Best Ohmmeter Megger Insulation Testers: Picks and How to Choose

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An ohmmeter megger is a resistance meter used for insulation checks, usually called a megohmmeter or megger. It measures very high resistance, so it shows whether insulation is holding up. This guide compares three listings that describe megger-style insulation testers. It explains the test voltage, range and safety details each listing gives, where the data is thin, and what to confirm before you order. Use the guide to compare what each listing states, not as a substitute for the equipment standard you follow.

Quick answer

Choose by test voltage, display and safety category. The first entry gives three test voltage choices in its title, which suits buyers who need to match a specific standard. The second gives a 500V test with a zone-style readout, which is enough when a go, caution or stop reading is what you need. The third gives a numeric LCD across a wide resistance span and names a CAT-II and CAT-III safety level. Confirm the display type and the safety category on any listing before you buy, and follow the manual before you connect a tester to equipment.

What matters for this keyword

Test voltage

An insulation tester applies a high DC voltage to the insulation under test and reads the resulting resistance. Megohmmeters provide high DC voltages, typically from 500 V to 5 kV, and some go up to 15 kV. Pick a tester whose voltage choices include the level your standard names. Two of the three entries state a test voltage. The third lists safety categories and gives no test voltage in its bullets. For related tools, see the megger test guide for electric motors and the insulation resistance equipment guide.

Resistance range

Megohmmeters report megohms, and acceptable insulator resistance is typically 1 to 10 megohms, depending on the standards referenced. The listings here go much higher. One states readings up to 1000 MΩ, and another states a span from 1MΩ to 20GΩ. A wide span is useful for checking how a value changes over time, but make sure the bottom of the range also covers your smallest expected value. For digital units, see the digital megger guide.

Display and readout

Numeric displays give a value, and zone or analog scales give a status. A general reference notes that digital instruments have numeric displays and are more precise than analog meters with a moving pointer. One listing describes a zone scale marked Good, Caution and Bad, yet its title calls it digital. Those descriptions conflict, so confirm the display type with the seller before ordering.

Safety category

A measurement category is a classification of live circuits by the IEC, and it reflects the energy available at a point in the circuit and the impulse voltages present. The required impulse withstand voltage varies from 500 V at CAT II to 12,000 V at CAT IV. One listing states CAT-II 1000V and CAT-III 600V. Match that rating to the circuit you will test, and read the manual for any limits that apply.

Warranty and calibration

One entry’s bullets list a three-year warranty and a calibration certificate. The other two entries give no warranty term. If calibration paperwork matters for your records, ask the seller whether the certificate comes with the unit you buy.

The picks

Each card below shows the specs the listing gives, followed by pros and cons from the same listing. The paragraphs here give the short version for each pick.

Best for three test voltage choices. The first entry is a digital and analog insulation tester whose title lists 250, 500 and 1000 V test voltages. Its bullets add a live circuit warning, a weatherproof rating to IP54 and a calibration certificate. It fits buyers who want a rugged tester with several voltage choices.

Best for a 500V zone readout. The second entry states a stable 500V output and readings up to 1000 MΩ. Its bullets describe a zone-style scale with Good, Caution and Bad regions, although its title calls it digital. Use it when a go, caution or stop reading is enough for the decision.

Best for a numeric LCD and a stated safety level. The third entry lists a 1MΩ to 20GΩ span on an LCD, with a CAT-II 1000V and CAT-III 600V safety level. It gives no test voltage in its bullets, so confirm that figure before ordering.

How to choose

Start with the standard your equipment follows, then match the test voltage, the display and the safety category to it.

• Choose the multi-voltage tester when your standard names more than one test voltage, such as the 250 V, 500 V or 1000 V settings in the first listing’s title.
• Choose the zone-readout tester when a status reading is enough and you do not need a number for records.
• Choose the LCD tester when you need a numeric value across a wide span and have confirmed its test voltage.
• Skip any tester whose display or voltage you cannot confirm.

Before you order, write down the test voltage, the resistance span, the display type, the safety category and the battery type. Compare that note with your equipment’s requirements. If a field conflicts with the title, ask the seller first.

Safety note. Insulation testers apply high DC voltages, so read the manual before any test. Follow the manual and local electrical rules. OSHA lists contact with power lines and a path to ground missing or discontinuous among the most frequent causes of electrical injuries. Panel or service work belongs to a licensed electrician.

Worked example: a motor check schedule

• Readings per month: 6 x 2 = 12 readings.
• Readings per year: 12 x 12 = 144 readings.
• Readings per quarter: 144 divided by 4 = 36 readings.

That schedule gives 144 readings across a year, or 36 per quarter. If you add motors or change the frequency, repeat the same arithmetic before you pick a tester with enough memory or a simple log sheet.

Common mistakes

• Choosing a tester by its resistance span without checking the test voltage.
• Treating a zone reading as a number for a written record.
• Buying a tester whose display type conflicts with its title until the seller confirms it.
• Ignoring the safety category on the equipment you plan to test.
• Skipping the manual before the first use on a new tester.

FAQ

What is an ohmmeter megger used for?

It measures very high resistance, usually to check insulation. A megohmmeter applies a high DC voltage and reports the result in megohms.

Is a megger the same as an ohmmeter?

Not quite. An ordinary ohmmeter reads lower resistances across two probes. A megger applies a high test voltage so it can read insulation resistance, which runs far higher.

What test voltage do I need?

Use the voltage your equipment standard names. Insulation testers typically apply from 500 V to 5 kV, and the listings here offer a range of choices. Confirm the exact setting before you connect the tester.

Why does the display type matter?

A numeric display gives a value for records, while a zone scale gives a status. One listing describes a zone scale although its title says digital, so confirm the display with the seller.

What does the CAT rating tell me?

A CAT rating classifies the circuit environment a tester suits. The listing for the LCD tester states CAT-II 1000V and CAT-III 600V, so match that rating to your circuit and read the manual before use.

Does one tester cover every insulation job?

No. The span, test voltage and display vary by listing. Compare each against your equipment before you assume one unit fits every job.

Should I call an electrician?

If a reading looks wrong on equipment you cannot identify, stop and call one rather than repeating the test.

Bottom line

Choose the tester whose test voltage, display and safety category match the equipment you check. The multi-voltage option suits standards with several test levels, the zone-readout option suits quick status checks, and the LCD option suits numeric records once its test voltage is confirmed. Skip any listing whose details conflict until the seller clears them up.

Sources

• Megohmmeter (Wikipedia): insulation resistance tester function and typical DC test voltages
• Measurement category (Wikipedia): IEC classification of live circuits and impulse withstand voltage
• Multimeter (Wikipedia): digital displays compared with analog meters
• OSHA electrical safety: most frequent causes of electrical injuries