Materials You'll Need

Multimeter with insulation resistance (IR) testing capability

Steps to Check Insulation Resistance



1. Disconnect the Wires from the Panel

Turn off the main breaker and use a non-contact voltage tester to confirm that the wires are de-energized. Disconnect all wires from the subpanel terminals.

2. Set Up the Multimeter

Set the multimeter to the "Insulation Resistance" or "Megaohm" (MΩ) range. The typical range to use is 500V to 1000V.

3. Test Between Each Pair of Wires

For a single-phase panel, you have two hots, a neutral, and a ground. Test each hot wire against each other, then each hot wire against the neutral and ground, and finally, the neutral against the ground.

4. The Insulation Test

When you touch the probes of the multimeter to each pair of wires, the multimeter will send a high voltage (500V-1000V) through the insulation and measure the resistance. A good insulation should have a resistance of at least several megaohms (MΩ).

Interpretation of Results



High Resistance

500kΩ or higher indicates good insulation.

Low Resistance

Readings below 500kΩ indicate a potential issue with the insulation.

Zero Resistance

A reading of 0 MΩ indicates a short circuit or severe insulation damage.

How the Test Works

The high voltage sent through the insulation causes a small leakage current. The multimeter measures this current and calculates the insulation resistance in megaohms. If there are any cracks, breaks, or other defects in the insulation, the leakage current will increase, resulting in a lower resistance reading.

Note: Do not touch the exposed wires during the test, as the high voltage can be dangerous. If you detect any low resistance readings, further investigation and repairs may be necessary.* Always follow local electrical codes and safety guidelines when performing electrical work. Flag for review