What is a Surge Protector? Function, Necessity, Use

Hey, are you know surge protector is one of the most useful electrical protective devices that can save huge losses and damages. It not only protects the electrical circuits, in fact, but it also protects so many costly devices, equipment, systems, etc. When it comes to point of electrical protection, surge protection is a very important topic. I may sure that you know there are a lot of electrical protective devices available, some of them are going to be discovered and waiting to release in the market.

In this long and detailed article, we are going to explore all the important information and knowledge about surge protectors. Before going start I highly recommend gathering the basic knowledge of electricity, voltage, current, and other key factors and terms. Because without having the basic electrical knowledge you will not able to understand the concept clearly.

What is a Surge Protector? Definition

Surge Protector is an electrical protective device that protects the electrical circuits, systems, or devices from the harmful effects of high voltage or high current caused by surge voltage.

It will be better, first of all, if we know what is a surge in electrical engineering. The term 'Surge' means a sudden increase by a large amount. Here, in case of the surge protection, voltage increases suddenly by a large amount and this device gives the protection against this suddenly increasing of voltage. That is why it is known as Surge Protector. And this suddenly increased voltage is known as Surge Voltage or Spike Voltage.

Now, you may ask when we consider a voltage as a surge voltage or spike voltage. There are two important variables that are used to express the surge voltage that is magnitude and duration. Generally, when the voltage reaches above 1000 volts and typically lasts 1 to 30 milliseconds can be called as a spike or surge voltage. Thunderstorms or lighting hit the power line which causes to reach the voltage over 100000 volts also. Remember that duration is more harmful than magnitude. For example, a spike of 1000V with 30 milliseconds is more dangerous than 2000V with 10 milliseconds.

The surge voltage and spike voltage is almost the same only the difference is spike voltage has an extremely low duration(a few nanoseconds) than the surge voltage.

A surge protector is also known by so many other different terms such as Surge Suppressor, Spike Suppressor, Surge Absorber, Surge Diverter, Surge Protection Device(SPD), Transient Voltage Surge Suppressor(TVSS), etc.

The Actual Function of a Surge Protector

The main function of a surge protector is to protect any electrical circuits, systems, sensitive parts, or sensitive devices from the surge or spike voltage. There may be additional functions or features available according to their design, construction, types, etc. For example, a surge protector inbuilt with a power strip not only protect the devices, in fact, it helps to distribute electrical power also. It helps to connect multiple devices to connect with a single power strip. 

We can understand the function in detail with an example. For example, you have an expensive home theater at your home. It is designed to operate from 120V to 230V or a maximum of 300V. Whenever the voltage applied to it crosses 300V, the home theater will damage. it is sure that there are so many reasons the supply voltage may increase above 300V. There are a lot of devices to overcome the high voltage or overvoltage problem. A great example is a stabilizer. A stabilizer is a device that make always constant its output voltage even if its input voltage goes down or high. But must note that it is only suitable for a constant voltage or long duration.

I mean to say that if your voltage goes high or low for a few minutes or hours, then the stabilizer is ok to use. But the surge voltage or spike voltage is quite different. It has a very short duration from some nanoseconds to a few milliseconds. So, in this case, the stabilizer can not do anything. In fact, the stabilizer may be damaged due to this surge voltage. So here we must need to install a surge protector that is specially designed to operate with high voltage with low duration surges or spikes. In the conclusion, we can say the function of a surge protector depends upon two key factors that are Voltage magnitude and Duration.

How does a Surge Protector Works?

Basically, a surge protector works by either blocking the high voltage or flowing a large shorting current to limit the voltage supplied to the external devices are to be protected. These two methods - voltage blocking and shorting current are mostly used by the all types of surge protectors.

Voltage Blocking Principle

The phenomenon of voltage blocking is very simple. When system voltage is normal the surge protector allows all the voltage across the external device. But when the voltage exceeds the normal voltage, it blocks the high voltage above the normal voltage. Generally, surge protectors are designed to operate with 3 or 4 times higher voltage than the normal voltage. For example, when the system voltage is 120V(for USA) or 230V (for India), the surge protector nothing does. But when the voltage exceeds 480V( for USA) or 920V(for India) which are four times higher than the normal voltage, the surge protector will be activated and it will block the voltage.

