How does A Surge Protective Device ( SPD ) work?

A Surge Protective Device (SPD) is designed to protect electrical systems and equipment from voltage spikes or surges. These surges can occur due to lightning strikes, power outages, or switching events within the power grid. SPDs act as a barrier to divert or absorb excessive voltage, preventing damage to sensitive equipment.

Here's how they work:

1. Detection of Surges: When there’s a sudden increase in voltage (a surge), the SPD detects it almost instantly. This surge could come from external sources like a lightning strike or internal sources like power switching.

2. Clamping or Diverting the Surge: SPDs use components like metal oxide varistors (MOVs), gas discharge tubes (GDTs), or transient voltage suppression diodes (TVS). These components are designed to conduct current only when the voltage exceeds a certain threshold. When a surge occurs, they "clamp" the voltage by conducting the excess voltage away from the protected equipment.

3. Dissipation: Once the surge is diverted, the SPD safely dissipates the excess energy, typically in the form of heat, or redirects it into the ground (depending on the type of SPD).

4. Returning to Normal Operation: After the surge has passed, the SPD returns to its normal, non-conducting state, allowing regular voltage to flow through the system again.

There are different types of SPDs, including whole-house models, which protect an entire electrical system, and point-of-use models, which protect specific devices. The effectiveness of an SPD is determined by its voltage clamping level, surge current rating, and response time.

SPDs are important for sensitive equipment like computers, servers, HVAC systems, and even home appliances, as surges can damage internal components.