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    25 Jul, 2022
    Posted by elcb_admin
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    Surge Protective Devices: Everything You Need To Know


    Surge Protective devices are components used in data and power systems to secure the hardware. They are affected in low power circuits. However, the operation of these systems is to prevent destruction or disruption due to transient over voltages.

    SPDs remove electrical surges or impulses by acting as a low – resistance path. Thus, turning transient voltages into currents and rerouting them along the ground. This is done to decrease the transmission line’s attack. This device is parallel-connected to the power supply circuits of the loads it is supposed to protect. This is the most widely used and effective unbalanced voltage Protective method.

    Categories of surges

    Surge transient voltages are induced by the switching operation of electrical loads in a building, as well as magnetic and inductive coupling caused by magnetic field formation as large currents flow. Static electricity and lightning storms can also end up causing surges. As Lightning is a significant source of electromagnetic interference in electrical systems.

    There are two types of lightning strikes:

    • Direct:Lightning strikes pass directly through lightning rods or transmitters can cause damage to electronic devices due to high energy impulses.
    • Induce:When a direct lightning strike strikes a line, the surge current is split in two flow path due to changes in the electromagnetic field caused by lightning strikes. Surges can also occur on power lines that are not directly affected by a lightning strike. Lack of surge Protective device in installation can destroy the nearby electric system. Plus, there may be a fire that poses a physical threat to humans.

    Lightning surges on power grids

    1.The lightning path is directly connected to the power structure transmission lines.

    2.Electro – magnetic pairing of energy into electric grid conductors caused by nearby thunder discharge radiant energy.

    Principle of surge Protective device

    The principle of operation of Surge Protective Devices (SPDs) is centered on safeguarding electrical systems from transient overvoltages, also known as surges. The main concept is to limit these voltage spikes by either diverting or limiting the surge current. Here’s how it works:

    Metal Oxide Varistor (MOV): One of the most common components within an SPD is the metal oxide varistor. A varistor is an electronic component with a resistance that varies with the applied voltage, showcasing a nonlinear, non-ohmic current-voltage characteristic. When the voltage is normal, the MOV has a very high resistance, allowing normal operation of the electrical system. However, during a surge event, the MOV’s resistance drops dramatically, becoming very low. This change allows the MOV to “absorb” excess voltage and then act as a “shunt” by diverting the excess current away from the protected load and safely to the ground.

    How SPDs Divert Current:
    1.When a voltage spike occurs, the SPD quickly reacts, creating a low-impedance (low-resistance) path to the ground.
    2.This diverts the impulse current away from the critical loads.
    3.By diverting the current, the SPD also reduces the resulting voltage experienced by the connected equipment to a safer level.

    Other Components of SPDs:
    SPDs may also use Gas Discharge Tubes (GDTs), Silicon Avalanche Diodes (SADs), or Transient Voltage Suppressor (TVS) Diodes, depending on the specific design and protection requirements.

    Result of SPD Action:
    By functioning this way, SPDs protect sensitive electronic devices from voltage spikes caused by lightning strikes, power surges, and other types of electrical disturbances.
    The goal is to prevent these transients from causing damage or operational issues, extending the lifespan of the equipment and ensuring its functionality.

    Selection of SPD:
    The proper selection of an SPD is based on several factors including the location within the electrical system, the types of surges expected, and the vulnerability of the connected equipment.
    The selection criteria involve the SPD’s Maximum Continuous Operating Voltage (MCOV), Nominal Discharge Current (In), and Voltage Protection Rating (VPR), among other parameters.

    Types of surge protectors

    1.SPD type 1

    Type 1 SPDs are installed at the service entrance of a building’s electrical system. Their primary function is to shield against large surges, typically originating from external sources, such as direct lightning strikes. They are the first line of defense and can dissipate high-energy impacts. In terms of installation, Type 1 SPDs are mounted on the line side of the main service entrance panel, between the utility pole and where the electrical service enters the building.

    2.SPD type 2

    Type 2 SPDs are used in the main distribution board (or at sub-distribution boards) and are designed to manage surges that originate from within the building, such as those caused by large equipment switching on and off. These SPDs provide protection to circuits and devices downstream and are particularly important in safeguarding sensitive electronic equipment. They manage the surges that Type 1 SPDs may not fully divert, capturing smaller, repetitive surges that may otherwise degrade or damage connected devices over time.

    3.SPD type 3

    Type 3 SPDs are installed at the point of use – close to the end-use devices they’re meant to protect, such as computers, televisions, or other electronic appliances. They are generally used in conjunction with Type 2 SPDs for a more comprehensive protection strategy. They are designed to suppress the remaining surge energy after Type 2 SPDs have functioned, therefore dealing with surges that infiltrate into individual pieces of equipment.

    4.Combined Type 1+2 SPDs

    Some SPDs combine features of both Type 1 and Type 2 devices. These Type 1+2 SPDs can protect all electrical installations against lightning strikes by discharging the current and are suited for locations with a high density of lightning strikes.

    Features of Surge protector devices

    1. Large Protection Flow: SPDs are designed to handle large surge currents, efficiently diverting them to prevent damage to the electrical system and connected devices.

    2. Extremely Low Residual Pressure:The residual voltage, or let-through voltage, after the SPD has acted is kept as low as possible. This is the voltage that equipment will actually experience during a surge event, and keeping it low is essential for protection.

    3. Fast Response Time: SPDs act swiftly to combat surges, often within nanoseconds, which is crucial to safeguard equipment from the rapid onset of voltage spikes.

    4. Arc Extinguishing Technology: Modern SPDs utilize advanced arc extinguishing technologies to prevent any fire hazards that could potentially arise from surge events.

    5. Temperature Control Protection Circuit: A built-in circuit that monitors temperature prevents overheating of the SPD components, ensuring stability and preventing thermal runaway or damage.

    6. Built-In Thermal Protection: SPDs often have thermal fuses or similar mechanisms to disconnect the SPD from the circuit in the event of overheating, providing an extra layer of safety.

    7. Maximum Continuous Operating Voltage (MCOV): The highest voltage an SPD can withstand on a continuous basis without degradation or failure, signifies the SPD’s ability to handle normal voltage fluctuations.

    8. Voltage Protection Rating (VPR): This rating indicates the maximum voltage that will be delivered to connected equipment during a surge event after the SPD has functioned.


    The field of ‘Surge Protective Devices’ encompasses a broad spectrum of types and applications tailored to varying needs from domestic to industrial scales. Selecting the right SPD calls for a comprehensive understanding of the underlying technology, its applications, and ensuring compliance with industry standards.

    These devices square measure helpful for preventing the loss or injury of delicate equipment, however they’re conjointly necessary for safety. Surge Protective is needed for any business, industrial, or public building that’s equipped by overhead lines, which suggests that the overwhelming majority of buildings would force it. Moreover, we’d like surge protective devices as their square measure type of electrical problems like lightning strikes, power outages, grid malfunctions.

    When it comes to securing an electrical network, there is no one-size-fits-all strategy. Each setup requires a detailed examination of its ‘Power Surge Causes and Prevention’ mechanisms and a thorough understanding of how the ‘Power Strips vs. Surge Protectors’ debate applies to their specific situation.

    Equipped with the knowledge of various SPD types, their applications, and vigilant maintenance practices, one can significantly increase the resilience of their electrical infrastructure against unpredictable and damaging electrical surges.

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