Insulation Resistance Tests

Short answer: Insulation resistance testing measures the integrity of cable and device insulation in megohms (MΩ) by applying a high DC voltage. Low insulation resistance indicates insulation degradation due to moisture, aging, or damage, raising a risk of leakage/short circuits.

The safety of electrical installations largely depends on the integrity of the insulation. Over time, moisture, heat, vibration, and aging degrade the insulation; this deterioration progresses without showing any visible signs.

Low insulation resistance is a harbinger of leakage current, short circuits, equipment failure, and fire. Periodic insulation measurement is one of the most effective preventive tests that catches this deterioration before a failure or fire occurs.

What is done during an isolation test?

• Phase-to-phase, phase-to-neutral, and phase-to-ground insulation measurement.
• Selecting the appropriate test voltage for the circuit voltage (e.g., 500/1000 V DC)
• Comparison of results with minimum limit values.
• Assessment of cable, motor winding, and panel insulation condition.
• Protecting sensitive electronic components from measurement.

Test Voltage and the Meaning of Results

Insulation resistance is measured under a high DC voltage applied to the insulator; the applied voltage is selected according to the operating voltage of the circuit (e.g., typically 500 V or 1000 V DC in low-voltage circuits). The higher the measured resistance, the more robust the insulation. A value below the minimum specified in the standard indicates that the insulation has absorbed moisture or deteriorated, and the cause should be investigated. In motors, monitoring the trend over time (trend analysis) is far more valuable than a single measurement; a downward trend offers an opportunity for maintenance before failure develops.

Legal Basis and Accurate Assessment

Insulation resistance measurement is one of the fundamental tests for periodic inspections of electrical installations and equipment; the results are documented with a TÜRKAK accredited report.

Frequently Asked Questions

What should the insulation resistance be in MΩ?

The circuit voltage must be above the minimum value specified according to the standard; lower values should be investigated.

What should be considered before measurement?

The circuit must be de-energized, and sensitive electronic components must be disconnected from or protected during measurement.

Why does value decrease over time?

Moisture, heat, contamination, and aging degrade insulation; regular measurements capture this trend.

Ensure your safety with accredited measurement.

For accredited measurement and control. Grounding Systems Please review our page for the legal framework. mandatory periodic inspection Check our guide.