An Earthing System (or Grounding System) is essential for electrical safety in industrial, commercial, and residential installations. It protects people and equipment from electric shock, prevents damage due to voltage surges, and ensures the proper operation of electrical systems.
The IEC 60364 standard classifies earthing systems based on how the neutral and exposed conductive parts of an installation are connected to the ground. The three main types of earthing systems are TN, TT, and IT.
1. TN System (Terra-Neutral)
In a TN system, the neutral of the power supply is directly grounded(Terra means Earth in Latin) at the transformer, and the exposed conductive parts of the installation are connected to this neutral point. There are three variations:
a) TN-C (Combined) System
- The Neutral (N) and Protective Earth (PE) conductors are combined into a single conductor called PEN (Protective Earth Neutral).
- Advantage: Simple and cost-effective for low-voltage distribution.
- Disadvantage: A broken PEN conductor can cause dangerous voltage levels on equipment.
b) TN-S (Separated) System
- The Neutral (N) and Protective Earth (PE) conductors are separate throughout the system.
- Advantage: Better safety and lower electromagnetic interference.
- Disadvantage: Requires additional wiring, increasing cost.
c) TN-C-S (Combined and Separated) System
- The system starts as TN-C (PEN conductor used) and then separates into TN-S (separate N and PE) inside the installation.
- Advantage: Combines cost-effectiveness and safety.
- Common Use: Residential, commercial, and industrial electrical systems.
2. TT System (Terra-Terra)
- The neutral of the supply is earthed at the transformer, but the customer must install their own local earth connection for exposed conductive parts.
- Advantage: Independent grounding improves protection against electrical faults.
- Disadvantage: Higher earth resistance requires an efficient RCD (Residual Current Device) for fault protection.
- Common Use: Used in rural areas where the supply company does not provide a grounding connection.
3. IT System (Isolated Terra)
- The neutral is either completely isolated from the ground or grounded through a high-impedance resistor.
- Exposed conductive parts are connected to a separate protective earth (PE).
- Advantage: Provides the highest continuity of service because a single fault does not cause an immediate disconnection.
- Disadvantage: Requires insulation monitoring devices to detect faults.
- Common Use: Hospitals, data centers, mines, and critical industrial processes where power continuity is essential.
Which Earthing System Is Best for Industrial Automation?
- TN-S is often preferred in industrial automation due to low interference, stable voltage levels, and better protection for sensitive equipment (PLCs, HMIs, SCADA).
- IT Systems are ideal for mission-critical operations where power interruptions cannot be tolerated (e.g., hospitals, semiconductor manufacturing).
- TT Systems are used where TN earthing is not available, but they require RCDs to ensure safety.
