ACHIEVING LOW EARTH RESISTANCE IN CHALLENGING SOIL CONDITIONS — OUR EXPERIENCE AT PRESCO PLC

In some certain locations, no matter how well you treat the soil, achieving an acceptable earth resistance reading can be a real challenge. Last week at Presco Plc, we encountered such a case and it turned out to be one of the most insightful experiences for our team.

Under the supervision of the Engineering Lead at Presco Plc, Engr. Raphael Orosun, we applied the Drill Type Earthing Method to overcome the soil challenge and achieve the desired results. In this post, I’ve provided a step-by-step guide detailing how the process was successfully executed.

1. Procured twelve pieces of 2” galvanized pipes and three 6ft galvanized earth rods.
2. Drilled three holes of 20 meters depth each, spaced at 10 meters apart.
3. Each drilled hole was designed to accommodate four galvanized pipes (each 5 meters long).
4. To ease handling, a nipple was welded on one end of each pipe and a socket on the other, both threaded for easy assembly. This approach was adopted instead of welding the entire 20 meters length together, as lifting a single pipe of that length would have been extremely difficult.
5. The galvanized earth rod was welded to the end of the first pipe, forming a javelin like shape.
6. A 70mmsq bare copper conductor was passed through the first pipe and clamped to the earth rod.
7. An extra length of conductor was intentionally left and wound around the earth rod to ensure a firm, long lasting connection, as experience has shown that the clamp used to fasten the bare conductor to the earth rod may wear out over time, potentially causing a loose grip; however, this winding method maintains a consistent and reliable connection throughout the lifespan of the installation.
8. Using a 3” drill pipe, the soil was drilled down to 20 meters typically encountering mud water between 16–18 meters.
9. Once the 3” drill pipe was removed, the first 2” galvanized pipe with the welded earth rod was inserted into the drilled hole, leaving about 2ft above ground, and was firmly anchored using a grip and wrench to prevent the entire length from slipping into the ground.
10. The second 2” galvanized pipe, also threaded, was inserted into the anchored first pipe with the bare conductor passed through it; since the first pipe had a socket and the second a nipple, both were screwed together and tightened with a wrench before lowering the assembly into the ground. This same process was repeated for the third and fourth pipes until the full 20-meter depth was achieved, with the first pipe (bearing the welded earth rod) ultimately seating firmly at the base of the drilled hole.
11. Approximately 10 meters of bare copper conductor was left at each drilled point for interconnection.
12. The remaining two drill points were completed using the same procedure.
13. Earth drill one and two were looped to earth drill three using the 10meters 70mmsq bare copper conductor left for interconnection in step 11, and they were securely clamped together. A maintenance pit was installed at this third drill point where all connections meet to facilitate future maintenance.
14. After the looping, an earth resistance test was conducted with impressive results; it is advisable to take the readings on the second day, after the drilled soil has properly stabilized around the earth rod, as the difference can be significant. In our case, the reading improved from 2.15ohms on day one to 1.12ohms on day two, which was an excellent outcome.
15. From the third earth drill, the main earthing connection was routed to the facility’s earth panel for distribution.
16. Once all readings were satisfactory and connections done, excavated areas were backfilled and site cleanup completed.

Conclusion:
When faced with challenging soil conditions that make conventional earthing methods ineffective, the drill type earthing method proves highly efficient in achieving low resistance and stable performance.