Surge Protector (Surge Protection Device, SPD)
A surge protector / surge protection device (SPD) is an electrical safety component designed to absorb, divert or clamp sudden-spiking over-voltage surges in power circuits. These short-duration high-voltage surges may come from lightning strikes, grid switching operations, large-equipment on-off transients, or utility grid faults. Its core goal is to limit excessive voltage before it reaches sensitive electrical and electronic equipment, preventing burnout, damage or premature ageing.
How it works
SPDs are normally connected in parallel across the live-neutral or live-earth lines of an electrical system.
Normal operating state: Under standard mains voltage, the SPD has very high impedance, behaving almost like an open circuit. It does not interfere with normal power supply and carries negligible current.
Surge event occurs: When a dangerous voltage surge arrives and exceeds the SPD's rated threshold voltage, its internal components (most commonly metal-oxide varistors MOVs, gas discharge tubes GDTs) instantly switch to very low-impedance state.
Surge diversion: The SPD creates a low-resistance path, diverting the surge current to the protective earth conductor. It clamps the voltage across the protected load down to a safe residual-voltage level.
Reset: After the surge passes and voltage returns to normal mains level, the SPD reverts to its high-impedance standby state.
Key note: SPDs cannot block direct lightning full-stroke current; they handle transient over-voltage surges. Severe surges may degrade or wear out SPD internal elements over time.
Difference Between Type 1 and Type 2 SPD
Type 1 and Type 2 are defined under IEC 61643-11 standard for low-voltage surge protective devices, for different installation locations and surge-current duties.
|
Item |
Type 1 SPD |
Type 2 SPD |
|
Main application |
Installed at the main incoming service of building, at the origin of the electrical installation (main distribution board). For buildings with external lightning protection systems (lightning rods). |
Installed in downstream distribution panels, sub-boards, close-to-load cabinets. Used after Type 1 protection. |
|
Surge duty |
Handles partial lightning strike current (direct-lightning-originated surge). Tested with 10/350 μs lightning current impulse waveform. |
Handles switching surges and induced lightning surges. Tested with 8/20 μs current impulse waveform. |
|
Core function |
Divert high-magnitude lightning-originated partial surge current at the building power entry point. |
Limit residual over-voltage passed-through from upstream, protect circuits and terminal equipment against induced surges. |
|
Typical installation position |
Main distribution board / service entrance, after the utility meter, before main circuit-breaker. |
Sub-distribution boards, floor panels, equipment power cabinets. |
|
Co-ordination requirement |
Often works together with Type 2 SPD downstream. Needs proper conductor length and impedance for energy coordination. |
Can be used alone in buildings without external lightning protection; best performance when coordinated with upstream Type 1. |
|
Typical components |
Frequently uses Gas Discharge Tubes (GDT) for high-current lightning impulse handling. |
Mainly uses Metal-Oxide Varistors (MOV), excellent for voltage clamping. |
Practical summary
Type 1: For buildings fitted with lightning-rod systems. Deploy at the very power inlet to shunt part of real lightning surge current.
Type 2: The most common SPD. It suppresses induced lightning surges and grid-switching transients. It protects distribution circuits and end-use devices.
Where full lightning risk exists: Type 1 + Type 2 cascaded installation gives complete multi-stage surge protection.
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