From Littelfuse, Inc.
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.
Products & Services
Fuses protect electrical devices and components from overcurrents and short circuits that occur in improperly operating circuits.
Load centers are used for the protection and distribution of power in a building or residence. They are also called circuit breaker boxes.
Circuit breakers are mechanical switching devices capable of breaking currents under specified abnormal circuit conditions.
Ground Fault Relays
Ground fault relays protect electrical equipment from ground faults. A ground fault is an unintentional current path between a current-carrying conductor and a grounded surface.
Fuse holders are devices for containing, protecting and mounting fuses. Blown fuses can be changed quickly and easily when used in conjunction with a fuse holder.
Topics of Interest
A characteristic is an inherent and measurable property of a device. Such a property may be electrical, mechanical, or thermal, and can be expressed as a value for stated conditions. A rating is a...
Varistors are voltage dependent, nonlinear devices which have an electrical behavior similar to back-to-back zener diodes. The symmetrical, sharp breakdown characteristics shown in Figure 1 enable the...
Littelfuse offers three device technologies for the suppression of ESD events and other EMC-related transients. These are the MultiLayer Metal Oxide Varistor, silicon (SCR/Diode Array and TVS...
5.5 Degradation and Ageing of ZnO Surge Arresters
The terms varistor degradation and varistor stability are often used to describe the electrical state of a varistor relative to its past or future...
Protection and Ratings
Motor Protection The typical method of starting a three-phase induction motor is by connecting the motor directly across the power line. Line starting a motor is done with a...