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

Roger (K8RI) on TT K8RI-on-TowerTalk at tm.net
Wed Jan 21 09:57:34 EST 2015 

On 1/21/2015 8:29 AM, Patrick Greenlee wrote:

It has been my experience that "Mother Earth" does not supply a very low 
resistance path, even with a large grounding system of multiple ground 
rods and lots of, large, bare Copper wire.  Much depends on your soil 
conditions, but do not be disheartened if you see more than 1 or two 
ohms.  Others may have had different results.

In dry soil  it may show as a high resistance even with very elaborate 
ground systems.

I would assume that the conditions that Ufer worked under he would have 
seen high resistances and resistivity to "Earth"

"We say" that the ground system provides a low impedance route to 
ground.  That the UFER ground works, there should be no doubt as the 
military has adopted its use in magazines located in very dry areas and 
it has been incorporated into the NEC.  It has also been endorsed by the 
IEEE.

Those are good enough credentials for me.

Whether the 3 tower leg anchors are sufficient?  I would hesitate to 
say,  They are close enough to each other that they "probably" act more 
like a single, large ground, or electrode than multiple units

I do not recall that WD8RXP used extra grounding on his tower.
  http://www.rogerhalstead.com/ham_files/skyhook.htm

73

Roger (K8RI)


> 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
>>>>> _______________________________________________
>>>>>
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> TowerTalk mailing list
>>>>> TowerTalk at contesting.com
>>>>> http://lists.contesting.com/mailman/listinfo/towertalk
>>>> _______________________________________________
>>>>
>>>>
>>>>
>>>> _______________________________________________
>>>> TowerTalk mailing list
>>>> TowerTalk at contesting.com
>>>> http://lists.contesting.com/mailman/listinfo/towertalk
>>>> _______________________________________________
>>>>
>>>>
>>>>
>>>> _______________________________________________
>>>> TowerTalk mailing list
>>>> TowerTalk at contesting.com
>>>> http://lists.contesting.com/mailman/listinfo/towertalk
>>> _______________________________________________
>>>
>>>
>>>
>>> _______________________________________________
>>> TowerTalk mailing list
>>> TowerTalk at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/towertalk
>>>
>>
>> _______________________________________________
>>
>>
>>
>> _______________________________________________
>> TowerTalk mailing list
>> TowerTalk at contesting.com
>> http://lists.contesting.com/mailman/listinfo/towertalk
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk


-- 

73

Roger (K8RI)


---
This email has been checked for viruses by Avast antivirus software.
http://www.avast.com

More information about the TowerTalk mailing list