Best Insulation Resistance Testers (Megohmmeters): 4 Models Compared
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This page covers insulation resistance testers, also called megohmmeters. The keyword named an insulation power factor tester, but none of the listings in our research set states a power factor measurement, so we did not keep that wording. Four listings do describe insulation resistance testing, and they are compared here. Figures for the three extra products were checked on 2026-10-18, and the research product on 2026-10-13. Each listing states its own test voltage and resistance range, and those are shown side by side below.
Quick answer
If you need a fixed 500 V test voltage with a zone scale on the display, three of the four listings state that set-up, and they all describe the same class of instrument. If you need a choice of test voltages up to 1000 V, the HIOKI IR4057-50 (B0FSSL8D1S) is the only listing that states one, and it also lists a pass or fail comparator and a continuity check. Its stated range starts at 100 megohms, so readings below that figure are not covered by its listing.
The four testers at a glance
| Tester | ASIN | Test voltage (as listed) | Resistance range (as listed) | Power (as listed) |
|---|---|---|---|---|
| Iexcauw M500 Megohmmeter Insulation Tester | B0FHKS3NCN | 500 V (title says DC; bullet says AC) | Up to 1000 megohms | 2 C batteries, not included |
| RCEKAHOD Insulation Tester Megohmmeter (M500 type) | B0GF31CMW5 | 500 V | Up to 1000 megohms | 2 C batteries, not included |
| HIOKI Insulation Tester IR4057-50 | B0FSSL8D1S | 50 V to 1000 V in five steps | 100 to 4000 megohms | 4 AA batteries, included |
| FRIGESWIFT M500 Insulation Tester Megohmmeter | B0FJ1FRR4G | 500 V | 20 to 1000 megohms | 2 C batteries, not included |
1. Iexcauw M500 Megohmmeter Insulation Tester
The listing gives the model as M500 and describes the unit for HVAC compressors, refrigeration equipment, motors, control boards, transformers and air conditioning units. The title states a range of up to 1000 megohms at 500 V DC. One bullet describes the same figure as 500 V AC, so the listing contradicts itself on the type of voltage. Check the test voltage type in the manual before you use it on a live system.
The bullets describe LED indicators that give a quick status result, a portable and battery-operated design, a heavy-duty carrying case and test leads. The batteries are two C cells, not included. The listing states a two-year limited warranty and a support response within 12 hours. This research product was checked on 2026-10-13.
Iexcauw M500 megohmmeter on Amazon
2. RCEKAHOD Insulation Tester Megohmmeter
This listing is labeled as compatible with the Supco M500 and gives a test of up to 1000 megohms at 500 V. Its LED zone scale is the most specific of the four. The listing states green for readings above 150 megohms (good), yellow for 40 to 100 megohms (caution), and red for below 20 megohms (bad insulation). The listing does not say what the display shows between 100 and 150 megohms, so that band has no stated zone.
The housing is described as heavy-duty ABS with impact resistance. The rear panel has a storage compartment for test leads, and the kit includes a soft zippered carrying case. The listing describes one-button operation and automatic discharge circuitry, and it says the batteries are two C cells, not included. The minimum operating voltage in the specification block is 500 volts.
RCEKAHOD megohmmeter on Amazon
3. HIOKI Insulation Tester IR4057-50
The HIOKI listing is the only one that offers a choice of test voltages. It lists five selectable voltages from 50 V to 1000 V, and it states an insulation resistance range from 100 megohms to 4000 megohms. The pass or fail comparator is described as giving a result in about 0.3 seconds, with a visual and audio indication. The listing also states a built-in AC and DC voltage meter and a continuity check, so the tester can check whether a circuit is live before a test.
The bullets describe a drop-proof design from 1 m, a backlit display and an LED light for low-light use. The unit has a live-circuit indicator and automatic discharge after each test. The specification block lists four AA batteries as included, a weight of 1.41 pounds and a size of 6.97 x 6.26 x 2.09 inches. The listing carries a first-available date of September 30, 2025.
