[TowerTalk] ground rods and angle...

[Roger (K8RI) on TT]

Cost of concrete: Where you are located, how much you get, and when you 
buy make all the difference.  Late last spring after the thaw, but 
before we could get trucks on the yard, let alone concrete trucks, I 
paid IIRC $111 or $120 per sq yd of 4000 psi for 5 cu yds.  plus the 
manual labor. There was no delivery charge, but two guys digging the 
hole, with 4 working on the pour ( they ran over 100 feet with 
wheelbarrows loaded with concrete, cost more than the concrete) They 
really did run too with those heavy loads. By the time we finished the 
single wheel was beginning to leave quite a depression, even though they 
avoided running in the same track. <:-)  Even then with only 5 yds (give 
or take), my asphalt driveway with a good sand and gravel base suffered 
damage.  If you have a couple of pickup trucks and load them your 
selves, it's even cheaper, but more labor.  Compared to heavy ground 
cable as required by the NEC, the price is relatively cheap.  Getting 
small loads of sand and gravel delivered, while renting a mixer should 
cut the cost in half.  You are trading expense for manual labor, 
although mixing in a mixer is not a lot of work.  One guy shovels sand, 
one shovels gravel, and a third adds a number of shovels of bagged 
cement.  If you know the ratios (which are easy to find), it goes fast 
and tales little elbow grease.  In days long gone bu, I've helped pour a 
lot of concrete like that out of a mixer including foundations and 
floors for milking parlors. Like some math, that would be far beyond my 
present abilities.

As Patric mentioned he has the equipment. Mixing the concrete is 
relatively inexpensive.  "I'd guess" about a third to a quarter of the 
cost of delivered concrete.
If my calculations are correct, even at $200 per yard, you could do 6, 
10" holes at $33 each, but likely fewer than half the rods required..  I 
t wouldn't take many of those to surpass a big network of rods and 
copper cable.  In many areas, 6' deep might be acceptable.

Unless you have money to burn, doing this kind of ground system is 
likely to be more for the do it your selfer, but not those with few 
mechanical abilities..

73

Roger (K8RI)


On 1/19/2016 Tuesday 10:10 AM, Chris wrote:
> Backfill with bentonite or similar conductive earth material.  I know a local installer who puts up broadcast towers who did this and created a ridiculously low resistance ground network on a rock mountaintop.   Concrete is expensive!
>
> Chris
> KF7P
>
> On Jan 18, 2016, at 10:59 PM, Roger (K8RI) on TT wrote:
>
>> I was just wondering and no, I have no plans on changing my system:  Yes, I am serious.  The topic of UFER, ground rods and safety ground "systems".
>> Would those of us with good soil benefit from boring a 6, 8, or 10" hole, filling it with concrete and sinking the ground rod in it?  The contact area is small, but huge compared to the rod accompanied by a low inductance.  It seems, at least in theory that the ground system could be reduced in size (number of rods) while possibly increasing the effectiveness of the system. A mini UFER ground system network. At first, it sounds like a lot of effort and cost, but out in the country, most of the equipment (Tractor mounted) is relatively common while those in the city could put down a much more effective ground system.  Compared to the price of copper, particularly large copper , concrete is relatively cheap.  From a practical approach, it'd be beyond many of us for a number of reasons. Availability and cost of equipment.  In addition, damage to the yard although temporary could be vetoed by a spouse
>>
>> Barring math errors:
>>
>> Instead of many ground rods, how about concrete encased rods, in each direction if possible?  The number of rods and the area is limited, so I would think this would greatly increase the effectiveness of said, limited ground system at a moderate increase in cost.  An 8" diameter hole  8' deep would have a surface area of
>> 16.75 sq ft
>>
>> Surface area = Pi * d * h  Volume =  Pi * 2d * h or Pi * r^2 * h
>>
>> Circumference = Pi*d 3.14159 X 8  = 25.132 X 8' X 12" =  2414.7412 sq in / 144 sq in (in a sq ft) = 16.755 sq ft of area  A 5/8th in dia Ground rod is 5/8  0.624 * Pi = 1.962 * 8 * 12 / 144 = 1.3 sq ft. An  8" hole filled with concrete would offer 12.8 times the area while a 10" hole  (20.0 sq ft offers) offers over 16 times the area.  10", 8' deep is roughly 4.4 cubic feet or 0.16 (1/6th) of a cubic yard
>>
>>
>> 73
>>
>> Roger (K8RI)
>>
>>
>> On 1/17/2016 Sunday 12:30 PM, Jim Brown wrote:
>>> On Sun,1/17/2016 8:01 AM, StellarCAT wrote:
>>>> I was thinking if I angled the rod at 45 degrees I’d both increase the area of the ‘coverage’ (out further away from the towers – UFER)
>>> Don't put your rods close to the concrete base to avoid interaction with the UFER ground. Put the first ring of rods at least 4-8 ft from the concrete.
>>>
>>> 73, Jim K9YC
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-- 

73

Roger (K8RI)



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