Solar earthing and lightning protection: why your rooftop system needs both

A rooftop solar system is, among other things, a large metal structure on the highest point of your building, wired into your home's electricity supply. That makes two protections essential: earthing, which gives fault currents and surges a safe path to the ground, and lightning protection, which deals with the far larger energy of a nearby strike. They are also the parts of a solar installation buyers see least and installers most often cut.

This guide explains what earthing and lightning protection do, why they must be done properly, and what to look for in your installer's design. It is especially relevant in Telangana and Andhra Pradesh, where pre-monsoon and monsoon thunderstorms are common.

Why a solar system needs protection

Without proper protection, a solar system can be damaged, and can endanger people, in several ways:

• Electric shock: if insulation fails and a metal frame becomes live, anyone touching it could be shocked. Earthing carries the fault current away and helps protective devices trip.
• Surges: lightning nearby, or switching on the grid, can send voltage spikes through cables, damaging the inverter and other equipment.
• Direct or nearby lightning strikes: a strike can carry enormous energy. Without a planned path to ground, it can damage the structure and electrics and start fires.
• Fire: faults with no safe path to ground can overheat cables and connectors.

Part 1: equipment earthing

Equipment earthing (also called protective earthing) connects every exposed metal part of the system to the ground:

• every panel frame;
• the mounting structure;
• the DC distribution box (DCDB);
• the AC distribution box (ACDB);
• the inverter.

How it works

If a fault makes any metal part live, the earth connection gives the current a low-resistance path to the ground. That limits the voltage on the metal part and lets breakers and fuses operate.

What good equipment earthing looks like

• Continuous bonding of every frame and enclosure, not just one point.
• Copper earth cable of adequate size. On every system we install, we use 6 sqmm copper earth cable, with 80 metres of it bonding every frame, enclosure and the inverter.
• A proper earth electrode (earth pit) with low resistance to ground.
• Secure, corrosion-resistant connections that stay tight for 25 years.

Part 2: lightning protection

Lightning protection deals with energy on a completely different scale from ordinary faults. Its job is to intercept a strike and carry it safely to ground, away from the building's electrics and the solar equipment.

The lightning arrestor

A lightning arrestor (air terminal) is a conductor mounted above the array. If lightning strikes in the area it protects, the strike hits the arrestor rather than the panels or structure. A down conductor carries the current to the ground.

Why it needs its own earth pit

This is the single most important point in this guide. The lightning arrestor must be connected to its own separate, dedicated earth pit, not to the equipment earth.

If the lightning arrestor shares the same earth as the panels, inverter and home electrics, a strike's huge current can raise the voltage of that shared earth and push energy back into the equipment it was meant to protect. A dedicated pit keeps the lightning current away from the electrical system.

On every system we install, the lightning arrestor has dedicated earthing in its own separate pit.

Positioning matters

The arrestor must be placed and sized so that its zone of protection covers the whole array. A single short arrestor at one corner of a large array may leave panels unprotected. The installer should be able to explain how the arrestor covers your array.

Part 3: surge protection devices (SPDs)

Earthing and lightning arrestors handle direct faults and strikes. Surge protection devices deal with voltage spikes travelling along cables, which can come from:

• lightning striking nearby (not necessarily on your building);
• switching operations on the grid;
• faults elsewhere in the network.

An SPD diverts the excess voltage to earth before it reaches sensitive equipment such as the inverter.

Both sides need protection

Surges can enter from the panel side (DC) or from the grid side (AC). Protecting only one side leaves the inverter exposed from the other. We install surge protection devices on both the DC and AC sides of every system, inside Siemens or Finder DCDB and ACDB enclosures, with a 25A MCCB on the AC side.

SPDs wear out

SPDs absorb energy each time they act. After a major surge they may need replacing. Many have a status indicator. Checking SPDs is part of a proper maintenance visit.

How it fits together

On a well-designed system:

1. Every metal part (frames, structure, DCDB, ACDB, inverter) is bonded to the equipment earth.
2. A lightning arrestor above the array connects to its own separate earth pit.
3. SPDs on the DC side protect the inverter from surges coming from the panels.
4. SPDs on the AC side protect against surges from the grid.
5. Breakers, fuses and isolators in the DCDB and ACDB disconnect faults and allow safe maintenance.

Our guide to the solar panel wiring diagram shows where each part sits.

