Surge protector
Scaled-down versions of these devices are sometimes installed in residential service entrance electrical panels, to protect equipment in a household from similar hazards.
Many protectors will connect between all three in pairs (line–neutral, line–ground and neutral–ground), because there are conditions, such as lightning, where both line and neutral have high voltage spikes that need to be shorted to ground.
These fast overvoltage spikes are present on all distribution networks and can be caused by either internal or external events, such as lightning or motor arcing.
[8] Applications of transient voltage suppression diodes are used for unidirectional or bidirectional electrostatic discharge protection of transmission or data lines in electronic circuits.
These bursts of overvoltage can be measured with specialized electronic meters that can show power disturbances of thousands of volts amplitude that last for a few microseconds or less.
If the overvoltage condition persists long enough to cause significant heating of the MOV, it can result in thermal damage to the device and start a fire.
The same kind of induction happens in overhead and above ground conductors which experience the passing energy of an atmospheric EMP caused by the lightning flash.
Transients similar to lightning-induced, such as from a high voltage system's fault switching, may also be safely diverted to ground; however, continuous overcurrents are not protected against by these devices.
The energy in a handled transient is substantially less than that of a lightning discharge; however it is still of sufficient quantity to cause equipment damage and often requires protection.
Without very thick insulation, which is generally cost prohibitive, most conductors running more than minimal distances (greater than approximately 50 feet (15 m)) will experience lightning-induced transients at some time during use.
In general, the induced voltage is not sufficient to do damage at the electric generation end of the lines; however, installation at the service entrance to a building is key to protecting downstream products that are not as robust.
These are some of the most prominently featured specifications which define a surge protector for AC mains, as well as for some data communications protection applications.
Some (especially older) electronic parts, like chargers, LED or CFL bulbs and computerized appliances are sensitive and can be compromised and have their life reduced.
The Joule rating number defines how much energy a MOV-based surge protector can theoretically absorb in a single event, without failure.
[16] Well-designed surge protectors consider the resistance of the lines that supply the power, the chance of lightning or other seriously energetic spike, and specify the MOVs accordingly.
Some manufacturers commonly design higher joule-rated surge protectors by connecting multiple MOVs in parallel and this can produce a misleading rating.
This can cause one MOV in a group to conduct more (a phenomenon called current hogging), leading to possible overuse and eventual premature failure of that component.
at time of this writing, are that minimum lightning-based power line surges inside a building are typically 10,000 amperes or 10 kiloamperes (kA).
Older surge strips had no thermal fuse and relied on a 10 or 15 amp circuit breaker which usually blew only after the MOVs had smoked, burned, popped, melted and permanently shorted.
The typical failure mode occurs when the triggering voltage rises so high that the device becomes ineffective, although lightning surges can occasionally cause a dead short.
Additional auxiliary circuitry may be needed in DC (and some AC) applications to suppress follow-on current, to prevent this from destroying the GDT after the initiating spike has dissipated.
[42] Carbon block suppressors are similar to gas arrestors (GDTs); but as the two electrodes are exposed to the air, their behavior is affected by the surrounding atmosphere, especially higher humidity.
[50][51] After passing through the SPDs in the marshalling cabinets, the wiring can pass through conduits into other remote, nearly adjacent, cabinets that contain the input & output connections to for digital system panels (fire alarm, security access control, computer clean power, programmable logic controllers (PLCs), etc.
They provide the most rugged available protection for RF signals above 400 MHz; at these frequencies they can perform much better than the gas discharge cells typically used in the universal/broadband coax surge arrestors.
Since a quarter-wave arrestor shorts out the line for low frequencies, it is not compatible with systems which send DC power for a LNB up the coaxial downlink.
These devices are not rated in joules because they operate differently from the above listed suppressors, and they do not depend on materials that inherently wear out during repeated surges.
SM suppressors are primarily used to control transient voltage surges on electrical power feeds to protected devices.
They are essentially heavy-duty low-pass filters connected so that they allow 50 or 60 Hz line voltages through to the load, while blocking and diverting higher frequencies.
Since the inductor in series with the circuit path slows the current spike, the peak surge energy is spread out in the time domain and harmlessly absorbed and slowly released from a capacitor bank.
SM suppressors do not present a fire risk should the absorbed energy exceed design limits of the dielectric material of the components because the surge energy is also limited via arc-over to ground during lightning strikes, leaving a surge remnant that often does not exceed a theoretical maximum (such as 6000 V at 3000 A with a modeled shape of 8 × 20 microsecond waveform specified by IEEE/ANSI C62.41).
