incredible price of copper

wrote:


I'm going to call "Bullshit" on this one, too. The insulation is molded onto the wire at the factory, it isn't slid inside like a garden hose. And they lash the wire to the insulators rather securely just to take the strain of keeping it up there - at the ends it's mechanically anchored to the insulators with U-bolts and 'Chinese Finger' strand grips, the tighter it gets the stronger the hold.
Now if this guy was pulling UNDERGROUND feeder wires WITH the insulation out of the conduits, and then reeling it into the truck when it was clear, that is plausible.
(In other words: Dear OP, Send that Urban Legend back to your "Friend Of A Friend" for a Rewrite...)
--<< Bruce >>--
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Not NOW it isn't. <grin>
A lot of the wire installed in the Texas Panhandle during the late '30s and the '40s WAS.
You must have missed the time frame, Bruce!
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- If your "From:" address isn't on my

#1: Thermal Expansion
    The Thermal Expansion/Contraction of Al wire results in the loosening of connections, particularly at switches/outlets.
    Over time, this results in the creation of an electrical arc which can (and often has) result in the ignition and combustion of (a.) the wire itself, (b.) the plastic housing of the switch/outlet, and/or (c.) the insulation surrounding the wire.
    This combustion, especially in a wood-framed building, can (and often did) result in a major house fire with a strong potential for loss of human life.
#2. Availability of proper switches/outlets
    Since the virtual abandonment of Al wiring, few manufacturers supply the Al-specific switches/outlets designed to address/reduce the problems with Thermal Expansion.
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There is NO differential thermal expansion/contraction if the system is ALL aluminium.
--
Free men own guns - www.geocities/CapitolHill/5357/

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Nick Hull wrote:

Who said anything about differential? The thermal expansion of the aluminum against the screw, be it brass, aluminum, whatever, results in the "cold flow" phenomenon where the soft aluminum alloy flows out towards the unrestrained sides. When the connection cools and the aluminum contracts it is now a looser connection and the mating surfaces are more exposed to air and oxidation.
Aluminum oxide forms on the areas newly exposed due to the cold flow and with aluminum oxide being an insulator the remaining contact surface will be more heavily loaded and will heat more the next time the connection is loaded. The problem will rapidly accelerate until the connection fails completely, if you're lucky, not starting a fire in the process.
Pete C.
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Too_Many_Tools wrote:

A connector that provides spring pressure below the force required for the cold flow will absorb the expansion and return maintaining pressure after the AL cools.
I don't have any AL here at all. No 14ga copper either, everything is 12ga or above. I did just replace the main panel, the shop sub panel, shop feeder and a number of outlets in the kitchen and baths (to GFCI and Decora style) so a good number of the connections have been recently serviced.

Connectors are always the largest issue in anything, be it high voltage, low voltage, AC, DC, plumbing, structural, etc. An unbroken length of anything is more reliable than a broken and reconnected one.

With current sprawl the issue is diminishing as many subject homes are demolished to make room for more sprawl.

Or when industry lobbyists push for a change to promote their product under the cover of potentially saving lives.

Not when the houses are being torn down and replaced with McMansions, apartment complexes and office parks.

Hopefully insured and no fatalities.
Pete C.
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wrote:

One. Thermal expansion rates and self-extrusion or creep. Aluminum expands much more than Steel or Copper does when heated, as compared to Copper conductors in common lugs or Steel screws and backing plates in devices. Aluminum wire in Aluminum screw lugs isn't bad because they'll both expand, but you still have to bolt that lug to the busbars.
Two. Copper Oxides are almost as conductive as pure Copper, and that is a good thing. Aluminum Oxide is a very effective insulator, and that is a very bad thing. Try taking an ohmmeter reading on the barrel of your Maglite without scratching through the anodizing layer, anodizing is a controlled aluminum oxide deposition.
Three. You can Tin plate the Aluminum to mitigate a lot of the oxidation problems when you want to use it for switchboard busbars and breaker stab busses, and that's fine - but only as long as the Tin coating isn't disturbed. Pierce the Tin, and the corrosion and oxidation moves underneath and hits with a vengeance.
Add Problem One and Problem Two together, and you have the cause of most Aluminum Conductor failures, and the few fires that occur if the symptoms of a bad connection are ignored for too long.
You put a full 20A load on the receptacle, the connection gets hot, the wire expands under the screw and extrudes itself out a bit. After a while, air starts getting under the screw, the wire starts to develop an aluminum oxide layer under the screw head and the connection resistance goes up.
With the higher resistance connection the next time you put a full 20A Load on the wire it gets much hotter, and arcs a little between the wire and screw which speeds the heating even more. The oxide layer gets deeper, the resistance gets higher...
It is a feedback loop. And the end result is the wire and the screw lug get hotter than the space heater you are trying to run from it. Cue the Fire Department...
FACT: They can not make an inexpensive effective and safe branch wiring device for using Aluminum branch circuit conductors.
FACT: You could use compression lugs, but they have to be done properly, and that's where that plan falls apart.
FACT: There are a surprising number of people out there who have their shingle hung out as an Electrician who DO NOT THINK. They are physically incapable of coherent thought. Just figuring out which end of the screwdriver to pick up was a major accomplishment...
They throw out the instruction sheet that says how the connections must be done and the steps tools and materials required, they do it the way /they/ think it should be done - and if the inspector doesn't catch it and make them redo the work, those are the connections that are going to fail in 10 years.
They could make a foolproof Aluminum-wire-safe convenience receptacle or light switch, but they would be very expensive - meaning nobody would buy them. And they would likely be designed for one-time-use - meaning someone will figure out how to reuse them to save money, ignoring the safety aspects.
Fact: Copper branch circuit wiring isn't cheap, but it can (and often is) installed by clueless induhviduals without too many safety repercussions.
Conclusion: Aluminum is fine for feeder conductors, but should be in compression connectors or compression pin transitions at both ends. (And if not possible, there should be a generous slack loop available at both ends for the inevitable reterminations.)
Any existing Aluminum branch circuits should be reterminated in special crimp connectors, or repull the whole house to be sure - there's always one odd box in the attic or crawl space they missed...
--<< Bruce >>--
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