🔹 Introduction
Across the deserts and mountains of the Middle East, thousands of high-voltage towers stand tall, carrying electricity over hundreds of kilometers.
But the true safety and reliability of these lines lie underground — in the grounding system.
Grounding (or earthing) in Overhead Transmission Lines (OHTL) provides a safe, low-resistance path for lightning strikes and fault currents to flow into the earth.
Without it, even minor faults can cause power outages, equipment failure, or serious hazards for maintenance crews.
This article offers a complete and SEO-friendly explanation of how grounding and tower footing resistance (TFR) work in OHTL systems — especially in Saudi Arabia, the UAE, Oman, and other Middle Eastern countries — where soil conditions like sand and rock make grounding design a serious engineering challenge.
⚙️ What Is Grounding in Overhead Transmission Lines?
In simple terms, grounding means connecting metallic parts of the tower (legs, stubs, and structure) to the earth through conductors and rods.
This connection allows electrical currents — caused by lightning, faults, or switching surges — to safely dissipate into the ground.
The grounding system ensures:
- Safety of personnel and equipment
- Stable operation of protection systems
- Reduction in lightning flashovers
- Control of potential rise across tower structures
In high-voltage transmission lines (110 kV to 400 kV), proper grounding is as vital as the tower design itself.
⚡ Why Grounding Is Critical in OHTL Systems
- Lightning Protection:
Transmission towers are natural lightning targets. A low-resistance ground path safely diverts these strikes away from insulators and conductors. - Fault Current Dissipation:
When a conductor accidentally contacts the tower, grounding provides a quick discharge path for the fault current, helping circuit breakers operate effectively. - Human and Equipment Safety:
It ensures that all metallic parts of the tower remain at the same potential, reducing step and touch voltages that can endanger workers. - Improved Reliability:
A properly grounded tower prevents unwanted tripping, equipment damage, and energy losses, enhancing network stability.
🧱 Key Components of the Grounding System
1️⃣ Counterpoise (Grounding Conductor)
A bare copper-clad steel wire, known as the counterpoise, is buried around the tower foundation. It’s the main horizontal electrode that spreads the current into the surrounding soil.
Design features:
- Buried 500 mm below finished ground level in normal soil.
- Buried up to 1.8 m deep in sand dunes or loose soil to prevent exposure.
- Installed parallel to the transmission line for uniform current distribution.
- Typical sizes:
- 19#7 AWG near substations
- 7#5 AWG for other locations
2️⃣ Ground Rods
Vertical copper-clad steel rods (usually 16–19 mm diameter and 3 m long) are installed beside each tower leg.
They provide deeper earth contact, especially useful in high-resistance desert soils.
When required, multiple rods are connected at 180° apart to improve dissipation.
3️⃣ Tower Stub and Rebar Bonding
Each tower leg (stub angle) is connected to the grounding system using compression lugs or exothermic welds.
Inside the concrete footing, reinforcing bars (rebars) are also bonded to the stub at two or more points, ensuring electrical continuity between tower steel and foundation.
To prevent corrosion, a galvanic inhibitor compound is used between dissimilar metals.
4️⃣ Exothermic Welding (Thermite Joints)
This is the most reliable, permanent connection method used in OHTL grounding.
Different weld molds (GT, GR, SS, VSC, RRC) are chosen depending on whether the connection is tower-to-wire, wire-to-rod, or stub-to-stub.
Exothermic welds:
- Provide molecular bonding
- Resist corrosion
- Remain maintenance-free for decades
5️⃣ Continuous Counterpoise System
For 132–400 kV transmission networks, engineers often design a continuous counterpoise — a grounding conductor that connects multiple towers together.
This dramatically reduces overall resistance, minimizes lightning backflashovers, and maintains a stable ground potential gradient across the line.
🧮 Tower Footing Resistance (TFR): The Heart of Grounding Design
🔹 What Is Tower Footing Resistance?
Tower Footing Resistance (TFR) is the total resistance between a tower’s grounded structure and the surrounding soil.
It determines how easily current can flow from the tower into the earth during a fault or lightning strike.
Simply put:
Lower TFR = Faster current dissipation = Higher safety and reliability.
🔹 Importance of Tower Footing Resistance
- Lightning Performance:
Low TFR minimizes tower potential rise during lightning, reducing the risk of flashovers to phase conductors. - Fault Clearance:
Ensures protective relays and breakers operate correctly by providing a stable return path for fault currents. - Safety Assurance:
Keeps touch and step voltages below hazardous limits, protecting both personnel and equipment.
