Fergus McMenemie wrote:

Hello,

I am confused. How come insulated aluminum cable corrodes so badly yet
overhead aluminum lines seem to last years.

The supply to my house failed over the week end. The repair crew arrived
and figured out that the break was 23.5m back from my meter box.
Wandering back though the garden the linesman noticed a "new" bush which
was about the right distance from the meter box. We had planted it last
spring. He pronounced that the break would be there.

He dug up the bush and started clearing the hole. He quickly found the
cable which was between 6 to 10 inches below the surface. Clearing more
earth from the hole, using a spade, the linesman brushed against the
cable. It broke clean in two.

He explained that this was common enough. I had apparently nicked the
cable when planting the bush in the spring and this had allowed mosture
to seep into the cable. The recent rain was the final straw and the
cable failed.

The cable consisted of an inner aluminum core surrounded by insulation,
a copper mesh braid and another outer layer of insulation. The inner
core had apparently totally disintegrated in the space of about 8
months. The copper braid had as good as failed as well.

Can anybody explain how this happens given that aluminum overhead lines
are constantly exposed to mosture.


Its not moisture. Its oxygen. That on air forms a nice tough aluminium
oxide layer, and thats it....unless of course some weak acid gets
in...in which case that dissolves the aluminium oxidejust about as fast
as it forms...

My guiess is you lost waterproofing somehow when the bush was planted,
and that plus acid soiil and water did the rest.