DC and AC Surge Protection for PV Systems
Induced surges from nearby lightning destroy more inverters than direct strikes. Surge protective devices on both sides of the inverter are standard practice, not an upgrade.
Where SPDs go
| Location | SPD |
|---|---|
| Array / combiner box (DC) | Type 2, rated ≥ system max DC voltage |
| Inverter DC input (if > 10 m from array SPD) | Type 2 DC |
| Inverter AC output | Type 2 AC |
| Main AC panel / service (if building has LPS or is exposed) | Type 1 + 2 AC |
Selecting the DC SPD
- Maximum continuous operating voltage (Ucpv) ≥ array Voc at coldest temperature.
- PV-specific SPDs use a fail-safe design (thermal disconnect + fuse) because DC arcs do not self-extinguish.
- Short, straight connecting leads — under 500 mm total — or the SPD’s protection voltage is degraded by lead inductance.
Grounding and bonding
SPDs only work against a low-impedance earth. Bond module frames and racking with a continuous equipment-grounding conductor to the array frame, then to the building grounding system. Use listed lay-in lugs and washers that bite through the anodising.
When to add a lightning protection system (LPS)
A risk assessment (IEC 62305 style) is warranted for tall or isolated buildings, ground-mount arrays in open terrain, and critical facilities. Where an LPS exists, keep a separation distance between air terminals/down-conductors and the array, or bond them per the standard.
EngEst Pro’s Solar PV Calculator adds DC and AC surge protective devices sized to your array voltage, plus grounding lugs and bonding conductor, to the protection section of the BOM.
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