The core component of a surge-protected power strip is the Surge Protective Device (SPD), which utilizes non-linear components such as Metal Oxide Varistors (MOVs) and Gas Discharge Tubes (GDTs). When a transient overvoltage (such as a lightning surge) occurs in the circuit, these components rapidly conduct, limiting the overvoltage to a safe range or shunting the overcurrent to the ground.
Taking the zinc oxide varistor as an example: it exhibits high impedance during normal operation but rapidly switches to low impedance when the voltage reaches the breakdown threshold, creating a discharge path; it reverts to a high-impedance state once the abnormal condition subsides.
Some surge-protected power strips incorporate multiple zinc oxide varistors-corresponding to the neutral, live, and ground lines-along with thermal fuses and ceramic gas discharge tubes (GDTs) to provide multi-layered protection. Ceramic GDTs are characterized by low inter-electrode capacitance, high surge current capacity, and excellent insulation properties.
Certain products employ a dual-technology approach combining a varistor with a thermal fuse: the varistor handles voltage limiting, while the thermal fuse blows automatically during abnormal conditions to provide comprehensive circuit protection.
Typical three-wire surge protection configurations include L-N (Live-Neutral), L-G (Live-Ground), and N-G (Neutral-Ground) protection modes.