In today’s electronics-reliant world, protecting sensitive equipment from sudden voltage spikes, known as surges, is crucial. Type 2 Surge Protective Devices (SPDs) play a vital role in this safeguard strategy. This article delves into the definition, working principle, and application scenarios of Type 2 SPDs.

What are Type 2 Surge Protective Devices (SPDs)?

Type 2 SPDs are secondary surge protection devices designed to mitigate indirect surges caused by lightning strikes or switching transients within a building’s electrical system. Installed downstream of the main service panel or after a Type 1 SPD (for direct lightning strikes), they provide an additional layer of protection for delicate electronic equipment.

How do Type 2 SPDs Work?

The core technology employed in most Type 2 SPDs is the Metal-Oxide Varistor (MOV). These MOVs behave like open circuits under normal operating voltages. However, when a surge strikes, the voltage rapidly increases. At this point, the MOV kicks in, acting as a conductor and diverting the surge current safely to the grounding system. This effectively shields connected devices from the damaging effects of the surge.

Dc Or Ac SpdWhen are Type 2 SPDs Used?

Type 2 SPDs are ideal for protecting a wide range of electronic equipment in various settings, including:

  • Residential Homes: Safeguarding household electronics like televisions, computers, and home entertainment systems.
  • Commercial Buildings: Protecting sensitive equipment in offices, retail stores, and restaurants.
  • Industrial Facilities: Guarding crucial control systems and automation equipment.
  • Telecommunication Systems: Ensuring the integrity of data and communication networks.

End-of-Life Considerations and Replacement

Type 2 SPDs require replacement upon reaching their end-of-life, influenced by both age and the number of surges they have absorbed. Two primary failure modes dictate replacement:

  • Thermal Disconnection: After handling multiple surges, the MOV’s leakage current increases, generating heat. A built-in thermal fuse then disconnects the MOV from the circuit as a safety measure.
  • Short-Circuit Failure: This occurs due to surges exceeding the SPD’s design capacity or continuous overvoltage situations.

Well-designed Type 2 SPDs often feature visual indicators to signal replacement needs. Additionally, some models come in a modular format, allowing for easy cartridge replacement. For industrial applications demanding utmost service continuity, remote signaling contacts are available to trigger alarms upon SPD end-of-life.


By implementing Type 2 SPDs, you can significantly enhance the protection of your valuable electronics against damaging voltage surges, ensuring their longevity and optimal performance.