What makes power surges so dangerous is their unpredictability. A power surge is an abrupt and significant increase in voltage that exceeds the standard electrical flow within an electrical system. Most outlets in U.S. homes operate at 120 volts of power, but a power surge can reach as high as thousands or even tens of thousands of volts. This sudden spike in electricity can last for a fraction of a second. Still, its effects can be devastating, potentially damaging electronic devices and appliances, shortening their lifespan, or making them unusable. Power surges vary in severity; some are minor and hardly noticeable, while others are significant enough to cause immediate damage.

Another characteristic of power surges that makes them so dangerous is that they can come from anywhere. Power surges can occur as a result of a variety of external and internal factors. Externally, lightning is one of the most dramatic and destructive sources of power surges. When lightning strikes near a power line, the energy can be transmitted through the electrical system, causing an enormous surge. Other external causes include utility grid switching and faults in the power supply system. Internally, power surges often occur when high-power appliances (like air conditioners and refrigerators) switch on and off, momentarily drawing a large amount of power that can disrupt the system's balance. There can also be other internal causes of power surges, such as malfunctioning appliances or electronics, overloaded circuits, bad wiring, and more.