AC SPD vs DC SPD: What’s the Difference and Which One Do You Need?

Solution

AC SPD vs DC SPD: What’s the Difference and Which One Do You Need?

Optimized Summary

AC SPDs and DC SPDs are both designed to protect electrical equipment from transient overvoltage, but they are engineered for different electrical environments.

AC SPDs are used in alternating current systems such as industrial power distribution, commercial buildings, and data centers. DC SPDs are specifically designed for direct current applications such as solar PV systems, battery energy storage systems (BESS), and DC fast EV charging stations.

Because DC current does not naturally cross zero like AC current, DC SPDs require different internal structures and extinguishing mechanisms. Therefore, AC SPDs and DC SPDs are not interchangeable.

Selecting the wrong SPD can result in equipment damage, fire hazards, or system failure.

Quick Answers

What Is the Difference Between AC SPD and DC SPD?

AC SPDs protect alternating current systems.

DC SPDs protect direct current systems.

Their internal structures and standards are different.

Can an AC SPD Be Used in a DC System?

No.

Using an AC SPD in a DC circuit can be dangerous and may lead to catastrophic failure.

Can a DC SPD Be Used in an AC System?

Generally, no.

Always use SPDs designed specifically for the system voltage and current type.

Which Industries Use DC SPDs?

Solar PV Systems
Battery Energy Storage Systems (BESS)
EV Charging Stations
Telecommunications
DC Distribution Systems

Which Industries Use AC SPDs?

Industrial Facilities
Commercial Buildings
Data Centers
Smart Buildings
Power Monitoring Systems

WHAT: What Are AC SPDs and DC SPDs?

What Is an AC SPD?

An AC SPD (Alternating Current Surge Protective Device) protects electrical systems operating with alternating current.

Typical AC voltages include:

120V AC
230V AC
400V AC
480V AC
690V AC

Common Applications

Industrial Distribution Panels
Data Centers
Power Monitoring Systems
Manufacturing Plants
Commercial Buildings

What Is a DC SPD?

A DC SPD (Direct Current Surge Protective Device) protects direct current circuits.

Typical DC voltages include:

48V DC
220V DC
600V DC
1000V DC
1500V DC

Common Applications

Solar PV Arrays
Battery Storage Systems
EV Charging Stations
Telecommunications Systems

WHY ARE AC SPDS AND DC SPDS DIFFERENT?

The biggest difference lies in current behavior.

AC Current

Alternating current naturally crosses zero voltage many times every second.

This makes arc extinguishing easier.

DC Current

Direct current flows continuously.

Arcs are much harder to interrupt.

Therefore, DC SPDs require:

Different MOV structures
Arc-extinguishing chambers
Higher insulation requirements
Specialized thermal protection

Visual Comparison

WHERE ARE AC SPDS USED?

Industrial Facilities

Protecting:

PLC Systems
Motor Drives
Power Meters
Energy Meters

Data Centers

Protecting:

Servers
UPS Systems
PDUs

Commercial Buildings

Protecting:

HVAC Systems
Smart Building Controllers
Monitoring Systems

Manufacturing Plants

Protecting:

Automation Systems
Production Lines
Industrial Equipment

WHERE ARE DC SPDS USED?

Solar PV Systems

Protecting:

PV Strings
Combiner Boxes
Solar Inverters

Battery Energy Storage Systems (BESS)

Protecting:

Battery Packs
PCS Systems
EMS Platforms

EV Charging Stations

Protecting:

DC Fast Chargers
Charging Controllers
Monitoring Systems

Telecommunications Systems

Protecting:

48V DC Equipment
Communication Networks

WHO NEEDS AC SPDs AND DC SPDs?

Electrical Engineers

Design reliable systems.

EPC Contractors

Meet project specifications.

Solar Developers

Protect PV assets.

Energy Storage Integrators

Improve system reliability.

EV Charging Operators

Protect charging infrastructure.

Data Center Operators

Ensure uptime.

HOW DO AC SPDs WORK?

Under normal conditions:

AC Voltage
      ↓
SPD Inactive
      ↓
Normal Operation

When a surge occurs:

Transient Overvoltage
        ↓
AC SPD Activates
        ↓
Energy Diverted to Ground
        ↓
Equipment Protected

HOW DO DC SPDs WORK?

DC SPDs perform the same function but must interrupt continuous DC current.

This requires:

Special MOV configurations
Enhanced thermal disconnection
Improved insulation design

Therefore, DC SPDs are usually more complex.

