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Electrical Blog: What Is SPD

SPD stands for Surge Protective Device. It is an electrical device designed to protect electrical systems and equipment from voltage surges or transients caused by lightning strikes, power grid switching, or other electrical disturbances. Surge events can result in high levels of electrical energy entering the system, potentially damaging sensitive equipment or causing electrical failures. Surge events pose a significant threat to the stability and integrity of electrical systems. To counter this risk, Surge Protective Devices (SPDs) play a crucial role in safeguarding equipment from damaging voltage surges. In this article, we will explore the importance, functionality, and benefits of SPDs in protecting electrical systems and the equipment connected to them.

The primary function of an SPD is to divert excessive voltage and current away from the protected equipment, ensuring that the voltage remains within safe limits. This is typically achieved by using metal oxide varistors (MOVs) or other similar technologies that have the ability to absorb and dissipate the excess energy generated by the surge.

SPDs are installed at various points within an electrical system to provide comprehensive protection. They can be installed at the main electrical service entrance to safeguard the entire building or at specific points such as distribution panels, subpanels, or individual equipment. The placement of SPDs depends on the specific needs and vulnerabilities of the electrical system.


Surge Protective Devices (SPDs) play a vital role in mitigating the risks posed by voltage surges in electrical systems. By diverting excessive energy away from sensitive equipment, SPDs protect against damage, improve reliability, and ensure safety. When properly selected and installed, SPDs provide an essential layer of defense, reducing equipment downtime, extending lifespan, and complying with relevant codes and standards. As technology continues to advance, SPDs will evolve to meet the evolving challenges of surge protection, ensuring the longevity and reliable operation of electrical systems.

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