Quick recommendations
There is no single best insulation resistance tester for every job. The right choice depends on the test voltages required by the equipment and procedure, the maximum resistance you need to measure, and whether you need timed tests, stored results or ordinary multimeter functions.
| Model | Best suited to | Test voltages | Manufacturer-stated range |
|---|---|---|---|
| Klein Tools ET600 | General electrical work and a clear four-voltage entry point | 125, 250, 500 and 1000 V | Up to 4000 MΩ |
| Fluke 1503 | Routine 500/1000 V testing by residential and commercial electricians | 500 and 1000 V | 0.01 MΩ to 2000 MΩ |
| Fluke 1507 | More advanced commissioning and maintenance | 50, 100, 250, 500 and 1000 V | 0.01 MΩ to 10 GΩ |
| Megger MIT420/2 | Users who need PI, DAR, variable voltage and result storage | 50, 100, 250, 500 and 1000 V, plus variable voltage | Check the current regional data sheet |
| Fluke 1587 FC | Technicians wanting an insulation tester and true-RMS multimeter in one | 50, 100, 250, 500 and 1000 V | 0.01 MΩ to 2 GΩ |
Our practical starting point: the Klein ET600 covers four common voltages and may suit straightforward work. The Fluke 1507 is the stronger dedicated all-rounder where 50 V and 100 V tests, PI/DAR and repeatable pass/fail work matter. The 1587 FC makes most sense when its full multimeter functions will genuinely replace a second instrument.
What an insulation resistance tester does
An insulation resistance tester—often called a megohmmeter or “megger”—applies a defined DC test voltage and measures the resistance of insulation around conductors, windings and other electrical parts. It is used in troubleshooting, commissioning and preventive maintenance.
This is not the same as the low-voltage resistance function on an ordinary multimeter. Insulation testing can apply hundreds or thousands of volts. The equipment must be isolated and the test procedure must account for stored charge, connected electronics and the manufacturer’s limits.
Safety note: insulation testing is not a casual live-circuit DIY task. Use the instrument only within its manual, measurement category and your competence. Isolate the circuit, verify it is de-energised with an appropriate method, disconnect sensitive equipment where required, and allow the tester’s discharge process to complete.
Best straightforward choice: Klein Tools ET600
Klein’s ET600 provides 125 V, 250 V, 500 V and 1000 V insulation test settings and measures up to 4000 MΩ. The four-voltage selection is useful because low-voltage control or electronic equipment may require a lower test voltage than ordinary power wiring.
Its appeal is clarity rather than advanced data management. It is a sensible candidate for users who need a dedicated tester with the common voltage steps but do not need stored results or remote reporting.
Check before buying: confirm that 4000 MΩ is sufficient for your procedure and that the included leads and safety category match the environment in which it will be used.
Best for routine 500/1000 V work: Fluke 1503
The Fluke 1503 is the simpler member of Fluke’s compact insulation-tester range. It provides 500 V and 1000 V tests, a 0.01 MΩ to 2000 MΩ range, live-circuit detection that inhibits a test above 30 V, and automatic discharge of capacitive voltage.
It also provides a 200 mA earth-bond continuity function, measures AC/DC voltage to 600 V and is rated CAT IV 600 V. That makes it a focused option for common residential and commercial tests where lower 50 V, 100 V and 250 V settings are not required.
Choose the 1507 instead if the extra voltage settings, higher resistance range, PI/DAR calculation or compare function are part of the work.
Best dedicated all-rounder: Fluke 1507
The Fluke 1507 expands the available test voltages to 50, 100, 250, 500 and 1000 V and measures insulation resistance from 0.01 MΩ to 10 GΩ. It automatically calculates polarization index (PI) and dielectric absorption ratio (DAR), and its compare function can simplify repetitive pass/fail checks.
Fluke also specifies live-circuit detection above 30 V, automatic capacitive discharge, a remote test probe, 200 mA earth-bond continuity and CAT IV 600 V protection. These features make it a better fit for contractors and maintenance teams performing varied or repeated work.
The trade-off is cost. If your documented procedure only ever calls for 500 V or 1000 V and basic resistance results, the 1503 may provide the functions you will actually use.
Best for stored results and configurable tests: Megger MIT420/2
Megger’s MIT420/2 combines 50, 100, 250, 500 and 1000 V settings with variable test voltage, PI and DAR, and result storage. Those capabilities are valuable when readings must be recorded consistently and compared over time rather than treated as a one-off pass or fail.
Availability, included accessories and exact specifications can vary by region, so use the current Megger product page and regional data sheet when choosing the kit. For formal maintenance programmes, also check the organisation’s calibration and record-retention requirements before purchase.
Best two-in-one option: Fluke 1587 FC
The Fluke 1587 FC combines an insulation tester with a full-featured true-RMS digital multimeter. It is intended for troubleshooting and preventive maintenance where the same technician needs insulation resistance plus voltage, current, frequency, capacitance and temperature measurements.
The two-in-one format can reduce the number of instruments carried. It is not automatically better value: a dedicated insulation tester can be clearer to issue, calibrate and control, and a failed combination instrument removes two capabilities at once.
How to choose
- Start with the required test voltage. Choose it from the applicable standard, equipment instructions or approved procedure—not from the tester’s maximum.
- Check the resistance range and accuracy. A larger headline maximum is useful only if the procedure needs it and the accuracy remains suitable.
- Match the safety category. CAT ratings describe transient environments, not general quality. The rating applies to the complete measuring setup, including leads and accessories.
- Look for live-circuit inhibit and automatic discharge. These are important safeguards, but they do not replace isolation and safe working practice.
- Decide whether PI, DAR and timed testing matter. They are useful for trending some motors, cables and larger insulation systems; they may be unnecessary for basic checks.
- Plan calibration and records. Professional and regulated work may require traceable calibration, result storage and a documented test method.
Final recommendation
For a clear, dedicated tester covering four common voltages, start with the Klein ET600. For professional users who need broader test voltages and automatic PI/DAR calculations, the Fluke 1507 is the stronger all-round choice. Choose the MIT420/2 where stored results and configurable testing justify the additional complexity, or the Fluke 1587 FC when a combined insulation tester and multimeter fits the workflow.
How this guide was prepared
This is a specification-led buying guide, not a hands-on laboratory comparison. Product functions were rechecked against current manufacturer pages on 2 September 2026. Prices and packages can change, so verify the current model, manual and included accessories before purchase.
