A review of TOP-5 best insulation testers features models of various brands, including consumer-grade devices for just $40 and products designed for professional use that come at a price of about $600. For your convenience, there is a comparative chart of the effectiveness of these devices to help you make the right choice. In this guide, you will also learn how to use insulation testers properly and what safety precautions need to be taken.

Wire insulation keeps the electrical current flowing along the wire as intended. Equipment insulation reduces early wear from heat and vibration. Insulation testers detect current leaks that occur as a result of deteriorated or damaged insulation.

Wire insulation failure may be due to electrical over- or under-voltages or frequent mechanical start ups/shut downs or imposed cable and installation stress experienced by rotary-type equipment/motors. Insulation ages when it is constantly exposed to variations in start up/shut down expansion/contraction temperatures. Common environmental conditions such as particulate (dust, mold, etc.) buildup can also cause deterioration.

It is important to perform insulation tests periodically to avoid potentially hazardous and costly incidents (fire, equipment damage, personal injury, etc.).

What You Will Learn From This Guide:

What Is An Insulation Tester And How Does It Work?

Insulation testers test for capacitance and current leakage in system cables, generators and motors, high voltage equipment, and switchgears. (Good) Insulation resistance is measured in megohms. Installations, routine maintenance, and real time surges (drops/returns) may be checked to prevent potential problems.

The type of equipment being tested and the reason for testing determines what test method you use. Low-capacitance testing, time, and equipment is used to determine leakage/absorption leak for electrical cable and switchgear. High-capacitance (long-time) equipment and testing are used to determine leakage in large motors, transformers, generators, and long cable runs. The insulation as well as each motor, generator, or transformer phase and/or winding is tested separately and sequentially.

What Types Of Testing Are There?

Spot Reading/Short-time Testing – is similar to a Proof (Go/No-Go) Test that quick-tests insulation after installation. A spot reading/short-time test is a low-capacitance test that applies a test voltage for approximately 60 seconds.

Time Resistance/Time Ratio Test and Leakage Tests – are low-capacitance tests that use polarization index (PI) and dielectric absorption rate (DAR) to determine cable, transformer, motor, electrical installation integrity. Absorption current and capacitive leakage is detected almost immediately. These tests provide good short-time resistance spot readings.

Step Voltage and Dielectric-Absorption Tests – are high-capacitance tests performed over a period of hours due to the inconsistent short term meter readings. These tests collect relative readings and measure those that are the same.

Purpose of Testing

Testing is a preventive procedure that catches insulation problems before they result in total equipment performance failure. Insulation resistance testing is performed at the time of installation and should be consistently performed during the equipment’s useful life. Proof tests insure proper conductor installation and integrity is maintained. They quick-test the insulation after (cable, wire, etc.) installation as well as detect cable system maintenance errors.

Measuring Polarization Current

The DC voltage insulation resistance/polarization index (IR/PI) tests are used to assess quality and identify abrasion and thermal deterioration in insulation, such as winding due to coil vibration. The PI measurement method is not recommended for oil-immersed equipment such as transformers.

The current pulsates at time=zero, decreasing during the polarization time (Tc) to the insulation conductivity value. Two readings are taken (at 1 min. and 10 min.). The PI = the 10 min. insulation resistance reading divided by the 1 min. insulation resistance reading.

The Polarization/De-polarization Current (PDC) test measures the discharging current from that passed through the grounded dielectric material for several minutes. The absorption current is set on HIGH for the first few seconds and slowly reduced to zero for low-capacitance equipment. The absorption current is set and maintained (with no decrease) for a long period for high- capacitance equipment or wet/contaminated insulation.

Measuring Leakage Current

Steady current that goes over and through insulation is the conduction or leakage current. An increase indicates insulation deterioration. To measure high DC voltage, press the test button. Micro-amp current flows through the conductor and the insulation. The current is the voltage applied, system capacitance, total resistance. The reading indicates the conductor’s internal resistance plus the insulation resistance.

Current to ground leakage of load equipment is measured when it is turned on. Test single-phase circuits by clamping the phase and neutral. Test three-phase circuits by clamping all conductors and neutral if present. The measured value is any current running into the ground.

Ground conductor leakage is measured by clamping the ground conductor.

Current to ground leakage/imbalance via an unintentional path is identified by clamping the phase, neutral, and ground together. A leakage at an electrical panel, bonding connection, or outlet is detected via their unintentional paths to ground (i.e.: concrete base, pipe ground, etc.).

