occasions that were melted and charred, one was red hot inside due to backwire connectors which had developed a poor contact and a large load was further down the chain. In my own house, the downstairs had been wired with the 49 cent variety of those, plugs wouldn't stay in them so I went to replace them and with almost every one, wires popped right out as I pulled the receptacle out of the box.

How reliable is solder joint between two aluminum wires?
Or between one single strand aluminum conductor and one multi strand tinned copper wire?
Which solder is better for this kind of connection? Solder with lead or without lead? I know worldwide people are changing to lead free solder but I want know which type of solder will make a reliable joint in aluminum conductors.
Thanks

You can't solder aluminum. Unless someone has come up with something new since I was doing a lot of soldering 30 years ago.
Bill Ranck Blacksburg, Va.

Alusol I've been using it for years..
Very, very effective and a lot easier than welding aluminium (although welding is obviously more fun an more effective..) -- Sue

Where would you use a soldered joint? I was under the impression that there are essentially no soldered joints in modern line voltage wiring (I'm not counting knob and tube).
Dave

My application involves using polyester coated winding wire. Becuase of copper wire price going up peole have started using pure aluminum wire and copper clad alumium wires
but at some stage these wire needs to be connected to a copper wire like mains lead or any input or output lead.
regards

I don't think any devices were ever approved for use with aluminum in "backstabs" - copper only. (But that doesn't prevent improper use.)
Tests show "properly" made connections could also fail.
One of the great mysteries of life - why does UL continue to allow "backstabs". At least the holes are too small for #12 now.

Virtually all of the "aluminum" problems were workmanship related. There was a problem with the binder screw devices and the expansion rate of the screw metal vs the wire. That was fixed with the CO/ALr device which uses a screw wityh a bigger head and an alloy that matches the wire expansion rate. When aluminum wire is used in an aluminum lug all of this is eliminated and it will actually perform better than copper. Most lugs are aluminum. That is why it hasn't been a problem in larger wire sizes. The Noalox is mostly a fewel good prodfuct and it is not required in the listing of any lug I know of but it is "recomended" by some. There are currently 3 principle devices on the market for splicing aluminum or aluminum to copper. You have the high end "Copalum" one time crimp system that requires a certified installer, special tools and is very expensive. There is the Ideal 65 purple wirenut that is /L listed but has a bad rep in a 30 year old CPSC article, still widely circulated. It is suspicious because it lools like it was really written by the Copalum people. (CPSC is a political organization so draw your own conclusions) Recently King Innovation has come out with the Alumiconn device that is an aluminum lug style device and I haven't heard anything bad about it yet. Since this is basically the same technology as we had in aluminum lugs for years it should work fine and you don't need any special tools or training.

|>> Apparently, much of the problem with aluminum with with the "backstab" |>> connection points on cheap devices. They typically have a single sharp |>> piece of metal that bites into the side of the wire - somewhat iffy with |>> copper but a failure waiting to happen with aluminum. |>> | | I don't think any devices were ever approved for use with aluminum in | "backstabs" - copper only. (But that doesn't prevent improper use.) | | Tests show "properly" made connections could also fail. | |> |> Those ought to be outlawed for any sort of wire. | | One of the great mysteries of life - why does UL continue to allow | "backstabs". At least the holes are too small for #12 now.
Oh great! Now they will be encouraging idiots to change the wire size to number #14. Let's see, what is the ampacity of #14 AL and how safe will it be on a 20 amp circuit? OTOH, I suppose for the most part this is the Darwin Effect in action (as applied to that error in the gene pool).

| Virtually all of the "aluminum" problems were workmanship related. | There was a problem with the binder screw devices and the expansion | rate of the screw metal vs the wire. That was fixed with the CO/ALr | device which uses a screw wityh a bigger head and an alloy that | matches the wire expansion rate. When aluminum wire is used in an | aluminum lug all of this is eliminated and it will actually perform | better than copper. Most lugs are aluminum. That is why it hasn't been | a problem in larger wire sizes. The Noalox is mostly a fewel good | prodfuct and it is not required in the listing of any lug I know of | but it is "recomended" by some.
So does that mean Co/Alr devices will have a _different_ expansion rate than copper?

