Introduction
When we think about designing a modern building, fire protection systems, alarm systems, surveillance cameras, or even energy efficiency often come to mind. However, few of us pause to consider one of the most modest yet critically important systems for the safety of lives and equipment : the Common Earthing System.
As an electrical engineering consultant, I have dealt with many facilities where this system was neglected. The results were troubling and confusing, including recurring faults, equipment malfunctions, and even damage to certain components. In this article, I will shed light on this essential system in a simplified manner, supported by real-life examples of the damages caused by its neglect.
First: What is the Common Earthing System?
The Common Earthing System is an electrically connected network that extends beneath and around the building. It connects all non-current-carrying metallic parts of the facility (such as the building structure, equipment enclosures, cable trays, and water and gas pipes) and links them to the earth mass (actual ground) through buried rods or plates.
In other words, it creates a low-resistance path (preferably less than 5 ohms) to safely discharge abnormal electrical currents (leakages, lightning strikes, or faults) into the ground instead of allowing them to pass through the human body or sensitive equipment.
Second: Why is it Important? Three Essential Pillars
1. Protection of Human Life (Safety from Electric Shock):
In the event of current leakage from an electrical wire to the body of a metallic device (such as a heater or appliance), a proper earthing system provides a low-resistance path that returns the current to its source. This causes the circuit breaker to trip immediately. Without earthing, the device remains energized, and anyone touching it becomes part of the electrical circuit.
2. Protection of Sensitive Electronic Equipment:
Common earthing systems stabilize the reference voltage for all equipment (zero volts). They also provide a safe path to discharge high energy resulting from lightning strikes or electrical surges, thereby protecting servers, PLC devices, and BMS systems from damage or burnout.
3. Proper Operation of Protective Devices:
Without proper earthing, residual current devices (RCD/GFCI) or miniature circuit breakers (MCB) will not function correctly during faults. This is because the fault current will not find a path back to the source, allowing the fault to persist for hours or even days without detection.
Third: Implementation of the Earthing System
In practice, the implementation of a common earthing system in buildings can be summarized in the following steps:
- Soil Resistivity Measurement:
The process begins by measuring soil resistivity at the project site using a Megger Earth Tester and the four-point Wenner method. This determines the required number of electrodes. In practice, initial earth pits are created at building corners, then resistance is measured to define the next steps.
- Excavation of Ring Trench (Ring Earth Electrode):
A trench is dug around the building perimeter to a depth of no less than 0.5 meters (preferably 0.7–1 meter), forming a closed loop (ring).
- Laying the Main Conductor:
A bare or stranded copper conductor with a cross-section of at least 70 mm² (depending on design) is placed داخل the trench. Some specifications recommend adding salt and activated charcoal around the conductor to improve soil conductivity, while others prefer leaving the soil untreated to ensure stable long-term resistance.
- Driving Earth Rods:
Copper or galvanized rods (1.5–3 meters long) are driven into the trench base at regular intervals (every 5–10 meters). These rods are connected to the conductor using exothermic welding or durable copper clamps داخل concrete chambers for protection and measurement access.
- Equipotential Bonding:
All of the following are connected:
• Structural steel foundations of the building
• Metallic water tanks
• Gas and water pipes at entry points
• Metal stair railings
• Main distribution boards (using green/yellow copper conductor)
- Testing and Measurement:
After installation, the final system resistance is measured. It should be less than (or equal to) 1 ohm for critical buildings (such as hospitals and data centers), or less than 5 ohms for residential buildings, according to standards such as NEC, IEC, and the Saudi Code.
Fourth: Real-Life Examples – When Earthing is Absent, Disaster Strikes
Numerous fire incidents have occurred due to the absence of proper earthing systems in residential buildings and shopping malls. A common factor among these incidents was the presence of continuous leakage over long periods, which went undetected due to the lack of a complete earthing system. This leads to high current flow in conductors, causing temperature rise, insulation breakdown, and ultimately ignition of the insulation and surrounding flammable materials.
Conclusion and Recommendations
The common earthing system is not a luxury, nor just a line in electrical drawings. It is mandatory insurance for any facility. As consultants, our responsibility is not only to design systems that function, but systems that protect. Negligence in this area can escalate into criminal liability if it results in harm to lives.
My recommendations to every engineer, contractor, and facility owner :
• Do not begin foundation casting without ensuring reinforcement steel is connected to the earthing network.
• Use exothermic welding or reliable mechanical clamps for underground connections.
• Test and measure the system after installation, and repeat testing annually (periodic measurement).
• Ensure the presence of a Main Equipotential Bonding conductor connecting all metallic systems to the main earthing panel.
Always remember:
Electric current always seeks the shortest path to earth. Either we provide that path through a buried copper conductor—or it will find it through our bodies or our equipment, God forbid.