The voltage blocking is done by series inductors. Yes, the surge protectors which are designed to operate with the voltage blocking principle have series inductors in their construction. Although a surge protector is constructed with so many elements but here the main element is a series inductor. We know that inductor is a passive element that always tries to change the sudden change in the flow of current through it. So when the surge voltage occurs it tries to a sudden change in the flow of current through the series inductor. And the series inductor will block the voltage when it detects the sudden change. This happens due to the self-inductance property of the inductor.

Shorting Current Principle

Another important principle on which the surge protector works, that is shorting current principle. In fact, most of the expensive, highly sensitive, and high sensitive surge protectors are works on this principle. Now the question is what is shorting the current principle. We know that the flow of electric current depends upon two factors - voltage and resistance. When the resistance is constant the flow of current is directly proportional to the voltage. Also, we know that when there is a large current flow due to a short circuit the drop in supply voltage is also more. For example, when we short both terminals of a 230V power source, the voltage will drop or decrease quickly. This phenomenon is used to limit the surge voltage. 

So the surge protector(which is designed to operate with shorting current principle) temporarily shorts the terminals wherever it detects the surge voltage. As a result, a very high shorting current flows that cause to decrease or reduce the surge voltage instantly into the normal voltage. This shorting is done by capacitors, spark gaps, discharge tubes, Metal Oxide Varistors(MOVs), Zener Diodes, or all the devices that start conducting current when the voltage across them crosses a threshold voltage limit.


The capacitor just does the opposite to the inductor. That means the inductor blocks the current when it suddenly changes or increased whereas the capacitor allows to flow of the current when the voltage across it suddenly changes or increased. For small devices, electronic circuits, capacitors, and different elements are used for surge protection.

Spark Gap

A spark gap is an arrangement of two conductors separated by a small gap and this gap is filled by either any gas or air. It is designed to conduct current from one conductor to another conductor through that gap when a very high voltage appears across those electrodes. The current flows in the form of a spark. So the spark gap arrangement is connected between the terminals is to be shorted during the occurrence of surge voltage. The spark gap arrangement is used for large and expensive devices.

The other important components are explained in the below section.

Construction of a Surge Protector and Its Components

As we know that the surge protector gives protection against surge voltage either by blocking it or reducing it by shorting current. So the different surge protectors have different constructions. Anyway, the most common primary components that are used to construct surge protectors are explained below.

Metal Oxide Varistors(MOVs)

MOVs are built with a bulk of semiconductor materials such as sintered granular zinc oxide and it is able to conduct a large current through it when the voltage across it exceeds the threshold voltage. MOV devices are designed to block the voltage 3 to 4 times higher than the normal circuit voltage. Basically, they reduce or limit the surge voltage by diverting the shorting current to another path instead of a load circuit.

A surge protector may be built with a single MOV or multiple MOVs are connected in parallel. Multiple MOVs are connected in parallel to increase the current conduction property. A single MOV-oriented surge protector can withstand less current than multiple MOV-oriented surge protectors.

The main drawback of the MOV device is its limited or finite life span. Yes, after every activation of the MOV, the threshold voltage decreased. After facing so many spikes, the threshold voltage got decreased to the normal circuit voltage. Hence the MOV may get melted or not be able to block the surge voltage.

Transient Voltage Suppression(TVS) Diode

Transient Voltage suppression or TVS diode is one type of avalanche diode. TVS diodes are very fast spike voltage limiting devices, in fact, in some cases, they can provide a better function than MOV devices. The life span of the TVS diode is more than the MOV device.

The main drawbacks of TVS diodes over MOV devices are,
  1. Low Clamping Voltage
  2. Low Energy absorption capability
  3. Low Current Wihstanding capability

Yes, the clamping voltage of the TVS diode is lower than MOVs. TVS diode can limit the spike voltage to less than two times the normal circuit voltage. The low energy consumption capability limits the use of the TVS diode. 

