Voltage Rise Calculator (Solar PV)

Voltage Rise Guide for AS/NZS 4777.1:2024

Voltage rise is the increase in voltage that occurs when a solar PV inverter exports power through cables back toward the grid. Unlike voltage drop (where current flows from the source to the load and voltage decreases along the way), voltage rise pushes the voltage at the inverter end higher than the voltage at the meter. If the voltage at any point exceeds the statutory maximum, the inverter must curtail output or shut down, reducing the system's energy yield and the owner's return on investment.

This calculator estimates the voltage at the inverter terminals based on the existing voltage at the meter, cable size, cable length, and inverter export current. It checks the result against the AS/NZS 4777.1:2024 limit of 2% voltage rise and the absolute maximum voltage of 253 V (single-phase) or 440 V (three-phase). If either limit is exceeded, the installation requires mitigation before the distribution network service provider (DNSP) will approve the connection.

Key concepts

• The 2% voltage rise limit. AS/NZS 4777.1:2024 requires that the voltage rise from the inverter to the point of common coupling (PCC), which is usually the meter, does not exceed 2% of the nominal voltage. For a 230 V single-phase supply, that is 4.6 V. Some DNSPs allow up to 3% on long rural feeders, but 2% is the default design target unless the DNSP confirms otherwise in writing.
• Cable resistance is the primary driver. Voltage rise is proportional to the cable resistance multiplied by the export current. Longer cable runs and smaller conductor sizes both increase resistance and therefore increase voltage rise. Increasing the cable size from 4 mm squared to 6 mm squared on a 30 m run can reduce the voltage rise enough to bring a marginal installation into compliance.
• Existing supply voltage matters. The absolute voltage at the inverter terminals equals the supply voltage at the meter plus the voltage rise along the cable. If the supply is already sitting at 248 V (which is common on lightly loaded suburban feeders during the middle of the day), even a small voltage rise can push the inverter past 253 V and trigger curtailment.
• Network impedance contribution. The total voltage rise at the PCC includes both the installation cable impedance and the upstream network impedance from the meter to the distribution transformer. On weak rural networks with long overhead feeders, the upstream impedance can be the dominant contributor to voltage rise, and the DNSP may impose an export limit regardless of the installation cable sizing.

Common scenarios

• Residential rooftop solar (5 to 10 kW). A typical residential installation runs a single-phase inverter with a cable length of 10 to 30 m from the inverter to the meter box. For a 6.6 kW inverter exporting at full rated current (approximately 29 A at 230 V), a 6 mm squared cable over 20 m produces around 3.4 V rise (1.5%), which is within the 2% limit. If the run is 35 m or longer, the installer may need to upsize to 10 mm squared or discuss export limiting with the DNSP.
• Commercial rooftop solar (30 to 100 kW). Larger commercial systems often use three-phase inverters with longer cable runs from the roof to the main switchboard. The higher currents and longer distances make voltage rise a more significant design constraint. A 100 kW three-phase system exporting 145 A per phase over a 50 m run of 35 mm squared cable produces approximately 3.0 V rise per phase (1.3%), which is compliant. However, the installer must also account for the voltage rise contribution of the submain from the switchboard to the meter.
• Rural property with long service cable. On a rural property where the meter is 100 m or more from the inverter location, voltage rise can easily exceed the 2% limit even with generously sized cables. In these cases, the designer typically needs to apply export limiting at the inverter, install reactive power compensation (Volt-VAR response per AS/NZS 4777.2), or negotiate a higher voltage rise allowance with the DNSP based on site-specific network modelling.