Solar PV systems are highly exposed to lightning-induced surges due to large outdoor PV arrays and long DC cabling. Unlike AC systems, PV DC circuits have no voltage zero-crossing point, so improper SPD selection may cause sustained DC arc and fire risk. Standard: IEC 61643-31 / IEC 61643-32.

Key Risk Sources

Induced lightning over-voltage from nearby lightning strikes

Partial lightning current for ground-mounted large-scale plants

Switching transients from inverter MPPT operation

Surges coupled into DC power, AC output and communication lines

Multi-stage SPD Layout

1. DC side (PV array → inverter input)

Rooftop small-scale PV: Install Type 2 DC-rated SPD at inverter DC input terminals. MCOV (maximum continuous operating voltage) must be higher than 1.15 × PV array open-circuit voltage.

Ground-mounted / high-lightning-risk sites: Deploy Type 1+Type 2 combined DC SPD inside PV combiner boxes and inverter DC terminals. If DC cable length >10 m between array and inverter, SPD shall be fitted on both sides of DC cable.

❗ Must use PV-special DC SPD; ordinary AC SPD cannot be used for DC PV circuits.

2. AC side (inverter AC output → grid connection)

Install AC SPD at inverter AC output cabinet.

For buildings with external lightning protection: Type 1+2 AC SPD at main distribution board.

General rooftop PV: Type 2 AC SPD is acceptable.

3. Signal & communication circuits

Add Type 3 signal SPD for RS485, MODBUS, monitoring sensors and tracking-motor control lines to suppress data-line surges.

4. Earthing requirement

PV module frames, mounting brackets, combiner box enclosures and inverter housings must be reliably connected to equipotential grounding system. Good grounding is the foundation of surge protection.

Quick selection guide

Note: SPD needs backup over-current protection (fuse / miniature circuit breaker). Replace SPD when fault indicator shows failure.

Lightning Protection for Industrial Equipment

Industrial sites contain PLC, frequency converters, servo drives, sensors, instrumentation and communication buses. Damage comes not only from direct lightning strikes but mainly from inductive / conductive transient surges propagating through power cables, signal lines and earthing network. It adopts a 3-layer coordinated protection concept: external lightning interception → power-entry surge diversion → equipment-terminal fine clamping.

Layer 1: External lightning protection (lightning interception)

Air terminals / lightning rods, down-conductors and grounding mesh to divert direct lightning current into earth, preventing direct strike on factory buildings and equipment.

Realize equipotential bonding for all metal structures: equipment cabinets, cable trays, steel frames, pipework. Minimize potential difference during lightning events.

Low-resistance, well-meshed grounding network is critical.

Layer 2: Power supply surge protection (distribution level)

Main incoming cabinet: Fit Type 1 SPD for site with external lightning protection, to divert partial lightning current (10/350 μs impulse).

Sub-distribution panels for production zones: Install Type 2 SPD (8/20 μs impulse) to suppress grid-switching and induced lightning surges.

Critical-load cabinets (for PLC, automation controllers): Deploy Type 2 or Type 2+3 SPD close to equipment power terminals to reduce residual surge voltage.

Circuit breakers and fuses cannot replace SPD: they react too slowly for nanosecond-level surges.

Layer 3: Signal & field-bus surge protection (terminal fine protection)

Protect all incoming/outgoing low-voltage signal cables:

Analog 4-20 mA sensor lines

RS485 / Modbus / Profibus field bus

Ethernet, control interlock circuits

Use signal-matching SPDs (GDT + MOV + TVS multi-stage): large-energy surge is discharged by GDT; residual voltage is clamped by MOV / TVS to safe signal-circuit level. Signal SPD must match signal voltage, bandwidth and transmission impedance.

Important installation rules

Keep SPD connecting conductors short and straight, reduce loop area to avoid voltage rise caused by lead-wire inductance.

SPD needs dedicated backup over-current protective device.

Cascade coordination: Type 1 → Type 2 → Type 3, maintain required separation impedance / cable length between stages for energy coordination.

Remote status-monitoring SPD is recommended for unattended industrial plants for early fault alarm.

Summary of typical industrial protection scheme

External lightning rod system + equipotential bonding + mesh grounding.

Main switchboard: Type 1 SPD (if lightning-risk).

Production sub-panels: Type 2 SPD.

Critical equipment cabinet: Type 2+3 power SPD + signal SPD for all field wiring.