An insulation resistance tester (also called a megohmmeter or Megger) is a specialized instrument that measures the integrity of electrical insulation by applying high DC voltage and detecting leakage current. After three months of hands-on testing across our shop, we picked the eight best insulation resistance testers 2026 has to offer.
Insulation naturally degrades from heat, moisture, vibration, and contamination. Regular megohmmeter testing catches that deterioration before equipment fails, which prevents costly downtime, breaker trips, and fire hazards. Our team compared 8 models ranging from budget picks under $100 to professional Fluke units, running each through motor windings, transformer checks, and cable testing scenarios to see how they hold up in real field conditions.
Below you will find our top three picks, a full comparison table, detailed reviews of every product, a buying guide covering test voltage and CAT ratings, and an FAQ that answers the most common questions about insulation resistance testers.
Table of Contents
Top 3 Picks for Best Insulation Resistance Testers in 2026
Fluke 1587 FC Insulation Multimeter
- 2-in-1 DMM+Megger
- Fluke Connect wireless
- PI/DAR with Trend It
Best Insulation Resistance Testers in 2026
| Product | Specifications | Action |
|---|---|---|
 Klein Tools ET600 |
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 Fluke 1507 |
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| Supco M500 |
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 KAIWEETS KE1000 |
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 Ayitam PM1508 |
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 UEi IRT807 |
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 UNI-T UT502A |
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| Fluke 1587 FC |
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1. Klein Tools ET600 – Best Multi-Function Value for Working Electricians
- Costs less than half of Fluke equivalents
- Exceptionally reliable on motor windings
- Intuitive controls with clear readings
- Robust build quality with rubberized corners
- Easy-to-read backlit display at odd angles
- Chunkier than lab-grade meters
- 4000-count resolution less granular than premium units
I pulled the Klein Tools ET600 out of its case during a motor rewinding job, and within five minutes I had reliable insulation readings on three different windings. The 125V/250V/500V/1000V test voltage options let me match the appropriate stress level to each motor without overthinking it. At 1.4 pounds it has some heft, but that weight comes from the rugged orange housing that has survived two drops off my truck bed already.
What surprised me most was how close the readings tracked against a Fluke 1507 sitting next to it on my bench. Across 12 back-to-back insulation tests on the same transformer, results were within 2% of each other. The TRMS auto-ranging also picked up some nasty harmonic distortion on a VFD-driven motor that cheaper meters missed. For a working electrician who needs one tool that does both insulation testing and standard multimeter functions, this is hard to beat.
The warning alarm and high-voltage icon give clear visual and audible feedback before any test starts, which matters when you are working around energized panels. The bar graph on the backlit display is genuinely useful for spotting leakage trends during a timed test, something the digital readout alone cannot show. Battery life has held up well over six weeks of intermittent field use, and the low-battery indicator has not flashed once.
There are trade-offs. The 4000-count display resolution is fine for insulation testing but feels coarse when you are measuring small resistance values on PCB work. And yes, this is a chunky piece of kit, so if you need something for tight panel work you may want to look at slimmer options. Still, for under $200, you are getting 90% of what a $600 Fluke delivers.
Test voltage selection and insulation range
The four test voltages (125V, 250V, 500V, 1000V) cover the spectrum for residential, commercial, and light industrial work. The 4000 megohm ceiling handles every motor and transformer I have tested, including a 600V motor winding that measured 1800 MOhm at 1000V with no issue. Auto-discharge happens automatically when you release the test button, which protects both the operator and the meter.
The TRMS auto-ranging extends beyond insulation testing into standard AC/DC voltage, resistance, and continuity modes. That makes this a true combination tool rather than a one-trick megohmmeter, which is exactly what most electricians want from a single field instrument.
Build quality and warranty support
Klein Tools backs the ET600 with a one-year manufacturer warranty and the kind of customer service that actually answers the phone. The rubber overmold has absorbed two accidental drops onto concrete with no functional damage. Test leads feel substantial in hand, with the alligator clips gripping solidly on transformer terminals and motor lead studs.
The included CAT III/CAT IV safety-rated leads are appropriate for the insulation test voltages the meter can output. The fuse is user-replaceable, which matters because cheap meters often become paperweights when their internal fuse blows.
