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.

Parameters

Every field this calculator accepts, what it means, the range it accepts, and how it feeds the result. The last two live under Advanced options but are always used.

Phase configuration (single phase or three phase)

Sets two separate factors. The current calculation divides by 1 for single phase and by the square root of 3 for three phase. The voltage rise calculation multiplies by 2 for single phase, because the current flows out along the active and back along the neutral, and by the square root of 3 for three phase, giving a line to line rise. Changing this selector in the form also resets nominal voltage to 230 or 400 and the maximum allowed voltage to 253 or 440.

Inverter rating (kilowatts, 0.5 to 100)

The alternating current output rating of the inverter, not the array size. Use the continuous rated output from the datasheet, because that is the worst case export the cable ever carries. If you export limit the inverter, the current at the limit is what actually flows, so entering the limited figure gives the rise you will really see, while the full rating gives the design worst case.

Cable size (square millimetres, 1.5 to 300)

Cross sectional area of one active conductor. Only the sixteen standard sizes are accepted: 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120, 150, 185, 240 and 300. Anything else returns zeros and a warning rather than an interpolated answer. Resistance is looked up from this size, so it is the main lever you have on the result.

Cable length (metres, 1 to 500, one way)

Route length from the inverter to the meter or point of supply, measured one way. Do not double it for the return path: the return is already in the phase multiplier. Measure the real route including drops down walls and runs around the roof space, not the straight line distance. Above 1,000 metres the input is rejected as unreasonable.

Conductor material (copper or aluminium)

Copper uses the resistance table directly. Aluminium divides the copper resistance by 0.78, giving a factor of about 1.28. See the limits below: that factor is lower than the real resistivity ratio, so aluminium results understate the rise.

Nominal voltage (volts, set by the phase selector)

The reference used both to convert the inverter kilowatts into amperes and as the denominator for the percentage rise. It follows the phase selector at 230 or 400 volts. It is not the measured voltage on site, which is entered separately.

Existing voltage at meter (volts, form range 200 to 280)

The supply voltage measured at the point of supply, ideally at the middle of a sunny day when the feeder is lightly loaded and sitting high. The calculated rise is added to this to get the voltage at the inverter terminals. Gotcha: the field range and the module validation are both built around single phase values, the field caps at 280 volts and the validator rejects anything above 300, so a three phase line voltage near 400 volts sits outside the intended range even though the arithmetic still runs. For three phase work, read the rise in volts and percent and compare the absolute voltage yourself.

Maximum allowed voltage (volts, default 253 single phase or 440 three phase)

The absolute ceiling the inverter terminal voltage is checked against, taken from AS 61000.3.100 for the default values. Some distributors set their own figure in the connection offer, so override it when the offer says something different. It must not be less than the existing voltage at the meter.

Assumptions and limits

This calculates one thing: the resistive rise along one cable run. Here is exactly what it assumes and where it stops.

What it assumes

• Unity power factor. The inverter is assumed to export at a power factor of 1.0, which is the normal case at rated output. If the inverter is running a volt var or fixed power factor curve, the current is higher for the same real power and the reactive component interacts with cable reactance, neither of which is modelled here.
• Reactance is ignored completely. The rise is current times resistance only. Reactance is a small share of the impedance on small conductors but becomes significant from about 95 square millimetres upward, so on large runs this understates the true rise. For anything above 50 square millimetres, treat the answer as a lower bound.
• The resistance table is a placeholder. The values are direct current resistance at 75 degrees Celsius held in the engine, not transcribed from a licensed copy of AS/NZS 3008.1.1. Assuming 75 degrees is also pessimistic for an inverter cable that typically runs well below its rating, so the real resistance in service is usually a little lower.
• Aluminium is approximated with the wrong factor. The engine divides the copper resistance by 0.78, giving about 1.28 times copper. The real resistivity ratio of aluminium to copper is closer to 1.6. On a 25 square millimetre run the engine uses 1.1128 milliohms per metre where about 1.39 would be expected, so the reported rise is roughly 20 percent low. Check aluminium jobs against the manufacturer resistance data.
• One cable, one segment. The model is a single run from inverter to meter. Parallel conductors, a run split into inverter to switchboard and then switchboard to meter, or a separate submain, all have to be worked out segment by segment and added up by hand.

What it does not do

• It does not model the network. There is no distribution transformer impedance, no service or mains impedance upstream of the meter, no contribution from neighbouring inverters exporting on the same feeder, and no shared neutral effect. On a weak rural feeder the upstream contribution is often larger than everything this tool calculates.
• It does not model inverter response. No volt watt curtailment, no volt var absorption, no export limiting, no generation profile across the day. It reports the rise at full rated export.
• It does not size the cable for current carrying capacity, check earth fault loop impedance, or select protection. Use the cable sizing calculator for the current side of the job.
• It does not cover the direct current side of the array at all.
• It does not produce anything a distributor will accept as a connection application.

The 2 percent figure is the AS/NZS 4777.1 recommendation and the 253 volt figure comes from AS 61000.3.100; both can be varied by the local distributor connection rules. Check every result against the current edition of the standard and the distributor requirements, and have the design signed off by the person responsible for the installation. Nothing here is validated or certified, and the underlying figures have not been reviewed by a chartered professional engineer.

Worked examples

Three complete runs with every intermediate figure shown, so you can check the tool against your own arithmetic. The formula throughout is rise in volts equals current times resistance in milliohms per metre times length times the phase multiplier, divided by 1,000.