Best Insulation Resistance Testers

For qualified users who already own a suitable multimeter, the Fluke 1507 is our best dedicated insulation resistance tester: five test voltages, automatic PI/DAR and a compare function. Choose the Fluke 1587 FC for combined multimeter work, or the Megger MIT420/2 for local result recall and a higher resistance ceiling, subject to the documentation caveats below. If the job only requires ordinary resistance or continuity checks, keep your suitable multimeter and skip the specialist purchase.

Quick picks: compare the job, then the instrument

Compare specifications and all conditions

Fluke 1507

Instrument CAT rating

CAT IV 600 V

Best fit

Dedicated testing alongside your DMM

Important limit

Match category and voltage; the lowest-rated lead or accessory limits the assembly.

All specifications

Fixed DC test voltages

50, 100, 250, 500, 1000 V

Advertised insulation range/ceiling

0.01 MΩ–10 GΩ

Timing and records

Automatic PI/DAR; compare/pass-fail

Fluke 1587 FC

Instrument CAT rating

CAT III 1000 V / CAT IV 600 V

Best fit

Insulation testing plus multimeter functions

Important limit

Match category and voltage; the lowest-rated lead or accessory limits the assembly.

All specifications

Fixed DC test voltages

50, 100, 250, 500, 1000 V

Advertised insulation range/ceiling

0.01 MΩ–2 GΩ

Timing and records

PI/DAR; Fluke Connect for graphs/storage

Megger MIT420/2

Instrument CAT rating

CAT IV 600 V

Best fit

Local storage and recall

Important limit

Match category and voltage; the lowest-rated lead or accessory limits the assembly.

All specifications

Fixed DC test voltages

50, 100, 250, 500, 1000 V

Advertised insulation range/ceiling

Up to 200 GΩ

Timing and records

PI/DAR, timed tests, onboard recall; no Bluetooth download

Full comparison table ↔

Swipe to compare. Row labels stay visible.

Pick	Best fit	Fixed DC test voltages	Advertised insulation range/ceiling	Timing and records	Instrument CAT rating
Fluke 1507	Dedicated testing alongside your DMM	50, 100, 250, 500, 1000 V	0.01 MΩ–10 GΩ	Automatic PI/DAR; compare/pass-fail	CAT IV 600 V
Fluke 1587 FC	Insulation testing plus multimeter functions	50, 100, 250, 500, 1000 V	0.01 MΩ–2 GΩ	PI/DAR; Fluke Connect for graphs/storage	CAT III 1000 V / CAT IV 600 V
Megger MIT420/2	Local storage and recall	50, 100, 250, 500, 1000 V	Up to 200 GΩ	PI/DAR, timed tests, onboard recall; no Bluetooth download	CAT IV 600 V

Pick	Best fit	Fixed DC test voltages	Advertised insulation range/ceiling	Timing and records	Instrument CAT rating
Fluke 1507	Dedicated testing alongside your DMM	50, 100, 250, 500, 1000 V	0.01 MΩ–10 GΩ	Automatic PI/DAR; compare/pass-fail	CAT IV 600 V
Fluke 1587 FC	Insulation testing plus multimeter functions	50, 100, 250, 500, 1000 V	0.01 MΩ–2 GΩ	PI/DAR; Fluke Connect for graphs/storage	CAT III 1000 V / CAT IV 600 V
Megger MIT420/2	Local storage and recall	50, 100, 250, 500, 1000 V	Up to 200 GΩ	PI/DAR, timed tests, onboard recall; no Bluetooth download	CAT IV 600 V

Sources: Fluke's 1507 specifications, 1587 FC datasheet and Megger's US datasheet. These are manufacturer specifications. The maximum insulation ranges are not available at every test voltage; CAT ratings here describe the instruments, with probe limits discussed below.

Best dedicated tester: Fluke 1507

Buy the 1507 when the missing tool is an insulation tester and your existing DMM already meets your other needs. Its US package, part 5066006, includes TL224 leads, TP74 probes, alligator clips, a holster and a remote test probe. Fluke positions the remote probe for repetitive or hard-to-reach tests.

The appeal is standalone operation: automatic polarization index (PI) and dielectric absorption ratio (DAR), plus compare/pass-fail for repeated checks. The 1507 manual defines PI as the ten-minute resistance divided by the one-minute resistance, and DAR as the one-minute resistance divided by the thirty-second resistance. Record the timing convention with the result.

The trade-off is limited general measurement capability: AC/DC voltage to 600 V and earth-bond resistance to 20.00 kΩ, rather than the 1587 FC's current, capacitance and temperature functions. The advertised 10 GΩ ceiling applies at 1000 V; the manual gives 50 MΩ at 50 V and 500 MΩ at 500 V. Buy for the range at your required voltage.

Variant trap: the 1503 offers only 500 V and 1000 V insulation settings in the shared manual. It is not the same five-voltage tester.

Check the standard US package with Fluke

Best combined instrument: Fluke 1587 FC

Choose the FLK-1587-FC, part 4691215, if consolidating instruments matters more than the 1507's higher insulation ceiling. Fluke specifies a 6,000-count True RMS multimeter, AC/DC voltage to 1000 V, AC/DC current ranges to 400 mA, capacitance, temperature, frequency, diode test and a VFD low-pass filter. Its lead-current input is not a high-current clamp; consider our clamp-meter guide for that separate purchase.

