I have a triangular tower with legs on 14 ft centers, yes, 14 feet, not
inches. I built it with three separate concrete foundations, one per
leg. It is currently tilted over so one leg is not touching its
concrete embedded mechanical connection/mount.
It would seem that if I take an ohm meter reading between the
unconnected leg's mount and one of the other mounts I will be getting a
valid estimate of the Ufer ground quality of my tower installation's
foundations. It could be argued that I am actually measuring two Ufer
grounds in parallel as two of the attachment points are bridged together
by the tower. I suppose I will also unbolt one of the hinged legs so I
can measure independently from the non hinged leg mount to each hinged
mount in turn.
There is plenty of rebar in the foundations. The rebar cages are welded
with allowances for the effect of welding on rebar (welded at ends and
overlaps so no structural degradation.) Each leg's foundation has three
each pier holes augered with a 12 inch tractor mounted auger. I moved
the tractor a little while augering to get a larger hole. There is rebar
in each pier hole and a rectangular cage connecting the three holes.
All rebar is welded so there is good conductivity throughout the rebar
armatures.
Each set of three pier holes is topped by a 2'x2'x7' horizontal concrete
beam with an extensive rebar cage that is well connected by welding to
the rebar in the augered holes. All rebar is at least 2 inches
(typically 3) from the dirt/concrete interface.
Am I missing something? Will a simple ohm meter test give a reasonable
measure of Ufer ground quality, sufficient to decide the question of
whether or not multiple copper clad ground rods need to be installed and
interconnected?
Is it too much of a leap of faith or otherwise to assume the inter-leg
resistance is an adequate predictor of tower mount to Mother Earth
conductivity?
Just write your opinion on the back of a US $20 bank note and mail to my
QSL address in QRZ.com including a SASE if you want a receipt and or
thank you note.
Patrick NJ5G
On 1/21/2015 1:08 AM, David Gilbert wrote:
You're going to need to duplicate the surface area of a typical Ufer
conductor, and you're going to need to somehow bond it intimately to
the bulk concrete. I'll be interested to see what your test setup is,
because I can't think of a legitimate method other than pouring some
new concrete on top of the old with the conductor embedded in it.
Possibly you're more clever than I.
And you should probably be prepared to compare it to alternate schemes
(ground rods, etc) to establish an appropriate baseline.
Dave AB7E
On 1/20/2015 5:22 PM, Brian Carling wrote:
I suspect it's not as conductive as some may have us think...
Best regards - Brian Carling
AF4K Crystals Co.
117 Sterling Pine St.
Sanford, FL 32773
Tel: +USA 321-262-5471
On Jan 20, 2015, at 1:22 PM, David Robbins <k1ttt@verizon.net> wrote:
just remember when you do it to not use the point of an ohm meter
probe.... it is not easy to measure bulk material resistivity like
in soil or concrete or other types of materials.
you need to have some relatively large surface area to contact the
material, which is hard to do with already poured concrete.
Jan 20, 2015 12:59:36 PM, bcarling@cfl.rr.com wrote:
So far I am not convinced about using concrete. I'm going to do some
resistance testing on the concrete in my yard.
Best regards - Brian Carling
AF4K Crystals Co.
117 Sterling Pine St.
Sanford, FL 32773
Tel: +USA 321-262-5471
On Jan 20, 2015, at 10:13 AM, Grant Saviers wrote:
If your house slab was installed correctly with a vapor barrier
and/or foam insulation, then it is insulated electrically from earth.
Tower bases make good Ufers as do perimeter foundations, so my
towers and shop both had the rebar set as Ufers when constructed.
I also noticed that a new service transformer I had installed is
set on a concrete vault that has a ground stub cast into the side.
The power company used it, no ground rods. I'd estimate its surface
area in contact with earth as more than 16 sq ft. Compare that to
less than 2 sq feet for a 10' 3/4" ground rod.
Grant KZ1W
On 1/19/2015 6:52 PM, Mike Reublin NF4L wrote:
The electrician I had (who does a LOT of grounding work here) come
out to connect my tower ground to the service ground told me he
would be glad to drive the extra rods extending out from the
tower, but doing so would add no benefit at all. I have no idea if
this is true or not. At some point, lacking personal knowledge, ya
have to take someone's word for it. My tower megged out at 4 ohms.
Mike NF4L
On Jan 19, 2015, at 8:29 PM, Brian Carling
wrote:
The advice varies about this considerably. This week is the first
time I've even heard of UF ER or conductive concrete!
The professional experts that I know recommend putting a 20 to 30
foot ground rod into the ground at each corner of your house and
connecting heavy gauge copper conductors up to lightning rodsup
on the roof.
It seems like if the only thing you need is a large area of this
allegedly conductive concrete stuck in the ground, why not ground
everything to the concrete slab your house sits on!!
Best regards - Brian Carling
AF4K Crystals Co.
117 Sterling Pine St.
Sanford, FL 32773
Tel: +USA 321-262-5471
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