Which earthing arrangement uses a local earth electrode?

• A. TT uses a local earth electrode.
• B. TN-S uses a local earth electrode.
• C. TN-C-S uses a local earth electrode.
• D. IT uses a local earth electrode.

Answer: (A)

In this earthing arrangement, the protective earth path relies on a local earth electrode installed at the installation. In TT systems, the neutral and the earth are earthed at the supply source, but the building’s exposed-conductive parts are connected to their own dedicated earth electrode. That means if a fault occurs, the current returns through the soil to the utility’s earth, rather than through a metallic earth conductor connected to the source. Because the fault current through soil is typically limited, protective devices often depend on residual current devices (RCDs) to trip quickly when a fault to earth occurs.

This is different from other arrangements, where the earth path is tied to the supply’s earth or a common PEN/neutral earth back at the source, so a local earth electrode isn’t used for the protective path in the installation. In those systems, the protective earth is provided by conductors that form part of the installation’s earthing network, rather than a separate local electrode.