Understanding Types of Grounding Systems in Electrical Networks

Understanding Types of Grounding Systems in Electrical Networks

by Ohm Engineering Works | Apr 01, 2025 | Electric Company

In electrical networks, grounding systems play a crucial role in ensuring electrical safety and stability. The grounding method you choose can significantly impact system reliability, protection levels, and compliance with international standards. This article explores the primary grounding systems in electrical networks, their characteristics, applications, and the advantages each system offers. By understanding these systems, facility managers, electrical engineers, and non-technical readers alike can make informed decisions regarding the most suitable grounding system for different applications.

1. Direct Grounding (TN System)

Direct grounding, or the TN (Terre Neutral) system, is a common grounding method used in modern facilities, especially in cities. It offers high levels of safety and quick fault response. The TN system directly connects parts of the electrical network to the ground, without resistors or transformers in the connection. Within the TN system, several sub-types exist, each with unique characteristics based on how the neutral and grounding conductors are configured:

TN-S (Separated Neutral and Earth): In this configuration, the neutral (N) and earth (E) conductors are kept separate throughout the network. This separation minimizes the risk of electrical shock and is commonly used in facilities where high safety levels are required.

TN-C (Combined Neutral and Earth): The TN-C system combines the neutral and grounding lines into a single wire, known as the PEN (Protective Earth Neutral) conductor. This configuration can be cost-effective in public distribution networks but is not recommended for consumer premises due to safety concerns. It is considered the "least safe" grounding system when used within consumer spaces because it does not provide isolation between the earth and neutral conductors, posing risks in case of faults.

TN-C-S (Combination of TN-C and TN-S): The TN-C-S system starts with a combined neutral and ground line (TN-C) and then splits them into separate lines (TN-S) further along the network. This approach allows the benefits of both methods, providing cost savings in public distribution and higher safety in consumer premises.

2. Indirect Grounding (TT System)

The TT (Terre Terre) grounding system is a form of indirect grounding where the grounding line is entirely independent of the electrical supply network. Instead of a centralized earth point, each consumer installation has its own earth electrode, often installed by the user rather than the regulator. This system is commonly used in rural or remote locations where establishing a centralized earthing system is impractical or expensive.

Characteristics and Applications: TT systems are less expensive to install and simpler in design, making them ideal for small homes and buildings where advanced fault protection is unnecessary. However, due to the lack of centralized grounding, TT systems can be less reliable in high-demand environments, as they may not respond as quickly to faults as other systems.

3. Insulated or Resistance Grounding (IT System)

The IT (Isolated Terra) grounding system is often chosen for applications requiring continuous power supply and heightened fault protection. In an IT system, the phase line is either not grounded at all or grounded through a high-resistance component, limiting the current flow to the ground. This grounding system is designed to minimize the risk of faults and is particularly beneficial in facilities that cannot tolerate power outages.

Applications in Critical Environments: For example, medical facilities (IEC 60364-7-710 Group 2 locations) use an IT system—referred to as a “Medical IT system”—to ensure power continuity during the first fault. The IEC 60364-4-41 standard acknowledges “electrical separation” as a protective measure against electric shock, making the IT system the "safest" option for sensitive locations, such as hospitals, industrial sites with critical equipment, and certain data centers. The IT system's ability to sustain power during an initial fault is invaluable for these applications.

4. Resistance Grounding

Resistance grounding involves adding a medium or high resistance between the neutral point of the system and the ground. This method reduces fault currents during ground faults, which helps protect equipment from damage and limits the fault impact on the electrical network.

Industrial Use: Resistance grounding is commonly used in industrial environments where higher fault currents could damage equipment and disrupt operations. By limiting the ground fault current, resistance grounding enables controlled handling of faults, reducing both the damage potential and the need for system shutdowns during minor faults.

Comparing the Grounding Systems

The four grounding systems—TN, TT, IT, and Resistance Grounding—each offer unique characteristics suited to different environments and safety requirements. Here’s a comparative look:

Types of Grounding Systems in Electrical Networks

1. Direct Grounding (TN System)

Connects directly to ground without resistors or transformers.

Sub-types:

TN-S: Neutral (N) and Earth (E) conductors are separate throughout the network.

TN-C: Combines neutral and earth lines into a single wire (PEN conductor); suitable for public distribution but not recommended within consumer premises due to safety concerns.

TN-C-S: Combines TN-C and TN-S methods, where the combined line (TN-C) is split into separate lines (TN-S) further along the network.

2. Indirect Grounding (TT System)

Grounding line is independent of the electrical supply network.

Each installation has its own earth electrode, often installed by the user.

Common in rural/remote areas or small buildings where centralized earthing is difficult to implement.

Simple and cost-effective but may respond slower to faults.

3. Insulated or Resistance Grounding (IT System)

Phase line is either ungrounded or grounded through high resistance to limit current flow.

Ideal for environments needing uninterrupted power supply, like hospitals and industrial facilities with critical equipment.

Medical Applications: IEC 60364-7-710 recommends IT systems for Group 2 medical locations to maintain power continuity during the first fault.

Recognized by IEC 60364-4-41 as providing "fault protection" through electrical separation.

4. Resistance Grounding

Medium to high resistance added between the neutral point and ground.

Reduces fault currents, protecting equipment and limiting fault impact on the network.

Commonly used in industrial settings where ground faults could disrupt operations.

Resistance Grounding: Reduces equipment damage by limiting fault current; useful in industrial environments.

Choosing the Right Grounding System

Selecting the appropriate grounding system requires consideration of several factors:

Building Type and Location: Urban buildings with extensive electrical demands often benefit from TN systems, while rural buildings may find TT systems more suitable.

Device Sensitivity: Facilities with sensitive equipment, such as hospitals or data centers, should consider IT systems for maximum fault tolerance.

Safety and Compliance: Compliance with standards, like IEC 60364-4-41, helps ensure that fault protection measures, such as electrical separation, are effectively in place. Public distribution often relies on TN-C-S systems for efficiency, while more isolated applications may require IT or TT configurations.

Conclusion

Grounding systems are fundamental to electrical network design, and selecting the right type is crucial for ensuring safety, reliability, and regulatory compliance. The TN system is preferred in cities due to its robust protection, while the TT system suits locations where centralized grounding is challenging. IT and Resistance Grounding systems provide specialized protection for sensitive equipment and industrial environments, respectively. In facilities requiring uninterrupted power, such as hospitals, the IT system stands out as the “safest” choice, thanks to its fault tolerance.

By aligning grounding system choice with building type, equipment sensitivity, and safety standards, facilities can ensure secure, reliable, and compliant operations. Each system has its advantages and trade-offs, but understanding their differences equips decision-makers to select the grounding solution best suited to their specific needs.