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Non-copper wire in ring main?
In article ,
(Simon Avery) writes:
Aluminium was a big test in electrical and telecomms industries a few
decades ago. Not sure of the exact reasons why it's now not used,
Aluminium very quickly coats itself with a hard oxide layer which
is an excellent insulator*. This can make getting a good contact
area very difficult, and special techniques are required such as hard
sharp contact serrations to break through the oxide and/or chemicals
to remove and keep the oxide away until the contact is assembled.
Add to this that if you do get a poor contact and it heats up,
it rapidly gets worse, and aluminium burns (important component
in fireworks), and it's a disaster waiting to happen.
Aluminium is used in the supply infrastructure, but in that case it
is assembled by people who (in theory at least) know its dangers
and use components specifically designed for use with it.
apart from a rapid degradation in salt-air conditions, but it's a
common reason why adsl can't be installed and it's not used now.
In telephony, the problem is mainly that of dissimilar metal
corrosion, particularly in the presence of any moisture, and
very much speeded up in salt-air, acids, or alkalis. BT stuff
their streetside distribution points with desiccant bags in areas
where aluminium wiring is used. I have one aluminium phone line,
and in my experience, the connections in the streetside cabinet last
around 5-6 years before they corrode through. You get about 2 weeks
advance warning by seeing modem speed rapidly dropping off, before
finally being completely cut off, but phoning BT and saying "my
line's going to break in a week's time" just doesn't wash.
* A couple of years ago, I was breadboarding a circuit which used
a couple of power MOSFETS directly switching mains. As a temporary
measure, I used a bulldog clip to clamp a MOSFET to an aluminium
heatsink. When I got to adding the second MOSFET into the circuit,
I clamped that to the same heatsink. It was only after all the
testing when I was disassembling the breadboard circuit in order
to make up the real thing, that I suddenly realised that I'd had
full mains voltage between the two mounting surfaces of the MOSFETS.
The thin layor of aluminium oxide which inevitably forms on the
heatsink was all that stopped it going bang!
--
Andrew Gabriel
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