What causes surges? Surges have a variety of causes, found inside as well as outside homes and businesses. External Causes - Lightning Strikes: Lightning is the most dramatic, and often most damaging, cause of surges. When lightning strikes the ground, it sends thousands of volts along nearby electrical lines to affect homes and businesses in the vicinity. Factories & Heavy Industry: When factories abruptly slow their electricity consumption (for example, at the end of a shift or during an assembly line shutdown), the excess voltage that they would normally have consumed is sent back through the electrical grid to affect homes and businesses nearby. Since the power rushes back from the factory or industrial site in a wave, they are often called "rolling surges". Utility Companies: When utilities are faced with wildly fluctuating electricity demand (during summer months, for example), utility companies may accidentally direct too much voltage to a certain area. Internal Causes - Surges can also be generated within a facility. Large Appliances: Large appliances cause surges in the same way that factories and industrial sites do, but on a much, much smaller scale. When large appliances (such as refrigerators or air conditioners) abruptly slow their electricity consumption (as they meet their cooling temperature and switch to idle, for example), the excess voltage that it would normally have consumed is sent back through the electrical circuits within the facility to affect devices nearby.