Rooftop Solar Earthing and Lightning: Practice vs Standard

Short answer: most Indian rooftop jobs use three earth pits (DC, AC, lightning arrester) and a lightning rod on a mast, which is a sound basic layout. The weak points are usually the down conductor and the bonding. A 16 sq mm aluminium cable is widely used as the LA down conductor, but IS/IEC 62305-3 sets a minimum of 50 mm² for aluminium (stranded or round), 50 mm² for copper and 50 mm² for galvanised steel. A 25 × 3 mm GI strip (75 mm²) meets the steel minimum. Pair that with proper SPDs, measured earth resistance and a bonding plan based on IS 3043 and IS/IEC 62305.

The three jobs earthing does

1. Protective earthing: keeps exposed metal (module frames, structure, inverter body, boards) at earth potential so a fault trips protection and nobody gets a shock.
2. Lightning protection (LPS): intercepts a strike with an air terminal and carries the current safely into the ground.
3. Surge protection: SPDs divert induced surges on DC and AC cables to earth.

The standards behind these are IS 3043:2018 (Code of practice for earthing), IS/IEC 62305 parts 1–4 (lightning protection) and the SPD product standards. CEA safety regulations also apply.

Typical market practice

The pits, SPDs and layout are generally reasonable. The down conductor is where practice and standard part ways.

What IS/IEC 62305-3 says about conductor size

The standard's table of minimum cross-sections for air-termination conductors and down conductors includes:

A 16 sq mm aluminium cable is about one-third of the aluminium minimum. Its PVC insulation also adds nothing to lightning performance. Practical compliant options:

• 25 × 3 mm GI strip (75 mm²): cheap, robust, easy to clamp; common on Indian commercial jobs
• 8 mm galvanised steel round (about 50 mm²)
• 50 mm² copper tape or stranded conductor, where budget allows

Bonding conductors that carry part of the lightning current have their own, smaller minimums in the standard (Table 8, for example 16 mm² copper). Do not confuse those with down-conductor sizes.

Routing the down conductor

• Take the shortest, straightest path to the LA pit; avoid sharp bends and loops.
• Keep it away from DC and AC cables. Never run it in the same conduit or tray.
• Respect the separation distance between the LPS and the PV structure or cables given by IS/IEC 62305-3; where you cannot, bond at that point and use suitably rated SPDs.
• Fix it with clamps every metre or so on the parapet and wall; use a test joint above ground.

Separate pits or integrated earthing?

Indian practice often keeps the LA pit completely isolated from the DC and AC pits. IS/IEC 62305-3 recommends a single integrated earth-termination system for a structure, combining lightning, power and telecom earthing, interconnected at or below ground. The reason: during a strike, isolated pits can sit at very different potentials, which can flash over to wiring or equipment.

Practical approach: 1. Install separate electrodes at least about 3 m apart (good for testing and resistance). 2. Decide the interconnection scheme with the design engineer, using test joints so each pit can be measured. 3. Follow the DISCOM, CEIG or tender specification where it is stricter or different, and record the decision.

Earth resistance

• IS/IEC 62305-3 suggests the lightning earth-termination system be 10 Ω or less where possible.
• Many tender and DISCOM specifications set lower values for equipment earthing. Check yours.
• Measure each pit with a proper earth tester at commissioning and yearly, and record the readings. See commissioning checklist.

Air terminal coverage

A single rod protects a zone defined by the protective angle or rolling sphere methods in IS/IEC 62305-3, depending on the protection class. For small arrays, a rod at the middle of the rear edge with enough height above the highest module corner usually works. Sunlectric Studio sizes the mast with a conservative protective-angle simplification and moves to a second rod or an ESE device for large roofs. ESE devices follow NFC 17-102, which is not an IEC or IS standard, though many insurers and inspectors accept them on large roofs.

Surge protection

• DC side: Type II SPD rated for the string voltage at the DCDB; another near the inverter if the run is long.
• AC side: Type II SPD at the ACDB. Use Uc around 320 V: tail-end Indian feeders often sit at 250–270 V, which ages 275 V devices.
• With an external LPS bonded to the system, Type I or Type I+II SPDs may be needed at the service entrance (IS/IEC 62305-4).
• Check SPD status windows yearly and after storms.

Equipment earthing conductors

• Module frames: bond every frame or use listed bonding clips; 4–6 sq mm copper jumpers are typical.
• Structure to DC pit: copper conductor or GI strip sized to the fault current and corrosion conditions.
• Inverter and ACDB to AC pit: size by the fault current and the protective device; Studio uses 6 sq mm up to 10 kW, 10 sq mm up to 30 kW, 16 sq mm above.

Checklist

• [ ] Three or more pits, at least about 3 m apart, with test points
• [ ] LA down conductor ≥ standard minimum (for example 25 × 3 mm GI strip)
• [ ] Down conductor routed separately from PV cables
• [ ] Interconnection scheme decided and recorded
• [ ] DC and AC Type II SPDs with suitable Uc
• [ ] Every frame bonded
• [ ] Earth resistance measured and recorded

Talk to Sunlectric

We stock chemical earthing kits, GI strip (25 × 3 and 25 × 6 mm), LA kits, masts, bonding hardware and DC/AC SPDs at our Pune hub for same-day dispatch. WhatsApp +91 89567 89307 (wa.me/918956789307) for a kit list for your job. The Academy electrical module covers earthing and lightning in depth. Related: monsoon readiness.

Sources

• IS/IEC 62305-3 minimum cross-sections for air-termination and down conductors (Table 6): reproduced in IPD Lightning Protection Guide, p. 111 (accessed 20 Oct 2026)
• Single integrated earth termination and 10 Ω guidance: Furse technical guide, p. 278 (accessed 20 Oct 2026)
• IS 3043:2018 Code of practice for earthing; IS/IEC 62305 (2010) parts 1–4; NFC 17-102 for ESE (check current editions)
• Sunlectric Studio earthing rules and engineering review, Oct 2026 (pits, AC conductor sizes, SPD Uc)