[TowerTalk] [Bulk] Re: RF Ground is a Myth

Wed Jan 21 08:29:08 EST 2015

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 at 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 at 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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