While they aren't perfect, they really do protect computers and other electronic devices from all but the strongest power surges. There are certain things, like an alarm clock or a fan used for cooling, that don't draw that much power.
Broken plugs are not only a shock hazard, but they can also spark or overheat, causing an electrical fire. FCI, AFC, and ACFCI circuit breakers are not recommended being used to wire surge protectors due to their tendency to trip when a surge protector diverts current during a surge event.
In the event that high-current devices such as space heaters, microwaves, toasters, ovens, and pumps are plugged into a power strip, overloading can occur resulting in tripped breakers or even electrical fires due to overheating. Most 120-volt power strips are rated at a maximum cord and plug load of 12 amps.
Fires have resulted when this connection is damaged, so it is important that the strips be above the floor and mounted to a fixed surface, such as a wall or cabinet. Overheating is usually caused by overloading or connecting appliances that consume more watts than the cord can handle.
Even if a surge (from power service) occurs, the lights will just absorb the energy or will simply blow some bulbs. If a surge to that extent occurs, there will be much more to be concerned with then your Christmas lights.
This article's lead section may be too short to adequately summarize its key points. A voltage spike is a transient event, typically lasting 1 to 30 microseconds, that may reach over 1,000 volts.
Lightning that hits a power line can give many thousands, sometimes 100,000 or more volts. Spikes can degrade wiring insulation and destroy electronic devices like battery chargers, modems and TVs.
A long term surge, lasting seconds, minutes, or hours, caused by power transformer failures such as a lost neutral or other power company error, are not protected by transient protectors. Long term surges can destroy the protectors in an entire building or area.
Long term surges may or may not be handled by fuses and overvoltage relays. Shorting is done by spark gaps, discharge tubes, zener-type semiconductors, and metal-oxide various (Move), all of which begin to conduct current once a certain voltage threshold is reached, or by capacitors which inhibit a sudden change in voltage.
The most common and effective way is the shorting method in which the electrical lines are temporarily shorted together (as by a spark gap) or clamped to a target voltage (as by a MOVE) resulting in a large current flow. The voltage is reduced as the shorting current flows through the resistance in the power lines.
The spike's energy is dissipated in the power lines (and/or the ground), or in the body of the MOVE, converted to heat. However, if the spike is large enough or long enough, like a nearby hit by lightning, there might not be enough power line or ground resistance and the MOVE (or other protection element) can be destroyed and power lines melted.
Sockets in a modern house uses three wires: line, neutral and ground. Many protectors will connect to 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.
A power strip with built-in surge protector and multiple outlets The terms surge protection device (SPD) and transient voltage surge suppressor (TOSS) are used to describe electrical devices typically installed in power distribution panels, process control systems, communications systems, and other heavy-duty industrial systems, for the purpose of protecting against electrical surges and spikes, including those caused by lightning. Scaled-down versions of these devices are sometimes installed in residential service entrance electrical panels, to protect equipment in a household from similar hazards.
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. UK type G socket adapter with surge protector Also known as the let-through voltage, this specifies what spike voltage will cause the protective components inside a surge protector to short or clamp.
The lowest three levels of protection defined in the UL rating are 330 V, 400 V and 500 V. The standard let-through voltage for 120 V AC devices is 330 volts. Underwriters Laboratories (UL), a global independent safety science company, defines how a protector may be used safely.
Therefore, a 3rd edition or later protector should provide superior safety with increased life expectancy. The design of the connected device determines whether this pass-through spike will cause damage.
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 Bio-based surge protector can theoretically absorb in a single event, without failure.
The MOVE (or other shorting device) requires resistance in the supply line in order to limit the voltage. For large, low resistance power lines a higher joule rated MOVE is required.
Every time a MOVE shorts, its internal structure is changed and its threshold voltage reduced slightly. At this point the MOVE will partially conduct and heat up and eventually fail, sometimes in a dramatic meltdown or even a fire.
