Safety is critical in testing and troubleshooting. Because the insulation resistance tester generates a large amount of dc voltage, it can never be connected to a live circuit. Similarly, the output of the tester will destroy the electronic circuit. Do not connect the insulation resistance tester to an electronic power supply, PLC, VSD, UPS system, battery charger or other solid state equipment. Some insulation resistance testers have built-in warning systems that alert technicians when a voltage is present on a circuit.

As with all testing tools, the insulation resistance tester shall be evaluated according to its application to fit its operating environment and shall be tested by a state-approved testing laboratory. If also used as a multimeter, the insulation resistance tester shall have a class rating. The test line shall be durable, graded and tested.

The insulation can hold a large voltage charge for a period of time after the insulation resistance test is completed. Most testers will automatically release the insulation after the test is completed; Some don't. This is an important point to consider when choosing insulation resistance tester. Some testers indicate voltage levels as well as insulation resistance. On this type of tester, it can be observed that the voltage level decays to zero after the test output voltage is turned off. Some manufacturers recommend that insulation resistance testers remain connected to the circuit or component under test as long as they have completed the test four times to ensure a safe discharge. After the test is completed, most technicians will ground the circuit under test to confirm that the insulation layer has been discharged.