Earthing a solar PV plant: a checklist for EPCs and installers

1. What has to be earthed

• Module frames and mounting structures. Bond every row continuously, at every joint where anodising or paint would otherwise break continuity. Use bonding hardware suited to aluminium-to-steel or aluminium-to-copper joints to avoid galvanic corrosion.
• Inverters, DCDB and ACDB enclosures, and transformer bodies. These are protective (equipment) earthing.
• The transformer or inverter neutral, where the system design calls for it. This is system earthing, and its arrangement is set by the electrical design.
• Lightning protection: air terminals and down conductors, terminated on their own earth electrodes.
• SPD earth terminals, which need a short, direct path to the equipotential bar.

2. Separate electrodes, one equipotential system

Most Indian EPC specifications ask for dedicated earth pits for:

• the array and structure,
• the inverter and AC equipment,
• the lightning protection system.

Separate pits are about keeping the high-frequency lightning current path short and defined. They do not mean the systems stay electrically independent. IEC 62305 requires equipotential bonding between the lightning earth and the other earthing systems, directly or through spark gaps or SPDs, so that dangerous potential differences cannot appear between them during a strike. Follow the bonding arrangement in your design and specification.

3. Choosing electrodes for solar sites

Solar sites are often on rocky, sandy or dry land with high soil resistivity. They also have long service lives of 25 years or more, with little maintenance. That combination favours:

• Copper-bonded rods driven to depth, using the 250 µm coating class for long life,
• Compound-filled pipe electrodes backfilled with earth enhancement compound in high-resistivity ground,
• enough pits in parallel, spaced apart, to reach the specified resistance.

See GI vs copper vs copper-bonded for the trade-offs.

4. Conductors and connections

• Size earthing conductors for the prospective fault current and its duration, as set out in IS 3043, not just to a minimum cross-section.
• Prefer exothermic welds for buried joints. Use bolted joints only at accessible, inspectable test points.
• Keep SPD earth leads short and straight. Length adds inductance and raises the voltage the equipment sees during a surge.

5. DC-side protection

• String fuses (gPV class, IEC 60269-6) are needed when enough strings are paralleled that a faulted string could be back-fed beyond the module's reverse-current rating. See sizing gPV fuses.
• DC SPDs rated for PV (IEC 61643-31 or EN 50539-11) at the inverter input. Add them at the array end too when cable runs are long.

6. AC-side protection

Install an AC SPD at the inverter output or ACDB. Add a Type 1 or Type 1+2 SPD at the main incomer if the plant has an external lightning protection system or an overhead supply. See SPD types explained.

7. Test and document

• Measure every pit at commissioning and record it against a pit layout drawing.
• Check continuity from structures to the earth bar.
• Re-test before each monsoon.

The method is in how to test earth pit resistance.

Supply for solar projects

Ashima supplies solar EPCs from Jaipur. We offer:

• ACME copper bonded rods and pipe electrodes (manufactured by us),
• ACME earth enhancement compound,
• pit covers,
• Mersen gPV fuses, fuse holders and SPDs,
• DC distribution boxes,
• lightning protection.

Send your BOQ and we will quote the full earthing and protection package.