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How Do Surge Protectors Work?

How Do Surge Protectors Work?

Surge protectors are voltage limiting devices that protect our electronic and electrical devices from high voltage. It is primarily used in computer power supply lines. Scroll down to learn how these devices work.
Suganya Sukumar
Surge protectors, also called surge suppressors, voltage limiters or surge arrestors, are electronic devices that are designed to prevent lightning strikes and other excess volts surging into the power lines of our house. You might have studied in physics, that the voltage of lightning is about 108 volts. What would happen if such voltage strikes the power lines of electronic devices in your home? Obviously it would damage it! Also, we know that, the standard voltage used in household and office appliances is 120 volts (in the US). If voltage above this value passes through any device, then there will be a problem for sure. Such problems can be averted by using surge suppressors.
What is a Surge
Surge is a steep rise of voltage in the power transmission lines due to lightning and other internal causes. A power surge is also known as transient voltage. Surge is a temporary voltage rise and it lasts only for a fraction of a power cycle wave. A power wave may have single or multiple voltage spikes that cause damage to the electronic devices. A surge should be protected properly; if not, it may lead to insulation failures in the electrical wiring or electrical devices due to high or excess voltage. As a result of high magnitude of the power wave, the parts of the electrical devices through which the surge passes, can be destroyed. The effect caused by a surge can be compared to the effect of applying high water pressure inside a hose. The hose will break open when high water pressure is applied to it. Similarly, a surge when passes through an electrical wiring, will burn the wire.
How Does a Surge Suppressor Work
This device passes current to electrical and electronic devices. If the voltage surges to a high value beyond the threshold level of the device, the surge suppressor diverts it to the ground, thereby saving the equipment. Generally, Metal Oxide Varistor (MOV) device is used in most of the surge suppressors. MOV consists of semiconductors which have a property of variable resistance. Now, let's see what happens when low voltage and high voltage passes through it.
  • When Low Voltage Passes Through: The bulky metal-oxide semiconductor maintains high resistance and so low current passes in the circuit. This is simple to understand if you know the Ohm's law, i.e., the current through a conductor between two points is directly proportional to the potential difference across the two points. In simple words, at constant temperature, as resistance increases, current decreases.
  • When High Voltage Passes Through: The resistance of the semiconductor reduces and consequently the current is increased. In order to eliminate excess voltage, the MOV conducts high current. This surge current is diverted to the ground and the device is powered with adequate current supply without any damage.

But what if the voltage is neither high nor low? MOV doesn't act during this situation.
Primary Components
Surge suppressor systems include one or more of the following primary electronic components mentioned below.
Component Function
Metal Oxide Varistors It consists of semiconductor material and limits the voltage to 3-4 times the accepted voltage inside the circuit, by diverting the surge current without affecting the protective load.
Transient Voltage Suppression (TVS) Diode It is a type of Zener diode and it limits the voltage less than twice the normal voltage with which, the device operates. It can withstand only small current spikes, which is a limitation in the device.
Gas Discharge Tube (GDT) This device conducts electric current when a special mixture placed in between two electrodes gets ionized. When the trigger voltage exceeds beyond a considerable level, the device will short it, thereby protecting the load from high voltage.
Thyristor Surge Protection Device (TSPD) It is another solid-state device that limits the voltage.
Selenium Voltage Suppressor This device is also designed to clamp excess voltage. It is mainly used in DC circuits.
Quarter-wave Coaxial Surge Arrestor This device deals with surges in RF (Radio Frequency) signal transmission paths. It is very useful in telecommunication applications by protecting the device when the frequency of the signal rises above 400 MHz.
Series Mode Surge Suppressors It is used to prevent transient voltage by blocking or diverting high frequency line voltage signals.
Carbon Block Spark Gap Overvoltage Suppressor It is one of the protective devices which consists of two electrodes (carbon rod electrode is held a certain distance away from the second electrode) exposed to air. A spark is produced when voltage rises high and the excess voltage is short to ground.


Generally, circuits consisting of electronic devices are highly vulnerable to voltage spikes, as they do not have high voltage or current withstanding capability. Though repeated surges don't harm the appliances such as computers, DVD players etc., it will reduce the lifespan of these devices.