Run a cable long enough or thin enough on a solar export circuit, and voltage at the far end climbs past what the grid connection allows. The Voltage Rise Calculator shows exactly how much.
Calculate Cable Voltage Rise for Grid-Connected Solar Inverters
This calculator works out the voltage rise along a single or three-phase cable run from conductor resistivity, length, size, and load current, then checks the result against the 2% limit applied to grid-connected inverter systems. Solar installers and electrical designers use it to confirm a proposed cable size will clear grid-connection voltage-rise checks before lodging a connection application.
How to Use the Voltage Rise Calculator
Select System Phase (1 or 3 phase AC), then enter Grid Voltage (V), Current Load (A), one-way Cable Length (m), Cable Size (mm²), and Conductor Material (copper or aluminium). The tool returns the voltage rise in volts and as a percentage of grid voltage, plus the remaining margin below the 2% limit.
Voltage Rise Formula (AS/NZS 3008.1.1 & AS/NZS 4777.1)
Conductor resistance uses the standard resistivity relationship:
$$R = \frac{\rho L}{A}$$
where $\rho$ is conductor resistivity in Ω·mm²/m, $L$ is the one-way cable length in metres, and $A$ is the conductor cross-sectional area in mm². For single phase, the current travels out and back through two conductors, so:
$$V_{rise} = I \times 2R$$
For three phase, the line current sees one conductor’s resistance scaled by $\sqrt{3}$ across the phase-to-phase voltage:
$$V_{rise} = I \times \sqrt{3} \times R$$
The percentage rise is then $\%V_{rise} = (V_{rise} / V_{grid}) \times 100$, compared against the 2% limit that AS/NZS 4777.1 sets for the rise between the point of supply and the inverter’s a.c. terminals.
This resistance-only approach mirrors the simplified method AS/NZS 3008.1.1 describes in Section 4.2; the standard’s full method (Section 4.5) also factors in conductor reactance and load power factor, which this calculator does not include, so treat results as an indicative check rather than a certified design figure.
Common input mistake: the 2% allowance is calculated from whatever figure is typed into Grid Voltage, not a fixed reference. Entering a measured live supply voltage (often 240–250 V on a nominal 230 V network) instead of the nominal 230 V/400 V that AS/NZS 4777.1 uses inflates the allowed rise in volts, which can make a marginal cable look compliant when it would fail against the nominal figure a network operator actually checks.
Common Voltage Rise Sizing Mistakes
- Entering the round-trip (there-and-back) tape-measure length instead of the one-way run — the calculator already applies the return-path multiplier internally, so a round-trip figure doubles the resistance.
- Entering the average or measured load current instead of the inverter’s rated output current from its compliance plate, since AS/NZS 4777.1 Clause 3.3.3 assesses rise at rated current, not typical operating current.
- Switching Conductor Material to aluminium but leaving the cable size taken from a copper-rated ampacity table, which understates the conductor’s real resistance for that size.
Voltage Rise Diagram: Grid to Export Point
Reference Resistivity Values (IEC 60028 / AS/NZS 4777.1)
- Annealed copper resistivity at 20°C: ≈0.0172 Ω·mm²/m (100% IACS, per IEC 60028, the International Annealed Copper Standard).
- Aluminium resistivity at 20°C: ≈0.0282 Ω·mm²/m (≈61% IACS relative to copper, per the same standard).
- Voltage rise limit for grid-connected inverter energy systems: 2% of nominal supply voltage, per AS/NZS 4777.1.
These are the standard’s 20°C reference figures. This calculator’s built-in resistivity constants read somewhat higher, since they include an allowance for typical loaded-conductor operating temperature rather than the cold 20°C bench value — a detail worth knowing if you’re cross-checking results against a different tool that uses the 20°C baseline directly.
Voltage Rise Calculator Questions
What voltage rise limit applies to solar PV grid connections?
AS/NZS 4777.1 sets a 2% limit, measured from the point of supply to the inverter’s a.c. terminals, for the rise caused by exported generation current.
Does conductor material change the result much?
Yes. Aluminium’s resistivity is roughly 60% higher than copper’s at the same temperature, so an aluminium cable of identical size and length shows noticeably more voltage rise.
Should I enter the actual load current or the inverter’s rated current?
Use the inverter’s rated output current. AS/NZS 4777.1 assesses compliance at rated current, not typical or measured operating current, so using a lower figure understates the rise.
Do I enter the one-way or round-trip cable length?
Enter the one-way length. The calculator already applies the return-path factor (×2 for single phase, √3 for three phase) internally.
Can I use this instead of a full AS/NZS 3008.1.1 calculation?
Treat it as an indicative check. It omits reactance and power factor, which the standard’s full method includes, so confirm marginal results with certified design software or a full manual calculation.