How To Use An Insulation Tester

Testing Environment

Temperature and humidity can affect insulation testing results. Insulation resistance and insulation temperature are inversely proportional. Resistance decreases as temperature increases. Measurements should be corrected when the temperature varies. For example, the Institute of Electrical and Electronics Engineers (IEEE) recommends a temperature baseline constant for electric machinery insulation testing of 104F. deg. (40C. deg.). The resistance value is reduced by half for every 18F. deg. (10C. deg.) above the baseline/reference temperature. Similarly, the resistance value doubles for every 18F. deg. (10C. deg.) below the baseline/reference temperature.

Humidity affects the insulation as “contamination.” Therefore insulation should not be measured when the temperature is lower than the dew point.

Calibrating An Insulation Tester

Insulation tester calibration verifies the accuracy of the insulation tester as well as the accuracy of short current testings, polarization index (PI) and dielectric parameter functions, and verifications of dielectric absorption and polarization ratios.

Calibrations must comply with ISO requirements. Data results (As Found/As Left) must be in accordance with National Institute of Standards and Technology (NIST) control and documentation procedures. Calibrator Quality Assurance should also systematically comply with applicable ANSI, NCSL, ISO, ASTM, EC, and CFR requirements.

Testing/Checking An Insulation Tester

A standard portable, programmable calibrator can be used to verify the resistance ranges and test voltage of multi-meters and insulation testers. Calibrators help ensure the insulation tester is accurate. Resistances are selected or dialed into the calibrator. The testing instrument’s leads are then attached and the resistance reading shown on the screen is compared to the calibrator’s “known resistance.”

Capturing Insulation Resistance Data

Insulation resistance values, time-stamps and test durations, test voltage output, and temperature corrections are part of the insulation resistance testing data that is collected. The insulation tester should readily capture and record this data in real time. DAR, DD, and PI data values and time-resistance and step voltage readings should be able to be recovered and displayed graphically. Various programs enable you to transmit data to the cloud.

Reading An Insulation Tester

Accurately interpreting your readings tells you how to proceed with operation, general maintenance, or repair/replacement of various installations, cables, and equipment.

  • Fair-High values and well-maintained cable/equipment - No action required.
  • Fair-High values with a cluster of lower-end values – Define location and reason for the low-values.
  • Low values – Signal unsafe conditions. Clean/service before putting cable/equipment into operation.
  • Previously Fair-High values of well-maintained cable/equipment that suddenly show lower values – More frequent testing to determine cause and stabilize values so cable/equipment can be put into safe operation.

Insulation Testing Equipment/Applications

The primary purpose of insulation resistance testing and testers is to save money in the long term. Periodic readings show gradual reductions in resistance. They are recommended as a forewarning of potential problems. Examine the system to be tested before testing/measuring.

The typical insulation resistance tester is portable, handheld, and operates on a rechargeable battery. Many can operate from online power even after the battery dies! Depending on their high- or low-capacitance, they can accurately test transformers, motors, generators, cables, circuit breakers, and other installations and equipment. Insulation resistance testers are expected to ensure reliable equipment operation and minimal equipment shutdown and/or power outages and/or downtime.

Voltage Requirements

The IEEE 43-2000 Guide lists recommended test voltages relative to the operating voltages of equipment and cable installations.

Equip. Op. Voltage – DC Test Voltage

24 to 50 V – 50 to 100 VDC

50 to 100 V – 100 to 250 VDC

100 to 240 V – 250 to 500 VDC 

440 to 550 V – 500 to 1000 VDC 

2400 V – 1000 to 2500 VDC

4100 V – 1000 to 5000 VDC

5000 to 12,000 V – 2500 to 5000 VDC

Safety Precautions

Always perform an insulation test on a de-energized piece of equipment, line, or circuit.

  • Avoid holding the test meter if possible (minimize your transients exposure).
  • Shut down equipment and disconnect/discharge all switches, circuits, and connections. Discharge terminals directly into the earth.
  • CAUTION: Arching can occur when damaged/deteriorating insulation is tested.
  • Check “dead” circuits using the 3-point test method: 1) test a “known live circuit”, 2) test the target circuit, 3) test the “known live circuit” again to verify your meter is properly working (before/after the measurement).
  • Use protective gear and insulated tools when working on live circuits or in potentially flammable environments. Stand on an insulation mat.
  • Insulated rubber gloves should be used when connecting the test leads. The presence of unnecessary personnel should be restricted.
  • Keeping one hand in your pocket reduces the risk of experiencing a closed circuit across your chest and through your heart.
  • Discharge equipment after testing to release accumulated energy before beginning other operations. Allow equipment to discharge for 5x the time of last test. Short-circuit the poles by discharging them into the earth.

