{"id":1741,"date":"2026-07-21T01:33:45","date_gmt":"2026-07-20T17:33:45","guid":{"rendered":"https:\/\/jutrion.com\/?p=1741"},"modified":"2026-07-21T01:33:47","modified_gmt":"2026-07-20T17:33:47","slug":"panduan-perangkat-pelindung-lonjakan-arus","status":"publish","type":"post","link":"https:\/\/jutrion.com\/id\/surge-protective-device-guide\/","title":{"rendered":"What Is a Surge Protective Device (SPD)? A Complete Guide to Types, Working Principles, and Selection"},"content":{"rendered":"
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What Is a Surge Protective Device (SPD)?<\/strong><\/strong><\/h2>\n<\/blockquote>\n\n\n\n

A Surge Protective Device (SPD) is an electrical protection device designed to limit transient overvoltages and divert surge currents. Under normal operating conditions, the SPD remains in a high-impedance state and has little to no effect on the electrical system. When lightning, utility switching, motor starting and stopping, or other transient events cause a sudden rise in line voltage, the SPD rapidly switches to a low-impedance conductive state. This provides a discharge path for the surge current while limiting the residual voltage reaching downstream equipment, thereby reducing the risk of insulation breakdown, electronic component damage, equipment failure, and unplanned downtime.<\/p>\n\n\n\n

The design, performance testing, and practical application of SPDs must comply with relevant standards. IEC 61643-11<\/a><\/strong> specifies the performance requirements and test methods for surge protective devices connected to low-voltage AC power systems, while Article 242 of NFPA 70, the National Electrical Code (NEC)<\/a>,<\/strong> addresses the application of surge protection in electrical installations in the United States. These standards provide important guidance for the testing, selection, and installation of SPDs, helping improve the safety and reliability of modern low-voltage power distribution systems.<\/p>\n\n\n\n

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What Is an Electrical Surge?<\/strong><\/h2>\n<\/blockquote>\n\n\n\n

An electrical surge is a short-duration spike in voltage or current that travels through a power, control, or communication circuit. It typically rises very quickly and then decays over a longer period.
Although the event may last only a few microseconds, the resulting voltage can be high enough to damage insulation, electronic components, control equipment, and other sensitive loads.
IEC 60050-161<\/strong> defines a surge as a transient wave that propagates along a line or circuit and is characterized by a rapid rise followed by a slower decay.<\/p>\n\n\n\n

What Causes Electrical Surges?<\/strong><\/h3>\n\n\n\n

Electrical surges are commonly associated with two major sources: lightning-related events and switching operations within the power system.
Lightning can introduce transient overvoltages through direct strikes, nearby strikes, or induced voltages in connected conductors. Switching surges may occur when motors, transformers, capacitor banks, contactors, relays, or other high-power loads are energized or disconnected.
IEC 61000-4-5<\/a> <\/strong>provides standardized methods for testing the immunity of electrical and electronic equipment against unidirectional surges caused by lightning effects and power-system switching transients.<\/p>\n\n\n\n

COMPARISON OF LIGHTNING SURGES AND SWITCHING SURGES<\/strong><\/p>\n\n\n\n

Parameter<\/strong><\/th>Lightning Surge<\/strong><\/th>Switching Surge<\/strong><\/th><\/tr><\/thead>
Typical Waveforms<\/strong><\/td>10\/350 \u03bcs for direct lightning current; 8\/20 \u03bcs for induced surge current; 10\/700 \u03bcs for communication lines<\/td>1.2\/50 \u03bcs voltage wave and 8\/20 \u03bcs current wave<\/td><\/tr>
Occurrence Frequency<\/strong><\/td>Relatively infrequent and mainly associated with thunderstorms<\/td>More frequent and may occur whenever electrical equipment is switched on or off<\/td><\/tr>
Energy Level<\/strong><\/td>Very high energy, potentially reaching hundreds of kilojoules and causing immediate equipment damage<\/td>Generally lower energy, but repeated exposure can gradually degrade components<\/td><\/tr>
Recommended Protection Approach<\/strong><\/td>Type 1 SPD at the main service entrance, followed by coordinated downstream surge protection<\/td>Type 2 or Type 3 SPD installed at distribution boards or close to sensitive equipment<\/td><\/tr>
Typical Overvoltage Range<\/strong><\/td>From several kilovolts to tens of kilovolts<\/td>From several hundred volts to several kilovolts<\/td><\/tr>
Common Sources<\/strong><\/td>Direct lightning strikes, nearby strikes, ground-potential rise, and induced lightning effects<\/td>Motors, transformers, capacitor banks, contactors, relays, and other switching devices<\/td><\/tr>
Typical Impact<\/strong><\/td>Insulation breakdown, flashover, cable damage, fire, or immediate equipment failure<\/td>Electronic component degradation, control-system malfunction, data errors, or reduced equipment life<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
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How does a surge protective device work?<\/h2>\n<\/blockquote>\n\n\n\n

A Surge Protective Device (SPD) works like an automated, ultra-fast electrical pressure relief valve<\/strong>.<\/p>\n\n\n\n

Under normal grid conditions, the SPD acts as an open switch with extremely high internal resistance (impedance), preventing any power from flowing through it. However, when an overvoltage spike (caused by lightning or grid switching) enters the system, the SPD instantly reacts within nanoseconds<\/strong>, dropping its resistance to near-zero. This creates a safe parallel path that diverts the massive surge current away from sensitive equipment and directly into the ground.<\/p>\n\n\n\n

\"How
Diagram showing how a surge protective device works in three stages: normal high-impedance operation, surge response, and current diversion to earth followed by automatic reset.<\/em><\/figcaption><\/figure>\n\n\n\n

The 3-Step Working Process<\/h3>\n\n\n\n
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  1. Normal State (High Impedance): When line voltage remains within normal operational limits, internal components maintain an impedance of several megohms. The SPD remains “invisible” to the circuit and draws virtually no leakage current.<\/li>\n\n\n\n
  2. Surge Event (Instantaneous Low Impedance): The moment a transient voltage exceeds the SPD’s clamping threshold (Uc), the non-linear internal elements switch from high resistance to low resistance in less than 25 nanoseconds.<\/li>\n\n\n\n
  3. Current Diversion & Reset (Energy Dissipation): The surge energy is safely channeled through the grounding conductor (PE). Once the transient spike subsides and the line voltage returns to normal, the internal components automatically recover to their high-impedance state, restoring standard circuit operations.<\/li>\n<\/ol>\n\n\n\n

    The Core Components Inside: MOV vs. GDT<\/h3>\n\n\n\n
    \"MOV
    Comparison of MOV and GDT, the two most common surge protection components used in SPDs.<\/figcaption><\/figure>\n\n\n\n

    The working mechanism relies on high-performance non-linear electrical components built inside the module:<\/p>\n\n\n\n