An article in the April QST by Ward Silver titled “AC Power Distribution” included a warning “MOV Surge Protectors — Avoid Them”. Ward and I have swapped a couple of emails and he agrees the statement was more broad than necessary.
An MOV is a Metal Oxide Varistor, commonly used as a primary surge arrester since the late 1970’s. 10’s, if not 100’s of millions are connected across the ac mains worldwide — in consumer products, business equipment, and industrial instrumentation. You’ll probably find several MOV’s in your home and office in computer power supplies, Audio/Visual equipment and of course, in the AC power strips we all use.
If you are buying a Power Strip, look for the UL (Underwriters Laboratories) mark, which ensures the product has undergone considerable testing for safety and ensures the protector (usually an MOV) has been properly selected and operates as expected.
When and MOV fails, it usually ruptures instantaneously resulting in an open-circuit; however, if you’re building your own power distribution box such as that shown in the QST article, and an MOV but put a small fuse in series with it just to be sure!