Top-5 Best Insulation Testers

This review covers products within the price range from $40 to $600. Consumer-grade devices have test range up to 2000 Megohms while that of more expensive model amounts to 4000 Megaohms and 10 Gigaohms. All the items are recommended for be used indoors to test appliances, motors, cables, etc, with Fluke 1507 insulation tester suggested forprofessional use. 

Digital Insulation Tester Megger MegOhm Meter | Victor VC60B+

Digital Insulation Tester Megger MegOhm Meter: photo

The Victor VC60B+ digital insulation tester is an accurate and reliable, 9V battery-powered, handheld meter. It is a “full-function protection/anti-high-voltage circuit” design. It allows you to test resistance at 250V, 500V, and 1000V. This meter offers a substantially wide test range from 0.1 Megaohm to 2000 Megaohm. Its standard reference temperature is 0C deg. to 40C deg. (32F deg. to 104F deg.) . Its operating relative humidity reference is 30% RH to 85%RH.

The Victor VC60B+ digital insulation tester features a large, easy-to-read, backlit LCD display screen and easy-to-use unit symbol display. It has a low battery indicator, a high-voltage, short-circuit input alarm, and an overload indicator light. It automatically powers off when not in use.

Recommendations:

The Victor VC60B+ digital insulation tester is intended for checking insulation resistance in telecom, electrical, and mechanical cable and equipment. It includes a 1-yr. warranty. The battery is not included.

Victor: Check the current price

Insulation Tester, 0 to 1000 megohms | Supco

Insulation Tester Supco: photo

The durable, 500VAC Supco M500 insulation tester is a fast and accurate, handheld, battery-powered meter. Its lightweight, impact-resistant design makes it ideal for field use. This meter measures insulation resistance within a 0 to 1000 Megaohms test range.

This is a cost-effective insulation tester that is easy-to-use and easy-to-read. It is a simple, one-button design with an easy-to-read vertical display. It has a 3-Zone, 10-LED-light, color-coded megaohms scale that indicates the condition of the insulation.

Recommendations:

The Supco M500 insulation tester is well-suited for checking insulation resistance, deterioration, and heat damage in appliances, compressors, relay circuits, and motors as well as for field use. It includes two (9 in.) test leads w/alligator clips and soft carrying case. Batteries (req.: two “C”) are not included.

Supco: Check the current price

R5600 Insulation Tester - REED Instruments

REED Instruments R5600 Insulation Tester: photo

The REED R5600 insulation tester is a durable, AA battery-powered, handheld/hands-free meter. It is constructed from solid, double-molded plastic. This meter allows you to test resistance at 250V, 500V, and 1000V test voltage intervals. It also offers a substantial test range up to 2000 Megaohms. Its standard operating temperature is 0C deg. to 40C deg. (32F deg. to 104F deg.) . Its operating relative humidity reference is a maximum 80% RH.

The REED R5600 insulation tester features a large, easy-to-read, backlit dual display screen. It includes a power-LOCK button and convenient hanging strap for hands-free operation.

Recommendations:

Although the REED R5600 has a solidly durable housing and mechanism, the manufacturer User Guide recommends the REED R5600 insulation tester be used indoors to test appliances, motors, power tools, and cables. This insulation tester includes two test leads w/alligator clips, a hard-sided carrying case, and batteries (req.: six “AA”).

REED Instruments: Check the current price

Digital Megohmmeter, 4000 Ohms Resistance | AEMC 1026

Digital Megohmmeter, 4000 Ohms Resistance: photo

The lightweight, battery-operated AEMC 1026 digital insulation tester is a four-function, handheld AC/DC voltmeter, ohmmeter, and continuity tester. Its low insulation test range is good for motors or testing old/flooded installations. It also allows you to perform high resistance/absorption, spot, timed-resistance, DAR, and PI tests. Resistance may be tested at 250V, 500V, and 1000V intervals. It measures insulation resistance from 1 kohm to 4000 Megaohms. Its standard operating temperature is 0C deg. to 40C deg. (32F deg. to 104F deg.) . Its standard storage temperature is 14F deg. to 140F deg.) .

