Surge protector
A surge protector is an appliance designed to protect electrical devices from power surges and voltage spikes. Surge protectors attempt to regulate the voltage supplied to an electric device by either blocking or shorting to ground voltage above a safe threshold.
Surge protectors can be built with one or more of the following electronic components:
- A fuse burns out or a circuit breaker trips when excessive power is being consumed and fed to a device within the designed time lag and current rating. These can protect both from surges caused by the device itself and from external surges that last long enough.
- An iron poor transformer can transmit AC power similar to a normal iron core transformer (although less efficiently), but will be unable to transmit sudden surges that saturate the small iron core.
- A metal oxide varistor (MOV) is a small device that will short when presented with a voltage above its rated "clamping voltage", passing the surge to ground through the MOV rather than through the protected device, provided the current rating (joule) is not exceeded. If the surge exceeds the joule rating, the MOV will be destroyed. Even if not destroyed, MOVs also deteriorate each time they receive a voltage spike, and thus stop working after some time. Some surge protectors have a light to tell you when this stage has been reached.
- 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 with the disadvantage of reacting to the high voltage more slowly.
- A quarter-wave coaxial surge arrestor is used in RF signal transmission routes. It features a tuned quarter-wavelength short-circuit stub that makes it pass a relatively narrow band of characteristic radio frequencies, but presents a short to any other signals, especially down towards DC. Quarter-wave coax surge arrestors have coaxial terminals, compatible with common coax cable connectors (N, BNC or F types). They provide the strongest available protection for narrow-band RF signals, much better than gas discharge cells typically used in the universal/broadband coax surge arrestors. Very useful for WiFi base band at 2.4 or 5 GHz, not much use for TV/SAT/CaTV, nor for systems sending phantom power for an LNB up the coax downlink.
- An inductor resists sudden changes in current flow. Surge protectors using inductors are sometimes called "series mode" surge protectors, because the inductor is connected in series with the load, rather than diverting current to neutral or ground as with MOVs and diodes.
- A capacitor resists sudden changes in voltage, and acts as a low pass filter, reducing spikes and noise.
- Devices having several outlets with surge protectors described may have all or some outlets protected. The better ones have higher ratings and offer more modes of protection against surges between the phase and neutral and grounding conductors; maybe for telephone and coax cable connections. (The best have insurance policies paying for damages from surges.)
- A UPS of the flywheel type seldom pass surges. The battery variety may absorb spikes much like a capacitor acts as a low pass filter. The battery ones also have protectors described above. "On line" UPSs provide the best protection.