One ohm, and the fire that starts in a connector

Two things on a rooftop system will cost you far more than they save if they are done cheaply: the earth pit and the DC connectors.

One of them is inspected. The other one burns.

Earthing, and the number inspectors care about

Earthing practice in India follows IS 3043, the code of practice for earthing. The working target for a solar installation is an earth resistance at or below one ohm, with a commonly quoted outer limit of about five ohms for a small residential rooftop.

This is also the item that the DISCOM checks physically at inspection, in almost every territory. Not the module datasheet, not your cable schedule. The inspector walks to the earth pit.

What actually goes wrong:

• Rocky or dry soil that will not give you the resistance, so the pit needs treatment, depth, or additional electrodes.
• One pit doing three jobs. Array frame, inverter body and lightning protection have different requirements, and combining them badly defeats all three.
• No test, ever. The resistance is measured at commissioning and then assumed forever, in soil whose moisture content changes with the season.
• The pit that cannot be found two years later because nobody recorded where it is.

Lightning is not a theoretical risk here

India records upwards of twenty lakh cloud-to-ground lightning strikes a year, concentrated heavily along a corridor running across West Bengal, Odisha, Jharkhand, Chhattisgarh and Madhya Pradesh.

A rooftop array is a large, grounded, metal-framed object placed at the highest point of a building. It does not attract strikes in the way folklore suggests, but when the building is struck, the array is part of the path.

Two different protections, often confused:

• A lightning protection system handles a direct strike, conducting it to earth away from the array. Whether one is required depends on the building, its height, its location and the local risk assessment. It is a building decision, not a solar accessory.
• Surge protection devices handle the far more common case: an induced surge from a nearby strike travelling in on the DC or AC side. These belong on both sides, and they are cheap relative to an inverter.

Surge devices also age. They have status indicators for a reason, and a device that has absorbed a surge may be doing nothing at all afterwards. Checking them belongs in the maintenance visit.

The fire risk is in the connectors

Rooftop fires that start in the array almost never start in a module. They start in the DC wiring, and the usual causes are consistent:

• Loose or badly crimped MC4 connectors, especially mismatched brands mated together.
• Damaged DC cable, from UV exposure, rodents, or being dragged across a sharp edge during installation.
• Improvised joints made on the roof with tape.
• Poor earthing and missing surge protection, leaving fault current with nowhere sensible to go.

DC is the dangerous part. An alternating current arc extinguishes itself at every zero crossing. A direct current arc does not, so once it starts it keeps burning, and a rooftop array can be producing hundreds of volts on a sunny morning with no switch anywhere near the fault.

Practical prevention is dull and cheap:

• Use connectors from one brand, crimped with that brand's tool, not pliers.
• Route cable in UV rated conduit or tray, never resting on the roof surface or over a parapet edge.
• Torque every terminal to the manufacturer's figure and re-check the critical ones at the first maintenance visit, because thermal cycling loosens them.
• Fit a DC isolator where the standards and the inspection require it, and label it so a fire crew can find it.
• Photograph every DC junction before it is closed.

What the standards say, roughly

Array design practice draws on IEC 62548, earthing on IS 3043, and the National Building Code's photovoltaic provisions cover the building side. The CEA's technical standards, amended in 2026 and effective April 2027, extend requirements further, including a twenty five year design life for solar plants, which is in new CEA standards land in April 2027.

Specific clause numbers vary between sources and editions, and quoting the wrong one into a tender is worse than quoting none. Take clause references from the current standard itself or from the DISCOM's own specification.

Why this is a commercial argument, not just a safety one

Because it is visible, and almost nothing else about your workmanship is.

A customer cannot evaluate your string design. They can see whether the cable is in conduit or draped across the terrace, whether the DC box is labelled, and whether you handed them an earth resistance reading. Those are the things that tell them which kind of company they hired, and they are the things a neighbour notices when deciding whom to call.

The short version

• Earthing follows IS 3043. Aim at one ohm, with about five ohms the outer limit for a small residential system, and it is the item the DISCOM inspector physically checks.
• Measure it at commissioning, record the figure and photograph the pit's location.
• India sees over twenty lakh cloud-to-ground strikes a year. Lightning protection and surge protection are different things; surge devices belong on both DC and AC sides and need checking.
• Array fires start in DC wiring: loose or mismatched connectors, damaged cable, taped joints. A DC arc does not self-extinguish.
• One connector brand, the right crimp tool, UV rated routing, torqued terminals, a labelled isolator, photographs before closing.
• Take clause numbers from the standard or the DISCOM specification, not from a summary.

Sources

• Solar Grounding and Earthing India, IS 3043 guide, trade guidance
• Solar Lightning Protection India: LPS and SPD guide, trade guidance
• Fire Safety in Solar Installations: hidden risks, International Fire and Safety Journal