Megohmmeter Insulation Testers Compared: 3 Listings
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A megohmmeter applies a test voltage to a cable, motor winding or transformer and reports the insulation resistance in megohms or gigohms. This page compares three listings whose titles name a megohmmeter or insulation tester. For each one it sets out the stated test voltages, the stated resistance ceiling, the display, the power arrangement and the included parts, and it marks where a listing’s own text disagrees.
The three listings differ a lot in their top figures, and one listing gives two different upper limits in its own title and bullets. Keep each number with the listing it came from. Listing data was checked on 2026-10-20.
Quick answer
The Ayitam pm1508 is the only listing here that states both a 1000 V test voltage and a resistance range up to 100 GΩ. The UNI-T UT501A states a 1000 V test capability and a 750 V AC setting, but its resistance ceiling is given two ways. The FRIGESWIFT M500 is the only one that stays at 500 V, and it states 20 to 1000 megohms.
If you need a 750 V AC check alongside the insulation test, only the UNI-T listing mentions that setting. If you need a carrying case stated in the listing, the M500 names a zippered carrying case, and the Ayitam lists its test leads and four AA batteries.
Comparison table
| Listing | Stated test voltages | Stated resistance ceiling | Power and display | Included |
|---|---|---|---|---|
| UNI-T UT501A megohmmeter, 1000v (first listing) | Up to 1000 V testing (bullets); 750 V AC setting (bullets) | 1000 megohms at 750 volts (title); reads up to 5 GΩ (bullets) | Battery powered; 2000 counts in the title, maximum display 9999 in the bullets | Not clear: the specification field reads “no”; the bullets mention included test leads |
| Ayitam pm1508 megohmmeter, 50V-1000V (second listing) | 50, 100, 250, 500 and 1000 V (title and bullets) | Up to 100 GΩ (title and bullets) | Battery powered; combined megohmmeter and multimeter | Test leads, alligator clip, four AA batteries, user manual (highlight and bullets) |
| FRIGESWIFT M500 insulation tester, 500V (third listing) | 500 V (title and minimum operating voltage field) | 20 to 1000 megohms at 500 V (bullets) | Battery powered; LED indicator and zone scale | Zippered carrying case; test leads stored inside (bullets) |
The first listing: UNI-T UT501A megohmmeter
The listing names UNI-T and model UT501A. Its title describes a 1000 V insulation tester that measures up to 1000 megohms at 750 volts, with a 0 to 5 G ohm meter and a 2000-count LCD display with backlight. The specification fields give a battery-powered design, a minimum operating voltage of 100 volts, a red color, an item weight of 1.32 pounds and dimensions of 5.91 x 3.94 x 2.8 inches. The specification fields also list CE and RoHS.
The bullets describe an LED display with a maximum reading of 9999, an automatic backlight that turns on during measurement, and a low battery warning. They state an auto shutdown after 10 minutes without operation and a red warning light during high-voltage output. The bullets also describe a 750 AC volts setting for checking cables and equipment, and they name transformers, motors, cables and switches as the target equipment.
- Test voltage: up to 1000 V (bullets); 750 V AC setting (bullets)
- Resistance: 1000 megohms at 750 V (title); up to 5 GΩ (bullets)
- Display: 2000 counts (title); maximum display 9999 (bullets)
- Shutdown: 10 minutes without operation (bullets)
The listing’s own text disagrees on two points. The title’s 2000-count display and the bullet’s maximum reading of 9999 are different descriptions of the same screen, and the title’s 1000 megohm figure and the bullet’s 5 GΩ ceiling are different limits. The worked example below sets out the difference in numbers.
The second listing: Ayitam pm1508 megohmmeter
The listing names Ayitam and model pm1508. Its title describes a megohmmeter and insulation resistance tester with test voltages from 50 V to 1000 V and resistance up to 100 GΩ. The specification fields give a battery-powered design, a minimum operating voltage of 50 volts, a measurement type of ohmmeter, a compact style, an orange and black color scheme and an item weight of 1.8 pounds. The specification field for safety reads CE.
The highlight field and the bullets describe a combined megohmmeter and multimeter that measures insulation up to 100 GΩ. They add a frequency measurement, a low voltage test, polarization index (PI) and dielectric absorption ratio (DAR) functions, auto discharge for capacitive loads and a compare function. The bullets give the safety rating as EN61010-1 and CAT III 600V. The package includes test leads, an alligator clip, four AA batteries and a detailed user manual.
