Hipot and megger are both electrical testing instruments, but they serve different purposes and operate on distinct principles. A hipot tester (high-potential tester) applies a high AC or DC voltage to electrical equipment to verify that insulation can safely withstand stress without breaking down. It checks whether insulation is adequate for the equipment's rated voltage, typically stressing it at 1.5 to 2 times the normal operating voltage. Hipot testing is a safety verification that confirms insulation integrity before equipment is put into service.
A megger (megohmmeter) measures the resistance of insulation using a much lower, safer voltage—typically 500V to 5,000V DC—and displays the result in megohms (millions of ohms). Rather than stressing insulation to its breaking point, a megger simply quantifies how well the insulation resists current flow. It provides numerical data about insulation condition over time, helping diagnose degradation.
The key practical difference: hipot testing is pass/fail—it confirms insulation won't fail under stress. Megger testing is diagnostic—it measures how much resistance the insulation provides and can reveal trends in deterioration. Hipot is more invasive and potentially damaging to marginal insulation; megger is non-destructive. Hipot is commonly used during manufacturing and after repairs, while megger testing is frequently done for condition monitoring and maintenance.