Insulation tester vs megohmmeter

Insulation testers, Fundamentals

Testing insulation resistance is essential to keeping wires and motors working properly. Megohmmeters provide a quick and easy way to determine the condition of the insulation on wire, generators, and motor windings. A megohmmeter is an electric meter that measures very high resistance values by sending a high voltage signal into the object being tested. Typically, however, this is the only function a megohmmeter performs.

While megohmmeters are often informally referred to as insulation testers, strictly speaking this is not accurate. Why? What’s the difference between a megohmmeter and an insulation tester? An insulation tester performs the basic measuring function a megohmmeter does — measuring very high resistance values by sending a high voltage signal into the object being tested — and it often does much more; it usually performs more functions, including more complex testing and recording of measurements.

A technician in a shop makes measurements on an industrial motor while watching the results on his smartphone

A full-featured insulation tester can perform high-voltage insulation resistance tests and much more

What makes insulation testers different

For example, unlike megohmmeters, insulation testers can also measure voltage and current. The Fluke 1587 FC insulation multimeter, for example, can perform insulation tests up to 1000 volts, and it is a full-function digital multimeter. The Fluke 1550C FC can generate up to 5000 volts for insulation tests.

Insulation testers can also perform more complex tests, such as compensating for ambient environmental conditions like humidity and temperature during a test, which provides information about how motors perform in changing conditions. Because environmental conditions and/or chemical contamination accelerates the rate at which insulation degrades, it’s critical to compare insulation resistance test results that are corrected for different test conditions.

Insulation testers like the Fluke 1587 FC and the Fluke 1550C FC offer another advantage over megohmmeters. Memory storage through Fluke Connect® saves measurements to your phone or the cloud so you don’t have write down results. This saves time, reduces errors, and saves data for tracking over time.

Choosing between an insulation tester and a megohmmeter depends on your business needs. A meg test may be all you need. But if you want increased power, convenience, prevention, and safety, an insulation tester may be your best choice.

Fluke insulation resistance meters and testers

Insulation tester featuresTwo-in-one tools: insulation test plus digital multimeterStand-alone tools: dedicated insulation testers
Fluke 1587 FC Insulation MultimeterFluke 1577 Insulation MultimeterFluke 1503 Insulation Resistance MeterFluke 1507 Insulation Resistance TesterFluke 1535 2.5 kV Insulation TesterFluke 1537 2.5 kV Insulation TesterFluke 1550C FC 5 kV Digital Insulation TesterFluke 1555 FC 10 kV Insulation Tester
Test voltages50 V
100 V
250 V
500 V
1,000 V
500 V
1,000 V
500 V
1,000 V
50 V
100 V
500 V
1,000 V
250 V
500 V
1,000 V
2,500 V
250 V to 2,500 V250 V to 5,000 V250 V to 10,000 V
Insulation resistance range0.01 MΩ to 2 GΩ0.01 MΩ to 600 GΩ0.01 MΩ to 2,000 GΩ0.01 MΩ to 10 GΩ1  kΩ to 500 GΩ200 kΩ to 500 GΩ200 k to 1 TΩ200 k to 2 TΩ
PI/DAR   xxx
+ DD Test
Auto dischargexxxxxxxx
Timed ramp test (breakdown)     xxx
Pass/fail comparison   xxxxx
Est. # of IRT tests1,0001,0002,0002,0001,3001,300VariousVarious
Voltage >30 V warningxxxxxxxx
MemoryWith Fluke Connect® App    xxx
Fluke Connect® Compatibilityx     xx
Remote test probexxxx    
Lo ohms/earth-bond continuity  200 mA source (10 mΩ resolution)200 mA source (10 mΩ resolution)    
AC/DC Voltsx    x  
DisplayDigital LCDDigital LCDDigital LCDDigital LCDDigital/analog LCDDigital/analog LCDDigital LCD/analogDigital LCD/analog
Hold/lockxxxx  xx
Multimeter Features
1577: AD/DC volts, current, resistance, continuity beeper, backlight
1587 only: temperature (contact), lo-pass filter, capacitance, diode test, frequency, MIN/MAX
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