The AEMC 1026 digital insulation tester features computer-controlled production line testing. Results may be stored for future analysis. The AEMC 1026 has a large, easy-to-read digital display screen and a data-hold/auto discharge and 3-minute LOCK button for hands-free operation. It also features a low-battery indicator and continuity alarm.

Recommendations:

The AEMC 1026 digital insulation tester is intended to be used to test cables, motors, insulators, transformers, and wiring installations. It includes test leads w/alligator clips, a soft carrying case, and Users Manual.

AEMC: Check the current price

Digital Megohmmeter Insulation Tester | Fluke 1507

Fluke Digital Megohmmeter Insulation Tester: photo

The lightweight The Fluke 1507 insulation tester is a simple, sturdy, high-end, noiseless, handheld meter. It operates on AA alkaline batteries. Resistance may be tested at 50V, 100V, 250V, 500V, and 1000V intervals. Its insulation test range is from 0.01 Megaohms to 10 Gigaohms. It automatically calculates PI and the dielectric absorption ratio.

This quality, compact Fluke 1507 insulation tester features an easy-to-read, large backlit screen display. It includes a power-LOCK button for hands-free operation and a safety, live-circuit detection and captive voltage auto-discharge feature that halts the insulation test when the voltage exceeds 30V. It automatically powers off when not in use.

Recommendations:

The top-rated Fluke 1507 insulation tester is recommended for professional, high-current industrial, or home troubleshooting and/or preventive maintenance. The Fluke 1507 kit comes with SureGrip insulated (remote) test probe and test leads w/alligator clips, a stray voltage eliminator, and a holster for easy carry. Batteries (req.: four “AA”) are included.

Fluke: Check the current price

Comparative Chart Of Insulation Tester Effectiveness

Product Features

Victor VC60B+

Voltage: VDC
Test Range: 0.1 to 2000 Megaohms
Insulation Test Voltages: 250V, 500V or 1000V

Supco M500

Voltage: 500 VAC
Test Range: 0 to 1000 Megohms
Insulation Test Voltages: Not listed

REED Instruments

Voltage: 1000 VDC
Test Range: 0 to 2000 Megohms
Insulation Test Voltages: 250V, 500V or 1000V

AEMC 1026

Voltage: 600 VAC, 1000VDC
Test Range: 1kohm to 4000 Megaohms
Insulation Test Voltages: 250V, 500V and 1000V

Fluke 1507

Voltage: 0.1 VAC/DC to 600 V AC/DC
Test Range: 0.01 Megaohms to 10 Gigaohms
Insulation Test Voltages: 50 V, 100 V, 250 V, 500 V, 1000 V

FAQ

What is the best insulation tester for laparoscopic instruments?
Any low-capacitance insulation resistance testing device.

What is the most reliable name brand model?
Fluke Corp. is considered a world leader in the manufacture, distribution, and servicing of electronic test tools and software.

What is the best insulation tester for a motor?
Any high-capacitance model.

Advantages And Drawbacks

New technology has made insulation testers valuable quality control, maintenance, and budget/cost control tools.

  • Many are portable, battery- or line-powered.
  • They generate stable results under changeable conditions (temp/humidity).
  • They have extended insulation resistance testing ranges.
  • They have stable voltages and sensitivity to accurately test small currents.
  • Records data in the instrument’s memory for later download or transfer to the cloud.
  • Modern battery-operated insulation testers are programmed to continue operating after the battery is dead.

The primary drawback of such devices are their sensitivity to temperature and humidity. Conditions will necessitate reading corrections. 

Conclusion

Insulation testers are used to detect current leaks in new and existing cable/wire installations, motors, transformers, etc. Routine testing and maintenance reduces costs due to breakdown or severe hazards (fire, explosion, etc.). Insulation deterioration may be caused by environmental conditions (mold, dust, etc.) or the stresses of constant temperature expansion/contraction during repeated motor start ups and shut downs.

Modern insulation testers are battery- or line-powered. They are designed to be portable and generate accurate, and reliable results under changeable temperature and humidity. Technology has made improvements to insulation testers such as extended insulation resistance testing ranges and more stable voltages and sensitivity that allow accurate small current testing. Programmable testers allow you to record data and store it for later download or transfer it to the cloud.