Yup, but I doubt it will be a problem. Copper is more forgiving

Comments apply only to US 15 & 20A branch circuits.
After known problems with aluminum wire connections (which resulted in UL delisting of aluminum wire and devices until new standards were written) the Consumer Product Safety Commission contracted with an *independent laboratory* to do extensive tests of aluminum connections. Over 7000 connections were tested. The testing showed ?properly? made connections could fail.
CO/ALR devices used with the new alloy wire, required in the revised UL standard, eliminates expansion problems. Most of the aluminum branch circuits are "old technology" wire with a higher expansion rate. The CO/ALR devices are not tested with "old technology" wire.
The extensive testing of aluminum connections resulted in a recommendation to apply antioxide paste then abrade the wire. Oxide was a cause of failure of aluminum connections. Antioxide paste is an important element of reliable connections (15 & 20A).
The testing done under a *professional engineer* by an *independent laboratory* found that Ideal65 wire nuts were not any better than other wire nuts used with antioxide paste.
I have not seen a "30 year old CPSC article".
There is a paper, revised in 2007, at on options for aluminum wire: paper was written by the *professional engineer* involved in the testing by the *indent laboratory* and is based on those tests. I know of no equivalent testing. The paper has never been published by the CPSC.
There is further information on Ideal65 wire nuts in the paper. Ideal65 does not solve oxide problems.
Preliminary independent testing looks like these are reliable, for the reasons you give.

#14 Al wire has never been allowed for US branch circuits.

|> |> |>> Apparently, much of the problem with aluminum with with the "backstab" |> |>> connection points on cheap devices. They typically have a single sharp |> |>> piece of metal that bites into the side of the wire - somewhat iffy with |> |>> copper but a failure waiting to happen with aluminum. |> |>> |> | |> | I don't think any devices were ever approved for use with aluminum in |> | "backstabs" - copper only. (But that doesn't prevent improper use.) |> | |> | Tests show "properly" made connections could also fail. |> | |> |> |> |> Those ought to be outlawed for any sort of wire. |> | |> | One of the great mysteries of life - why does UL continue to allow |> | "backstabs". At least the holes are too small for #12 now. |> |> Oh great! Now they will be encouraging idiots to change the wire size to |> number #14. Let's see, what is the ampacity of #14 AL and how safe will |> it be on a 20 amp circuit? OTOH, I suppose for the most part this is the |> Darwin Effect in action (as applied to that error in the gene pool). |> | | #14 Al wire has never been allowed for US branch circuits.
But I was referring to an idiot's choice of wire. Likely he'll find that #14 Al is nearly impossible to find. And that would be sad because we'll lose the chance to remove that idiot gene from the pool.

| | snipped-for-privacy@ipal.net wrote: |> |> |> | |> | #14 Al wire has never been allowed for US branch circuits. |> |> But I was referring to an idiot's choice of wire. Likely he'll find that #14 |> Al is nearly impossible to find. And that would be sad because we'll lose the |> chance to remove that idiot gene from the pool. | | | Not if it's someone elses's home, or it lasts long enough to sell it.
If you hire an idiot as an electrician, you get what you deserve. This is what inspectors are for (among other things).
If you buy a home from an idiot (and don't inspect it to discover this error), you get what you deserve.

| | snipped-for-privacy@ipal.net wrote: |> |> |> | |> | snipped-for-privacy@ipal.net wrote: |> |> |> |> |> |> | |> |> | #14 Al wire has never been allowed for US branch circuits. |> |> |> |> But I was referring to an idiot's choice of wire. Likely he'll find that #14 |> |> Al is nearly impossible to find. And that would be sad because we'll lose the |> |> chance to remove that idiot gene from the pool. |> | |> | |> | Not if it's someone elses's home, or it lasts long enough to sell it. |> |> If you hire an idiot as an electrician, you get what you deserve. This is |> what inspectors are for (among other things). |> |> If you buy a home from an idiot (and don't inspect it to discover this error), |> you get what you deserve. | | | You are a self righteous idiot. I hope that is a close family member | of yours who dies at the hand of one of the free range goof balls.
Gee, and I thought you had come out of your four year long attitude of making personal attacks on people. But I guess I was wrong.
[note: fours years is a long as I have observed this; it might be longer]