The dominant method used to measure GPR during a Current Injection Test is the ‘Fall of Potential Method’ (FoPM). The recognized literature describing grounding system performance assessment describes various forms of the FoPM, resulting from the increasing interference levels as the system impedance decreases.
This paper investigates the critical features of the various FoPM forms, particularly when subject to the various mutual interference effects the tests are inherently exposed to, allowing their respective range of application to be defined. Each FoPM form is evaluated as a suitable test method for measuring grounds with low impedances, their level of independence from design or correction processes, and appropriateness for assessing a safety critical system.