What is a surge arrester and what does it protect against?

Surge arrester definition and protection scope:

• Surge arrester (surge protective device / SPD) : Non-linear protective component installed between live circuits and earth. Diverts high-voltage transients (surges) to ground, limiting voltage spike to safe range.
• Overvoltage protection scope : - Direct lightning strikes (rare but catastrophic: 20kV–100kV transients, microseconds duration). - Nearby lightning strokes (induced surge via building earthing). - Switching transients (utility grid switching, reactive load sudden disconnection). - Load dump surges (generator transients). - Harmonic resonance overvoltages (capacitor bank energization, motor soft-starter transients).
• Voltage clamping mechanism : Normal operation (~400V AC), arrester impedance very high (blocks current). Overvoltage surge detected (>900V typical threshold), arrester impedance drops dramatically (low resistance). Surge current diverted to earth; voltage limited to safe 1.5–2kV.
• Technology types : - Metal oxide varistor (MOV): ceramics with non-linear I-V curve. Most common commercial installations. - Spark gap: air/gas breakdown at threshold voltage. Requires follow-on breaker for energy dissipation. - Combination (hybrid): MOV + spark gap for high-current capability.
• Energy dissipation : Surge energy (joules) absorbed by arrester thermal mass or diverted to earth grid. Size arrester per maximum surge energy (typically 10 kJ–100 kJ at 10/350μs waveform per IEC 61643-11).
• Installation requirement : Arrester installed at circuit entry point (main distribution board) to protect downstream equipment (switchgear, motors, control systems). Additional stage-2 arresters at sub-panels for sensitive loads (IT, instrumentation).

Socomec surge arresters (SURGE range) rated per IEC 61643-1 (LV SPD standard) and IEC 61643-11 (lightning impulse test 10/350μs). Multi-stage protection (Type 1/2/3) recommended for critical facilities. Optim-Elec designs surge protection system per installation risk assessment. Contact optim-elec.com.