earth pit resistance in sandy areas 1

[jucagua77]

I am the in-charge to construct a small electrical facility in sandy area and the maximum acceptable (permissible) value for protective earth system is 10 ohms. For the first earth pit I use a copper rod 15mm diameter, 5 meters long in a hole 100mm diameter filled with Marconite/cement mix but the resistance value was 110 ohms (measured with TAGG/3 pins method).
Aprox. 200 meters distance from my earth pit a cathodic protection company had drilled a hole for deep groundbed of 170 meters and stem resistance value was found to be more than 1000 ohms.
Somebody have any idea to improve/reduce the earth pits resistance in sandy areas??

 

[jghrist]

If there is no lower resistivity layer that can be reached with deep wells, then increasing the area of the grounding electrode may be the only practicable way to reduce grid resistance. This could be done with a ground grid that covers a large area (if a large area is available). It would be helpful to measure the multi-layer ground resistivity and design the grounding system with software that can model the multi-layer soil.

You may also want to rethink the reasons for the 10 ohm requirement. If there is no really good technical reason for the requirement, then you might not want to spend a lot of money to achieve it.