Alluminium wiring.

"Dave Plowman (News)" realised it was Wed, 08 Feb

2006 17:45:49 +0000 (GMT) and decided it was time to write:

It's a US newsgroup - what do you expect?

Since when did the Merkins know anything about car electrics? The very idea of using aluminium for vehicle wiring is laughable - much more expensive, more prone to corrosion, and has a higher resistivity than copper. And pointless, as the weight saving on cars with so few wires would be negligible. The insulation weighs as much as the conductors.

Quite a lot of houses were wired with Aluminium during the copper shortage of the late 70's and early 80's, and BT certainly put a lot of aluminium phone cabling in then (one of the reasons why ADSL has such problems in certain areas), perhaps the yanks are getting confused again, as aluminium wiring in a care would be impracticable due to vibration fractures

Alex

Power transmission wiring (that's 'transmission' in the electric power industry generation and distribution sense) is invariably aluminium, not copper. When you're carrying a gazillion volts per wire between transmission towers a quarter of a mile apart, it makes a lot of sense weight-wise, and you lose a negligible conductivity benefit over copper.

For domestic wiring, the only real problem with aluminium wire was with terminating the wire at junctions. It has to be done right, and the average Joe homeowner couldn't be trusted to do that, like he can more readily be trusted with the more tolerant copper wire. I'm in the US right now, and sections of my 40 year old house wiring are aluminium. I know where that wire is and it's never going to be a problem. It doesn't keep me awake at night.

I don't know why anyone would want to put it in a car though.

While that is true, those cables being 40mm thick on average, they also have a significantly higher resistance than the same thickness of copper, which is another reason why _very_ high voltages are used on those lines (high voltage = low current = lower power losses = elementary physics). Not a good idea on a car at 12 volts.

But they're not pure aluminium. They have a steel multi strand core to carry the weight. And 'skin effect' at high voltages makes a difference as opposed to 12 volt wiring.

Ah, yes. The 'skin' effect. It's why high tension kills you by burning, not electrocution.

Regardless, aluminum is still a pretty good conductor.

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "Dave Plowman (News)" saying something like:

They're full of shit, so what do you expect?

Skin effect has nothing to do with voltage, it is frequency dependent, there is no skin effect for DC, and it is negligable at 50 Hz. The brave might look at:

Lucas did however use aluminium fied coil windings in M35G starter motors from the mid (or late?) 60s. Despite all the potential problems with vibration and corrosion, the only problem I remember was the difficulty in DIY brush replacement.

Mike

I wonder if their confusion is down to the silver coating on some vehicle wiring.

Is that with an aluminium coating, then?

Tinned copper you mean?

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Ian Dalziel saying something like:

Probably sprayed on after being cur(ri)ed properly.

Yup, the colour silver, rather than the metal.

In the electronics industry in which I've worked most of my life, wire is nearly always tinned. Why is it that the majority of car wiring is untinned bare copper? Given that the PVC insulation is slightly porous, and the copper isn't oxygen-free, then surely tinned copper wire would reduce the black corrosion that car wiring suffers as it gets old?

: And pointless, as the weight saving on cars with so few wires : would be negligible. The insulation weighs as much as the conductors.

A fair number of rural phone lines in Scotland had aluminium wiring - not for weight saving reasons, but because they were renewed during the copper crisis of 1974 (?) and aluminium became cheaper. That's also why my house has stainless steel central heating plumbing. The aluminium phone lines were noisy, and were one reason why broadband took longer to roll out everywhere here than was originally planned.

A shortage of copper late in the Second World Unpleasantness meant that some aircraft radios were made with silver wiring. They were carefully collected up afterwards ...

Ian

: : Power transmission wiring (that's 'transmission' in the electric power : industry generation and distribution sense) is invariably aluminium, : not copper. When you're carrying a gazillion volts per wire between : transmission towers a quarter of a mile apart, it makes a lot of sense : weight-wise, and you lose a negligible conductivity benefit over : copper.

Actually, you lose a lot of conductivity: the resistivity of copper is about 16.8 nOhm m, pure aluminium is 27 and dural (I imagine that transmission lines would not be pure - too many fatigue problems) is around 50. However, since aluminium is around a third of the density of copper, you can simply use more of it: twice the area of pure Al will have 33% less weight and 25% more conductance than Cu.

In other words, it's not conductivity that matters but conductance.

Yours electropedantically,

Ian

: While that is true, those cables being 40mm thick on average, they also : have a significantly higher resistance than the same thickness of : copper, which is another reason why _very_ high voltages are used on : those lines (high voltage = low current = lower power losses = : elementary physics). Not a good idea on a car at 12 volts.

As a rough guide, the cost of a power line is proportional to the current and the cost of insulating it is proportional to the voltage. For a given power, than means cost is partly proportional to I and partly to 1/I, and that means there's a minimum possible. That's why high power uses high voltages, medium powers uses medium voltages and so on. You could supply a house with 110kV through tiny wee conductors, but the insulation would be prohibively expensive: similarly you could send the output of Sizewell B away at 24V but the conductors and support structures would not be cheap.

Ian

PS I^2 losses also need taken into account, of course

The power losses on 25kV overhead line railways are roughly the same as those on 750v DC third rail lines. High voltage = high leakage on damp days. Most of that is tracking across the insulators.