Short the 2 test leads together and push the test button.
The test leads may have been nulled incorrectly. Try and null them again. If this continues to occur, replace your test leads.
Some insulation testers have a maximum reading of 99, 199 or 299 MOhms for different test voltages so good insulation may be shown as greater than (>) the maximum reading.
Polarisation Index is the ratio of insulation resistance at 1 minute to 10 minutes. It shows how the insulation is charging up and can identify if insulation is clean and dry.
The continuity range uses most battery power so may cause the battery symbol to show before other ranges.
This would depend on the application. Usually 500 V is used on standard electrical installations. Lower voltages are used for control circuits and for quick checks that nothing is left in circuit.
As the insulation value increases, the test current decreases and becomes harder to measure with the same level of accuracy.
Certification usually requires a test current of 200 mA. Changing to a lower test current, such as 20 mA, when not certifying will give a better battery life.
Most insulation testers will not operate if they detect a voltage on the circuit under test and will display the voltage that has been identified.
This symbol indicates that the instrument has experienced an overcurrent causing the fuse to blow. The fuse is located in the battery compartment and can be replaced with the spare fuse.