What is the key difference between AC and DC SPDs？

What are AC SPDs?

AC Surge Protective Devices (AC SPDs) are specialized surge protection devices engineered to safeguard alternating-current power systems from damaging voltage spikes, power surges, and transient overvoltages. These AC surge protectors rapidly channel excess energy away from sensitive electronics and appliances, diverting surges to the grounding or neutral conductor to maintain safe voltage levels.

Modern AC SPDs deliver ultra-fast response times—often under a few nanoseconds—to clamp sudden overvoltage events before they harm connected equipment. By integrating metal-oxide varistors (MOVs), gas discharge tubes (GDTs), or hybrid components, they provide reliable electrical surge protection for a wide range of applications, including:

• Residential power strips and whole-house surge protectors
• Commercial panel-mounted surge protection devices
• Industrial control cabinet SPD units
• Data center rack mount surge protectors

According to IEC 61643-11 standards, AC SPDs are classified into three types, each tailored for a specific level of defense and installation point:

• Type 1 SPD (Class I): Installed at the service entrance to absorb high-energy lightning strikes and external surges.
• Type 2 SPD (Class II): Mounted downstream in distribution boards to clamp residual switching transients from motors, HVAC systems, and industrial equipment.
• Type 3 SPD (Class III): Point-of-use devices protecting final equipment—such as sensitive electronics, home entertainment systems, and precision instruments—by filtering any remaining low-energy spikes.

By selecting and combining the appropriate Type 1, Type 2, and Type 3 surge protectors, facility managers and homeowners can achieve comprehensive power surge protection, minimize downtime, and extend the lifespan of their electrical and electronic assets.

Types of AC Surge Protective Devices

When evaluating AC surge protective devices (SPDs) for your electrical network, it’s essential to match the SPD to your specific AC power distribution system. The three primary earthing schemes—TN, TT, and IT—each require tailored surge protection solutions:

TN Systems (Terra Neutral):

TN-C combines neutral and protective earth conductors, demanding SPDs with combined N-PE protection.

TN-S separates neutral (N) and protective earth (PE) conductors, allowing use of dedicated N-PE SPDs for higher performance.

TN-C-S (PME) uses a shared N-PE conductor in part of the system, where SPDs must handle mixed-mode (L-PE/N-PE) surge clamping.

TT Systems (Terra-Terra):

In TT networks, the consumer’s earth electrode is separate from the utility’s, so TT surge protectors must be rated for larger ground potential differences. This configuration often employs Type 2 SPDs at distribution boards and Type 3 point-of-use protectors near critical equipment for layered defense.

IT Systems (Isolated Terra):

With no direct connection between live conductors and earth, IT surge protection devices focus on L-L clamping and require SPDs that tolerate floating or high-impedance grounds. These SPDs frequently integrate gas discharge tubes (GDTs) plus metal oxide varistors (MOVs) for robust line-to-line and line-to-earth safeguarding.

Selecting the correct AC surge protection device for TN-C, TN-S, TN-C-S, TT, or IT systems ensures the effective suppression of transient overvoltages—whether from lightning-induced surges, switching spikes, or grid disturbances—while preserving uptime and protecting valuable electronics.

What are DC SPDs?

DC surge protective devices (DC SPDs) are critical for safeguarding direct-current power networks in applications such as solar PV systems, telecommunications, automotive electronics, and industrial automation. Functionally akin to AC SPDs, these DC surge protection devices are optimized for constant-voltage environments, featuring specialized MOVs, GDTs, or hybrid components rated for the higher voltage and polarity requirements of DC circuits.

Solar & Photovoltaic (PV) Applications:

PV SPDs protect solar modules, combiner boxes, inverters, and charge controllers from lightning-induced surges, grid disturbances, and switching transients. High-voltage DC surge protectors help maintain uninterrupted energy production and extend equipment life.

Telecommunications & Data Centers:

DC surge protectors on 85V and 300V DC power feeds prevent transient spikes from damaging routers, base stations, and UPS systems.

Automotive & EV Charging:

EV charger SPDs and automotive DC surge arresters defend against voltage spikes in electric vehicle supply equipment and vehicle powertrains, ensuring reliable charging and system safety.

Industrial Automation & Control:

In factory floor environments, industrial DC SPDs secure PLCs, motor drives, and sensor networks by clamping overvoltages from motor switching and inductive loads.

By installing the correct DC surge protection device, engineers and installers can minimize downtime, avoid costly repairs, and ensure consistent performance across all DC-powered systems.