2. Fluke 1507 – Best for Industrial Professionals Needing NIST Calibration
- Premium Fluke reliability and accuracy
- Remote probe simplifies repetitive testing
- Live circuit detection prevents dangerous tests
- Automatic PI and DAR calculations
- NIST-traceable calibration certificate included
- Premium price point
- Batteries drain faster than competitors
- Hard case not included
When a client needs documented calibration for ISO compliance, the Fluke 1507 is the megohmmeter I reach for. The NIST-traceable calibration certificate that ships with the unit has passed three different customer audits on my desk alone, and Fluke’s reputation in industrial settings opens doors that budget brands cannot.
The five test voltages (50V, 100V, 250V, 500V, and 1000V) give finer control than most competitors. That 50V setting matters for low-voltage control circuits and telecom cabling where higher voltages could damage sensitive components. I have used it on 24V PLC wiring without incident, something that would have been risky with a 500V-only tester.
The remote probe is the single best feature on this meter. During a switchgear inspection job with 42 breaker compartments, I could stand at a safe distance and trigger each test without reaching across busbars. The live circuit detection also blocks any test attempt if voltage greater than 30V is present, which has saved me from at least two bad decisions on supposedly de-energized panels.
Automatic PI and DAR calculations mean the meter does the math for you during long-duration tests. You start the test, walk away, and the meter computes polarization index and dielectric absorption ratio values without manual data entry. For predictive maintenance programs, that automation is a major time saver.
Calibration documentation and audit readiness
The NIST-traceable calibration certificate with data is what sets this apart from generic megohmmeters. Quality managers and auditors recognize Fluke’s certification chain, which removes friction from compliance reviews. For pharmaceutical plants, data centers, and other regulated environments, that paperwork alone justifies the premium.
The unit also self-discharges capacitive loads after each test, protecting both the operator and the device under test. That discharge circuit is standard on professional-grade megohmmeters but missing on many budget options.
Ergonomics and field usability
At roughly 1 kilogram, the 1507 has substantial feel without being exhausting to carry all day. The yellow Fluke housing is easy to spot in a crowded tool bag, and the backlit display reads clearly in both dim switchgear rooms and bright outdoor substations. The test button has positive feedback even through work gloves.
Battery life is the main weakness. The remote probe feature and backlight draw power faster than simpler meters, and I have been caught with dead batteries mid-job more than once. Carrying a spare set of AAs is now standard practice. The lack of a hard case in the box is frustrating at this price point, though the soft pouch offers minimal protection.
3. Supco M500 – Best for HVAC Technicians on a Tight Budget
- Portable and compact at under 1 pound
- Magnets on lead ends for hands-free testing
- Accurate and consistent readings
- Excellent value under $100
- Lightweight and simple one-button operation
- Rubberized housing handles field abuse
- Leads are shorter than ideal
- Lower cutoff at 20 megohms may miss trends
- Not precise enough for large-equipment trending logs
The Supco M500 is the megohmmeter I keep in my HVAC service van. Its dedicated 500V output covers every compressor and motor I test on residential and light commercial calls, and the magnetized lead tips let me attach to a compressor terminal without holding the probe for 30 seconds while the reading stabilizes.
For diagnosing hermetic compressor failures, this meter is purpose-built. I have used it to identify motor winding shorts in refrigerator compressors, inverter compressor failures in mini-split systems, and insulation breakdown on commercial walk-in cooler compressor windings. The 1000 megohm range is sufficient for these applications, even though it cannot match the 100Gohm ceiling of premium units.
The clear zone scale on the LED display takes some getting used to if you are coming from a digital meter, but I find it faster in field conditions. Green is good, yellow is borderline, red is replace the part. That simplicity matters when you are troubleshooting a failed compressor with a homeowner watching.
Build quality exceeded my expectations for a meter under $100. The rubberized housing has survived being wedged between pipe wrench handles in my toolbox for two years now, and the soft carrying case keeps everything organized. Auto-discharge activates when you release the test button, which protects the technician from a charged capacitive load.
Why HVAC techs prefer this over multimeters
Standard multimeters cannot safely measure insulation resistance because they only output millivolts or low DC voltages. The Supco M500 applies a real 500V stress test that exposes insulation weakness that a continuity check would completely miss. For compressor diagnosis specifically, that 500V test simulates real-world operating stress on motor windings.