🔹 Recommended Tower Footing Resistance Values (380KV LINE)
| Tower Location | Ideal TFR (Ohms) | Remarks |
|---|---|---|
| Within 3 km of substation | ≤ 3 Ω | Critical safety zone |
| Beyond 3 km from substation | ≤ 10 Ω | Suitable for normal soil |
| Rocky or dry desert terrain | ≤ 15 Ω (target) | Achieved with enhanced grounding techniques |
These values are widely accepted across KSA & Middle Eastern power transmission projects.
🔹 Factors Affecting TFR
- Soil Resistivity (ρ):
Sandy or rocky soil has high resistivity, increasing TFR. - Electrode Length & Depth:
Longer counterpoise and deeper ground rods provide better current dissipation. - Moisture & Temperature:
Dry, hot soil has poor conductivity — a common issue in Middle Eastern deserts. - Material Type:
Copper-clad steel provides better conductivity and corrosion protection. - Connection Quality:
Poor joints or loose bolts increase resistance; exothermic welds are ideal.
🔹 Measuring Tower Footing Resistance
The Fall-of-Potential (FOP) method is the standard procedure:
- Inject test current between the tower and a remote current electrode (~100 m away).
- Measure voltage drop using a potential electrode placed between them.
- Calculate resistance (R = V/I).
- Plot readings vs. distance to find true resistance value.
Modern test kits like Fluke Earth Tester or Megger DET series simplify TFR measurement.
🔹 How to Reduce Tower Footing Resistance
If the measured TFR exceeds the target value, engineers can:
- Extend the counterpoise conductor length.
- Install additional vertical rods at 180° spacing.
- Interconnect nearby tower grounds (continuous system).
- Improve soil conductivity using bentonite or chemical backfill.
- Recheck all exothermic welds and stub connections for continuity.
With proper design and enhancement, TFR can be reduced to below 5 ohms, ensuring superior lightning performance.
ALSO READ: PLS-CADD for Beginners: Complete Introduction to Overhead Line Design Software
🧩 Ground Resistance Design and Testing
📏 General Resistance Requirements
| Soil Type | Typical Target Resistance |
|---|---|
| Normal soil | ≤ 10 Ω |
| Substation area | ≤ 3 Ω |
| High-resistivity rocky area | ≤ 15 Ω (acceptable) |
If results are unsatisfactory:
- Increase conductor depth or length.
- Add more rods or radial electrodes.
- Use soil enhancers and ensure strong mechanical joints.
🔹 Testing Procedure Summary
- Measure tower footing resistance after initial installation.
- If higher than specified, bond all four stub angles.
- Extend the counterpoise if required.
- Add additional rods and remeasure.
- Continue improvements until desired resistance is achieved.
🌍 Grounding Challenges in Middle Eastern Soils
Grounding design in the Middle East faces extreme challenges:
- High soil resistivity due to dry sand and rock.
- Shifting sand dunes that expose conductors.
- Limited moisture, reducing natural soil conductivity.
To overcome these:
- Engineers bury conductors deeper (up to 1.8 m).
- Use bentonite or conductive cement around electrodes.
- Apply Ufer grounding (concrete-encased electrodes) in rocky terrain.
🧰 Installation Best Practices
- Maintain a minimum bending radius of 75 mm for all conductor turns.
- Ensure all connections are exothermically welded.
- Backfill trenches with compacted soil or concrete after installation.
- Apply anti-corrosion compounds between copper and steel joints.
- Conduct resistance testing after final backfilling under natural soil conditions.
🧠 Common Mistakes to Avoid
- Using undersized or unapproved materials.
- Shallow counterpoise burial in desert regions.
- Ignoring step and touch potential checks.
- Loose bolted connections instead of welds.
- Not maintaining measurement records per tower.
Each mistake increases footing resistance and compromises the line’s safety and reliability.
🔧 Maintenance and Monitoring
A grounding system is not a one-time installation — it requires periodic testing and maintenance.
Annual checks include:
- Ground resistance measurement
- Continuity verification between tower legs
- Visual inspection for corrosion or exposure
- Replacement of damaged or rusted components
Long-term data helps track changes in soil conditions and system performance.
🧩 Key Takeaways
- Grounding ensures lightning protection, fault clearance, and human safety in OHTL systems.
- Tower Footing Resistance (TFR) is the main performance indicator — keep it below 10 Ω, ideally under 5 Ω.
- Use copper-clad steel conductors, deep ground rods, and exothermic welds for lasting performance.
- Adapt grounding designs for rocky or sandy Middle Eastern terrains.
- Conduct regular resistance testing and maintenance for long-term reliability.
🔹 Conclusion
Grounding is the silent safeguard of every overhead transmission line.
A properly designed and maintained grounding system with low tower footing resistance ensures uninterrupted power flow, protects lives, and enhances grid stability.
Whether installed in the deserts of Saudi Arabia, coastal Oman, or the rocky terrain of Jordan — the principles remain the same:
Low resistance, strong bonding, and smart design mean safe and reliable power transmission