AC SPD vs DC SPD Comparison Table

Feature	AC SPD	DC SPD
Current Type	AC	DC
Typical Voltage	230V-690V	48V-1500V
Main Applications	Buildings, Industry	Solar, BESS, EV Charging
Arc Extinguishing Difficulty	Lower	Higher
Standards	IEC 61643-11	IEC 61643-31
Installation Location	AC Panels	DC Combiner Boxes
Interchangeable	No	No
Typical Protection Objects	Meters, PLCs, Servers	PV Strings, Batteries

Type 1 and Type 2 AC SPD Applications

Type 1 AC SPD

Installed at:

Main Switchboards
Service Entrances

Protects against:

Direct Lightning Current

Type 2 AC SPD

Installed at:

Distribution Panels
Control Cabinets

Protects against:

Switching Surges
Residual Lightning Energy

DC Type 1+2 SPD Applications

Commonly used in:

Solar PV Systems

PV Array
     ↓
DC Type 1+2 SPD
     ↓
Combiner Box
     ↓
Inverter

Battery Energy Storage Systems

Battery Pack
       ↓
DC SPD
       ↓
PCS
       ↓
Grid

Solar SPD Explained

Why Do Solar PV Systems Need DC SPD?

Solar photovoltaic systems are exposed to one of the harshest electrical environments.

Common surge sources include:

Lightning strikes
Induced lightning currents
Grid switching
Long cable runs
Ground potential differences

Even small voltage transients can damage:

Solar inverters
Combiner boxes
MPPT controllers
Monitoring devices
Communication modules

According to IEC 62305 and IEC 61643-32, surge protection is strongly recommended in solar PV systems.

Typical Solar Protection Architecture

PV Array
     ↓
DC Type 1+2 SPD
     ↓
Combiner Box
     ↓
Solar Inverter
     ↓
AC Type 2 SPD
     ↓
Distribution Board
     ↓
Grid

Where Should DC SPDs Be Installed?

String Combiner Box

Protect PV strings from lightning-induced surges.

Near the Inverter DC Input

Protect inverter MPPT circuits.

DC Distribution Cabinet

Protect the DC bus and communication modules.

AC Output Side

Install AC Type 2 SPD to protect grid-connected equipment.

EV Charger SPD Applications

EV charging stations contain sensitive power electronics.

These include:

Charging controllers
DC power modules
Communication gateways
Energy meters
OCPP communication units

Surges can result in:

Charger shutdown
Controller damage
Communication failure
Revenue loss

Typical EV Charging Protection Architecture

Utility Grid
      ↓
Type 1 SPD
      ↓
Main Panel
      ↓
Type 2 SPD
      ↓
AC Charger

DC Fast Charging Architecture

Grid
 ↓
Transformer
 ↓
Type 1 SPD
 ↓
Rectifier Cabinet
 ↓
DC SPD
 ↓
Charging Gun
 ↓
EV Vehicle

Why EV Charging Stations Need Both AC and DC SPDs

AC Side

Protects:

Switchboards
Power meters
Communication systems

DC Side

Protects:

Power modules
Battery charging circuits
DC contactors

Battery Energy Storage System (BESS) Protection

BESS is one of the fastest-growing applications for DC SPDs.

Battery systems contain:

Battery Packs
PCS (Power Conversion System)
EMS
BMS
DC Busbars

All are vulnerable to transient overvoltage.

Typical BESS Protection Architecture

Battery Pack
      ↓
DC SPD
      ↓
PCS
      ↓
AC Type 2 SPD
      ↓
Grid

Why BESS Requires DC SPD

Unlike AC circuits, DC arcs are difficult to extinguish.

Improper surge protection may lead to:

Fire hazards
PCS failure
Battery damage
System downtime

Technical Parameters Comparison

Selecting the right SPD requires understanding several key parameters.

Ucpv (Maximum Continuous Operating Voltage)

Specific to DC SPDs.

Typical values:

PV System Voltage	Recommended Ucpv
600V	600V DC
1000V	1000V DC
1500V	1500V DC

Incorrect Ucpv selection can cause:

Premature SPD aging
Thermal failure
Reduced protection

Imax

Maximum discharge current.

Common values:

20kA
40kA
60kA
80kA

Higher values indicate stronger surge capability.

In

Nominal discharge current.

Represents long-term surge endurance.

Typical values:

10kA
20kA
40kA

Up (Voltage Protection Level)

Represents residual voltage after SPD operation.

Lower Up means:

✓ Better equipment protection

Typical values:

1.2kV
1.5kV
2.5kV

IEC 61643-11 vs IEC 61643-31

One of the most frequently asked questions is:

Are AC and DC SPDs governed by the same standard?

The answer is:

No.