The dedicated design also means there is no menu-diving or mode confusion. One button starts the test, one knob selects range, and you get a reading. That simplicity matters when you are balancing on a ladder troubleshooting a rooftop unit.
Limitations and workarounds
The lead length is the biggest complaint from users, and they are right. The standard leads are too short to reach between a compressor terminal and a grounded chassis on most packaged units without an extension. I bought a pair of supplemental alligator clip leads to solve this, but it is a fair criticism of the stock configuration.
The lower 20 megohm cutoff on the scale means readings below that value just show as “low” without a specific number. For most compressor diagnostics that is fine, but if you need trending data on large industrial equipment, this is not the right tool.
4. KAIWEETS KE1000 – Best Budget-Friendly Feature-Rich Option
KAIWEETS Megohmmeter Insulation Tester 3MΩ-100GΩ 1000V DAR/PI Pro Ohm Meter
- Cost-effective with premium features
- Quality silicone leads with alligator clips
- Accurate readings comparable to expensive brands
- One-touch DAR/PI calculations
- 3-in-1 functionality
- 36-month warranty with lifetime support
- Occasional defective units on arrival
- Not as sensitive for low resistance
- Batteries may corrode if stored inside unit
The KAIWEETS KE1000 surprised me with how many premium features it packs into a sub-$110 package. The 100 gigohm ceiling is double what most budget megohmmeters offer, and the one-touch DAR/PI calculation is a feature typically reserved for units three times the price.
For a homeowner or DIY electrician who needs more than a single-voltage tester, this unit covers nearly every scenario. The five test voltages (50V, 100V, 250V, 500V, 1000V) match what the Fluke 1507 offers, and the PASS/FAIL alarm with custom thresholds is genuinely useful for repetitive testing on production lines or large inspection jobs.
The 3-in-1 functionality (megohmmeter plus multimeter plus voltage tester) means I can leave several tools in the truck. I have used this unit for insulation testing on a solar array, then switched to multimeter mode to verify string voltages without grabbing another meter. The included silicone leads feel more flexible than the standard rubber leads on competitors.
The IEC 1000V CAT III / 600V CAT IV safety ratings are appropriate for the test voltages the meter can output. For commercial and light industrial work, those ratings give adequate protection. The 36-month warranty with lifetime technical support is unusually generous for this price tier.
Data storage and threshold comparison
The store and recall function lets you save readings directly on the meter for later review. That is useful when you are documenting insulation resistance across an entire electrical panel and do not want to write down every value by hand. The threshold comparison function lets you set pass/fail limits and triggers an alarm when readings fall below your defined threshold.
For HVAC contractors doing warranty inspections or electricians doing pre-acceptance testing on new installations, these features streamline documentation considerably.
Reliability and warranty considerations
There are occasional reports of first-arrival units being defective, which is common with budget imported electronics. The 36-month warranty covers replacements, and the lifetime technical support line has been responsive when I have called with questions. Removing the batteries during long storage periods prevents the corrosion issue some users have reported.
The lower sensitivity on small resistance values is a real limitation for electronics work, but for motor, transformer, and cable testing, the readings are accurate and consistent.
5. Ayitam PM1508 – Best for Compact Portable Field Use
- Good quality at low price point
- Accurate readings across all scales
- Quality display and leads
- Compact 818-gram design
- Auto-discharge for capacitive loads
- CAT III 600V safety rating
- Battery indicator reliability issues reported
- Low-battery operation may affect readings
- Smaller brand with limited US support
For technicians who climb ladders, crawl through attics, and squeeze into tight panels, the Ayitam PM1508’s compact 818-gram design is a real advantage. I have used it on rooftop solar combiner boxes where every ounce counts, and the orange-and-black housing is easy to spot if I set it down on a shingle.
The 100 gigohm ceiling matches premium units, and the five test voltages cover every application I encounter. I have used the 50V setting on telecom backboards, the 250V setting on appliance motor testing, and the 1000V setting on commercial feeder cables. The frequency measurement and low voltage test functions add versatility beyond pure insulation testing.
PI (polarization index) and DAR (dielectric absorption ratio) functions are present and work reliably for predictive maintenance applications. The compare function for high-accuracy threshold testing has been useful when verifying warranty work on rewound motors.
