Surge protector
A surge protector is an appliance designed to protect electrical devices from power surges and voltage spikes. It works by monitoring the voltage supplied to an electric device. If the voltage level rises beyond a safe threshold, the dangerous excess voltage will be grounded (earthed) with the ground wire, protecting the device from being spiked (damaged by an electrical surge). The threshold varies depending on the region in which the surge protector is intended for use. The protection offered by the surge protector is rated by the Underwriters Laboratories.
Surge protectors can be built with one or more of the following electronic components:
- An iron poor transformer can transmit AC power (inefficently) but will be unable to transmit sudden surges that saturate the small iron core.
- A MOV is a small device that will short out when presented with a sufficently high voltage, hopefully passing the surge to ground through the MOV rather than through the protected device. Unfortunately, these devices tend to self destruct (and are therefore one-shot devices) with sufficently strong surges. Many cheap surge protectors only have MOV's, and probably will not survive even a single lightning strike.
- A zener diode is a small diode designed to protect against normal spikes in a circuit, especially motor controller circuits. These are sometimes paired as a transient voltage suppression diode.
- A gas discharge tube is used much like a MOV, except that it relies on a trapped gas to become ionized to pass the voltage. This has the advantage of being able to pass much more power without self destructing, but the disadvantage of reacting to the high voltage more slowly.
- In an Uninterruptible power supply (in addition to other surge protection devices listed above) typically passes external power past the unit's battery, which will absorb spikes much like a capacitor acts as a low pass filter. (This also keeps the battery charged, and in the event of a failure, the battery can continue to supply power without any interruption otherwise needed to switch it in.)