An insulation resistance (IR) tester — often called a "megohmmeter" — verifies the integrity of insulation in cables, motors, transformers and switchgear by applying a DC test voltage and measuring leakage. Choosing the right one comes down to a few key parameters.
Match the test voltage to the equipment's operating voltage. Common ranges: 250 V / 500 V / 1 kV for low-voltage installations and motors, and 2.5 kV / 5 kV / 10 kV / 15 kV for medium- and high-voltage cables, machines and transformers. Testing at too low a voltage misses defects; too high can stress good insulation. As a rule, use roughly the equipment's rated voltage for routine tests.
Higher test voltages need higher resistance ranges (up to TΩ for HV testers). For maintenance you also want a stable, repeatable low-end reading to trend results over time.
If you maintain rotating machines, prioritise a tester with automatic PI/DAR.
Check the CAT rating (CAT III / CAT IV) and voltage — critical for field work near live plant. Reputable HV insulation testers are built to IEC 61010.
Controware is an authorized Megger distributor. For general LV work the MIT400/MIT2500 series is ideal; for cables and machines the 5 kV/10 kV MIT/S1 families deliver PI, DAR and step-voltage testing. Browse the full Megger range or the wider electrical test instruments category.
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