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.



--
Fergus McMenemie .
Technical Basis PhoneUK) 07721 376021

Unix/Mac/Intranets Analyst Programmer

Fergus McMenemie wrote:

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

Aluminium is a very reactive metal. In open air, it forms a
closely bound oxide layer, which protects it from further
oxidation despite it's reactivity.

In soil, this layer is under constant attack from acidic soil
water, and is constantly eroded. It doesn't last long once the
insulation has gone.

--
Grunff

In uk.d-i-y, Fergus McMenemie wrote:

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.

As well as the likely absence of the protective oxide layer which Grunff
mentioned, the presence of the copper close to the aliminium in your
soil (plenty of dissolved carbonate, nitrate, and other anions to help)
is likely to set up a nice electrolytic reaction to help the aliminium
(and the copper) turn into nice soluble salts. (Allegedly. It's twenty-
mumble years since I did any chemistry, and I always got much better
with the organic than the inorganic; so correction and ridicule from
the better-informed would be welcome and deserved, respectively).

Stefek

"Fergus McMenemie" wrote in message
. uk...
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.



Fergus McMenemie

It's called the electrolytic effect and also occurs when boats are in the
water. The aluminium acts like a sacrificial anode when an arc of electric
current is passed between it and the copper braiding. The arc then sets up
a hot spot and the two metals eventually burn through. Very common.

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.

On Wed, 05 Nov 2003 11:41:04 +0000, The Natural Philosopher wrote:

Fergus McMenemie wrote:

Hello,

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

snip

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...

Aluminium is pretty much OK when used by itself for overhead lines. The
problems come with connections between dissimilar metals or with the
build-up of oxides in joints.

Cu/Al joints were made either using split-bolt mechanical connectors -
line taps - covered with denso tape to stop ingress of moisture, or much
better these days using compression fittings. Bimetal Cu/Al compression
fittings are made with a friction weld between the two metals, and these
are not prone to corrosion, for some reason that I never did fully
understand.

All compression fittings have an abrasive grit-grease inside, and the
conductors are (should be!) scratch brushed before making the
connection, to break down the surface oxidation.

All compression fittings have an abrasive grit-grease inside, and the
conductors are (should be!) scratch brushed before making the
connection, to break down the surface oxidation.

very well put, and as ACSR conductor has now been replaced by all alliminum
alloy the need for compression anchor clamps has been reduced from 16
individual joints on a 400kv quad bundle to 4. There are 61 strands in a piece
of conductor and all the inner strands are greased to help prevent corrosion,
and as said this grease must be cleaned off and brushed back to bear metal
before jointing.

Hi Wanderer,

Do you know someone is spoofing your name and e-mail address, and is sending
out these posts.

http://groups.google.com/groups?q=yd...TF-8&oe=UTF-8&
hl=en&btnG=Google+Search

Just to let you know.

"Wanderer" wrote in message
.. .
On Wed, 05 Nov 2003 11:41:04 +0000, The Natural Philosopher wrote:

Fergus McMenemie wrote:

Hello,

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

snip

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...

Aluminium is pretty much OK when used by itself for overhead lines. The
problems come with connections between dissimilar metals or with the
build-up of oxides in joints.

Cu/Al joints were made either using split-bolt mechanical connectors -
line taps - covered with denso tape to stop ingress of moisture, or much
better these days using compression fittings. Bimetal Cu/Al compression
fittings are made with a friction weld between the two metals, and these
are not prone to corrosion, for some reason that I never did fully
understand.


I remember about 12 or 15 years ago watching an LEB lineman splicing a new
feed to a house into the main cable in the street. Apart from being quietly
gobsmaked at the whole procedure of working live (fitter standing on a
rubber mat with knobbles on it of the sort you used to buy at Halfords as a
car floor mat, which the fitter's mate dried off with a blast from the
propane blowtorch before putting it down in the bottom of the hole) I was
surprised that he was soldering the joint between the Ali spur and the
copper main cable. I asked him about it but forget what the explanation
was - maybe something in the flux?

The soldering itself was a performance: pouring molten solder from a ladle
over the joint, catching the run-off in another ladle!


--
John Stumbles
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-+
The most dangerous component in a car is the nut that holds the steering
wheel

On Wed, 05 Nov 2003 22:29:13 GMT, BigWallop wrote:

Hi Wanderer,

Do you know someone is spoofing your name and e-mail address, and is sending
out these posts.

http://groups.google.com/groups?q=yd...TF-8&oe=UTF-8&
hl=en&btnG=Google+Search

Just to let you know.

Had someone doing it a few weeks ago, but I complained to their ISP and
I think their plug was pulled. Just tried the link you posted but that
got me nowhere, and a quick search with my name only brought up the
groups I post to.

"Wanderer" wrote in message
...
On Wed, 05 Nov 2003 22:29:13 GMT, BigWallop wrote:

Hi Wanderer,

Do you know someone is spoofing your name and e-mail address, and is
sending
out these posts.


http://groups.google.com/groups?q=yd...TF-8&oe=UTF-8&
hl=en&btnG=Google+Search

Just to let you know.

