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Safe isolation procedures for low voltage installations

Fluke 1587 FC Insulation Multimeter, performing a high-voltage megohm test

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 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 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 to provide 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 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 historical 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.

Comparing insulation testers and megohmmeters

 Fluke 1587 FC Insulation multimeterFluke 1550c Insulation testerMegger MIT230Extech 380363
Test voltage50 V, 100 V, 250 V, 500 V, 1000 V250 V, 500 V, 1000 V, 2500 V, 5000 V250 V, 500 V, 1000 V250 V, 500 V and 1000 V
Resistance measurements2.2 GΩ2 TΩ1 GΩ10 GΩ
Temperature compensationxx  
Data recordingUnlimited w/ Fluke Connect®99 internal, unlimited w/ FC Manual entry 9 records
Data transmissionxx  
Voltage measurement0-1000V 25V – 600V999V
Current measurement400 mA ac or dc   
Diode testx   
Continuity testx xx
Frequency measurement99.99 kHz   
Capacitance measurement9999 μF15 μF  
Temperature measurement-40 °C to 537 °C
-40 °F to 998 °F

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