A new commercial radio hilltop vault is being installed in my area....
and the contractor has installed the tower and vault ground ring with
aluminum wire/cable, I have been advised. I do NOT know the gauge of
the wire, but I am curious what your thoughts are on this issue. I have
been involved the past 35 years of my career in a number of ground
installations and every one of those used large copper cable... no
aluminum anywhere. The last of these I saw was 6 or 7 years ago.

QUESTION: Are aluminum ground systems becoming common? Are they
reliable, even after absorbing some heavy strikes? Any other comments?

Ed K7AAT on the Oregon Coast






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"Ed" wrote in message
. 192.196...

A new commercial radio hilltop vault is being installed in my area....
and the contractor has installed the tower and vault ground ring with
aluminum wire/cable, I have been advised. I do NOT know the gauge of
the wire, but I am curious what your thoughts are on this issue. I have
been involved the past 35 years of my career in a number of ground
installations and every one of those used large copper cable... no
aluminum anywhere. The last of these I saw was 6 or 7 years ago.

QUESTION: Are aluminum ground systems becoming common? Are they
reliable, even after absorbing some heavy strikes? Any other comments?

Ed K7AAT on the Oregon Coast

Isn't aluminium in the presence of air naturally coated with a thin layer of
aluminium oxide which doesn't conduct? In which case aluminium might be
fine for lightning conductors but hopeless for RF. What will the tower
carry? ... if it's all VHF and upwards then there's probably no problem.

Chris

Ed wrote:
A new commercial radio hilltop vault is being installed in my area....
and the contractor has installed the tower and vault ground ring with
aluminum wire/cable, I have been advised. I do NOT know the gauge of
the wire, but I am curious what your thoughts are on this issue. I have
been involved the past 35 years of my career in a number of ground
installations and every one of those used large copper cable... no
aluminum anywhere. The last of these I saw was 6 or 7 years ago.

QUESTION: Are aluminum ground systems becoming common? Are they
reliable, even after absorbing some heavy strikes? Any other comments?

Ed K7AAT on the Oregon Coast

My only experience with an aluminum wire ground system was one I laid
many years ago in Denver, with buried aluminum radials. It was pretty
badly corroded in a few years. But the soil there is alkali, not like
the acid soil you have on the coast. Interestingly, aluminum corrosion
is minimum at a pH of about 5.5 (see
http://www.tpub.com/content/doe/h101...015v1_121.htm), which is
likely roughly what your soil is. So while there might be a lot of
places where corrosion would be a problem your location might be one of
those where it wouldn't.

Roy Lewallen, W7EL

christofire wrote:

Isn't aluminium in the presence of air naturally coated with a thin layer of
aluminium oxide which doesn't conduct? In which case aluminium might be
fine for lightning conductors but hopeless for RF. What will the tower
carry? ... if it's all VHF and upwards then there's probably no problem.

Chris

Yes, aluminum is immediately coated by a few-molecule-thick layer of
aluminum oxide when exposed to air. It's a non-porous, brittle, ceramic
material commonly used for hybrid circuit substrates and for sandpaper
grit, among other things. It's why aluminum, despite its extreme
chemical activity, doesn't corrode -- unless the environment is capable
of dissolving the aluminum oxide, which some are. Aluminum oxide is an
excellent dielectric, into at least the microwave range.

But an insulating film doesn't make a conductor "hopeless" -- after all,
the most perfect bare conductor is surrounded -- "coated" if you will --
by air.

Nor does a highly conductive coating degrade a conductor's performance.
Only a layer of poorly conductive material of sufficient thickness is
detrimental.

Roy Lewallen

I am only interested in the long term reliability of an aluminum ground
system in comparison to the more common copper system. This is for
lightning suppression only, I am not addressing RF issues. I am wondering
if aluminum can handle the potential surge currents that copper can... and
how well does its ground conductivity work when buried, when compared to
copper.

Ed K7AAT

Ed wrote:
I am only interested in the long term reliability of an aluminum ground
system in comparison to the more common copper system. This is for
lightning suppression only, I am not addressing RF issues. I am wondering
if aluminum can handle the potential surge currents that copper can... and
how well does its ground conductivity work when buried, when compared to
copper.


For surge currents only, Al would need to be thicker than Cu of equal
handling capacity. If you are stressing things to the max, Al has a
lower melting point.