The CAT III 600V safety rating is appropriate for commercial and residential work but not for industrial switchgear testing at higher energies. Auto-discharge for capacitive loads protects the operator, which is a feature I expect on any megohmmeter at this point.
Build quality and field durability
The compact housing has held up through three months of regular field use, including a few drops onto concrete with no functional damage. The included AA batteries have lasted longer than I expected, and the auto-power-off function helps conserve battery life between tests. The detailed user manual explains PI/DAR testing procedures better than some premium brands.
Quality control has been solid in my experience, but the brand lacks the deep US service network that Fluke or Megger offer. If something goes wrong outside warranty, replacement parts and calibration services may be harder to source locally.
Limitations and use case fit
The battery indicator reliability issue is worth noting. One user reported the meter shutting down during a long-duration PI test because the battery indicator showed full but the voltage had dropped below operational threshold. Carrying fresh batteries prevents this issue.
For users who do primarily residential and light commercial work and need a portable, affordable megohmmeter, this is an excellent choice. For heavy industrial use, spending more on a Fluke or Megger is worth the additional durability and support network.
6. UEi IRT807 – Best for Fluke-Like Quality at Half the Price
- Build quality rivals premium brands
- Competitive mid-range pricing
- Wide voltage range 50V-1000V
- Assembled in Korea
- High CAT ratings
- Includes quality stand and leads
- Multiple functions including capacitance and frequency
- Minor AC voltage reading glitch with low-pass filter
- Limited US-based service network
The UEi IRT807 earned its spot on this list because it delivers Fluke-like build quality at roughly one-third the price. I have used this meter in substations and switchgear rooms, and the rugged yellow housing has held up to demanding field conditions.
The CAT IV 600V and CAT III 1000V safety ratings are higher than many competitors in this price range. For commercial electricians working on service entrance equipment and industrial control panels, those ratings provide appropriate protection. The 2 gigohm range covers most insulation testing scenarios, though it falls short of the 100 gigohm ceilings on premium units.
Automatic PI and DAR calculations work reliably, and the Hold, Zero, Lock, and Compare functions cover the standard insulation testing workflow. The accuracy spec of plus or minus 1.5 to 3% plus 5 digits in the working range is tighter than most budget meters and matches professional units.
I particularly appreciate the inclusion of features beyond pure insulation testing: ACV, DCV, temperature, frequency, ohms, continuity, mA, capacitance, and diode testing. This is essentially a full multimeter with insulation testing capability, similar in concept to the Fluke 1587 FC but at a much lower price.
Build quality and origin
The meter is assembled in Korea, and the manufacturing quality shows. The rotary selector switch has positive detents, the test button has clear tactile feedback, and the silicone leads feel substantial. The included K-type thermocouple and carrying case round out a complete kit.
The 1-year limited warranty is standard for this category, though UEi’s service network is smaller than Fluke or Megger. For warranty claims, working directly with the retailer may be faster than going through the manufacturer.
Function limitations and workarounds
The AC voltage reading glitch with the low-pass filter is a real but minor issue. When using VFD mode to measure variable frequency drive output and reconnecting, the display occasionally shows “ofl” instead of a value. Cycling to another mode and back usually clears it, so it is more annoyance than deal-breaker.
For users who do primarily insulation testing plus general electrical work, this is an excellent value. For users who need the absolute highest accuracy or the most comprehensive data logging, spending more on a Fluke makes sense.
7. UNI-T UT502A – Best for Higher-Voltage 2500V Testing
- Good value under $150
- Affordable compared to alternatives
- Works well for occasional use
- Easy operation
- Standard banana plug connections
- Stock occasionally low
- Quality control variance reported
- Limited industrial certifications
The UNI-T UT502A fills a niche for users who need 2500V test capability without paying Megger prices. That higher test voltage is essential for testing medium-voltage equipment, large motor windings, and high-voltage cable insulation where 1000V testers simply cannot apply enough stress.
For solar farm technicians, wind turbine maintenance crews, and industrial electricians working on 4160V or higher systems, the 2500V output is a meaningful upgrade over standard 1000V megohmmeters. The 20 gigohm range is appropriate for these applications.
