How many earth pits and what earth resistance does a rooftop solar plant need under the Ministry of New and Renewable Energy specification?
The Ministry of New and Renewable Energy (MNRE) specification says earth resistance shall never be higher than 5 ohms. For systems of 10 kilowatts and above it asks for three separate earth pits, one each for direct current side earthing, alternating current side earthing and the lightning arrestor.
Earthing, clause 8.1
These are clauses from the technical specification in Annexure 3 of MNRE's guidelines for its residential rooftop solar scheme, Pradhan Mantri Surya Ghar: Muft Bijli Yojana. A factory is not bound by them, but they are a published checklist to hold a quotation against.
- Each array structure, the low tension power system, the earthing grid, all electrical equipment, the inverter and all junction boxes shall be grounded as per IS 3043-2018, where IS is Indian Standard.
- All metal casing and shielding shall be grounded in accordance with the Central Electricity Authority Safety Regulation 2010. The lightning arrester or masts should also be earthed inside the array field.
- Earth resistance should be as low as possible and shall never be higher than 5 ohms.
- For 10 kilowatt (kW) and above systems, separate three earth pits shall be provided for the three earthings: direct current (DC) side, alternating current (AC) side and lightning arrestor.
Lightning and surge protection
- Clause 8.2: lightning protection as per NF C 17-102:2011 (a French standard) or the International Electrotechnical Commission (IEC) standard 62305. A lightning arrestor shall not be installed on the mounting structure.
- For a lightning protection system of class III (LPS III) the minimum requirement is 6 square millimetres of copper, 16 square millimetres of aluminium, or galvanised iron (GI) strip of 25 x 3 millimetres (mm). A separate pipe shall be used for the arrestor's earth wires.
- Clause 8.3: internal surge protection, wherever required, of three type-II surge protective devices or metal oxide varistor type connected from the positive and negative terminals to earth.
- Clause 7.9: a residual current breaker shall be used if the inverter does not have the earth fault or residual current protection.
Points to put in the quotation
- The count of earth pits by name: DC, AC and lightning, if your plant is 10 kW or more.
- A resistance reading for each pit, taken after the plant is wired, signed by the installer.
- Whether pits use chemical earthing. The standards list names IEC 62561 for earthing enhancing compounds.
- The clause sets three pits at 10 kW and above. It does not say more pits for a bigger plant, so ask the designer how many your roof layout needs.
Pit count by plant size (reading clause 8.1.5)
- 8 kW plant: below the 10 kW line, so the three-pit clause is not triggered, though earthing still applies
- 10 kW plant: three pits (DC, AC, lightning arrestor)
- 100 kW plant: three pits at a minimum, and the clause is silent on more
- Resistance reading of 3.8 ohms passes the 5 ohm limit; 6.2 ohms does not
Plant sizes and readings are examples. The 5 ohm limit and the 10 kW line are MNRE's.
What Senseible does here
Senseible reads fuel invoices and electricity bills into monthly records. It does not check earthing, protection or any site safety item.
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Last reviewed 2026-11-06. Re-check clause numbers and figures against the current version of the guidelines before you rely on them. Clause numbers are from Annexure 3, sections 7 and 8. A safety design is for a qualified electrical engineer to approve.