Skip to main content

DC insulation testing

Accuracy, Reliability, and Efficiency in DC Insulation Testing

Megger’s S1 and MIT insulation testers deliver unmatched accuracy and reliability across a range of applications, from utility substations to industrial maintenance and OEM quality control. Designed for demanding environments, these testers offer advanced insulation diagnostics with superior noise immunity, enhanced guard terminal performance, and efficient data management through CertSuite Asset. For OEMs, simplified pass/fail options and seamless result reporting via PowerDB Lite streamline production testing, ensuring consistent quality. Industrial maintenance teams benefit from rugged, versatile designs that enhance safety and efficiency, helping to prevent asset failures and keep operations running smoothly.

Frequently asked questions

Instruments in the Essential category are:

  • MIT515
  • MIT1015

Instruments in the Advanced category are:

  • MIT525
  • MIT1025
  • MIT1525

Instruments in the Expert category are:

  • S1-568
  • S1-1068
  • S1-1568

Megger’s Essential, Advanced, and Expert insulation testers are designed to meet different user needs, from basic go/no-go testing to advanced diagnostics in extreme environments. The key differences between these categories are:

Range of tests:

  • Essential: Insulation resistance, DAR, PI (with PI predictor).
  • Advanced & Expert: Adds DD, SV, ramp voltage, PDC (with PowerDB/CertSuite Asset).

Burn mode current:

  • Essential & Advanced: 3 mA
  • Expert: 6 mA

Test/charge current:

  • Essential & Advanced: 3 mA
  • Expert: 6 mA

Noise immunity:

  • Essential, 5 kV & 10 kV Advanced: 3 mA (up to 45 kV)
  • 15 kV Advanced: 6 mA (up to 230 kV)
  • Expert: 8 mA (up to 1,000 kV, with advanced filtering)

Data storage:

  • Essential: No on-board storage
  • Advanced & Expert: Extensive storage for results

Communication:

  • Essential: No communication features
  • Advanced: USB transfer & live graphing
  • Expert: USB + Bluetooth® for wireless data download

Remote control:

  • Only available on Expert models via USB

PI Predictor is a time-saving feature that estimates the Polarization Index (PI) of an insulation resistance test without requiring the full 10-minute test duration. Instead of waiting for the standard 10-minute insulation resistance measurement, PI Predictor uses the early part of the IR test curve to extrapolate the expected 10-minute result. This allows testers to obtain a reliable PI ratio in as little as 3 to 7 minutes, significantly reducing testing time.
Key Benefits:

  • Faster Testing: Saves time by predicting PI results instead of requiring a full 10-minute test.
  • Efficiency Gains: Particularly beneficial for high-volume testing, reducing hours of maintenance work annually.
  • Smart Automation: The test stops automatically when a confident prediction is reached or if an issue (e.g., noise interference) is detected.

This feature helps industrial maintenance teams, utilities, and OEMs streamline insulation testing while maintaining accuracy and reliability.

A Guard Terminal is a dedicated connection on high-voltage insulation testers that helps eliminate surface leakage current from insulation resistance measurements. This ensures that test results reflect only the true insulation condition, without interference from contaminants like dirt or moisture on the surface.
During an insulation test, leakage current flows both through the insulation and over its surface. The Guard Terminal diverts surface leakage current away from the measurement circuit, preventing it from distorting the insulation resistance reading. This is particularly useful when testing high-voltage components like cables, transformers, bushings, and circuit breakers, where large surface areas can introduce significant leakage errors.
Megger ensures that its insulation testers provide accurate, repeatable measurements by specifying that their Guard Terminals achieve only a 2% error when guarding leakage currents up to 200 times the load current. This high level of precision helps engineers track insulation degradation more reliably, leading to better predictive maintenance.

Key Benefits of Using the Guard Terminal:

  1. More Accurate Insulation Testing – Removes errors caused by surface contamination, ensuring reliable insulation resistance measurements.
  2. Prevents Unnecessary Component Replacement – Helps distinguish between actual insulation breakdown and simple surface contamination, preventing costly and unnecessary equipment replacements.
  3. Essential for High-Voltage Testing – Particularly useful for transformers, cables, and outdoor circuit breaker bushings, where leakage currents can be significant.
  4. Improves Predictive Maintenance – Allows engineers to compare tests with and without the Guard Terminal to quickly diagnose insulation conditions, leading to better asset management and fewer unexpected failures.

By incorporating a Guard Terminal, Megger insulation testers provide more precise diagnostics, reduced maintenance costs, and improved asset reliability in high-voltage applications.

Additional resources

Take a deeper dive into DC insulation testing solutions through our comprehensive guides.