About 4 years ago I had a subpanel put in my house to accommodate some new circuits. They ran #2 aluminum from the panel to the subpanel. The electrician was careless and the stiff wires torqued the larger knockouts out at the cable clamp, so there were large gaps. I got tired of looking at it, and decided to fix it. I pulled the wires out, removed all the knockouts, reinstalled the cable clamp with an adapter to fit the full hole, cleaned the aluminum wires, put anti-oxidant on, and reinstalled the wires. All went well, though working with #2 in a crowded panel was not much fun.
But... although the aluminum wires were still bright and shiny, there was no sign of antioxidant on them. The stuff I put on was purple; but I don't know if it is all purple (a visual check to be sure it was done properly?)
So, my question; if there was no sign of anti-oxidant on 4 year old wires does that mean the electrician didn't bother to put any on, or does the fact that they were still shiny mean they are okay? I am concerned about his connections at the subpanel; if it was simple I would just redo them there also to be sure, but it would require ripping the wall open and I would prefer to avoid that. Thanks.
The wires are only about 6' long; why on earth couldn't he have used copper?!?!
A buck's a buck I guess. The real question is why didn't he use the anti-oxidant? That's a few pennies. I assume you did the other end too. If the wires show no signs of heating you dodged the bullet.
He probably didn't use antioxidant. They didn't 10-20 years ago. Massive torquing of the clamp and a clamp designed for aluminum seemed to work well enough.
PS go back a month later and retorque the wires particularly if they are stranded (which #2 certainly is).
On 10/31/03 10:51 PM, in article _YGob.11519$ snipped-for-privacy@news01.roc.ny, "John" wrote in part:
The stuff we use is black. It should be noticeable if any was applied. Antioxidant won't disappear completely.
Am I reading this right? The subpanel is inside a wall? That isn't supposed to be. Panels are always supposed to be accessible. Are the panels rated for aluminum wire? Some boxes are copper only.
Almost anything that will retard the air from contact with AL wire will work. I have used axle grease in a pinch. My home was wired in AL, did not know that until I moved in. I took a megger and tested everything. Been fine for the 8 years I have been here. I checked most of the switches and recpts and they are the correct ones for AL. None of them have anti oxidant on them.
I would recommend that you check the AL connections once a year for a while. I check my service panel once a year and have not had one problem. As someone else recommended check the panel for AL/CU rating. Most are there are a few that are not.
Well, the subpanel is recessed, but it has an accessable cover. The problem is that without ripping the wall open there is no access to the cable clamps, and the #2 is too stiff to move without loosening the cable clamps.
Now... the subpanel is upside down, so that the breakers point down when on; but that's a whole different story.
Damn good question. Also, the proper way to make an Al connection is to apply the antioxidant paste to the cable end, then work it into the aluminum with an emery cloth. This will remove the extremely hard, nonconductive and invisible oxide layer that forms almost immediately upon contact with air. It's a bit messy doing it this way, but will remove the oxide while preventing subsequent contact with air.
Very odd method - where was this derived? I ask this because I have seen the results of emery-cleaned conducting surfaces, I have done the aluminum-copper current density test that is the reason we have certain practices for aluminum and not for copper , and I have bonded aluminum to aluminum on fatigue-rated nylon epoxy connections using the one working protocol I have ever found. And while cleaning and limiting oxidation are a part of the story, they are definitely not the base reason, and the use of emery to clean aluminum is as banned a practice as cleaning aluminum using steel wool.
First, the use of emery cloth imbeds emery grit shards (it's carborundum, I believe) in contact metals such as aluminum, which then burns and leaves carbon pits, reducing contact area. Bad practice. Contact files for contacts, silicon carbide/bonded aluminum oxide paper for soft metals.
Second, the standard for cleaning aluminum mechanically in preparation for adhesive bonding is to clean with 120 grit silicon carbide, wipe with same paper and no hands etc., wash lightly with alcohol or tri-chlor, and apply bond within two hours. The same practice applies to aluminum conductors to be pressure welded, except use flux rather than adhesive in the last step
Third, the "anti-oxidant" in not so much for stopping oxidation as it is for decreasing local-micro temperature and current density to below the level where the peak-to-peak contact micro-explosions occur. That is done because, unlike copper, aluminum has the characteristic of exploding when it's heat from current density reaches a critical point.
background - Why we have to protect aluminum contact surfaces more than we do copper:
The two conducting surfaces are irregular, with many tiny microscopic peaks and voids. When the surfaces are pushed together, the current flows only through the contacting parts. Because only peaks are in contact, the current will bypass the micro-voids and you will have a larger - (sometimes several times larger) current density in the contacting "flattened " peaks.