IEC 61643-11

Applies to:

AC SPD

Applications:

Industrial distribution
Commercial buildings
Data centers

IEC 61643-31

Applies to:

DC SPD

Applications:

Solar PV systems
Battery energy storage
DC distribution

Standards Comparison

Standard	Application
IEC 61643-11	AC SPD
IEC 61643-31	DC SPD
IEC 62305	Lightning Protection
UL1449	North America
EN61643	Europe

Real-World Applications

Solar Farm

AC + DC SPD Combination

Protects:

String inverters
Monitoring systems
Data loggers

Benefits:

Increased uptime
Reduced inverter failures

Data Centers

Primarily use:

AC Type 1 + Type 2 SPD

Protect:

UPS
Servers
PDUs

Benefits:

Improved availability
Reduced downtime

EV Charging Networks

Require:

AC SPD + DC SPD

Protect:

Charging piles
Controllers
Billing systems

Benefits:

Increased charger reliability

Battery Energy Storage Systems

Require:

High Voltage DC SPD

Protect:

PCS
Battery racks
EMS

Benefits:

Reduced maintenance cost

Common Mistakes

Mistake #1

Using AC SPD in DC circuits.

This is extremely dangerous.

Mistake #2

Ignoring AC-side protection in solar systems.

Many failures occur on the AC side.

Mistake #3

Choosing incorrect Ucpv.

Underrated voltage capability causes premature failure.

Mistake #4

Ignoring grounding quality.

Poor grounding significantly reduces SPD effectiveness.

Mistake #5

Focusing only on Imax.

Up and response time are equally important.

Expert Recommendations

Industrial Buildings

AC Type 1 + Type 2 SPD.

Solar PV

DC Type 1+2 SPD + AC Type 2 SPD.

BESS

High-voltage DC SPD + AC SPD.

EV Charging Stations

AC Type 1 + Type 2 + DC SPD.

Data Centers

Multi-level AC SPD coordination.

YADA AC and DC SPD Solutions

YADA provides complete surge protection solutions for:

Solar PV

600V DC SPD
1000V DC SPD
1500V DC SPD

Industrial Distribution

Type 1 SPD
Type 2 SPD
40kA SPD
60kA SPD

EV Charging

Battery Energy Storage

Data Centers

SPD
Branch Circuit Meter
Power Quality Analyzer
EMS Platform

Frequently Asked Questions (FAQ)

1. Can AC SPD be used for solar systems?

Only on the AC output side.

The PV string side requires DC SPD.

2. Can DC SPD replace AC SPD?

No.

They are not interchangeable.

3. Which SPD is used in 1000V solar systems?

1000V DC SPD.

4. Which SPD is used in 1500V solar plants?

1500V DC SPD.

5. Do EV chargers need both AC and DC SPDs?

Yes.

6. Why is DC arc interruption difficult?

Because DC current has no zero-crossing.

7. Which standard applies to DC SPD?

IEC 61643-31.

8. Which standard applies to AC SPD?

IEC 61643-11.

9. Is SPD mandatory for solar systems?

Strongly recommended by IEC standards.

10. Can SPD improve inverter lifespan?

Yes.

11. What is Ucpv?

Maximum continuous DC operating voltage.

12. What is Imax?

Maximum surge discharge current.

13. What is Up?

Residual voltage level.

14. Which SPD is used in BESS?

High-voltage DC SPD.

15. What industries use DC SPD most?

Solar, BESS, and EV charging.

Glossary

AC

Alternating Current.

DC

Direct Current.

SPD

Surge Protective Device.

Ucpv

Maximum continuous DC voltage.

Imax

Maximum discharge current.

In

Nominal discharge current.

Up

Voltage protection level.

BESS

Battery Energy Storage System.

PCS

Power Conversion System.

EMS

Energy Management System.

MPPT

Maximum Power Point Tracking.

Key Takeaways

AC SPD protects AC systems.

DC SPD protects DC systems.

AC SPD and DC SPD are NOT interchangeable.

Solar PV systems usually require both AC and DC SPDs.

EV charging stations require coordinated AC and DC protection.

BESS systems rely heavily on DC SPD.

IEC 61643-11 governs AC SPD.

IEC 61643-31 governs DC SPD.

Integrated protection + monitoring is the future trend.

Summary

AC SPD and DC SPD serve different purposes and are not interchangeable. AC SPDs protect industrial power systems, buildings, and data centers, while DC SPDs are designed for solar PV systems, battery energy storage systems, and EV charging infrastructure. Because DC current is harder to interrupt, DC SPDs require different designs and are governed by IEC 61643-31. For solar and EV charging applications, using both AC and DC SPDs provides the most effective surge protection.