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AS/NZS 1768-2007
Why SPD Coordination Matters
Surge Protection Devices (SPDs) must be selected and coordinated to work as a system, not in isolation. A Type 2 SPD at the switchboard that encounters the full unclamped energy of a direct lightning strike will itself be destroyed — taking out the switchboard with it. A Type 1 SPD at the switchboard and a Type 2 SPD at the inverter, coordinated with adequate cable separation, forms a proper protection cascade.
SPD Types and Their Roles
Type | Function | Location | Standard |
|---|---|---|---|
Type 1 (Class I) | Handles large direct lightning current (Iimp) — 12.5–100 kA tested. Contains the surge from reaching Type 2. | Main switchboard or LPS equipotential bonding point | IEC 61643-11 |
Type 2 (Class II) | Handles residual surges after Type 1; limits residual voltage to protected equipment. Imax 5–40 kA tested. | Inverter AC input, DC combiner box, sub-switchboards | IEC 61643-11 |
Type 3 (Class III) | Fine protection at sensitive equipment terminals. Up voltage protection 1.5 kV. | At inverter terminals, at monitoring equipment | IEC 61643-11 |
DC Side SPD Selection
DC string cable SPDs must be specifically rated for DC — AC-rated SPDs will be destroyed immediately by DC voltage. Key DC SPD parameters:
Maximum continuous operating voltage (Uc): must exceed the maximum system DC voltage at minimum temperature (calculated VOC)
For 600 V DC residential: specify Uc ≥ 700 V DC
For 1000 V DC commercial: specify Uc ≥ 1100 V DC
SPD must be fitted in each conductor (positive to earth, and negative to earth) — not just one conductor
Engr. Jason Morales — Founder, SolarEnergyPH