Earth pit basics

An earth pit is where the earthing system meets the ground. Its effectiveness depends on:

• soil type and moisture: dry, rocky soil gives higher resistance, which is common in parts of Rayalaseema and Telangana;
• the electrode and backfill used;
• depth and installation quality;
• upkeep: earth resistance can rise as soil dries or connections corrode.

Earth resistance can be measured. Ask your installer how the earth pits will be made and whether they will test them.

Signs your earthing or protection may be inadequate

If you already have a solar system, watch for:

• a single earth wire connecting only one point of the structure;
• the lightning arrestor connected to the same earth as the panels and inverter;
• no visible SPDs in the distribution boxes;
• corroded or loose earth connections;
• repeated inverter faults or failures after storms;
• a tingle when touching metal parts. Stop and call an electrician immediately.

Protection and your warranty

Inverter and panel manufacturers expect proper installation. Damage from surges or lightning on a system without adequate earthing and surge protection may not be covered. Good protection is not just about safety; it protects your investment and your warranties. The panels we install carry a 10-year product and 25-year performance warranty, and we give a 5-year workmanship warranty on our installation.

Why buyers rarely see this, and why it matters

Earthing and lightning protection are invisible once installed. A buyer comparing quotes sees panel brands, inverter brands and price. A quote can look cheaper by leaving out the dedicated earth pit, using a thin earth wire, or skipping SPDs on one side. The difference only shows up after a storm.

That is why we list protection explicitly in our quotations, and why we built our Built to Last page around exactly this kind of hardware.

Questions to ask your installer

1. How will panel frames, the structure, DCDB, ACDB and inverter be earthed? What cable size?
2. Will there be a lightning arrestor, and how does it cover the whole array?
3. Will the lightning arrestor have its own separate earth pit?
4. Are there SPDs on both the DC and AC sides?
5. How will the earth pits be made, and will earth resistance be tested?
6. Will protection devices be checked during maintenance?

Maintenance of earthing and protection

Protection systems need occasional checks:

• inspect earth connections for corrosion and tightness;
• check SPD status indicators;
• check earth pit condition, especially after long dry spells;
• inspect the lightning arrestor and down conductor after major storms.

Our maintenance visits, scheduled every three months, include checking protection devices and connections, and we respond within 48 hours when customers report issues. See solar maintenance and AMC.

How Origian protects every system

Every system we install includes, as standard:

• dedicated lightning-arrestor earthing in its own separate pit;
• 80 metres of 6 sqmm copper equipment earth cable bonding every frame, enclosure and the inverter;
• surge protection devices on both the DC and AC sides;
• Siemens or Finder DCDB and ACDB, with a 25A MCCB;
• galvanised structures with stainless steel bolts, rated to 150 km/h wind.

To see what this means for your roof, book a free site survey, or read about the full specification on our Built to Last page.

What happens during a thunderstorm

To see why each part matters, follow what happens when a storm passes over a home with a well-protected solar system.

1. Lightning strikes nearby, not on the building. The strike induces surges in cables over a wide area. On your system, the SPDs on the DC and AC sides divert the surge to earth before it reaches the inverter.
2. Lightning strikes the building. The lightning arrestor above the array intercepts it. The down conductor carries the current to the dedicated lightning earth pit, away from the solar equipment's earth.
3. A fault occurs in the system (for example, damaged insulation makes a frame live). The equipment earth carries the fault current to ground, limiting the voltage on the frame, and protective devices act.

Without the SPDs, scenario 1 can destroy an inverter. Without a separate lightning earth, scenario 2 can push lightning energy into the electrical system. Without equipment earthing, scenario 3 can leave a live metal frame on your roof.

After a storm: what to check

After a major thunderstorm, especially one with strikes nearby:

• Check the inverter display or app for errors, and whether generation has resumed normally the next sunny day.
• Look at SPD indicators in the DCDB and ACDB, if you can see them without opening anything. Some show a colour change when they have operated and need replacing.
• Look for visible damage to panels, the arrestor, cables or conduits.
• Do not open any boxes yourself. If anything looks wrong, call your installer.

We respond within 48 hours when customers report issues, and protection devices are checked during our maintenance visits every three months.

Soil and earth pits in our region

Earth resistance depends heavily on soil. Parts of Rayalaseema and Telangana have rocky or very dry soil, which makes it harder to achieve low earth resistance. Approaches include deeper electrodes, suitable backfill materials and, where needed, more than one electrode. Earth resistance also changes with the seasons, rising in long dry spells. That is one reason to check earthing periodically rather than assume it stays the same for 25 years.

