Surge protection devices limit transient overvoltage caused by lightning, switching operations and disturbances in the power system. Correct selection depends on the system type, voltage, exposure and coordination with other protective devices.
SPD types
| SPD type | Typical location | Purpose |
|---|---|---|
| Type 1 | Main service entrance | Handles partial lightning current |
| Type 2 | Main/sub-distribution boards | Protects against induced and switching surges |
| Type 3 | Near sensitive equipment | Fine protection after upstream SPDs |
1. Confirm AC or DC application
AC and DC SPDs are not interchangeable. Solar PV systems require DC-rated SPDs designed for the maximum continuous operating voltage and polarity of the array.
2. Check maximum continuous operating voltage
The Uc rating must be above the normal system voltage but low enough to provide effective protection. For PV systems, calculate the maximum open-circuit voltage under the lowest expected temperature.
3. Review discharge current ratings
Key ratings include nominal discharge current (In), maximum discharge current (Imax) and impulse current (Iimp) for Type 1 devices. Select according to exposure level and system design.
4. Choose the number of poles
Match the SPD configuration to the earthing arrangement and number of conductors. Single-phase, three-phase and PV systems may require 2P, 3P, 4P or dedicated positive/negative modules.
5. Use proper backup protection and wiring
Install the recommended fuse or breaker, use short conductors, avoid unnecessary loops and maintain correct earthing. Long leads increase residual voltage and reduce performance.
Frequently asked questions
Does an SPD stop all lightning damage?
No device can guarantee protection from every direct strike, but a coordinated SPD system significantly reduces surge risk.
When should an SPD be replaced?
Replace it when the status indicator shows failure, after a major surge event if required by the manufacturer, or during scheduled maintenance when performance is uncertain.
Do solar systems need SPDs on both DC and AC sides?
Many installations benefit from protection on both sides, depending on system size, cable routes, lightning exposure and local standards.
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