The insulation ceiling is 2 GΩ at 1000 V; at 500 V it is 500 MΩ, and at 50 V it is 50 MΩ. The manual describes on-meter PI/DAR. The datasheet places graphs, memory storage and temperature compensation in the Fluke Connect Measurements app workflow. Check the app on your intended phone before buying for reporting. Fluke separately identifies Fluke Connect Assets as sold separately.

Case conflict: the US page lists a soft case in its box/model sections, but says hard case in its overview; the datasheet also says hard case. Confirm the supplied case. The manual's unpack list names TL224 leads, TP74 probes, AC285 clips, a holster, thermocouple and remote probe, with a soft case.

Variant trap: the standard instrument is different from the Advanced Electrical Troubleshooting Kit, which adds an i400 clamp and 62 MAX+ infrared thermometer. The 1577 has only 500/1000 V insulation settings; do not transfer the FC's features to it.

Check the standard US package with Fluke

Best for local result recall: Megger MIT420/2

Choose MIT420/2, US order code 1004-739, when onboard storage and recall fit your maintenance records. Megger's US datasheet documents that order code and includes 1002-001 red/black silicone leads with probes and clips, an SP5 remote switch probe, six AA alkaline batteries, a carry case and calibration certificate. This establishes the US ordering package; it does not establish a particular seller's stock.

Its resistance ceilings are 10 GΩ at 50 V, 100 GΩ at 500 V and 200 GΩ at 1000 V. The insulation-accuracy specification includes a resistance-dependent term, so the largest displayable value is not a promise of equal precision across the range. PI/DAR and timed tests are documented; Bluetooth downloading belongs to MIT430/2, whereas the 420/2 provides local storage/recall.

Resolve the revision before ordering for variable voltage. The US datasheet describes 10–1000 V in 1 V steps. The linked user guide lists 50–1000 V in its setup table and 1 V increments to 100 V, then 10 V increments in its variable-voltage section. Confirm the delivered instrument's lower limit and steps with Megger. Those documents also print PI/DAR ratios in opposite orders; resolve the reporting convention before comparing historical ratios.

This is our conditional specialist pick for its local memory and range. If the unresolved voltage revision is central to your job, defer purchase until Megger confirms it.

Check the US configuration with Megger

How we choose

We compare official specifications, model-specific manual tables, documented accessories and US ordering information. Recommendations reflect those documents, without physical product testing or claims of verified accuracy. We separate shared-family features from the selected model and flag conflicting descriptions. ASINs await owner verification, so purchase routes here lead to the manufacturers. See how we choose and how we measure.

Buying guide: insulation tester vs multimeter

An insulation tester applies a specified DC test voltage to evaluate insulation; an ordinary resistance check answers a different question. Fluke's selection guide explains why the test voltage, charging/absorption currents and test duration matter. A continuity result alone cannot substitute for a required insulation test.

• Yes: Choose an insulation tester when the equipment procedure specifies a DC insulation-test voltage.
• Partly: Choose a combined insulation multimeter when its additional functions replace tools you need to carry.
• No: Skip the specialist purchase when ordinary resistance or continuity is the entire job.

For ordinary electrical troubleshooting, use our multimeter shortlist; start with the multimeter beginner guide if you are still choosing functions. A professional multimeter label is less useful than the exact function and ratings your job requires.

Match voltage, range and timing together

Fluke says to base the output test voltage on the equipment manufacturer's recommended DC insulation-test voltage. Do not use a higher setting as an automatic upgrade. If your procedure requires an output beyond 1000 V, this shortlist does not cover it.

Next check resistance range at that voltage, the applicable accuracy conditions, and the required timing mode. A large maximum range cannot replace the right voltage. For trending, use the same documented test conditions and timing convention; Fluke explains that capacitive charging and absorption currents settle differently over time. Use the equipment's acceptance procedure, rather than treating a tester's configurable pass/fail setting as a universal insulation standard.

Compare discharge provisions and indications

Both Flukes specify automatic discharge in less than 0.5 second for 1 µF or less, with a 1 µF maximum operable capacitive load and test inhibition when terminal voltage is greater than 30 V before starting. Those are bounded specifications, not promises for every cable or connected load. Megger documents automatic discharge and a configurable live-circuit inhibit, default 50 V; the cited manual does not provide the same numeric discharge-time specification.

Buy the complete, correctly rated kit

The two Fluke unpack lists name TL224 leads and TP74 probes. Fluke rates the TL224 CAT III 1000 V / CAT IV 600 V, but its TP74 page states CAT II 1000 V, with CAT III 1000 V only with the protective cap. Do not assume the instrument's CAT IV rating applies through every supplied probe configuration. Check the markings and caps on the actual leads, remote probe and clips.

For Megger, match the listed lead set and SP5 to the exact kit; the instrument's CAT rating alone does not verify each accessory's rating. Its manual calls for Megger-approved leads. Confirm the calibration paperwork your employer requires rather than treating a bundle name as proof of its scope.

1. 1

   Write down the requirement

   Equipment-specified test voltage, resistance range and timing mode come first.

2. 2

   Choose the record workflow

   Compare standalone timed results, local recall and the Fluke Connect app workflow.

3. 3

   Confirm the supplied kit

   Match the model and order code, probe markings, protective caps, case and calibration paperwork.

Verdict

Choose Fluke 1507 to add dedicated insulation testing to an existing DMM kit, 1587 FC to combine functions with Fluke Connect reporting, or MIT420/2 for local recall and a higher resistance ceiling after resolving its documentation conflicts. Buy the required voltage, usable range and complete probe configuration together. If ordinary resistance is all you need, keep the suitable meter you already own.