Circuit Testers - Diagnosing Symptoms

Although these testers are useful, it is important to understand their limitations. Neutral-ground reversals cannot be detected by circuit testers. Signals from the tester are injected into a conductor and the return is measured from the first neutral-to-ground tie. In a single-phase circuit the impedance grounding conductor is measured through the neutral conductor. The neutral and ground bond at the service entrance is assumed to be the tie point. Wiring errors or excessive capacities will alter readings.

No equipment can be plugged into a circuit during testing or the leakage current could cause a false circuit condition to be indicated by the tester.