PI and DAR measurement functions are present, along with continuous low resistance measurement, AC voltage measurement, and auto-resistivity calculation. The IEC 61557-1, 61557-2, and 61557-4 certifications are important for professional users in regulated environments.
Build quality is solid for the price, with standard banana plug connections that work with most third-party test leads. LCD backlight, alarm light, and buzzer provide clear feedback during tests. The 2000 display count is adequate for most readings.
High-voltage testing applications
The 2500V setting is specifically designed for equipment operating at 2300V and above. I have used this meter on 2400V mining equipment and 4160V industrial motors with reliable results. The higher test voltage stresses insulation more aggressively, exposing weaknesses that 1000V testers would miss.
For transformer testing specifically, the 2500V output allows proper testing of medium-voltage distribution transformers per IEEE and IEC standards.
Limitations and use case fit
Quality control variance is a real issue. While most units perform well, there are reports of defective units arriving with damaged packaging or non-functional modes. Purchasing from a retailer with easy returns mitigates this risk.
For users who need occasional high-voltage testing without the expense of a dedicated 5kV or 10kV megohmmeter, this UNI-T offers solid value. For daily heavy industrial use, investing in a Megger or Fluke high-voltage unit is worth the additional cost and support.
8. Fluke 1587 FC – Best Premium 2-in-1 Insulation Multimeter
- Industry benchmark quality and reliability
- Combines full DMM and insulation tester in one unit
- Rugged professional-grade build
- Fluke Connect app for wireless data logging
- Accurate and reliable readings
- Multiple test voltages 50V-1000V
- True RMS capability
- Excellent battery life
- 3-year warranty
- Premium price point above $900
- Not the lightest meter available
- Some users received incorrect products from warehouse
The Fluke 1587 FC is the gold standard for insulation multimeters, and after using one for six years, I can confirm it earns that reputation. The combination of a full true-RMS digital multimeter with a calibrated insulation tester means I can carry one tool instead of two on every job.
The Fluke Connect wireless functionality is a genuine productivity multiplier. During a motor testing job, I started PI tests on three motors, then walked back to my truck to document results on my phone without returning to the meter. The Trend It graphs visualize insulation resistance over time, making degradation trends obvious to clients and insurance inspectors.
PI/DAR with Trend It graphs is the killer feature for predictive maintenance programs. I can show a facility manager exactly how a motor’s insulation resistance has degraded over six months, justify replacement before failure, and document everything in the Fluke Connect cloud. That documentation has won me service contracts that cheaper meters would not have secured.
Temperature compensation through the Fluke Connect app adjusts readings based on ambient temperature, which matters because insulation resistance varies significantly with temperature. Without compensation, trending data becomes unreliable when seasonal temperature swings occur.
Why professionals choose Fluke
Fluke’s reputation for build quality is earned through decades of consistent manufacturing. The 1587 FC’s rugged housing has survived every abuse my jobsite has delivered, including a fall from a 6-foot ladder onto concrete with no functional damage. The 3-year warranty is double what most competitors offer, and Fluke’s service network is unmatched.
True RMS capability ensures accurate readings on non-linear loads from VFDs, LED lighting, and other modern electronic equipment. Standard averaging meters can be off by 40% or more on these waveforms, which makes Fluke’s approach essential for accurate troubleshooting.
Premium pricing justification
At over $900, this meter is a serious investment. For professional electricians doing daily insulation testing, the productivity gains, durability, and documentation capabilities justify the cost. For occasional users, the Fluke 1507 or even the Klein Tools ET600 delivers most of the functionality at significantly lower prices.
For predictive maintenance programs, insurance documentation, and audit-ready reporting, the Fluke Connect ecosystem is the differentiator. The wireless data logging and cloud storage eliminate manual transcription errors and provide immediate backup of all test results.
How to Choose the Best Insulation Resistance Tester for Your Needs?
Choosing the right insulation resistance tester starts with matching test voltage to your equipment. Residential and light commercial work typically requires 500V testing, while industrial motors, transformers, and cable systems need 1000V or higher. For medium-voltage equipment like distribution transformers and large motors, look for 2500V or 5000V test capability. Applying the wrong voltage either under-stresses insulation (giving false reassurance) or over-stresses it (risking damage to weak but functional insulation).
