What is the difference between earth resistance and insulation resistance?
Earth resistance is the resistance current faces from a grounding system into the ground. It gauges the efficiency with which fault current can be ground-dipped. Earth resistance testing mostly serves to make sure that, should a failure arise, harmful voltages do not build up on exposed conductive parts. Usually with a low earth resistance of less than 10 ohms, fast fault current dissipation is guaranteed, therefore reducing the risk of electric shock. Usually infusing current between two sites in the ground and detecting the voltage drop, it is tested using a ground resistance tester.
Conversely, insulation resistance measures the resistance provided by insulating materials (like wire insulation) to stop leakage current. It is tested across insulating paths using a high DC voltage e.g., 200V then measuring leakage following a one-minute polarization time. Usually expressed in megohms, >4 MΩ, higher insulation resistance indicates good quality of insulation, therefore reducing the short circuit or fire danger. An insulated resistance tester (megohmmeter) measures it.
Key Differences:
Insulation resistance should be strong while earth resistance should be low.
Earth resistance pertains to grounding systems, insulation resistance to dielectric quality.
Insulation resistance guarantees current isolation; earth resistance guarantees safe fault current flow.
Every measurement calls for unique testing tools and techniques.
For electrical systems to be safe and compliant, both are very vital.