What is the difference between the volt-ohm-meter and the ground impedance meter?

What is the difference between the volt-ohm-meter and the ground impedance meter?

• A. Both indicate resistance, but impedance devices provide for both high and low current ground faults, whereas the standard volt-ohm meter would only tell us about protection from low current faults.
• B. They measure different quantities
• C. The volt-ohm-meter measures impedance while the ground impedance meter measures insulation resistance
• D. They are interchangeable, with no difference

Answer: (A)

Testing these instruments centers on the difference between simple resistance checks and evaluating a grounding system’s behavior under fault conditions. A volt-ohm-meter is a general-purpose tool for measuring voltage and resistance, typically used to check continuity or insulation with low test currents. It gives you resistive readings for circuits at a small current level, but it doesn’t simulate fault currents or tell you how the grounding path will perform when a fault occurs. A ground impedance meter, on the other hand, is designed to assess the earth grounding system by injecting a test current and measuring the resulting impedance of the grounding path. This matters because protective devices must respond to fault currents, and that response depends on the impedance the fault current encounters—not just a simple resistance at a low current. So, while both are related to resistance, the ground impedance meter provides information about how the grounding path behaves under fault conditions (high and low current), whereas the volt-ohm-meter does not. The other options misstate what each instrument measures or incorrectly imply they’re interchangeable.

Testing these instruments centers on the difference between simple resistance checks and evaluating a grounding system’s behavior under fault conditions. A volt-ohm-meter is a general-purpose tool for measuring voltage and resistance, typically used to check continuity or insulation with low test currents. It gives you resistive readings for circuits at a small current level, but it doesn’t simulate fault currents or tell you how the grounding path will perform when a fault occurs. A ground impedance meter, on the other hand, is designed to assess the earth grounding system by injecting a test current and measuring the resulting impedance of the grounding path. This matters because protective devices must respond to fault currents, and that response depends on the impedance the fault current encounters—not just a simple resistance at a low current. So, while both are related to resistance, the ground impedance meter provides information about how the grounding path behaves under fault conditions (high and low current), whereas the volt-ohm-meter does not. The other options misstate what each instrument measures or incorrectly imply they’re interchangeable.