It would work for RF ground also. The oxide layer would not affect the
performance. Lots of us use insulated copper wire for ground radials.

Only concern I would have is that the electrical connections are
properly made. AL's talent for oxidizing has been a problem in the past
with house wiring.

- 73 de Mike N3LI -

"Michael Coslo" wrote in message
...
Ed wrote:
I am only interested in the long term reliability of an aluminum ground
system in comparison to the more common copper system. This is for
lightning suppression only, I am not addressing RF issues. I am
wondering if aluminum can handle the potential surge currents that copper
can... and how well does its ground conductivity work when buried, when
compared to copper.


For surge currents only, Al would need to be thicker than Cu of equal
handling capacity. If you are stressing things to the max, Al has a lower
melting point.

It would work for RF ground also. The oxide layer would not affect the
performance. Lots of us use insulated copper wire for ground radials.



The OP referred to a 'vault ground ring', not radials.

Furze is a major supplier of lightning protection products in the UK and
they don't favour aluminium for earth connections:
http://www.furse.com/elp/earprod.htm. I understand copper and
copper-plated-steel is still used for neutral earth connections by UK
electric power supply companies as well - the oxide layer on aluminium and
its alloys, if present, must have some value of breakdown voltage and
anything that elevates neutral above earth that can be avoided has to be a
bad thing.

Chris

In article 8,
Ed wrote:

I am only interested in the long term reliability of an aluminum ground
system in comparison to the more common copper system. This is for
lightning suppression only, I am not addressing RF issues. I am wondering
if aluminum can handle the potential surge currents that copper can... and
how well does its ground conductivity work when buried, when compared to
copper.

Ed K7AAT

For Lightning Protection Aluminum is NOT the grounding material of
choice. Higher resistance per foot. (Less conductivity) and the Oxide
boundary layer, make it unsuitable for this type of use. For RF Grounding
use, it will work just as well as copper as the Oxide layer really has
no effect at RF Frequencies.

In article ,
Michael Coslo wrote:

Only concern I would have is that the electrical connections are
properly made. AL's talent for oxidizing has been a problem in the past
with house wiring.

A good point.

The National Electric Code has some fairly specific requirements for
how grounding system connections must be made. Soldering is not
permitted, as the high temperatures which can occur at such
connections during a lighting strike can blow the soldered connection
apart. Strong mechanical connections, or welding (e.g. "CadWeld"
thermite-type welding) is required.

I just ran across the following:

http://www.homeinspector.org/resourc...-Grounding.pdf

It indicates that the NEC forbids the use of aluminum conductors for
grounding "where in direct contact with masonry or earth. Aluminum
conductors require 18 inches of clearance from earth." (NEC
paragraphs 250-91a and 250-92a are cited).

There's also a note on the citation: "ATJ note: we have field
reports of complete failure of uninsulated bare aluminum grounding
conductor wire when it was not properly protected from corrosion - for
example where left touching a masonry foundation wall."

It sounds to me as using aluminum wire as a lightning ground system
is a poor idea.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Below is good information, but only applies to electrical systems'
grounding... not commercial radio vault lightning ground systems. Also,
the aluminum system I came across certainly had crimp or other mechanical
bonding methods which avoids the connection issues discussed in the NEC.

I have no control or great concern on this, but was surprised to see
aluminum for my first time. I just wondered if it was common.

Ed K7AAT


..

The National Electric Code has some fairly specific requirements for
how grounding system connections must be made. Soldering is not
permitted, as the high temperatures which can occur at such
connections during a lighting strike can blow the soldered connection
apart. Strong mechanical connections, or welding (e.g. "CadWeld"
thermite-type welding) is required.

I just ran across the following:

http://www.homeinspector.org/resourc...lectrical-Grou
nding.pdf

It indicates that the NEC forbids the use of aluminum conductors for
grounding "where in direct contact with masonry or earth. Aluminum
conductors require 18 inches of clearance from earth." (NEC
paragraphs 250-91a and 250-92a are cited).

There's also a note on the citation: "ATJ note: we have field
reports of complete failure of uninsulated bare aluminum grounding
conductor wire when it was not properly protected from corrosion - for
example where left touching a masonry foundation wall."

It sounds to me as using aluminum wire as a lightning ground system
is a poor idea.