Most modern surge protectors have circuit breakers and temperature fuses to prevent serious consequences. 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 Move accordingly.
Some manufacturers commonly design higher joule-rated surge protectors by connecting multiple Move in parallel and this can produce a misleading rating. This can cause one MOVE in a group to conduct more (a phenomenon called current hogging), leading to possible overuse and eventual premature failure of that component.
A second MOVE might start at 290 volts and another at 320 volts, so they all can help clamp the voltage, and at full current there is a series ballast effect that improves current sharing, but stating the actual joule rating as the sum of all the individual Move does not accurately reflect the total clamping ability. The effective surge energy absorption capacity of the entire system is dependent on the MOVE matching so debating by 20% or more is usually required.
According to industry testing standards, based on IEEE and ANSI assumptions, power line surges inside a building can be up to 6,000 volts and 3,000 amperes, and deliver up to 90 joules of energy, including surges from external sources not including lightning strikes. The common assumptions regarding lightning specifically, based ANSI/IEEE C62.41 and UL 1449 (3rd Edition) at time of this writing, are that minimum lightning-based power line surges inside a building are typically 10,000 amperes or 10 kiloamperes (a).
This is based on 20 a striking a power line, the imparted current then traveling equally in both directions on the power line with the resulting 10 a traveling into the building or home. These assumptions are based on an average approximation for testing minimum standards.
A whole house product is more expensive than simple single-outlet surge protectors and often needs professional installation on the incoming electrical power feed; however, they prevent power line spikes from entering the house. Damage from direct lightning strikes via other paths must be controlled separately.
Surge protectors don't operate instantaneously; a slight delay exists, some few nanoseconds. With longer response time and depending on system impedance, the connected equipment may be exposed to some surge.
However, surges typically are much slower and take around a few microseconds to reach their peak voltage, and a surge protector with a nanosecond response time would kick in fast enough to suppress the most damaging portion of the spike. Thus, response time under standard testing is not a useful measure of a surge protector's ability when comparing MOVE devices.
Slower-responding technologies (notably, Gets) may have difficulty protecting against fast spikes. Therefore, good designs incorporating slower but otherwise useful technologies usually combine them with faster-acting components, to provide more comprehensive protection.
A subsequent revision in 2015 included the addition of low-voltage circuits for USB charging ports and associated batteries. IEC Standards are used by members of the CB Scheme of international agreements to test and certify products for safety compliance.
None of those standards guarantee that a protector will provide proper protection in a given application. A specialized engineering analysis may be needed to provide sufficient protection, especially in situations of high lightning risk.
Systems used to reduce or limit high-voltage surges can include one or more of the following types of electronic components. Some surge suppression systems use multiple technologies, since each method has its strong and weak points.
The last two methods also block unwanted energy by using a protective component connected in series with the power feed to the protected load, and additionally may shunt the unwanted energy like the earlier systems. Single-outlet surge protector, with visible connection and protection lights A metal oxide variety (MOVE) consists of a bulk semiconductor material (typically sintered granular zinc oxide) that can conduct large currents (effectively short-circuits) when presented with a voltage above its rated voltage.
Move may be connected in parallel to increase current capability and life expectancy, providing they are matched sets. (Unmatched Move have a tolerance of approximately ±10% on voltage ratings, which may not be sufficient.
) For more details on the effectiveness of parallel-connected Move, see the section on Joules rating elsewhere in this article. Every time an MOVE activates (shorts, ) its threshold voltage reduces slightly.
In a power circuit, you may get a dramatic meltdown or even a fire if not protected by a fuse of some kind. Most modern surge strips and house protectors have circuit breakers and temperature fuses to prevent serious consequences.
Only the MOVE is disconnected leaving the rest of the circuit working but not protected. Older surge strips had no thermal fuse and relied on a 10 or 15 amp circuit breakers which usually blew only after the Move had smoked, burned, popped, melted and permanently shorted.
