Earth Resistance Measurement Guide | Duncan Instruments – Duncan Instruments Canada Ltd

Earth resistance measurement

How to Measure Earth Resistance – Methods, Tips & Best Tools

Good grounding isn’t just a best practice—it’s required for electrical safety, performance, and code compliance. Whether you’re designing a new installation, testing an existing ground system, or troubleshooting voltage fluctuations, understanding earth resistance measurement is essential.

In this guide, we’ll explain how it works, which methods are used, and what tools professionals rely on in the field.


What Is Earth Resistance?

Earth resistance (also called ground resistance) is the measure of how easily electric current can flow from a grounding electrode into the surrounding soil. A low-resistance ground is critical for:

  • Dissipating lightning strikes
  • Stabilizing voltage in power systems
  • Protecting people and equipment from faults

The resistance is typically measured in ohms (Ω) using specialized test instruments.


Common Measurement Methods

2-Point (Simple Resistance Test)

Used in basic continuity checks or validating a single grounding rod.

3-Point Fall-of-Potential Method

The most common standard method (per IEEE/IEC). It uses:

  • 1 current probe
  • 1 voltage probe
  • The system under test

This method plots resistance versus distance and provides a highly accurate reading.

4-Point Soil Resistivity (Wenner Method)

Used in site surveys to determine soil conditions before installation. It’s key for:

  • Substations
  • Solar arrays
  • Telecom towers

Clamp-On Method

Non-invasive, fast, and convenient. Ideal for bonded systems with multiple ground paths. It eliminates the need to disconnect rods or install temporary probes.


Recommended Tools

We carry a full lineup of ground resistance testers from trusted brands:

  • 🟢 AEMC (6416, 4620, 4630)
  • 🔵 METREL
  • 🟡 KYORITSU
  • 🟠 REED Instruments

These include:

  • Digital clamp meters for fast testing
  • Portable stake kits for 3- and 4-point methods
  • Combination models with leakage current and voltage measurement

🔗 Browse Ground Resistance Testers →


Tips for Better Accuracy

  • Use adequate spacing between electrodes (typically 5m–50m)
  • Avoid testing during very dry or frozen soil conditions
  • Remove or isolate parallel grounding paths unless using a clamp-on method
  • Repeat measurements with different spacing to confirm consistency

When in Doubt, Ask

Not sure which tester fits your application? We’ve been helping Canadian engineers, contractors, and technicians since 1968.

📞 Call us at 416-742-4448
📩 Request a quote


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