Electrical Testing Tool

Insulation Resistance Test Calculator

Calculate the recommended megger test voltage and minimum acceptable insulation resistance for motors, cables, and transformers based on IEEE 43 and IEC 60034 standards.

Equipment Parameters

Line-to-line rated voltage of the equipment

Used to compute IEEE 43 minimum insulation resistance

IEEE 43 values are referenced to 40 °C

Test Results

Recommended Megger Voltage
— V DC
Standard Basis
—
Min. Acceptable Insulation Resistance
— MΩ
IEEE 43: R_min = (V + 1000) / √(kW × 100)
Safety: Always discharge equipment before and after testing. De-energize and isolate before connecting the megohmmeter.

Quick Reference — Megger Voltage vs Rated Voltage

Rated Voltage IEC 60034-18-51 IEEE 43 Typical Megger
≤ 100 V100 V DC—100 V
100 – 500 V250 – 500 V DC2 × Vrated500 V
500 – 3300 V500 – 1000 V DC2 × Vrated1000 V
3.3 – 6.6 kV1000 V DCVrated + 10002500 V
6.6 – 15 kV2500 V DCVrated + 10005000 V
> 15 kV5000 V DCVrated + 1000 (≤ 10 kV)10 kV

Frequently Asked Questions

How do I calculate megger test voltage for motors?

Per IEEE 43, the recommended DC test voltage is 2× rated voltage for machines rated 1000 V or less, and rated voltage + 1000 V for machines above 1000 V, with a minimum of 500 V DC and a maximum of 10,000 V DC.

What is the minimum acceptable insulation resistance for a motor?

IEEE 43 defines the minimum insulation resistance at 40°C as R_min = (V_rated + 1000) / √(kW × 100) megohms, with a recommended floor of 5 megohms for most industrial equipment.

What megger test voltage should be used for low voltage cables?

For cables rated up to 1000 V, a 1000 V DC megger is standard. For cables rated above 1000 V, a 2500 V or 5000 V DC megger is typically used depending on cable class and IEC 60502 requirements.