Earth Resistance Question

Forget the soil go directly into the rock..Drill hole in rock at least 2 Mt's deep. Copper. bronze alloy rod triangular cut out like rawlplug, drive into hole then add water..and test resistance if necessary repeat and join in series..

o yes but one thing very important you does not get the right value of resistance, you may put some calciam carbonate and pore water daily then you will may get the right value of resistance.

Wouldn't it work to lay the grounding rod, or rods in trenches horizontally? I have read of that being done in rocky environments.

Getting less then 3 ohms is going to be tough. You will more then likely need more then one hole and a whole bunch of GEM and Bentonite back fill. Here is a link. These work well. We have many locations here where such is used.

http://www.erico.com/public/library/fep/LT0359.pdf

Well, how i perform the 2-3 ohm resistance measurements ?

Between what and what ?

IN ROCKY AREA THE FOLLOWING IS RECOMMENDED.

1.DRILLLIKE BOREWELL -ATLEAST TWO SETS OF GI PIPE OF 100-140MM OD HEAVY GAUGE UPTO 20MTRS ,THERE MAY BE THREE PIPES LENGHTS NEEDED AS THE PIPE LENGHTS ARE GENERALLY 6MTR FOR A SINGLE PIECE(IN SUCH CASE YOU HAVE TO DO A PROPER OVERLAP BUTTWELDING AND PROPER TREATMENT WITH CHIPPING AND ZINC ENRICHIING PAIN AND COVERING WITH BITUMEN AND HESSIAN TAPE)IF SINGLE PIPE IS AVAILABLE ITS VERY GOOD.

2.THERE SHOULD BE ATLEAST TWO SUCH PITS AND THEY ARE TO BE CONNECTED WITH EARTH FLAT MESH RING FORMATION UNDERGROUND ATLEAST AT A DEPTH OF -600CM .

3.FOR TOWER EARTHING YOU HAVE TO TAKE RISERS FROM THE EARTH MESH ON BOTH SIDES OF THE TOWER SIZES PREFERABLY ATLEAST 75X8 MM GI OR 50X6COPPER STRIPS.

WITH THIS ARRANGEMENT I HOPE YOUR PROBLERMS WILL BE SOLVED.

EVEN YOU DONOT GET EARTH RESISTANCE VALUE NOT LESS THAN 3OHM YOU MAY HAVE TO DRILL ADDITIONAL POLES AS BOREWELL EARTHING.

You do not necessarily need to reach the soil or to drill holes in solid rock or to arrange artificial watering.

Practically tower earthing is conveniently accomplished in rocky areas by EARTHING MAT arrangement.

By description it would be concentric squares of bare copper conductor or GI strip around tower at a burrial depth of about 0.5 meters in rocky soil;

Seperation between individual square arrangement is 2 meters,

Use 75 MM SQ, bare copper conductor, spacing 3-4 meters in mesh form, integrating main squares in sub square formation,

All joints by thermoweld finally coated with 2mm thick bitumen paint.

About six to eight concentric main square formation buried conductor will give you the desired results in rocky areas with soil resistivity of the order of 1000 ohm meter.

The above method is in conformity with BS7430

If conditions permit use standard eath rods (2.5 m length) directly driven in soil at the four outer corners of the square, this will reduce the number of concentric squares.

At 350m length of cable, using 10mm² copper, the cable resistance will be ~0.6Ω. If you make an experimental earthing (normal with electrodes or mat...) and can get a resistance of < 2.4Ω, then this gives the 3Ω required.

To get lower and depending on the result at the site where you dug (350m away), you can increase the cross section of the cable (or flat copper bar ?).{25mm² ==>0.25Ω approx}

Now all depends on the cost of each of the proposed methods you received, and the ease of execution, the nature of the soil and the practicality of the routing to the remote site, etc. You work it out.

How i can measure the final resistance after placing the copper rod in the earth ?

There are special instruments used specifically for the measurement of the earth pit resistance.

It injects a current with a voltage of 500 to 1000 Volts, using One or two electrodes (Auxiliaries), short pieces, and give the average value measured.

You should use one of them to be accurate.

Otherwise, you can plant a small electrode of ~ 30cm long far from the earth rod / pit you made, at a distance at least equal to the depth reached x 2. Use a Megger injecting a voltage as high as possible (~1000V ?). Measure the resistance between the auxiliary small rod and the earth rod/mat you built. I can only advice the use of the Megger but check that it can read the 1 Ohm with enough resolution to make sense. Otherwise, other methods need to be done by someone more qualified to avoid errors and for safety (using mains voltage supply!)

Instead of making fun on us,what is your golden (or silver) information you have, let us see what you have,if you have any.

HALLO :

CAN YOU GET MORE THAN ONE HOLE, IN THE GROUND 350m AWAY ?

IF THE HOLE HAS IN THE CENTER A METAL WHO MAKE A GOOD GROUND

CONTACT FOR TO BE SUBMERGED IN AN ELECTROLITIC....

YOU BEST CHANCE IS PARALELL CONECTIONS.FROM THE TOWER TO THE

GROUND CONECTIONS AS SHORT IS POSSIBLE .

krasnopolsky

I suggest the following line of action:

1) Use Strip or Round Electrodes of copper. Each strip should not be less than 25 mmX 1.60 mm and if round conductor is used it should have minimum cross-section of 3.0 mm2.

2) The length of the buried conductor should not be less than 15M.

3) Bury the conductors in trenches or ditches not less than 0.5 M deep.

4) In your case, you may have to lay more than one strip/ round conductor, these shall be laid either in parallel or in radial trenches. I would suggest use a circular trench with tower as centre of the circle.

5) Use the following formula to arrive at the value of earth resistance by changing length of strip/rod. Width of strip or depth of burial will have little impact on resistance value.

R= 100p/2pil Loge 288 lenght (sqrd)/wt ohms

where p (rho) = resistivity of soil in ohm-metre

l= length of strip/round conductor in cm

t= width of strip in cm or twice the diameter in case of round conductor

w= depth of burial of electrodes in cm.

Keep thickness of the strip some available optimum value and work with length of the strip /round conductor. Consider the tower as centre of a circle of radius 5, 10 metre. Find length of strip/round conductor using cicumference = 2pir formula.

Hope you will be able get at the required earth resistance value. Use other suggestions made by experts on this thread.

Best of luck

BB Raina