Earthing and grounding are the most safety-critical aspects of any solar PV installation. Get it right and you have a system that is safe to work on, protects equipment from transient overvoltages, and satisfies utility grid connection requirements. Get it wrong and you face a lethal shock risk, PID-induced module degradation, nuisance ground-fault trips, and potential inverter warranty invalidation.
This guide covers the main international standards — IEC 60364-7-712 (the IEC standard dedicated to PV power supply systems) and NEC Article 690 (the US National Electrical Code) — along with practical design guidance for the most common system configurations.
Solar PV arrays generate high DC voltages that persist as long as sunlight falls on the modules — unlike AC systems, you cannot simply switch off the source at a breaker. The DC side of a 1500 V utility-scale array poses a lethal electrocution risk and an arc-flash hazard that demands careful grounding design to:
| Requirement | IEC 60364-7-712 (International) | NEC Article 690 (USA) |
|---|---|---|
| DC system earthing | IT (unearthed) or TN-S; country-specific | Ungrounded or functionally grounded systems permitted for 1000 V+ with GFDI |
| Equipotential bonding | Required for all exposed metalwork (690.43) | Required via Equipment Grounding Conductor (EGC) |
| Ground fault detection | RCD/IMD on DC side; GFDI for ungrounded | Ground Fault Detection and Interruption (GFDI) required per 690.5 |
| EGC minimum size | Based on IEC 60364-5-54 Table 54.2 | Per NEC Table 250.122 based on OCPD rating |
| Grounding electrode | IEC 62305 for lightning protection | NEC Article 250; rod, plate, or ring electrode |
| AC system earthing | TN-S preferred; transformer secondary earthed | Solidly grounded neutral (multi-grounded neutral) typical |
In an IT configuration, neither pole of the DC array is connected to earth. This is the most common configuration for transformerless string inverters from Sungrow and Huawei because it avoids PID-inducing negative-to-ground voltage. A single ground fault does not create a complete circuit (no return path through earth), so the system continues operating. However, a second ground fault on the opposite pole creates a short circuit through earth — hence the requirement for continuous Insulation Monitoring Devices (IMD) to detect the first fault before a dangerous second fault develops.
Modern string inverters incorporate built-in IMD and will alarm or trip on detection of leakage currents above a threshold (typically 30–300 mA depending on array size and inverter model).
In a negative-grounded TN-S configuration, the negative pole of the DC array is connected to the protective earth (PE) conductor at a single point — typically at the DC input of the inverter or at the array combiner. This is the traditional configuration for older central inverters.
Negative-grounded systems eliminate PID for cells with negative-to-ground voltage bias (p-type PERC cells are most vulnerable). The trade-off: a single ground fault on the positive pole causes an immediate fault current, so protection devices must clear the fault rapidly to prevent arc damage. Module-level ground fault detection is essential.
Rarely used in modern installations. Required by some thin-film module manufacturers (e.g., older CdTe technology) to prevent PID on positively-biased cells. Not compatible with most modern inverters. Largely obsolete for crystalline silicon modules.
The EGC connects all exposed metal parts — module frames, mounting rails, inverter enclosures, conduit — to the grounding electrode system. It must carry the maximum ground fault current without voltage drop that would prevent protection device operation.
Under NEC 690.45, the EGC for PV source circuits must be sized per NEC Table 250.122 based on the overcurrent protective device rating, but not smaller than the current-carrying conductor. For a typical 20 A fuse on a 10 A Isc string, this yields a minimum 10 AWG (6 mm²) copper EGC.
Under IEC 60364-5-54, the EGC cross-section (S_PE) relative to the phase conductor (S) follows:
Equipotential bonding connects all metalwork to prevent dangerous touch potentials. On a ground-mount system, this means:
For anodised aluminium rails (common on systems using mounting from Chinese manufacturers), the oxide layer is non-conductive. Use serrated stainless bonding clips that pierce the anodising to make reliable metal-to-metal contact. Verify bonding resistance with a low-resistance ohmmeter (<0.1 Ω) during commissioning.
IEC 62305 and its PV-specific companion IEC TS 61730-2 define lightning protection zones (LPZ) for PV installations. For most commercial and utility-scale systems:
PID (Potential-Induced Degradation) is caused by high voltage bias between the cell active layer and the module frame (earth potential). In a floating/IT system, the DC midpoint voltage above earth depends on the insulation resistance distribution, and can be positive or negative depending on system operating point.
Sungrow and Huawei string inverters with built-in PID recovery function apply a small AC voltage offset to the module midpoint at night, reversing the ion migration that causes PID. This requires the DC system to remain in IT (floating) configuration — grounding either pole will disable the PID recovery function.
For n-type TOPCon modules (LONGi Hi-MO 7, Jinko Tiger Neo NEG72R20), PID susceptibility is significantly lower than p-type PERC, because the cell structure means the degradation mechanism does not apply in the same way. This is one of the key advantages of the n-type transition for projects in high-voltage systems.
The transformer secondary (LV winding) connected to the utility grid is typically solidly earthed at the MET. For TN-S distribution systems common in Europe and Asia, the neutral and protective earth are separated throughout the installation — no shared N-PE conductor beyond the MET. For utility-scale projects feeding into the MV grid via a step-up transformer, the LV neutral is earthed at the inverter output terminal, and the MV winding earthing depends on the utility's network configuration (usually solidly earthed or resistance earthed).
Anti-islanding protection on the inverter (required by IEEE 1547-2018 and IEC 62116) also depends on correct AC-side earthing to detect a loss-of-mains condition reliably. A floating AC neutral can cause the anti-islanding detection to fail, which is why IEC and NEC both require confirmed earthing of the transformer secondary before commissioning.
Econo Solar sources ground-mount structural components, earthing clips, copper EGC cable, and Type 2 SPD protection devices alongside modules and inverters. Our project teams can review your grounding design and confirm that the specified equipment meets IEC 60364-7-712 or NEC 690 requirements for your target market.
For a project-specific grounding equipment quote, submit your enquiry here.
For modern transformerless string inverters (Sungrow SG350HX, Huawei SUN2000-330KTL), an ungrounded (IT) DC system is standard and recommended. It maximises PID resistance, enables PID recovery functions, and is compatible with built-in IMD. Grounded DC systems are typically only used with central inverters that have isolated DC inputs or for specific legacy configurations. Always consult the inverter manufacturer's installation manual, as using the wrong configuration may void the warranty.
IEC 60364-5-54 does not specify a single resistance value; instead, it specifies that the earth electrode resistance must be low enough that the touch voltage during a fault does not exceed 50 V (or 25 V in wet locations) for more than 5 seconds. In practice, most designers target ≤ 10 Ω for single electrodes; for lightning protection per IEC 62305, ≤ 10 Ω is the target, and in high-resistivity soils, a ring earth electrode buried at 0.5 m depth around the array perimeter is used to achieve this.
Under NEC Article 690, each module frame must be individually bonded unless the module manufacturer has listed and tested the module for use with a system that relies on rail-to-frame contact (rail bonding). Under IEC 60364-7-712, the equipotential bonding requirement can be met by a continuous bonded rail system provided ≤ 0.1 Ω resistance is demonstrated between any two module frames. Most quality Chinese mounting systems include pre-installed stainless serrated bonding clips; verify these are IEC-compliant and test continuity during commissioning.
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