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 >>--
#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
#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.
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
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
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.
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
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
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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