What is a DC Surge Protection Device?
With widespread solar energy and the rise of DC powered devices, protecting your precious equipment from surges is of the utmost importance.....
What is a DC Surge Protection Device? A Complete Guide for Solar & Electrical Systems
With widespread solar energy and the rise of DC powered devices, protecting your precious equipment from surges is of the utmost importance. One of the critical components of doing this is a DC Surge Protection Device (DC SPD).
This blog will help you understand:
- What a DC SPD is
- Why it is important in solar and other DC systems
- How it works
- Where it's installed
- And how to choose the appropriate one
What is a DC Surge Protection Device (DC SPD)?
A device utilized to protect DC circuits (solar panels, batteries, EV charging systems, etc.) to transient over voltages typically caused by lightning strikes, switching events, grid irregularities or any electrical phenomenon.
AC SPDs are used to protect circuits flowing alternating current. But DC SPDs are designed specifically for direct current because it works differently and requires different protection.
Why is Surge Protection Necessary in DC Systems?
- Lightning strikes on PV systems can induce high-voltage surges
- Switching operations in the grid can create transient voltages
- Expensive equipment like inverters and batteries can be damaged or degraded without protection
- Long DC cables in solar arrays act like antennas and attract surges
Without protection, a single event can cost thousands in repairs and downtime.
How Does a DC SPD Work?
A DC SPD functions as a pressure release valve for electrical surges. It monitors the DC voltage level and reacts in microseconds when it detects a surge. It diverts the excess energy away from sensitive equipment to the ground safely.
Most DC SPDs use MOVs (Metal Oxide Varistors) or gas discharge tubes to absorb or redirect the surge.
Types of DC Surge Protection Devices
- Type 1 DC SPD
Installed at the main distribution board. Designed for direct lightning strikes. Common in commercial and industrial solar systems. - Type 2 DC SPD
Installed at sub-distribution or inverter level. Protects against switching surges and indirect lightning strikes. Widely used in residential solar systems. - Type 3 DC SPD
Used for sensitive loads like data loggers and smart devices. Provides fine protection (only after Type 1 or 2 is in place).
Where is a DC SPD Installed in Solar Systems?
- Between solar PV panels and inverters
- Near combiner boxes or junction boxes
- At battery banks in hybrid systems
Tip: Use separate SPDs for the DC and AC sides of a solar inverter. Mixing them is a safety hazard.
Selecting the Appropriate DC SPD: Important Things To Consider
Some of things to consider, with their definitions, in order to select the appropriate DC surge protection device are:
| Parameter | Definition |
|---|---|
| System Voltage (Vdc) | Align the SPD voltage rating with your system voltage (i.e., 600Vdc, 1000Vdc). |
| Short-Circuit Current | Ensure the SPD can withstand the fault current. |
| Response Time | Should be in the nanoseconds or microseconds time domain. |
| Nominal Discharge Current (In) | The current which the SPD can withstand without any damage to the surge protective device. |
| Material of the Housing | Material should be fire-resistant and UV-proof if installed outdoors. |
| Certification | Look for IEC 61643-31 or UL 1449. |
Difference Between AC SPD and DC SPD
| Feature | AC SPD | DC SPD |
|---|---|---|
| Current Type | Alternating Current | Direct Current |
| Voltage Polarity | Alternates + / - | Fixed polarity |
| Protection Curve | Different waveform | Constant voltage |
| Application | Homes, offices | Solar, EV charging, DC systems |
Installing an AC SPD in a DC circuit is dangerous and ineffective. Always employ the proper type.
Avoid These Common Mistakes
- Using an AC SPD for a DC system
- Not grounding the SPD properly
- Installing after the inverter instead of before
- Ignoring system voltage match
- Skipping surge protection altogether
Benefits of Using DC SPDs
- Protects costly solar and DC equipment
- Increases system lifespan
- Reduces downtime due to faults
- Essential for safety in high-lightning zones
- Saves money by avoiding replacement costs
FAQs
Conclusion: Protecting Your Solar Asset
A DC Surge Protection Device is not for consideration - it’s essential protection for your solar and DC systems. It safeguards your clean energy investment against unforeseeable spikes and power irregularities.
Whether you are installing a residential rooftop solar system or a commercial power station, you need to choose and add a certified (and guaranteed) DC SPD to your design.
