When electrically grounding one's station, is there any particular
advantage of a single 8-foot ground rod over two 4-foot ground rods, or an
8-foot length of heavy gauge wire buried 6-12 inches under the ground?

On Sat, 07 Jul 2007 15:31:51 -0400, "Rick (W-A-one-R-K-T)"
wrote:


When electrically grounding one's station, is there any particular
advantage of a single 8-foot ground rod over two 4-foot ground rods, or an
8-foot length of heavy gauge wire buried 6-12 inches under the ground?


Hi Rick,

Ground is notable for having complex answers to simple questions. One
very good resource is:

UNITED STATES DEPARTMENT OF AGRICULTURE
Rural Electrification Administration
REA BULLETIN 1751F-802
SUBJECT: Electrical Protection Grounding Fundamentals

Another resource can be found in:

DEEP EARTH GROUNDING vs SHALLOW EARTH GROUNDING
by
Martin D. Conroy and Paul G. Richard
Computer Power Corporation
Omaha, Nebraska

Both can be found somewhere on the Web. The first is a PDF, the
second is a web page. I don't know specific locations, but the
details above should be suitable to Google.

73's
Richard Clark, KB7QHC

"Rick (W-A-one-R-K-T)" wrote in message
news

When electrically grounding one's station, is there any particular
advantage of a single 8-foot ground rod over two 4-foot ground rods, or an
8-foot length of heavy gauge wire buried 6-12 inches under the ground?



yes. first there is the electrical safety code that you must comply with
which i believe generally calls for 8' rods. 4' rods may not be below the
frost line in the winter so may not provide any useful grounding for part of
the year. shallow buried wire has the same problem.

on rf issues, lots of shallow buried radials can help reduce ground loss
under certain antennas... but these are not substitutes for good electrical
safety grounds.

Dave wrote:
"Rick (W-A-one-R-K-T)" wrote in message
news
When electrically grounding one's station, is there any particular
advantage of a single 8-foot ground rod over two 4-foot ground rods, or an
8-foot length of heavy gauge wire buried 6-12 inches under the ground?




yes. first there is the electrical safety code that you must comply with
which i believe generally calls for 8' rods. 4' rods may not be below the
frost line in the winter so may not provide any useful grounding for part of
the year. shallow buried wire has the same problem.

on rf issues, lots of shallow buried radials can help reduce ground loss
under certain antennas... but these are not substitutes for good electrical
safety grounds.


The NEC allows a wide variety of electrical safety grounds (and,
interestingly, a ground rod is not usually allowed as the only grounding
electrode). The old standby of "cold water pipe" is specifically not
allowed any more (too many places with plastic pipe from street to house).

The preferred ground in most jurisdictions is a concrete encased
grounding electrode (aka a Ufer Ground, after the inventor's name Herb
Ufer).. 20 ft of appropriate conductor encased in concrete.

As far as rods go, you can dig a trench and lay it sideways and meet the
code requirement. 2 rods 4 feet long might meet code (if all of the rod
is buried and they are far enough apart).


However, in addition to any regulatory requirements, there's a
difference between a "good ground" for
a) electrical safety
b) RF
c) lightning

A grounding system that's good for one isn't necessarily good for the
others.


There's a good writeup on grounds, with particular attention to
antennas, cable TV, telephone, etc. at Mike Holt's website (He's a
electrical code guru that does seminars, etc.)

http://www.mikeholt.com/ is the site, look for the "low voltage
handbook", which is a free download and has all the relevant code
sections explained, with diagrams, etc.

Isn't concrete an insulator??

"The preferred ground in most jurisdictions is a concrete encased grounding
electrode (aka a Ufer Ground, after the inventor's name Herb Ufer).. "

What am I missing here?

"Jim Lux" wrote in message
...
Dave wrote:
"Rick (W-A-one-R-K-T)" wrote in message
news
When electrically grounding one's station, is there any particular
advantage of a single 8-foot ground rod over two 4-foot ground rods, or
an
8-foot length of heavy gauge wire buried 6-12 inches under the ground?




yes. first there is the electrical safety code that you must comply with
which i believe generally calls for 8' rods. 4' rods may not be below
the frost line in the winter so may not provide any useful grounding for
part of the year. shallow buried wire has the same problem.

on rf issues, lots of shallow buried radials can help reduce ground loss
under certain antennas... but these are not substitutes for good
electrical safety grounds.
The NEC allows a wide variety of electrical safety grounds (and,
interestingly, a ground rod is not usually allowed as the only grounding
electrode). The old standby of "cold water pipe" is specifically not
allowed any more (too many places with plastic pipe from street to house).

