Power Surges: A Growing Threat to DC Power Systems
Direct current (DC) power now drives solar farms, electric vehicle charging stations, and automated manufacturing lines. But as these systems expand, so does a quiet and costly threat: power surges.
A surge is a brief, sharp spike in voltage, lasting microseconds to milliseconds. It can be caused by:
- Lightning strikes – direct hits or nearby strikes can induce thousands of volts into cables.
- Switching events – starting or stopping large motors, or switching high-current circuits.
- Fault conditions – short circuits or grounding faults that send transient spikes through the network.
Why are surges especially dangerous for DC systems?
Unlike AC systems, which naturally cross zero volts and give components a tiny recovery window, DC systems maintain a continuous voltage. That means any surge rides on top of a constant supply, hitting electronics harder.
Surges can:
- Destroy sensitive devices such as inverters, PLCs, or battery management units.
- Gradually degrade insulation, solder joints, and semiconductors, reducing service life.
- Trigger unexpected shutdowns, leading to lost production or power supply interruptions.
How to Choose the DC SPD Properly?
Selecting the right DC Surge Protection Device (SPD) means balancing surge-handling capacity, system voltage, and environmental conditions. Rushing this step often leads to over-specification (wasting money) or under-specification (risking downtime).
1. SPD Type: : Your First Line of Defense
DC SPDs are defined under IEC 61643-31 as:
- Type 1 – Handles high-energy surges, including those from direct lightning (10/350 µs waveform). Installed where there’s a high risk of strikes, such as PV systems in tropical storm zones.
- Type 2 – Protects against indirect lightning and switching surges with an 8/20 µs waveform. Common in residential and commercial solar installations.
- Type 3 – Protects individual devices with low surge tolerance. Usually installed close to sensitive electronics as a final layer.
Practical setup: A PV system in Florida (lightning capital of the U.S.) might use Type 1 SPDs at the combiner boxes, Type 2 at the inverter inputs, and Type 3 at control boards. This layered defense reduces risk at every stage.
2. Voltage, Current, and Temperature Ratings
Parameter | Why It Matters | Practical Tip |
Max. Continuous Operating Voltage (Uc) | SPDs may falsely trigger during typical voltage surges if Uc is set below required thresholds. | Choose ~10% above the highest system voltage. For a 1000 V PV array, use ~1100 V DC SPDs. |
Specified Discharge Rating (In) and Maximum Surge Handling (Imax) | Specifies the maximum surge current the SPD can withstand without damage. | Match to lightning risk and cable length. |
Operating Temperature Range | Ensures SPD performance in all climates. | Outdoor PV sites often need –40 °C to +85 °C models. |
Case study: An EV charging hub in Dubai initially used SPDs rated for +60 °C. In summer, internal temperatures exceeded 70 °C, causing premature failure. Switching to –40 °C to +85 °C rated units eliminated downtime (Source: internal facility maintenance report, 2022).
3. Flash Density
Lightning flash density — measured in flashes/km²/year — directly impacts SPD selection.
- High density (>2 flashes/km²/year) – Use Type 1 SPDs with high surge current ratings at main DC entry points.
- Medium density (1–2 flashes/km²/year) – Type 2 may be acceptable for less exposed systems.
Example: According to the World Bank’s Global Lightning Density Map, central Africa experiences >8 flashes/km²/year. For PV arrays there, skipping Type 1 SPDs would be a costly gamble.

Installation and Application of DC Surge Protection Device SPD
Even the best SPD will fail if installed incorrectly. Proper application is half the battle.
1. Placement and Wiring
- Install SPDs as close as possible to the point of surge entry — for PV systems, that’s often the combiner box or inverter terminals.
- Keep leads short and straight. A 30 cm longer lead can increase residual voltage by several hundred volts.
2. Connection Method
- Protected circuits usually have SPDs wired across their terminals (in parallel).
- Always ensure a low-impedance earth connection; poor grounding is a top cause of SPD malfunction.
3. Layered Protection
The “cascade” or multi-stage approach improves reliability:
- Type 1 – Main distribution or combiner box.
- Type 2 – Downstream at sub-panels or inverter inputs.
- Type 3 – Close to sensitive loads.
4. Monitoring and Maintenance
- Choose SPDs with clear status indicators and, if possible, remote monitoring contacts.
- Inspect regularly — many failures go unnoticed until the next surge event.
Mini tutorial:
- Switch off DC supply.
- Mount SPD inside the designated protection enclosure.
- Connect + and – to SPD terminals; bond earth to ground bus.
- Restore power and confirm indicator shows “OK” (usually green).
Conclusion
The standard parallel installation of SPDs protects circuits. This is crucial for DC systems, where predictable surges can be prevented, avoiding otherwise significant costs. A well-selected and properly installed DC SPD is an inexpensive insurance policy against lightning and switching transients.
To protect your system:
- Choose the SPD type based on lightning risk and application.
- Select proper voltage, current, and temperature ratings.
- Consider lightning flash density before sizing surge capacity.
- Install with best practices and maintain regularly.
Whether you run a solar farm, an EV charging network, or an industrial control facility, adopting these SPD principles keeps your system running — and your repair budget under control.