The Varistor Used In Appliances

Excerpts from the book The Complete Microwave Oven Service Handbook
--NOW available on CD-ROM (CLICK HERE)
and from the video You Can Fix Your Microwave Oven, Plus VCR Know-How Copyright ©, 1989-2000 by J. Carlton Gallawa

The varistor is a surge protection device that is connected directly across the AC input. When a power surge or voltage spike is sensed, the varistor's resistance rapidly decreases, creating an instant shunt path for the over-voltage, thereby saving the sensitive control panel components (hopefully). Because the shunt path creates a short circuit, the varistor and the line fuse are subject to be damaged or weakened in the process.

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