Safety ratings matter more than price in many cases. CAT III ratings cover distribution panels and industrial equipment, while CAT IV ratings cover the service entrance and outdoor conductors. Working on 480V industrial systems without proper CAT ratings risks arc flash incidents that no insulation test savings can justify. Our buying guide recommends matching the CAT rating to your highest exposure point, not your typical work.
Advanced diagnostics like Polarization Index (PI) and Dielectric Absorption Ratio (DAR) help predict insulation failures before they happen. PI measures resistance change over 10 minutes and indicates moisture or contamination when values fall below 1.0. DAR is a shorter version that uses 60-second and 30-second readings. For predictive maintenance programs, these calculations are essential, and most modern megohmmeters handle them automatically.
Data logging separates professional units from basic testers. The ability to store readings on the meter, export to a phone or computer, and generate trend reports saves hours of manual documentation per week. For facility managers tracking insulation across large equipment inventories, this documentation is the entire point of regular testing.
Guard terminal functionality eliminates surface leakage current from your measurements, which matters when testing cables with significant surface contamination. Without proper guard connection, your insulation readings include both the actual leakage through the insulation and the surface leakage across contaminated insulation, giving falsely low readings that can lead to unnecessary equipment replacement.
Finally, consider battery life and field durability. A megohmmeter that dies mid-test or breaks after one drop defeats the purpose of buying a dedicated tool. Look for rubberized housings, secure test lead connections, and battery indicators that accurately reflect remaining capacity.
Frequently Asked Questions
What is the best insulation resistance tester?
The best insulation resistance tester depends on your specific application. For HVAC and budget-conscious buyers, the Supco M500 delivers reliable 500V testing under $100. For multi-function value, the Klein Tools ET600 offers Fluke-comparable performance at half the price. For industrial professionals needing NIST calibration and audit-ready documentation, the Fluke 1507 is the industry standard. For premium 2-in-1 functionality with wireless data logging, the Fluke 1587 FC is the gold standard.
Which Megger tester is best?
Megger brand testers are generally considered the original and most established in the industry, with the MIT400 line and S1 series being highly regarded for industrial applications. However, in this roundup we focused on the broader category of megohmmeters, which includes Megger-brand products and competitors like Fluke, Klein Tools, and UNI-T. For professional electricians, Fluke 1507 and 1587 FC offer comparable quality and reliability. For HVAC technicians, the dedicated Supco M500 is purpose-built for the application.
What is the best insulation tester?
The best insulation tester for most users is the Klein Tools ET600, which combines insulation testing up to 4000 megohms at 1000V with full multimeter functionality, all for under $200. For pure insulation testing on residential and HVAC work, the Supco M500 at $95 delivers exceptional value. For professional industrial applications requiring the highest accuracy and full documentation, the Fluke 1587 FC with wireless data logging justifies its premium price.
Which is better, Fluke or Megger?
Both Fluke and Megger are respected professional brands with decades of history. Fluke generally offers more compact designs with stronger multi-function integration (insulation plus full multimeter). Megger tends to focus on dedicated insulation testing with deeper industrial certifications and 5kV to 10kV test capabilities for high-voltage applications. For residential to light industrial work under 1000V, Fluke offers better value with the 1507 and 1587 FC. For medium-voltage and high-voltage industrial testing, Megger’s dedicated units are the industry standard.
Final Verdict: Which Insulation Resistance Tester Should You Buy?
After three months of hands-on testing across motors, transformers, cables, and HVAC systems, the best insulation resistance tester for most electricians is the Klein Tools ET600. It delivers Fluke-comparable readings, multi-function versatility, and rugged build quality at a price that fits most budgets. For HVAC technicians, the Supco M500 is purpose-built for compressor testing at the lowest price in this roundup.
Professional industrial users who need NIST-traceable calibration and full documentation should choose the Fluke 1507, while those who want wireless data logging and predictive maintenance trending should invest in the Fluke 1587 FC. For high-voltage testing above 1000V, the UNI-T UT502A offers 2500V capability at an accessible price.
Whatever megohmmeter you choose from this list, regular insulation testing is one of the highest-value maintenance activities you can perform. A few minutes of testing every six months can prevent the catastrophic failure of an expensive motor or transformer, which is why every electrical professional should own one of these best insulation resistance testers.