As solar installations continue to expand globally, Solis inverters are connected to a variety of grid topologies and earthing systems. Understanding earthing system compatibility is essential to ensure safe operation, compliance with local regulations, and optimal system performance.

Important: Local electrical regulations and Distribution System Operator (DSO) requirements always take priority over this general guidance. Installations must be completed by qualified electrical professionals and in accordance with applicable national and local standards.

Understanding Common Earthing System Abbreviations

TT (Terra-Terra)

• The power source is directly connected to Earth.
• The consumer installation has its own local earth electrode, independent from the utility earth.
• Common in residential installations across many European countries.

TN-S (Terra-Neutral Separate)

• The power source is connected to Earth.
• Neutral (N) and Protective Earth (PE) are separate conductors throughout the installation.
• Considered one of the safest and most common earthing systems.

TN-C (Terra-Neutral Combined)

• The power source is connected to Earth.
• Neutral and Protective Earth functions are combined into a single conductor called a PEN (Protective Earth and Neutral) conductor.
• Often found in older distribution networks.

TN-C-S (Terra-Neutral Combined-Separate)

• Also known as PME (Protective Multiple Earthing) in some countries.
• The supply network uses a combined PEN conductor which is separated into Neutral (N) and Protective Earth (PE) at the installation.
• Widely used in residential and commercial applications.

IT (Isolé-Terra)

• The power source is isolated from Earth or connected through a high impedance.
• Exposed conductive parts are connected to Earth.
• Common in certain industrial, medical, marine, and isolated power systems.
• Not all inverter models support operation on IT networks.

Solis Inverter Earthing System Compatibility Overview

Legend

✅ Supported
⚠️ Supported with special considerations / not recommended
❌ Not supported

Important TN-C System Considerations

While some Solis inverter models can technically operate in TN-C systems, Solis generally does not recommend TN-C installations for residential hybrid inverter applications.

If connection to a TN-C system is unavoidable:

• The inverter's unbalanced output function must not be enabled.
• Under certain operating conditions with significant load imbalance, touch voltage may occur on the inverter enclosure.
• Whenever possible, the installation should be converted to a TN-C-S system before connecting the inverter.
• Installation must always be performed by a qualified electrician and in accordance with local electrical regulations.

Hybrid Inverter Considerations for TN-C Networks

When connecting compatible hybrid inverters to a TN-C (3W+PEN) system:

• The grid-side Neutral connection may be connected at the PE-N split point or left unconnected, depending on local requirements.
• During backup/off-grid operation, the inverter internally connects Neutral (N) and Protective Earth (PE) on the backup port to create a local neutral reference.
• The Neutral conductor on the backup side should not be externally bonded to Earth when connected to a TN-C system.
• The backup port PE terminal is not internally connected to the grid-side PE terminal. Installers must ensure the backup-side earthing arrangement complies with local regulations.

Commercial and Utility Inverter Considerations

Certain commercial and utility-scale models support operation on all major earthing systems, including IT networks.

When operating on three-phase systems:

• Loads should be balanced across all phases.
• If a neutral conductor is not present, loads must not be connected to a neutral terminal.
• Site-specific requirements should always be verified during system design and commissioning.

Best Practices

✅ Verify the site's earthing system before inverter installation.

✅ Confirm compatibility between the inverter model and local grid topology.

✅ Ensure all Neutral (N) and Protective Earth (PE) connections comply with local regulations.

✅ Follow the latest Solis installation manual for the specific inverter model.

✅ Use a qualified installer for all electrical work.

✅ Contact Solis Technical Support if the site topology falls outside standard configurations.

✅ Never modify earthing arrangements without approval from the relevant electrical authority or qualified engineer.

Conclusion

Solis inverters are designed to support a wide range of earthing systems used in residential, commercial, and utility-scale applications. However, compatibility varies by model and voltage variant. Careful consideration of the local grid topology, inverter specifications, and applicable regulations is essential to ensure safe, compliant, and reliable system operation.

For project-specific requirements, always consult the latest Solis installation manual and applicable local electrical standards. Disclaimer: Please note that this article is intended as general product information only. Local regulations, grid operator requirements, and national wiring standards may vary by country and shall always take precedence. Installation, commissioning, and any electrical work must be carried out by a qualified electrical professional. Solis reserves the right to update product specifications without prior notice.