Varistor Testing

This note details the common tests of varistor parameters and describes suitable test methods using simplified test circuits. All tests are performed at 25 o C, unless otherwise specified. The test circuits and methods given herein are intended as a general guide. Since the tests frequently entail high voltages and currents, the user must exercise appropriate safety precautions. It is important to focus on the key characteristics and ratings to determine if the component can perform as expected. Typically, for a varistor, its nominal voltage, clamping voltage, standby current, insulation resistance, and capacitance are measured. The surge current, or energy, and waveshape available in the circuit together with its frequency of occurrence should be measured or computed. The characteristics of these expected transients should then be checked against the pulse ratings and the power dissipation ratings of the selected varistor type. Where suitable equipment is available, these ratings may be verified.