Myths about solar and lightning

"Solar panels attract lightning." Panels do not make a building more likely to be struck. But a large metal structure on the roof must be protected so that, if a strike does happen, it is handled safely.

"The building already has a lightning conductor, so the solar system is covered." Not necessarily. The existing conductor may not cover the array, and the solar equipment still needs its own earthing and surge protection.

"One earth pit is enough for everything." The lightning arrestor should have its own dedicated pit, separate from the equipment earth.

"Surge protection is only needed on the AC side." Surges can arrive from the panels' side too. Protect both.

Earthing for different roof types

The basic principles stay the same on every roof, but the details vary.

RCC flat roofs: the mounting structure is bonded with copper earth cable, and down conductors run to earth pits at ground level. Cable routes are planned so they do not create trip hazards or interfere with roof waterproofing.

Metal sheet roofs (factories and sheds): the roof itself is a large conductive surface. The solar structure and the roof sheeting need proper bonding, and the lightning protection design must take the whole building into account.

Tall buildings: longer down conductors are needed, and wind and lightning exposure are higher. Earth pits at ground level may be some distance from the array, so the routing needs care.

Earthing on hybrid systems with batteries

Hybrid and off-grid systems add a battery bank and its cabling. The battery enclosure and its metal racks also need earthing, and the battery circuit needs proper fuses or breakers sized for the high currents batteries can deliver. The inverter manufacturer's earthing instructions must be followed, as different inverter designs have different requirements. See our guide to hybrid inverters.

Protection costs little compared with what it protects

The inverter is usually one of the most expensive single components in a rooftop system, and it is the one most vulnerable to surges. Proper earthing, a separate lightning earth pit and SPDs on both sides add a modest amount to the system cost. Compared with replacing an inverter after a storm, or the safety risk of an unearthed frame, that is a small price. That is why we include them on every system as standard rather than as optional extras.

A note for existing systems

If your solar system was installed some years ago, and you are not sure how it is protected, a site inspection can check whether:

• every frame and enclosure is bonded;
• a lightning arrestor covers the array, with its own separate earth pit;
• SPDs are fitted on both DC and AC sides and are still healthy;
• earth connections are tight and free of corrosion.

Frequently asked questions

Is earthing necessary for solar panels? Yes. Every exposed metal part of a rooftop solar system, including the panel frames, the structure, the DCDB, the ACDB and the inverter, should be earthed. If insulation fails and a frame becomes live, earthing carries the fault current to ground and lets protective devices trip, protecting people and equipment.

How many earth pits are needed for a rooftop solar system? A rooftop solar system needs at least two earth pits: one for the equipment earth and a separate, dedicated pit for the lightning arrestor. Larger systems, or sites with dry and rocky soil, may need more. On every system Origian installs, the lightning arrestor has its own separate earth pit.

Do solar panels need a lightning arrestor? A rooftop solar array is a large metal structure on the highest point of the building, so a lightning arrestor covering the whole array is strongly recommended, especially in thunderstorm-prone Telangana and Andhra Pradesh. It should connect to its own dedicated earth pit, kept separate from the equipment earth.

What is an SPD in a solar system? An SPD (surge protection device) in a solar system diverts voltage spikes from nearby lightning or grid switching to earth before they reach the inverter. A good rooftop system has SPDs on both the DC and AC sides. SPDs can wear out after major surges, so they should be checked during maintenance.

Do solar panels attract lightning? No. Solar panels do not make a building more likely to be struck. But a rooftop solar array adds a large metal structure, so if a strike happens it needs a planned path to ground: a lightning arrestor with its own earth pit, plus equipment earthing and surge protection on both sides.

What size earth cable is used for solar panels? Earth cable size depends on the design, but it must be adequately sized copper. On every rooftop solar system Origian installs, we use 6 sqmm copper earth cable, with 80 metres of it bonding every panel frame, enclosure and the inverter, plus a separate lightning-arrestor earth pit.

How do I check if my solar system is properly earthed? Check that every panel frame, the structure and each distribution box is bonded with earth cable, that the lightning arrestor has its own separate earth pit, and that SPDs are visible on both the DC and AC sides. Earth resistance can be measured. If unsure, have a qualified installer inspect the solar system.