Electrical Earthing

Understanding Electrical Grounding (Earthing) Systems

Grounding or Earthing is the process of connecting metallic parts of an electrical system to the ground. This connection ensures the safe dissipation of fault currents into the earth, providing a pathway for electricity that prevents electrical shocks and equipment damage in case of electrical faults.

A well-designed grounding system follows local electrical codes and international standards like IEE. It is a crucial part of electrical installations, contributing to safety, protection, and operational stability.

Why Grounding is Essential

1. Safety: Protects individuals from electric shock hazards caused by leakage currents.
2. Protection System: Enhances system reliability and prevents equipment damage.
3. Over-Voltage Limitation: Regulates voltage surges, maintaining equipment safety.
4. Discharge Path: Provides a controlled path for fault currents to flow into the ground.
5. Compliance: Adheres to legal and regulatory requirements for electrical installations.

Components of Grounding Systems

Grounding systems are generally divided into two main types:

1. Grounding System (System Earthing):
   • Isolates faults within the system.
   • Limits potential differences between conductors.
   • Reduces over-voltage under fault conditions.
2. Grounding Equipment (Protective Earthing):
   • Protects users from electric shock by providing a safe path for fault currents.
   • Directs electricity to the earth instead of through the human body, which has higher resistance.

Key Grounding Accessories

1. Earth Electrode

• Typically made of copper-coated steel rods.
• Provides a low-impedance path for fault currents to flow into the ground.

2. Equipotential Bonding

• Ensures all metallic parts are at the same electrical potential.
• Minimum cable size: 10 mm².

3. Protective Conductor

• Connects the earth to various parts of the electrical installation.
• Cable size requirements:
  • Same size as phase cable for cables up to 16 mm².
  • 16 mm² for phase cables between 16 mm² and 35 mm².
  • Half the size of the phase cable for cables above 35 mm².

Standard Color Coding for Earthing Cables

• Green
• Green/Yellow

Areas Requiring Grounding

1. All metallic structures in the wiring system (e.g., conduits, trunking, and shielding).
2. The secondary winding of transformers.
3. Metal roof frames.

Areas Not Requiring Grounding

1. Isolated short metal parts used for mechanical protection of cables.
2. Lamp covers made of metal that are isolated.
3. Chains for hanging light fixtures.

Earthing or Grounding Resistance Standards

• RCD (100 mA): ≤ 10 ohms
• Lightning Arresters: ≤ 10 ohms
• Substation Earthing: 0–3 ohms
• Consumer Installations: ≤ 500 ohms

Termination in Earth Chambers

Proper termination in earth chambers ensures system reliability. Connections must be solid and corrosion-resistant to maintain long-term efficiency.

Conclusion

A robust grounding system is vital for safe and efficient electrical installations. Adhering to regulations, using proper components, and maintaining low resistance levels ensure safety for both people and equipment. Always consult professional guidelines and local standards for optimal installation.