Effective earthing is essential for the safe operation of every electrical system and the only way to ensure that earthing installations are effective and that they remain so, is to test them rigorously and regularly.
The vast majority of power distribution systems are designed so that, if an insulation failure or similar fault occurs, the resulting fault current is diverted to earth. This prevents exposed conductive parts from rising to a dangerous potential, while allowing the fault current to flow for long enough and at a high enough level for protective devices to operate and isolate the fault.
The fall-of-potential test method is used to measure the ability of an earth ground system or an individual electrode to dissipate energy from a site. The ability to properly measure ground resistance is essential in preventing costly downtime due to service interruptions caused by poor ground. The earth electrode of interest must be disconnected. The tester is then connected to the earth electrode.