TVS Diode-oriented surge protectors are mostly suitable for data transmission circuits where fast operation is required at a low voltage.

The other important components that are used to build surge protectors are,
  • Line Reactors
  • Choke Coils
  • Gas Discharge Tubes
  • Semiconductor oriented Voltage Suppressors

Important Specifications and Ratings of Surge Protector

Rating and specifications are very important points. It helps a lot to understand the surge protector deeply.

Operating Voltage

Operating voltage is a basic voltage rating for which level of voltage the surge protector is used. For example, the domestic operating voltage in India is 230V whereas in the USA the operating voltage is 120V. So you cannot use a 120V surge protector in India and a 230V surge protector in the USA. So, the basic operating voltage is important to select a proper device wherever it is to be used. Also, we know that the surge protector is designed to operate with 3 or 4 times higher voltage than the normal operating voltage. So if the operating voltage is different, the protection level also be different.

Clamping Voltage

The clamping voltage is also known as let-through voltage. The let-through voltage or clamping voltage ensures that what spike voltage or surge voltage will cause to activate the surge protector to take the protective action. Remember that the lower clamping voltage is better than the higher clamping voltage. Because it will help to protect your device from small spikes also. But sometimes it is seen that the lower clamping voltage rating shortens the life expectancy for the overall protection system.

The standard clamping voltage of a 120V device is 330 volts. That means when the system voltage increased to 330 volts due to the surge faults, the surge protector will be activated. The common low-level recommended let-through voltage for 120V devices are 330V, 400V, and 500V. Always it is recommended to use low-level let-through voltage devices for highly sensitive circuits or devices. Because some surge voltage of 400V can highly damage the sensitive devices. In that case, you should not use the surge protector of 500V or more than that clamping voltage. Because it will pass a higher voltage than 400V to the external device.

So the clamping voltage not only ensures the efficiency of the surge protector but also ensures that how it will be effective for your circuit or device is to be protected.

Response Time

We know that there are two main important factors in a surge voltage that is magnitude and duration. The magnitude is handled by the clamping or let-through voltage of the surge protector. And the duration can be handled by the response time of the surge protector. We know that a surge voltage lats a few milliseconds and the spike voltage lats a few nanoseconds. In this case, if your surge protector takes a long time to respond then what is the worth of it.

Surge protectors are responding very quickly whenever a fault occurs but it does not respond instantly also. So the response time of a surge protector is also a very important factor while it is designed or constructed. The lower response time ensures the high efficiency of the surge protector. Metal Oxide Varistor or MOV devices are very efficient in case of the response time. In fact, almost all the MOV devices have a response time of a few nanoseconds so they are useful for both surge faults as well as spike voltage.

Energy Absorption/ Dissipation or Joule Rating

This measure is most relevant to the MOV-based surge protectors. Other types of surge protectors such as series inductor type, and spark gap type is not relevant to this measure because they do not absorb any energy they just block or short or bypass the voltage and current. The joule rating of a MOV device ensures that how much energy it can absorb in a single event. Remember that it gives you only a theoretical value. There is a large difference between theoretical and practical. 

For example, if the joule rating is 1000 joule then it implies that in a single event the surge protector can absorve 1000 joule. The energy absorption is also calculated with shorting current. A standard device can withstand shorting current up to 40000 amperes. 

The energy absorption also depends upon the duration of the event. In practicality the event duration s low, hardly a spike voltage lasts up to 10  milliseconds so the power dissipation also is low. Surge protectors are designed in such a way that if the current exceeds the maximum withstand current the MOV device will be isolated from the circuit by blowing fuse otherwise it may be got melted. 

The joule rating is a very important factor as it relates to the overall efficiency fo the surge protector, heat production, life expectancy, etc. More rating means better protection.

