Proper earthing in a solar system requires bonding all non-current-carrying metal (racking, inverter chassis, conduit) with an Equipment Grounding Conductor (EGC) and tying it to earth via a Grounding Electrode Conductor (GEC). For a standard residential system under 100A, this means running continuous 6 AWG bare copper from the array to the inverter, and from the inverter to a ground rod measuring less than 25 ohms of resistance. Get this wrong, and you risk lethal touch potentials or catastrophic DC arc faults.
The Hazard: What Fails Without Proper Solar Earthing?
The primary hazard prevented by earthing in a solar system is lethal touch potential combined with DC arc fires. Solar panels generate voltage whenever exposed to light; you cannot "turn off" the array on the roof.
If a rodent chews through the DC insulation on your roof, or a micro-crack in a panel degrades and shorts the live DC conductor to the aluminum racking, the entire metal mounting system becomes energized at 400V+ DC. Without a low-impedance path to earth (the EGC), the racking stays energized indefinitely. The moment a person touches the racking while standing on the ground, they complete the circuit. Because DC current causes sustained muscle tetany (you cannot let go), this is frequently fatal.
Furthermore, without a proper Grounding Electrode Conductor (GEC) tying the system to the earth, lightning-induced voltage transients have nowhere to dissipate. These spikes will arc across the internal circuitry of your inverter, destroying thousands of dollars of equipment and potentially igniting the surrounding structure. Earthing provides a dedicated, low-resistance highway for fault currents to trip your overcurrent protective devices (OCPDs) and for surges to dissipate safely into the dirt.
Ground vs. Bond vs. Neutral in PV Arrays
Misusing these terms leads to miswired systems. Here is how they apply specifically to solar PV installations:
- Ground (Earthing): The physical connection to the earth (dirt). In a solar system, this is achieved via ground rods, ufer grounds (concrete-encased electrodes), or ground plates. Its job is to stabilize voltage to earth and dissipate lightning/surges.
- Bond (Bonding): The physical, electrical connection between all non-current-carrying metal parts. When you attach a grounding lug to your solar rail and connect it to the inverter chassis, you are bonding them. This ensures that if a fault occurs, the voltage potential between the rail and the inverter remains zero, allowing fault current to flow back to the source to trip the breaker.
- Neutral (Grounded Conductor): The current-carrying conductor that is intentionally grounded at the service entrance. Never use the neutral wire to bond your solar racking. In a standard grid-tied solar setup, the inverter outputs AC via Line (Hot) and Neutral, but the DC side and the equipment chassis rely strictly on the EGC/GEC, not the neutral.
Sizing and Selecting Your Solar Grounding Components
Sizing your conductors correctly ensures the fault current can actually trip the breaker before the wire melts. The following decision path follows NFPA 70 (NEC) Articles 250 and 690. Note: Always verify with your local AHJ, as local soil conditions or utility interconnection agreements may mandate larger conductors.
| System Parameter | Conductor Type | Sizing Rule (NEC Guidance) | Concrete Pick / Part Number |
|---|---|---|---|
| Inverter Output < 100A (Standard Residential) | Grounding Electrode Conductor (GEC) - Inverter to Earth | NEC Table 250.66 (Based on largest ungrounded DC/AC conductor) | 6 AWG Bare Copper |
| Racking & Module Frames (Equipment) | Equipment Grounding Conductor (EGC) - Array to Inverter | NEC 690.43 / Table 250.122 (Based on DC OCPD rating, typically 15A-30A) | 6 AWG Bare Copper (Oversized for physical durability on roofs) |
| Ground Rod Connection | Acorn Clamp / Ground Rod Clamp | Must be listed for direct burial and match rod diameter (typically 5/8") | Harger HCC-100 or ILSCO GBC-58 |
| Inverter / Busbar Termination | Grounding Lug | Must be rated for the wire size and material (Cu/Al) | ILSCO GBL-4 (Torque to 15 in-lbs) |
What About WEEBs and Mid-Clamps?
Many modern racking systems (like IronRidge or Unirac) use Washer, Electrical Equipment Bonds (WEEBs) built into the mid-clamps to bond the solar module frames to the rails. While WEEBs are UL-listed for this purpose, you still must run a continuous copper EGC (like the 6 AWG bare copper mentioned above) along the rail, bonding to the rail at regular intervals and running all the way back to the inverter. Relying solely on the mechanical friction of WEEBs and rail splices for your primary fault path is a known failure point in high-vibration or high-wind environments.
Step-by-Step Installation & Verification
Follow these steps to establish and verify your earth connection. For deeper testing methodologies, refer to Fluke's official ground resistance testing guidelines.
- Drive the Ground Rod: Drive a 5/8-inch by 8-foot copper-bonded ground rod into the earth as close to the inverter as possible. The top of the rod should be flush with or slightly below grade to prevent physical damage.
- Attach the Ground Clamp: Slide the Harger HCC-100 clamp onto the rod. Tighten the bolt securely. Do not use standard plumbing clamps; they will corrode rapidly in soil.
- Run the GEC: Route your 6 AWG bare copper from the ground rod clamp to the inverter's grounding busbar. Protect the wire with PVC conduit if it is buried or subject to physical damage (NEC 250.64(B)).
- Terminate at the Inverter: Strip the insulation (if using THHN, though bare is preferred) and terminate the wire into the ILSCO GBL-4 lug on the inverter chassis. Torque the set screw to the manufacturer's specification (typically 15 in-lbs) using a calibrated torque screwdriver. A loose ground lug is a high-resistance fault waiting to happen.
- Bond the Array: On the roof, attach your 6 AWG EGC to the racking using listed grounding lugs (e.g., IronRidge GND-LUG-10). Route the wire down the conduit alongside your DC conductors to the inverter busbar.
- Verify Earth Resistance: This is the step most DIYers skip. Use a clamp-on ground tester like the Fluke 1630-2 FC. Clamp the meter around the GEC wire above the ground rod. The meter induces a voltage and measures the returning current to calculate the loop resistance.
- Target: Less than 25 ohms (NEC 250.56 requirement for a single made electrode).
- If > 25 ohms: Drive a second ground rod at least 6 feet away, bond them together with 6 AWG bare copper, and re-test. Alternatively, treat the soil with a conductive earth-enhancement compound like bentonite clay or GEM (Ground Enhancement Material).
When to Call a Licensed Electrician
While running the EGC on the roof and driving a supplementary ground rod for the inverter are well within the scope of a competent DIY solar builder, certain tasks legally and safely require a licensed electrician:
- Main Service Panel Tie-Ins: If your solar system requires upgrading your main service grounding electrode conductor, or altering the main bonding jumper inside your primary service disconnect, this is strictly licensed work. Messing with the service entrance neutral-to-ground bond can energize your entire home's plumbing and chassis.
- Utility Interconnection Grounding: Many utilities require a specific, verified grounding scheme (often a separate, dedicated ground rod just for the solar system, bonded to the main house ground) before they will install the net-metering bi-directional meter. An electrician will ensure this meets the utility's specific "Green Book" or interconnection manual.
- Ufer Ground Integration: If you are pouring a new concrete pad for a ground-mount array or a new service, tying into the rebar for a Ufer ground (Concrete-Encased Electrode) requires coordination with the concrete crew and the AHJ inspector before the pour happens.
By defaulting to 6 AWG bare copper, using listed lugs torqued to spec, and verifying your earth resistance is under 25 ohms, you build a solar array that will safely clear faults and survive lightning transients for its entire 25-year warranted lifespan.
