Specifications and Safety Requirements for Grounding Installation of Solar Inverters

Specifications and Safety Requirements for Grounding Installation of Solar Inverters

I. Grounding System: The "Lifeline" of Inverter Safe Operation

Grounding is a core component of Photovoltaic System electrical design. Essentially, it reliably connects the exposed conductive parts of the equipment to the earth through a conductor, achieving three core benefits:

Personnel Safety Protection: In the event of an inverter leakage, grounding reduces the casing potential to a safe level. Data shows that the risk of electric shock in an ungrounded system is 7.2 times higher than in a properly grounded system. This protective effect is even more critical in humid environments, where human impedance is reduced.

Equipment Fault Isolation: Working grounding stabilizes the grid neutral point potential, preventing equipment damage caused by phase lines contacting the casing. For example, in low-voltage distribution systems, neutral grounding prevents the voltage of non-fault phases from rising to three times the phase voltage.

Disaster Risk Mitigation: Lightning protection grounding directs direct and induced lightning currents into the earth, while shielding grounding reduces electromagnetic interference with RS485 communication lines. Anti-static grounding is suitable for special environments such as dry equipment rooms.

II. Global Core Standards: Regional Differences and Standardized Requirements

(I) International Basic Standards
IEC 62109: Specifies that the grounding resistance of photovoltaic inverters must be ≤4Ω, and requires the DC and AC sides to be isolated by a transformer to prevent stray current circulation.

Supplementary Lightning Protection Requirements: In areas prone to lightning, surge protective devices (SPDs) must be installed, and the ground loop impedance must be ≤0.1Ω. (II) Special Regulations for Major Markets

Region
Core Specifications
Key Requirements
Reference Standards
European Union
EN 50521
Equipotential bonding is mandatory, and SPDs must be CE certified.
EN 50521:2018
United States
NEC Section 690
Grounding resistance ≤ 25Ω, requiring installation of a GFPD device.
NEC 2023 §690.5
China
Distributed Photovoltaic Specifications
Grounding resistance ≤ 10Ω, single-point grounding preferred.
GB/T 37954-2019

Specific US GFPD requirements: The device must have four functions: fault detection, current interruption, status indication, and conductor disconnection. The operating current is typically set at 0.5-5A, and there is no automatic reset function.

III. Standardized Installation Process: Full-Process Control from Materials to Testing

(I) Preliminary Preparation
System Selection: Determine the grounding system type. For PV projects, the TN-S system (with separate PE lines) is preferred to avoid the safety hazards of the TN-C system.
Material Selection:
Grounding Electrode: Hot-dip galvanized angle steel (50×50×5mm) or steel pipe, length ≥ 2.5m
Grounding Wire: Yellow-green two-tone copper stranded wire, cross-sectional area ≥ 4mm² (device end), ≥ 16mm² (grounding terminal end)
Supplementary Materials: Resistance reducer (use when soil resistivity > 100Ω·m), anti-corrosion paint, copper lug
(II) Core Construction Steps
Grounding Electrode Installation:
Location: 3-5m from the inverter, in a moist area, away from underground pipelines
Technology: Drive vertically into the ground, top buried ≥ 0.6m, inter-electrode spacing ≥ 5m
Connection Technique:
Grounding Electrode and Grounding Wire: Use exothermic welding, weld length ≥ 6 times the grounding wire diameter
Inverter End: Fasten with M8 galvanized bolts. Polish the terminals to remove oxide layers before wiring
Testing and Acceptance:
Instrument: Use a ground resistance tester (such as the FLUKE 1625), using the three-pole method.

Criteria: ≤4Ω in ordinary areas, ≤25Ω in rural areas of the United States. Three retests are required to obtain an average value in areas prone to lightning.

IV. Safety Assurance System: Risk Prevention and Control and Compliance Key Points

(I) Construction Safety Red Lines

Work must be performed only after disconnecting the AC and DC power supplies. Wear protective equipment such as insulating gloves and shoes.

Grounding wires must not be bundled with communication or DC lines to avoid electromagnetic interference.

A scaffold must be erected for overhead work. Grounding electrode excavation must be performed after confirming the underground facility drawings.

(II) Common Error Avoidance

Error Types

Risk Consequences

Corrective Measures

Poor Solders/Loose Connections

Sudden increase in grounding resistance, resulting in protection failure

Knock off weld slag after welding. Bolt torque must reach 12N·m

Insufficient grounding wire cross-sectional area

Fire caused by burnt conductors during a fault

Based on a current carrying capacity of 10A/mm² Model Selection
Multi-System Mixed Connection
Stray Current Corrosion Equipment
Strictly Distinguish Between Protective Grounding and DC Grounding Systems

(III) Export Compliance Support
EU Market: LVD test report for the grounding system is required, and the SPD must comply with EN 61643.
North American Market: GFPD devices must be UL 1741 certified, and the grounding conductor must be marked with the UL certification mark.

V. Operation and Maintenance and Lifespan Management: Ensuring Long-Term Safety

Regular Inspection Plan:
Daily: Check the grounding terminals monthly for rust and looseness.
Regular: Re-measure the ground resistance every six months, and add SPD testing before the thunderstorm season.
Lifespan Maintenance Measures:
Apply anti-corrosion paint to welding points every two years.
Water every quarter in dry soil areas to maintain stable ground resistance.
Fault Emergency Response:
Sudden increase in ground resistance: Check the grounding electrode for rust and add an auxiliary grounding electrode if necessary.
GFPD Action: Troubleshoot DC side insulation faults. Disconnect the array power supply before resetting.