Difference between Surge Protector and Power Strip

(1) The main difference between a surge protector and a power strip is, the surge protector is basically protective whose main function is to give protection against surge voltage or spike voltage whereas the power strip is a combination of multiple electrical sockets whose main function is to distribute the electrical power to the multiple devices connected to it.

(2) A basic power strip is built with the combinations of multiple sockets connected to the end of a flexible cable. But the modern specially designed power strips are inbuilt with different types of protective devices, circuit breakers, indicators, etc. In fact, some home-used power strips come with inbuilt surge protectors.

(3) It is not sure that a surge protector is always in built with a power strip, a power strip, and surge protector both may be standalone devices. We can say the surge protector is an automatic device that operates automatically whenever faults are detected whereas the power strip is not an automatic device, it is turned off or turned on manually by operating the switch.

(4) Most of the surge protectors have a single input and a single output whereas the power strip has a single input and multiple outputs. So, it is connected to a single source of power supply and distributes power to the different multiple devices.

(5) Surge protectors do not have any energy-saving features whereas some power strips come with inbuilt energy-saving features.

(6) Surge protectors are available from all the low voltage to high voltage applications whereas the power strips are available for low voltage applications such as household purposes, electronics uses, etc.

Different Types of Surge Protector Devices

Based on the construction, working principle, operation, and function there are different types of surge protectors available in the market.

Power Surge Protectors

The surge protectors are used to protect electrical power lines, electrical devices, electrical power distribution, electrical power transmission, etc are called power surge protectors. In our homes, domestic uses, industries, and power surge protectors can be seen.

Data Surge Protectors

The surge protectors are used in data transmission lines, and communication systems are called Data Surge Protectors. Basically, data surge protectors are used in data lines, communication network lines, etc.

The common examples and uses of data surge protectors are,
  1. Video surveillance lines are highly affected by the surge or transient overvoltages that affect the video transmission. Here, you will see the application of Data Surge Protector.
  2. These protectors are also used in ethernet lines such as category or CAT6, CAT5E, and CAT5 lines.
  3. These are also used with Power Over Ethernet(PoE) equipment, and devices.
  4. These protectors are also used with patch panels.

Differences between Power Surge Protectors and Data Surge Protectors

The main differences between power surge protectors and data surge protectors are,
  1. Power surge protectors are designed to work with high voltage and power whereas data surge protectors are designed to work with low voltages.
  2. The response time of the data surge protectors is very lower than power surge protectors.
  3. Data surge protectors are very compact and they are more expensive than power surge protectors for the same voltage level.
  4. Power surge protectors are used in electrical power lines whereas the data surge protectors are used in data lines, communication lines, etc

Surge Protection Device(SPD)

Surge Protection Device or SPD is a low voltage surge protector. It is mostly used in domestic low voltage distribution boards. Its structure is very similar to a double pole MCB. Basically, it is installed in the main incoming circuit. SPD mostly comes with a double pole, four pole configurations.

Generally, the SPD is connected in parallel with the power circuit for the load. The SPD connected in parallel has a very high impedance in normal conditions. But when the surge voltage occurs and it is detected by the SPD, the impedance of the SPD goes very low so it bypasses the excessive current to the ground through it so the voltage in the power circuit remains normal.

SPDs are available for both power surge protection and data surge protection.

There are three types of SPD,

Type 1 SPD

Type 1 SPD is used to protect the electrical installations against direct lightning strokes. It provides high protection than other devices. This type of protection device is used in commercial buildings, service sectors, and industrial electrical installations. Type 1 SPD is characterized by a 10/350 micro-second current wave.

Type 2 SPD

Type 2 SPD is characterized by an 8/20 micro-second current wave. It is the most useable low voltage surge protection device. You will be seen its applications in low voltage electrical power distribution boards, switchboards, etc. The main function of this device is to protect the devices or circuits from high or overvoltage sure faults.

Type 3 SPD

Type 3 SPD is used as a supplement to type 2 SPD. It has a very low discharge capacity. Basically, it is characterized by the combination of the voltage waves(1.2/50μs) and current waves (8/20 μs).

