When the power grid experiences a sudden increase in current, your home gets an electrical surge. Like a dam breaking, this sudden inrush of electrical current exposes unprotected equipment to damaging voltages. It can overheat motors, burn out lights and damage electronic components. Surge protectors, such as those used in power strips, safely absorb the excess energy in an electrical surge
A lightning strike delivers very large currents. Though equipment in the electrical grid has some protection from lightning strikes, it can still cause surges. Lightning can also produce surges from secondary effects such as by hitting a transformer which then fails. If you see a storm coming, turn off sensitive equipment and leave them off until after it passes.
When a large area loses electricity, the current in the power lines goes to zero. When power comes back on, the lines experience a large inrush surge of current. This surge can damage electrical and electronic equipment. Fortunately, this surge is both predictable and manageable. As with electrical storms, you can prevent damage by switching lights, appliances and computers off during a blackout. When the utility restores power, wait a few minutes for the current to stabilize, then you can switch the equipment back on.
Large industrial equipment can draw large amounts of electricity when it first turns on, causing a brief drop in current for neighbors. When it shuts off, it causes the current to surge. While this seldom poses enough of a problem to damage most appliances, over time it can cause problems with sensitive electronics.
Grid Infrastructure Problems
The modern electrical grid is a complex network of distribution equipment and power plants. If a community experiences high electricity demand, the utility may decide to switch in additional power plants. The switching action can make the line voltage surge. Problems with electrical distribution equipment, such as overheated transformers and broken power lines can also cause surges. These kinds of surges are impossible to predict, though a surge protector will prevent major damage to sensitive equipment.