Types of Earthing Systems Used for Electrical Installations

September 27, 2018

In a recent post, Earthing System Designs and Installation services were explained. An earth connection is essential. It connects to bonded exposed metal parts, acts as a low-impedance pathway for fault currents, and generally protects lives and property. Briefly, the different types of earthing systems were mentioned. Used in all electrical installations, those grounding systems take different shapes and forms. Today, then, we're describing their layouts in more detail.

Defining the Tricky Acronymns

In truth, these are individual letters, which combine to describe the different earthing systems. Follow along as we add technical labels to each of the key alphabetical characters listed here:

T - The transformer windings are arranged in a star pattern, and they have a physical connection to the ground.

N - A ground conductor, possibly insulated in green or supplied as the armoured cable sheathing. It's routed directly from the transformer ground connection to the consumer power supply.

S - In this situation, the ground and neutral wires are combined. They're one and the same wire, so fewer conductors are required in the underground cabling.

C - The opposite of S denotated systems, the ground and neutral wires travel as two distinctly different conductors. However, there are variations in this layout, including a C and S system that takes a ground tapping off the neutral conductor at the cable entrance point.

The 5 Earthing System Configurations

Think of the TN earthing arrangement as the core life protection system. The star-shaped transformer windings have a centre point, and that centre is directly connected to the ground. Coming off that ground, a neutral conductor travels alongside the electrically live wires. That system evolves into TN-C, a configuration that combines the protective ground and neutral wire into what's known as the PEN (Protective Earthed Neutral). Moving away from that combined grounding solution, we arrive at TN-S, which separates the earth wire and neutral wire at the transformer. TN-C-S, as one could guess, again combines the two wires (Neutral and Ground), but they separate down-line.

Finally, isolated grounding systems, such as TT networks, use the bulk of the ground beneath our feet instead of an actual ground wire. In this scenario, earthing electrodes are installed on-site. For IT systems, well, this substation-oriented option either doesn't employ a source earth or it incorporates a special high impedance connection.

It's up to the system designer to look at the load factors and power distribution layouts. This expert considers occupant safety first, then adds fire and property protection. Enhancing each network design, the distribution boards fit Residual Current Devices (RCDs), overcurrent protection devices, and more. Finally, each of these systems can be further split down, perhaps by installing a local earthing rod.

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