If current impulses remain within the device ratings, life expectancy is exceptionally long. If component ratings are exceeded, the diode may fail as a permanent short circuit; in such cases, protection may remain, but normal circuit operation is terminated in the case of low-power signal lines.
TVS diodes are also used where spikes occur significantly more often than once a year, since this component will not degrade when used within its ratings. These devices can be paired in series with another diode to provide low capacitance as required in communication circuits.
A Redactor is another thruster type device used for similar protective purposes. These thyristor-family devices can be viewed as having characteristics much like a spark gap or a GDT, but can operate much faster.
They are related to TVS diodes, but can “break over” to a low clamping voltage analogous to an ionized and conducting spark gap. After triggering, the low clamping voltage allows large current surges while limiting heat dissipation in the device.
Note Move (blue disks) and Gets (small silver cylinders). A gas discharge tube (GDT) is a sealed glass-enclosed device containing a special gas mixture trapped between two electrodes, which conducts electric current after becoming ionized by a high voltage spike. 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.
Gets take a relatively long time to trigger, permitting a higher voltage spike to pass through before the GDT conducts significant current. Unlike other shunt protector devices, a GDT once triggered will continue to conduct at a voltage less than the high voltage that initially ionized the gas; this behavior is called negative resistance.
Additional auxiliary circuitry may be needed in DC (and some AC) applications to suppress follow-on current, to prevent it from destroying the GDT after the initiating spike has dissipated. Some Gets are designed to deliberately short out to a grounded terminal when overheated, thereby triggering an external fuse or circuit breaker.
Due to their exceptionally low capacitance, Gets are commonly used on high frequency lines, such as those used in telecommunications equipment. Because of their high current-handling capability, Gets can also be used to protect power lines, but the follow-on current problem must be controlled.
It can dissipate power continuously, and it retains its clamping characteristics throughout the surge event, if properly sized. The two brass hex-head objects on the left cover the suppressors, which act to short overvoltage on the tip or ring lines to ground. A spark gap is one of the oldest protective electrical technologies still found in telephone circuits, having been developed in the nineteenth century.
The gap dimension determines the voltage at which a spark will jump between the two parts and short to ground. The typical spacing for telephone applications in North America is 0.076 mm (0.003 inches).
Carbon block suppressors are similar to gas arrestors (Gets) but with the two electrodes exposed to the air, so their behavior is affected by the surrounding atmosphere, especially the humidity. Since their operation produces an open spark, these devices should never be installed where an explosive atmosphere may develop.
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 an LNB up the coaxial down link.
These devices are not rated in joules because they operate differently from the earlier suppressors, and they do not depend on materials that inherently wear out during repeated surges. SM's 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. This type of suppressor differs from others by using banks of inductors, capacitors and resistors that suppress voltage surges and inrush current to the neutral wire, whereas other designs shunt to the ground wire.
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. Experimental results show that most surge energies occur at under 100 joules, so exceeding the SM design parameters is unlikely.
SM's 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). SM's suppression focuses its protective philosophy on a power supply input, but offers nothing to protect against surges appearing between the input of an SM device and data lines, such as antennae, telephone or LAN connections, or multiple such devices cascaded and linked to the primary devices.
Data transmission requires the ground line to be clean in order to be used as a reference point. In this design philosophy, such events are already protected against by the SM device before the power supply.
The initial costs of SM filters are higher, typically 130 USD and up, but a long service life can be expected if they are used properly. An Exploration of ... Paralleling Multiple Lower Energy Move (PDF).
^ Circuit Components Inc. “Filtering and Surge Suppression Fundamentals” (PDF). Includes extensive comparison of design trade offs among various surge suppression technologies.
CS1 main: archived copy as title (link) ^ “Application Note 9773 “Variety Testing” Jan 1998. See “Variety Rating Assurance Tests” on page 10-145 for definition of “end-of-lifetime (PDF).