If more voltage is introduced than an electrical appliance is designed to handle, this is called a power surge or transient voltage. Any such voltage increase that lasts at least three nanoseconds is considered a surge. If the increase is only present for one or two nanosecond, that's called a power spike. Just like if having much more water in a hose than it can handle, having too strong a power surge can damage your electric appliance. The greater voltage that runs along the electric wires causes great heat that can burn up the wire. Even if the wire doesn't get burned up in a single power surge, the surge can damage the wire. So repeated occurrences of power surges can accumulate enough damage to the wires that the appliance eventually burns out.
The good news is that you can buy surge protectors to keep your electric appliances from frying if a power surge occurs. These power strips do more than just let you increase the number of outlets by plugging them into a single wall outlet. Whether the increased voltage can be classified as a surge or a spike, the surge protector uses its metal oxide varistor (MOV) to channel the extra voltage to the outlet's grounding wire. The MOV has three parts: a piece of metal oxide, and two semiconductors. The metal oxide is connected to each of the semiconductors. One semiconductor is connected to the grounding wire and the other one is connected to the power line. The MOV does nothing if the voltage is correct, but it is able to divert only the extra voltage during a power surge to the grounding line, making sure that the right voltage is still flowing to the appliance. This design ensures that your appliance can still operate, even during a power surge or spike.