In a TT system, which of the following best describes an earth electrode and its test?

• A. A metal rod connected to the building's neutral, tested with a megger
• B. An electrode connected to earth; test with an earth tester to measure earth resistance, ensuring it is low enough to provide proper protection
• C. A device that measures fault current and triggers protection
• D. A protective device that isolates the supply in a fault

Answer: (B)

In TT systems, the protective earth path comes from an earth electrode installed at the premises, not from the neutral at the building. The important point is that the resistance of that electrode to earth directly affects how quickly a fault current can return to the source and cause the protective device to operate.

The best description is that the earth electrode is connected to earth and tested with an earth resistance tester to measure its resistance, ensuring it is low enough to provide proper protection. This testing approach checks whether the path to earth is impedance-wise adequate to allow enough fault current to flow so devices like RCDs or fuses trip promptly if a fault occurs.

A megger tests insulation resistance, which is useful for other types of insulation checks, but it’s not the standard method for evaluating the earth path in a TT system. The other options describe fault-current monitoring or isolating devices, not the earth electrode and its test.