- Test voltages: 50, 100, 250, 500 and 1000 V (title and bullets)
- Resistance: up to 100 GΩ (title and bullets)
- Safety: EN61010-1 and CAT III 600V (bullets); CE (specification field)
- Included: test leads, alligator clip, four AA batteries, manual (bullets)
The PI and DAR functions are the main addition to a basic insulation check. The listing states them as functions but does not give the values they return for any particular cable or winding, so they are a feature to confirm, not a result to expect.
The third listing: FRIGESWIFT M500 insulation tester
The listing names FRIGESWIFT and model M500. Its title describes a 500 V insulation tester and electronic megohmmeter with a soft carrying case. The specification fields give a battery-powered design, a minimum operating voltage of 500 volts, a lower temperature rating of 32 °F and an upper rating of 120 °F. The listed color is blue, the weight is 10.8 ounces and the dimensions are 7 x 3.8 x 2.4 inches. The compatible uses are refrigeration and air conditioning compressors, motors, appliances, panel boards and relay control circuits.
The bullets state a range of 20 to 1000 megohms at 500 V, with LED indicators for fault detection and a zone scale for insulation condition. They say the case is impact resistant, waterproof and corrosion resistant, and that it stores the test leads inside. The bullets say the unit runs on two C batteries, which are not included.
- Test voltage: 500 V (title and minimum operating voltage field)
- Resistance: 20 to 1000 megohms at 500 V (bullets)
- Power: two C batteries, not included (bullets)
- Case: zippered carrying case with test leads stored in the back panel (bullets)
The M500 does not state a test voltage above 500 V, so it is the one listing here for which the 1000 V question does not arise. Its battery arrangement differs from the Ayitam listing, which includes its batteries.
How these three were chosen
Each listing above has a title that names a megohmmeter or insulation tester. Other products in related results, including a clamp tester, multimeters and circuit testers, are left out because they are not insulation testers. Figures come from each listing’s own fields and bullets, and all three were checked on 2026-10-20.
Worked example: the top reading in each listing
Start with the UNI-T’s two ceilings. Its title says 1000 megohms, and its bullet says it reads up to 5 GΩ. One GΩ is 1000 MΩ, so 5 GΩ is 5000 MΩ, five times the title’s figure. The listing does not say which of the two applies at which test voltage, so use the more conservative 1000 megohm figure until the product page clarifies it.
Next compare the Ayitam and M500 ceilings. The Ayitam states up to 100 GΩ, which is 100,000 MΩ. The M500 is capped at 1000 megohms, read at 500 V. The Ayitam’s stated ceiling is therefore 100 times the M500’s stated ceiling. The two figures measure the same kind of quantity, but the Ayitam listing does not state the test voltage at which it reaches 100 GΩ, so the two top readings cannot be compared at equal conditions.
What the listings do not say
- None of the three states an accuracy percentage for its insulation reading.
- The UNI-T specification field reads “no” for included components and for part number, which does not match its bullets about included test leads.
- The Ayitam listing does not say which test voltage gives the 100 GΩ reading.
- The M500 listing does not state a discharge or auto-discharge function.
- None of the three states a response time or a reading update rate.
Related buying guides
For a wider view of insulation checks, the megohmmeter guide covers the general category, the insulation resistance tester guide covers the testers in this family, and the megohmmeter tester guide covers handheld models.
FAQ
Which listing states the highest resistance figure?
The Ayitam pm1508 states up to 100 GΩ in its title and bullets. The UNI-T states up to 5 GΩ in its bullets and 1000 megohms in its title. The M500 tops out at 1000 megohms, measured at 500 V.
Which listing states a 750 V AC setting?
The UNI-T UT501A is the only one of the three whose bullets mention a 750 AC volts setting.
Are batteries included with each listing?
The Ayitam includes four AA batteries. The M500 says two C batteries are not included. The UNI-T listing does not state battery inclusion, and its specification fields read “no” for included components.
Why does the UNI-T listing give two resistance figures?
Its title says 1000 megohms at 750 volts, and its bullets say it reads up to 5 GΩ. Those figures are not the same limit, and the listing does not explain the difference.
What should I confirm before buying?
Confirm the test voltage you need, the resistance ceiling at that voltage, the battery type and whether batteries are included. Check the current listing, because the UNI-T’s figures need clarifying before you rely on either one.
Bottom line
For the widest stated test voltage and resistance ceiling, the Ayitam pm1508 gives the most consistent figures across its title and bullets. The UNI-T UT501A adds a 750 V AC setting but gives two conflicting resistance limits. The M500 is the one that stays at 500 V, with a stated 20 to 1000 megohm range and a carrying case. Pick by the test voltage your equipment needs, and confirm the top figure at that voltage on the product page.
