Measuring insulation resistance not only on PV installations

Jan Pfoff
Jan Pfoff
4. 8. 2025

In this article, we'll take a look at the recently introduced IR5050 and IR5051 pair of handheld insulation testers from Hioki. These are the successors to the previous successful IR3455 model, which has been directly replaced by this new product.

Like their predecessors, the new IR5050 and IR5051 are portable high-voltage insulation resistance testers, supplied in a durable protective case as standard. With a wide range of measured voltages (250 V to 5 kV) and resistances (10 MΩ to 10 TΩ), they offer versatile applications in industrial, energy and infrastructure applications. Both models combine superior performance, compact and rugged design, wireless data transfer capability, and advanced diagnostic functions that greatly expand the capabilities of conventional measurement.

Common features and benefits of both models

  • wide measuring range: up to 5 kV test voltage and 10 TΩ insulation resistance
  • compact and lightweight design for convenient use in the field
  • Durable housing with IP65 protection, suitable for dusty and humid environments
  • CAT III 2000 V safety class - for safe measurements in high voltage systems
  • automatic discharge of residual voltage after measurement for increased safety
  • shielded cables and guard function to minimize noise and ensure stable results
  • Bluetooth connectivity (with optional Z3210 adapter) for direct data transfer to mobile devices and easy documentation

Advanced isolation diagnostics

In addition to the normal insulation resistance measurement, both instruments offer three key diagnostic functions:

  • PI - Polarization Index: evaluates the long-term condition of the insulation based on resistance changes over time (1 min vs. 10 min), particularly sensitive to humidity.
  • DAR - Dielectric Absorption Ratio: quick diagnosis of the insulation within the first 30 to 60 seconds, useful when the current is rapidly settling.
  • DD - Dielectric Discharge: monitors insulation behaviour after power is removed, ideal for assessing multi-layered insulation structures and internal degradation.

IR5051 - extended version for photovoltaic systems

While the IR5050 focuses on general-purpose applications in high-voltage installations, the IR5051 adds a dedicated function for measuring insulation in photovoltaic (PV) systems - even during active operation.

  • Measure up to 2000 V test voltage and up to 100 GΩ resistance in PV mode.
  • Measurement without having to switch off the PV system - ideal for daily operation and large installations.
  • Measurement speed - approximately 4 seconds, which significantly increases efficiency when checking hundreds of points.

These features make the IR5051 an invaluable tool for managing and maintaining PV systems without having to wait for the sunlight intensity to drop or the entire installation to shut down.

Conclusion

The IR5050 and IR5051 are powerful tools for professionals who need to quickly, safely and accurately assess insulation conditions. While the IR5050 provides comprehensive diagnostics for common electrical equipment, the IR5051 adds the added value of a dedicated mode for testing photovoltaic systems - even in operation.

IR5051 = everything the IR5050 offers + PV measurement without interruption of operation.

If you want to increase safety, reduce measurement time and get reliable diagnostics even under field conditions, the IR5050 and IR5051 are the ideal choice.