If aluminum didn't explode when near current capacity and at temperature, no problem. But unlike copper, it does - and on the microscopic level as well.
If those microscopic peaks are coated with harder aluminum oxide, the peaks resist flattening more than soft aluminum, and the contact surface is less for the same wire nut pressure. Which means hotter peak-to-peak, and of greater current density than the gross area calculation would suggest.
And if those microscopic peak-to-peak contact points are coated with oxide, they have a larger contact resistance - and the larger resistance and their higher current density means a double-whammy higher temp right at the contacting peaks - which in turn means some of the the micro peaks in contact will explode, and in time you will have a loose connection from that erosion.
The "anti-oxidant": it will do its job as long as it keeps the temperature and current density below that where the micro-erosion occurs - e.g.,
1) it removes the very hard aluminum oxide or allows the oxides to slide or slip off the aluminum base at bonding, and allows the soft aluminum to weld together at connection pressures (pressure melts the aluminum locally without current present, and it melts together under the connector so there are no peaks) - or
2) it increases conductivity in the connection by filling the voids and setting as a bridge under pressure - or
3) it increases conductivity going around the peak-to-peak hard surfaced oxide to that below where temperature and current density create the local micro-erosion.
or some combination of the above.
Today's derates of aluminum's wire size capacity, use of connecting devices designed to assure extra contact length, and use of protective cleaners aka anti-oxidants to prevent excessive levels of current density and heat has pretty much stopped the loosening problems of power-conducting aluminum connections.
Emery - It is my understanding that emery defeats the purpose of the applied compound - now, you might not see the manifestation of a problem under the wire nut or connector even when it occurs, or you might get lucky and the current density on aluminum conenctions is sized with such a margin that even with the shards the density and heat are below the threshold - or not - but having cleaned up after emery in switches and conenctions numerous times, it is my belief that the use of emery was best left to plumbers, not electricians.
On 11/1/03 6:39 PM, in article GmYob.24007$ snipped-for-privacy@nwrddc02.gnilink.net, "Nukie Poo @verizon.net>"
Good question. That is one of those things I always knew but didn't attribute to a source. I came up with these from the 2002 U.S. national code book:
240.24(B) says each occupant shall have ready access to the overcurrent devices for the conductors supplying that occupancy. There are exceptions.
314.29 says boxes and conduit bodies shall be installed so that the wiring contained in them can be rendered accessible without removing any part of the building. To quote "Jim" from the old "Taxi" TV show "Am I right"?
Before this gets out of hand, I suspect we just have a misunderstanding here. The inside of any panelboard enclosure, box etc must be accessible but you can bury the cables and clamps feeding the box. The OP was simply saying he couldn't replace the cable without "disturbing the building finish" He did say he was able to get to the terminations.
On 11/1/03 8:49 PM, in article Jg_ob.53922$ snipped-for-privacy@nwrddc01.gnilink.net, "Nukie Poo @verizon.net>"
I misunderstood what the OP meant by ripping open his wall to get to the wiring. My house and the shop at work have lots of recessed electrical boxes. I was thinking maybe there was some sort of terminal or junction box completely enclosed in a wall. It did me good to look up those references.
On Sun, 02 Nov 2003 00:37:28 GMT, "Nukie Poo" Gave us:
Man.. somebody took you for a ride.
I used to polish Stainless, and Aluminum sheets... Titanium, Brass, etc.
It is 'raw' for quite some time. The reason one wants to abrade aluminum wiring is because their surfaces DO get oxidized when the wire gets it sheath put on during manufacture. Freshly exposed Aluminum doesn't suddenly "oxidize up right before one's eyes..." Sorry.
Your "almost immediately" is a figment of your imagination. One doesn't have to hurry, and one doesn't have to abrade the wire "wet" either.
The poster that said axle grease was OK is incorrect as well. That grease has acids in it, and will eventually have a reaction with the wire. A conductive matrix of anti-oxidant is required.
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