ElecAS
Voltage Rise Design Guide — How to Calculate Solar Inverter Voltage Rise to AS/NZS 4777.1
A step-by-step guide to inverter-path voltage rise for Australian solar PV and battery systems. Learn why AS/NZS 4777.1 Clause 3.3.3 caps the rise from the point of supply to the inverter a.c. terminals at 2% of nominal voltage (4.6 V single-phase, 8 V line-to-line three-phase), then work the calculation line by line: full-export current, cable impedance from AS/NZS 3008.1.1, the volt-drop coefficient Vc = K·Z, the per-segment rise and the total path percentage. An embedded interactive calculator lets you change the inverter, cables and route and watch every line update against the 2% limit, and the guide shows exactly how to fix a design that fails — upsize the worst cable, shorten the run, apply an export limit or switch to copper.
Why this page matters
A step-by-step guide to inverter-path voltage rise for Australian solar PV and battery systems. Learn why AS/NZS 4777.1 Clause 3.3.3 caps the rise from the point of supply to the inverter a.c. terminals at 2% of nominal voltage (4.6 V single-phase, 8 V line-to-line three-phase), then work the calculation line by line: full-export current, cable impedance from AS/NZS 3008.1.1, the volt-drop coefficient Vc = K·Z, the per-segment rise and the total path percentage. An embedded interactive calculator lets you change the inverter, cables and route and watch every line update against the 2% limit, and the guide shows exactly how to fix a design that fails — upsize the worst cable, shorten the run, apply an export limit or switch to copper. This static content is published so the canonical route has meaningful crawlable HTML even before the interactive application hydrates.
Who this page is for
CEC accredited solar designers and installers, electricians and electrical engineers learning or teaching the AS/NZS 4777.1 voltage rise check for grid-connected solar PV and battery inverters.
Relevant standards
- AS/NZS 4777.1:2016 (Grid connection of energy systems via inverters — Clause 3.3.3 voltage rise)
- AS/NZS 4777.2:2020 (Inverter requirements — over-voltage response)
- AS/NZS 3008.1.1:2025 (Cable selection — conductor R and X impedance)
- AS 60038 (Standard voltages — 230 V / 400 V nominal)
What this tool helps with
- Understand the 2% AS/NZS 4777.1 limit and why voltage rise is the mirror image of voltage drop.
- Work the formula one line at a time: current, impedance Z, volt-drop coefficient Vc = K·Z, per-segment rise, total %.
- Interactive calculator with a live “voltage along the path” profile against the 2% ceiling.
- See a failing design and the four ways to fix it — upsize, shorten, export-limit, or copper.
- Links straight to the full ElecAS Voltage Rise calculator for multi-inverter projects and PDF reports.
How to calculate solar inverter voltage rise under AS/NZS 4777.1
- Find the full-export current — Convert the inverter rated kW to current: I = P × 1000 ÷ (√3 × V × pf) for three-phase, or P × 1000 ÷ (V × pf) for single-phase. Default power factor to unity unless the inverter injects or absorbs reactive power.
- Read R and X for each cable — From AS/NZS 3008.1.1 read the a.c. resistance R and reactance X (Ω/km) for each cable size, material and installation method along the path.
- Combine into an effective impedance — Use the worst-case magnitude Z = √(R² + X²), or Z = R·cosφ + X·sinφ at a set power factor.
- Calculate the rise on each segment — Vc = K × Z (K = 2 single-phase, √3 three-phase), then V = length × current × Vc ÷ 1000 for each cable.
- Sum the path and check against 2% — Add every segment’s rise, divide by the nominal voltage and express as a percentage. Pass if the total from the point of supply to the inverter terminals is 2% or less; if not, upsize the biggest contributor and re-check.
How to calculate solar inverter voltage rise under AS/NZS 4777.1
What voltage rise is and why AS/NZS 4777.1 limits it to 2%
When a grid-connected inverter exports active power, current flows the other way along the cable — from the inverter back through the final subcircuit, any submain, and the consumer mains toward the point of supply. The impedance of each conductor lifts the inverter terminal voltage above the nominal supply voltage. Voltage rise is the exact mirror image of voltage drop: the same resistance and reactance, the same run length, only the direction of power flow is reversed.
AS/NZS 4777.1:2016 Clause 3.3.3 limits the rise from the point of supply to the inverter a.c. terminals to 2% of nominal voltage, evaluated at the rated current of the inverter energy system. On a 230 V single-phase supply that is about 4.6 V; on a 400 V three-phase supply it is about 8 V line-to-line. The limit is tight because the grid can already sit near the +10% steady-state ceiling (253 V on a 230 V system) — your rise stacks on top of it, and once the inverter terminal voltage nears the AS/NZS 4777.2 over-voltage response point it curtails or disconnects, quietly losing generation on the sunniest days.
The voltage rise formula, one line at a time
Step 1 — full-export current. Convert the inverter rating to the current the cable carries: I = P × 1000 ÷ (√3 × V × pf) for three-phase, or I = P × 1000 ÷ (V × pf) for single-phase. Default the power factor to unity unless the inverter is set to absorb or inject reactive power.
Step 2 — effective impedance. From the AS/NZS 3008.1.1 tables read the conductor a.c. resistance R and reactance X in Ω/km for each cable. Combine them as the worst-case magnitude Z = √(R² + X²), or as R·cosφ + X·sinφ when a specific power factor is used.
Step 3 — volt-drop coefficient. Vc = K × Z, where K = 2 for single-phase (active plus neutral) and K = √3 for balanced three-phase (the line-to-line factor).
Step 4 — rise per segment. V = length × current × Vc ÷ 1000, applied to every cable in the path.
Step 5 — total and compliance. Add the rise of each segment, divide by the nominal voltage and express as a percentage. The design passes when the total from the point of supply to the inverter terminals is 2% or less.
A worked example — 15 kW three-phase rooftop solar
A 15 kW three-phase inverter on a 400 V supply draws I = 15 × 1000 ÷ (√3 × 400) ≈ 21.7 A at full export. Run it through 30 m of 16 mm² copper consumer mains and a 25 m 10 mm² copper final subcircuit.
The mains contributes about 1.30 V (0.32%) and the final subcircuit about 1.72 V (0.43%), for a total of roughly 3.0 V — about 0.75% of 400 V. That sits comfortably inside the 2% allowance, so the design passes. Change the inverter size, the cable sizes or the run lengths in the interactive calculator and every line of the working updates against the 2% ceiling.
How to fix a design that fails the 2% limit
A non-compliant result has four common levers, and you should always target the cable segment contributing the most volts first. Upsizing the worst cable is the usual fix — rise falls roughly in proportion to conductor cross-sectional area, so one or two sizes up on the dominant segment is often enough.
Shortening the route helps in direct proportion to length — relocating the inverter or board closer to the point of supply can be cheaper than jumping cable sizes. A hard export limit reduces the current (and rise) in the shared consumer mains, though the final cable still carries full inverter output. Finally, copper has appreciably lower resistance than aluminium for the same size, so switching material can recover margin without a size increase.
Voltage rise vs voltage drop
The two checks use identical cable impedance and the same route method, but they are assessed separately and against different limits. Voltage drop (AS/NZS 3000:2018 Clause 3.6) applies to load-side circuits with a 5% total budget; voltage rise (AS/NZS 4777.1 Clause 3.3.3) applies to the inverter export path with a 2% limit. The same cable on the same installation has both — drop under maximum demand and rise under maximum export — so a solar retrofit onto an existing installation must satisfy both independently.