Important Parameters of Surge Protection Device

There are three main parameters rated on the SPD to describe its characteristics and capacity. Remember that understanding these parameters will help you to characterize any surge protectors.

Maximum Continous Operating Voltage(Uc)

This voltage rating describes that when the system voltage level exceeds that voltage the SPD will activate. For example, if the Uc of an SPD is 300V then the SPD will activate when the system voltage increased beyond 300V. You must select a proper Uc voltage of the SPD according to your normal system voltage and the earthing arrangement.

Voltage Protection Level(Up)

When the SPD is activated and conducting the discharge current then also some voltage present across the terminal of the SPD. Up is the maximum voltage across the SPD while it is activated and conducting the discharging current. So during the surge fault, the voltage across the SPD is generally lower than the Up. So it is very important to choose the Up rating that should be lower than the maximum overvoltage withstand capacity of the load. If you select an SPD that have higher Up than the maximum overvoltage withstand capacity of the load, then it will not give the proper protection to the load.

Nominal Discharge Current(In)

It is the discharging current that can be conducted by the SPD during the surge fault. Generally, an SPD is designed in such a way that it can withstand the Nominal Discharge Current(In) at least 19 times. So the higher value of In means longer life. It is recommended to choose the SPD having more than 5KA In rating.

Surge Protector Connection and Wiring Diagram

Here, you can see a basic surge protector connection diagram.

Click on the image to enlarge

Surge Protector Connection and Wiring Diagram

We know that surge protectors come in single pole, 2 pole, 3 poles, 4 pole, and many more categories. Here, we have shown a double pole surge protection device. In our home, a surge protector is connected in such a way.

Here, you can see three protective devices are connected between the energy meter and external loads. Just after the energy meter, a double pole MCB(Miniature Circuit Breaker) is connected. You can see the phase and neutral from the energy meter are connected to the MCB as input. The output of the MCB is connected to the input of the RCCB(Residual Current Circuit Breaker). MCB and RCCB are connected n such a way that the power lines go through them. But you can see the SPD is connected in parallel. The phase and neutral are connected to the input of the SPD. But the output of the SPD is connected to the ground.

So, you may understand the SPD does not control the power flow in the circuit. In normal conditions, the SPD provides a very high impedance so no current flows from the phase or neutral to the ground. But when the surge voltage occurs, the SPD will activate and its impedance will go to very low. So the excessive current produced due to the surge voltage will bypass to the ground so the voltage in the system will be normal.

Here, a single-phase system is shown that is why a double pole SPD is used. But in a three-phase three-wire system, the triple pole SPD should be used where all the three phases are connected at the input and output will be connected to the ground. On the other hand, in a three-phase four-wire system, a four-pole SPD should be used where all the three phases and neutral are connected to the input and output is connected to the ground.

Basic knowledge for Surge Protector Installation, Operation, and Maintenance

Surge Protector Installation

Before installing a Surge Protector in your system, you must select a proper Surge Protector that will suitable for your system. In this case, you have to consider the important parameters such as Clamping Voltage, Response Time, Continous Operating Voltage, Nominal Discharge Current, Impulse Current Rating, Autoextinguish flow current, Maximum Discharge Current, and Open Circuit Voltage(UoC). These parameters are already explained in the above section so you will get all the knowledge.

After selecting the proper Surge protector for your system, you should know the proper connection and wiring procedure. Generally, all the instructions are given in the manual of the device you purchased. To implement the actual installation, you must have the proper authorization or contact an authorized person.

After installing a surge protector, you must test its operation. There are so many surge protectors available in the market, they have some additional buttons for testing.

Surge Protector Operation

The operation of the surge protector is automatic. Yes, it is an automatic device. Whenever the surge fault occurs, it will activate and give protection automatically. If the surge protector has any switch for power ON, then you must be turned on it.