HIOKI IR4057-50 insulation tester on Amazon
4. FRIGESWIFT M500 Insulation Tester Megohmmeter
This listing states a measurement of 20 to 1000 megohms at 500 V, and it names refrigeration and air conditioning compressors, motors and appliances, panel boards and relay control circuits as applications. The bullets describe LED indicators and a zone scale for insulation condition. It also lists an impact-resistant thermoplastic case, a zippered carrying bag, and a back panel that is removable for test lead storage. Power comes from two C cells that the listing does not supply.
The bullets say the case is waterproof and corrosion-resistant. The listing gives an operating temperature range in the specification block of 32 to 120 degrees Fahrenheit, and the dimensions as 7 x 3.8 x 2.4 inches. Its stated floor of 20 megohms is lower than the 100 megohm floor of the HIOKI listing, while the RCEKAHOD and Iexcauw listings state no floor at all.
FRIGESWIFT M500 megohmmeter on Amazon
How we chose these four
We kept listings that describe an insulation resistance test with a stated test voltage and a resistance range. The rest of the research set held an IP camera tester, a fiber optic power meter, a network cable tester, automotive circuit testers and an electronic load tester, and their titles do not name an insulation test. The extra set also included an energy-saving box for home use. Its listing describes lower electricity bills, not a power factor test of insulation, so it is not part of this comparison. We did not test any of these instruments. All figures come from the listing text.
Worked example: reading the RCEKAHOD zone scale
Take three readings on the 500 V setting of the RCEKAHOD as an illustration only. A reading of 60 megohms falls in the yellow band of 40 to 100 megohms, so the listing’s caution zone applies. A reading of 12 megohms is below 20 megohms, so it falls in the red band for bad insulation. A reading of 120 megohms is above 100 megohms but below 150 megohms, so the listing gives no zone for that value.
The same 60 megohm reading is also inside the FRIGESWIFT range of 20 to 1000 megohms, and inside the RCEKAHOD range up to 1000 megohms. On the HIOKI, however, the lowest stated range is 100 megohms, so a 60 megohm result sits below that listed floor and would not be covered by the stated range.
Where the listings disagree
- Voltage type: the Iexcauw title gives 500 V DC, while one of its bullets gives 500 V AC.
- Lower limit: the RCEKAHOD and Iexcauw list up to 1000 megohms without a stated floor, the FRIGESWIFT lists 20 megohms as the floor, and the HIOKI lists 100 megohms as its lowest range.
- Battery supply: the HIOKI includes four AA batteries, while the other three list two C batteries as not included.
What the listings do not say
None of the four listings states a power factor measurement, a dielectric absorption test or a polarization index, so none of them supports a claim that it is a power factor tester. The zone scales on the RCEKAHOD and FRIGESWIFT do not give boundaries for every value between their bands. The Iexcauw listing does not give a zone scale in its bullets. None of the listings gives an accuracy figure for insulation resistance readings, so the comparison here rests on the stated ranges and voltages only.
Frequently asked questions
Does any of these testers measure power factor?
No listing in this set states a power factor measurement. All four describe insulation resistance testing, and the HIOKI also lists a voltage meter and a continuity check.
What test voltages do these testers offer?
Three listings state a fixed 500 V test voltage. The HIOKI lists five selectable test voltages from 50 V to 1000 V.
Which tester has the widest resistance range?
The HIOKI lists 100 to 4000 megohms, which has the highest top value. The three M500-type listings state up to 1000 megohms at the top, and the FRIGESWIFT starts its range at 20 megohms.
How are the batteries supplied?
The HIOKI includes four AA batteries. The RCEKAHOD, FRIGESWIFT and Iexcauw listings state two C batteries, not included.
Is the Iexcauw test voltage AC or DC?
The listing gives both. The title says 500 V DC, and one bullet says 500 V AC. Check the manual before you use the tester on a live system.
Conclusion
These four listings are insulation resistance testers, and none of them is sold as a power factor tester. The HIOKI is the choice with stated test voltages up to 1000 V, a pass or fail comparator and a continuity check. The three M500-type listings are the fixed 500 V option, and the RCEKAHOD gives the clearest zone scale boundaries. Confirm the test voltage type and the battery supply on the live listing before you buy.
For related reading, see best megohmmeter tester, megohmmeter, and insulation resistance test equipment.
Iexcauw M500 on Amazon · RCEKAHOD megohmmeter on Amazon · HIOKI IR4057-50 on Amazon · FRIGESWIFT M500 on Amazon