Had someone doing it a few weeks ago, but I complained to their ISP and
I think their plug was pulled. Just tried the link you posted but that
got me nowhere, and a quick search with my name only brought up the
groups I post to.

It was a weird one of post with your nickname in the from line. I had
deleted it before I thought to pass it on. They're also using the
nickname " Whatever " but have used your nickname and e-mail address as a
return option. Try just this section of the link:

http://groups.google.com/groups?q=yd...UTF-8&oe=UTF-8

I think the other link was still under a session with my machine and was
still linked only to me. Sorry.


---
www.basecuritysystems.no-ip.com

Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.536 / Virus Database: 331 - Release Date: 03/11/03

On Thu, 06 Nov 2003 08:30:21 GMT, BigWallop wrote:


"Wanderer" wrote in message
...
On Wed, 05 Nov 2003 22:29:13 GMT, BigWallop wrote:

Hi Wanderer,

Do you know someone is spoofing your name and e-mail address, and is
sending
out these posts.


http://groups.google.com/groups?q=yd...TF-8&oe=UTF-8&
hl=en&btnG=Google+Search

Just to let you know.

Had someone doing it a few weeks ago, but I complained to their ISP and
I think their plug was pulled. Just tried the link you posted but that
got me nowhere, and a quick search with my name only brought up the
groups I post to.

It was a weird one of post with your nickname in the from line. I had
deleted it before I thought to pass it on. They're also using the
nickname " Whatever " but have used your nickname and e-mail address as a
return option. Try just this section of the link:

http://groups.google.com/groups?q=yd...UTF-8&oe=UTF-8

I think the other link was still under a session with my machine and was
still linked only to me. Sorry.

Could you email me, the addy is live. I had a look through the posts
your link threw up but couldn't see anything obvious that looked as
though it appeared to come from me, unless I'm missing something
obvious.

On Wed, 5 Nov 2003 22:54:06 -0000, "John Stumbles"
] wrote:

I remember about 12 or 15 years ago watching an LEB lineman splicing a new
feed to a house into the main cable in the street. Apart from being quietly
gobsmaked at the whole procedure of working live (fitter standing on a

You mean you haven't worked on live wires before? Chicken

I have bought me a decent set of electrical pliers which have
insulated handles with little protusions to stop your fingers
wandering too close to the metal bits. Very reassuring when cutting
into cable, even if you have switched the mains off first.

PoP

"Wanderer" wrote in message
...
On Thu, 06 Nov 2003 08:30:21 GMT, BigWallop wrote:


"Wanderer" wrote in message
...
On Wed, 05 Nov 2003 22:29:13 GMT, BigWallop wrote:

Hi Wanderer,

Do you know someone is spoofing your name and e-mail address, and is
sending
out these posts.



http://groups.google.com/groups?q=yd...TF-8&oe=UTF-8&
hl=en&btnG=Google+Search

Just to let you know.

Had someone doing it a few weeks ago, but I complained to their ISP and
I think their plug was pulled. Just tried the link you posted but that
got me nowhere, and a quick search with my name only brought up the
groups I post to.

It was a weird one of post with your nickname in the from line. I had
deleted it before I thought to pass it on. They're also using the
nickname " Whatever " but have used your nickname and e-mail address as
a
return option. Try just this section of the link:


http://groups.google.com/groups?q=yd...UTF-8&oe=UTF-8

I think the other link was still under a session with my machine and was
still linked only to me. Sorry.

Could you email me, the addy is live. I had a look through the posts
your link threw up but couldn't see anything obvious that looked as
though it appeared to come from me, unless I'm missing something
obvious.

Can you try your own e-mail address on the google to see what it brings up.
The e-mail address I searched for was another one used by this creep sending
posts about Christina Agulerra (?) and I've just found my real e-mail
address had been used as well. I've sent the obligatory report to the abuse
on three ISP's and I'm sure there'll be more people doing the same.

I only noticed it when I was going to answer one of your posts and when I
looked through the group again, this one popped it's ugly head up. Of
course I deleted it without thinking and thought you were a fan of hers too.
:-))

PoP wrote in message . ..
On Wed, 5 Nov 2003 22:54:06 -0000, "John Stumbles"
] wrote:

I remember about 12 or 15 years ago watching an LEB lineman splicing a new
feed to a house into the main cable in the street. Apart from being quietly
gobsmaked at the whole procedure of working live (fitter standing on a

You mean you haven't worked on live wires before? Chicken

D'you mean "I hadn't before" or "I haven't since"?! Anyway: Yes and
Yes (though not always intentionally :-)

I have bought me a decent set of electrical pliers which have
insulated handles with little protusions to stop your fingers
wandering too close to the metal bits. Very reassuring when cutting
into cable, even if you have switched the mains off first.

I have various electrical/electronic tools with bits missing from them
.....

John S