Surge Protector Maintenance

The low voltage or domestic surge protectors does not need any special type of maintenance. But the industrial high voltage surge protectors required preventive maintenance. For example,
  • Daily inspection visually if there are any damaged air terminals, loose nuts, loose contacts, etc.
  • Unexpected heat, tripping, etc.
  • Continuity test between surge protection devices, earthing system, load circuit, etc.
  • Replace parts if required after a particular number of events.
Even most industries inspect the surge protection system by an expert or professional every three or five years and gather a report or certification.

Common application and uses of Surge Protector

  1. Low discharge capacity surge protectors are used in power sockets, power trips, etc.
  2. Low Voltage Surge Protection devices are used in distribution boards, switchboards, etc.
  3. Very fast response surge protectors are used in data transmission and communication systems.
  4. High voltage surge protectors are used in industrial electrical installation and electrical transmission systems.

When you should use a Surge Protector?

When you are using very sensitive electronic items such as computers, smart sensors, electronic controls systems, etc then you must use a surge protector with your power source.

Even when you charge your mobile, laptop, iPod, etc then also you need to use a surge protector if your charger is not inbuilt with a surge protector.

Generally, the battery-operated loads(such as power banks, and emergency lights do not require a surge protector as it is not connected to the utility power circuit so there is no chance of lightning stroke on the circuit.

Is Surge Protector necessary for your Home?

Of course, you must need to use surge protectors in your home. You can use either power strip surge protectors or the whole surge protectors.

Power Strip Surge Protectors

Power strips surge protectors are used to protecting a certain amount of devices connected to it. For example, you connected a computer and a TV with a surge protector inbuilt power strip. So, here only the TV and Computers will be protected. Other devices in your home would not be protected.

The main advantages of using a power strip surge protectors are,
  1. These are portable so you can use them anywhere outdoor as well as indoors.
  2. The cost is also very lower than a whole-house surge protector.
  3. Easy to plug or unplug devices.

  1. It cannot protect all the devices used in a home.
  2. It provides a very low-level protection system.
  3. They failed to protect some exceptional cases.

Whole House Surge Protector

The surge protector used to protect all the loads in a house is called a whole house surge protector. Generally, it is installed at the incoming power circuit of the house. You can see in the above working diagram, the surge protection device is connected in parallel with the output of the main incoming MCB.

The main advantages of using a surge protector for the whole house,
  1. These protectors provide very high-level protection.
  2. They can protect all the devices used in the home.

  1. High cost.
  2. Required professional for installation
  3. Not portable.

How to purchase the best Surge Protector according to your requirement?

1. Type/Rating/Pole

For a single-phase electrical system we need to install a single pole or double pole surge protector. It is recommended to purchase a double pole surge protector. A single-pole device allows you to connect either phase or neutral. If you connect the phase. The surge attack that happens on the neutral wire cannot be protected. If you connect the neutral wire then the surge attack that happens on the phase wire cannot be protected. But if you use a double pole device that allows connecting both the phase and neutral wire will protect against surge that happens in any wire between phase or neutral.

As we know there are three types of surge protectors. Type 1 is used for industrial high voltage protection purposes whereas type 2 is used for low voltage domestic purposes.

2. Status Indicator

While you purchasing a surge protector, you must check if it is inbuilt with a status indicator. It helps you to stay always informed is your protector working or not.

3. Types of technologies Used

Some surge protectors are built with MOV devices whereas some of them are built with TVS diodes or other devices. MOV-enabled devices have a very low life span than others but they can be used for high voltage protection. So according to your requirement and budget, you can choose the appropriate device.

4. Warranty

While purchasing a costly device you must check if it comes with a warranty or not. Because quickly damaging can make a huge loss of your money.

5. Testing Certification

While you purchasing, you must ensure that the seller gives you the testing certification or that the device has an identification for it.

6. Branding

It is always recommended to purchase an electrical product, especially a protection device from a branded seller. Because it is related to electrical safety. The local products can not give proper protection, reliability, and long life span.

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What is a Surge Protector? Function, Necessity, Use What is a Surge Protector? Function, Necessity, Use Reviewed by Author on 7/05/2022 Rating: 5

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