What can cause surges? First, everyone is going to think of lightning. If there is a lightning strike on a facility, on power lines leading to a facility, or even just on the ground near a facility, it can cause serious problems for electronic equipment. As discussed earlier, lightning only accounts for about 20% of surges, leaving switching to be the greater cause of surges. That means large loads like roof top air conditioners or inductive motors inside a facility are creating transient overvoltages. Anything with a capacitor has a transient property, and well, there are capacitors in just about all electronics.