The preferred ground in most jurisdictions is a concrete encased grounding
electrode (aka a Ufer Ground, after the inventor's name Herb Ufer).. 20 ft
of appropriate conductor encased in concrete.

As far as rods go, you can dig a trench and lay it sideways and meet the
code requirement. 2 rods 4 feet long might meet code (if all of the rod
is buried and they are far enough apart).


However, in addition to any regulatory requirements, there's a difference
between a "good ground" for
a) electrical safety
b) RF
c) lightning

A grounding system that's good for one isn't necessarily good for the
others.


There's a good writeup on grounds, with particular attention to antennas,
cable TV, telephone, etc. at Mike Holt's website (He's a electrical code
guru that does seminars, etc.)

http://www.mikeholt.com/ is the site, look for the "low voltage handbook",
which is a free download and has all the relevant code sections explained,
with diagrams, etc.

John Doe wrote:

Isn't concrete an insulator??

"The preferred ground in most jurisdictions is a concrete encased grounding
electrode (aka a Ufer Ground, after the inventor's name Herb Ufer).. "

What am I missing here?

That while dry concrete is a pretty good insulator it is hard to
find such just about anywhere other than Southern Arizona.

--
Jim Pennino

Remove .spam.sux to reply.

wrote:
John Doe wrote:


Isn't concrete an insulator??


"The preferred ground in most jurisdictions is a concrete encased grounding
electrode (aka a Ufer Ground, after the inventor's name Herb Ufer).. "


What am I missing here?


That while dry concrete is a pretty good insulator it is hard to
find such just about anywhere other than Southern Arizona.

And even there, the concrete is probably damper and a better conductor
than the surrounding soil. Ufer's original work was developing
grounding techniques for ammo bunkers in desert areas, since the ground
rods didn't work.

John Doe wrote:
Isn't concrete an insulator??

"The preferred ground in most jurisdictions is a concrete encased grounding
electrode (aka a Ufer Ground, after the inventor's name Herb Ufer).. "

What am I missing here?

Concrete is a conductor, and generally a better conductor than the soil
around it (it's hygroscopic), so rather than the sort of iffy contact
between the rod and soil, you have a much larger contact area between 20
feet of wire and concrete, and an even larger contact surface area
between the concrete and the soil. Run some numbers, and it turns out
that capacitive coupling from concrete to soil is probably lower
impedance than resistance.


There ARE high resistivity concretes (used for things like supporting
rails on electric trains), but that's unusual.

There's lots and lots of field tests, lab work, and theoretical analysis
to back up the consistent good performance of Ufer grounds.

Rick (W-A-one-R-K-T) wrote:

When electrically grounding one's station, is there any particular
advantage of a single 8-foot ground rod over two 4-foot ground rods, or an
8-foot length of heavy gauge wire buried 6-12 inches under the ground?



The easy answer is "it depends".

Where I live, it is virtually impossible to get an 8 foot ground rod in
vertically, without first having someone core-drill the site. Living on
a volcano has it's problems, and one of them certainly is grounding.

Solid rock with perhaps a few feet of earth on top makes for tough
grounding situations. Here, most electrical services are grounded to
something called a "ufer" ground, which is about 20 feet of #6 copper
inside the perimeter foundation and clamped to at least two 20 foot
lengths of rebar, all of which is embedded in the concrete.... external
ground rods (if any) are typically pounded onto the ground at an angle,
so they can follow the interface of the lava and earth. If the
individual is making any pretense of having a vertical rod, they'll bend
it vertical just before it sticks up out of the earth.

Even at 4000 feet elevation, it is rare to see frost on the ground more
than once every 3 to 5 years, so getting a ground below the "frost line"
is easy. When I lived near sea level, I built a workshop of 32' x 52'
and put about a thousand feet of bare copper wire underneath the slab in
a gridded configuration, with all long runs brought to a single point
where the ham shack was to be. It worked great as RF ground and was
tied to the ufer as well, so everything was at the same potential.

Here, multiple short rods would be used (and accepted by the electrical
inspector) for the sercvice entrance ground, if he hadn't already
inspected the ufer ground prior to the concrete pour. (I know someone
that put in the required ufer and poured the slab without getting the
electrical inspection, and had to do just that, add several vertical
rods, all tied together to satisfy the inspector). I've heard rumor
that new code is minimum of 2 each 8 foot rods, but people here aren't
on the newest code level by a long shot.

Best thing is to make sure what local code is first, then go for
overkill if you are at all thinking it isn't enough, especially if you
are putting in a tower and/or worried about lightning.

RF ground is a whole different matter than safety or lightning
grounding, as you are likely aware already.