Choose voltage rise, length, current, or voltage coefficient. Copper and aluminum AWG presets provide a stated 20°C DC resistance estimate, not an installation-compliance check.
Voltage Rise Formula
Voltage rise is the product of conductor length, current, and the conductor’s resistivity factor. When Vd is expressed in millivolts per ampere-meter (mV/A·m) as listed in Australian and IEC cable tables, the /1000 factor converts the result to volts. When Vd is in V/A·m as used in this calculator’s basic mode, the formula applies directly without the divisor.
Variables:
- Vr is the Voltage Rise (volts)
- L is the cable run/length (m)
- I is the current (amps)
- Vd is the voltage drop per ampere meter (mV/A·m in the /1000 form; V/A·m when used directly)
For this resistance-only preset model, the per-conductor coefficient is Vd = ρ / A, where ρ is resistivity (Ω·m) and A is cross-sectional area (m²). The retained approximate 20°C assumptions are 1.72 x 10⁻⁸ Ω·m for copper and 2.65 x 10⁻⁸ Ω·m for aluminum. Under those assumptions, aluminum requires about 1.54 times the copper area for equal resistance. Actual cable resistance depends on material and construction; use manufacturer data for design.
Voltage Rise vs. Voltage Drop
Both phenomena describe the resistive potential difference across a conductor carrying current. In a conventional load circuit, current flows from the supply toward the load, so the terminal voltage at the load is lower than the source (a drop). In a generation circuit, current flows from a distributed source such as a solar inverter, battery, or generator back toward the main supply point, so the inverter terminals are at a higher voltage than the grid connection point (a rise). The magnitude is identical for the same current, cable length, and conductor size. The distinction is directional: which end of the cable sits at higher potential.
A separate phenomenon sometimes confused with resistive voltage rise is the Ferranti Effect, which occurs in long, lightly loaded high-voltage transmission lines. In that case, the distributed capacitance of the line raises the open-circuit receiving-end voltage above the sending end. The Ferranti Effect is reactive and capacitance-driven, not resistive, and does not apply to low-voltage distribution or building wiring circuits where this calculator is used.
Conductor Resistivity Factor (Vd) by Cable Size
The table below gives the DC resistivity factor at 20°C for copper and aluminum conductors by AWG size in millivolts per ampere per meter. For two equal outgoing and return conductors, multiply the one-way length by 2 once. The preset path selector performs that multiplication. These approximate 20°C DC values do not establish AC design accuracy: operating-temperature resistance, reactance, power factor and circuit configuration may be required.
| AWG | Area (mm²) | Copper Vd (mV/A·m) | Aluminum Vd (mV/A·m) |
|---|---|---|---|
| 18 | 0.823 | 20.9 | 32.2 |
| 16 | 1.31 | 13.1 | 20.2 |
| 14 | 2.08 | 8.27 | 12.7 |
| 12 | 3.31 | 5.20 | 8.01 |
| 10 | 5.26 | 3.27 | 5.04 |
| 8 | 8.37 | 2.06 | 3.17 |
| 6 | 13.3 | 1.29 | 1.99 |
| 4 | 21.2 | 0.811 | 1.25 |
| 2 | 33.6 | 0.512 | 0.789 |
| 1/0 | 53.5 | 0.321 | 0.495 |
| 2/0 | 67.4 | 0.255 | 0.393 |
| 3/0 | 85.0 | 0.202 | 0.312 |
| 4/0 | 107.2 | 0.160 | 0.247 |
Examples of Different Electrical Requirements
The following documents address different quantities and cannot be treated as interchangeable cable-rise limits. Check the current edition, application, jurisdiction and network requirements. A two-wire return-path factor does not represent every AC circuit configuration.
| Standard | Region | Application | Requirement or scope |
|---|---|---|---|
| AS/NZS 4777.1:2024 | Australia / NZ | Grid-connected inverters (solar, battery) | Cited Queensland small-inverter rules: no more than 2% rise from inverter AC terminals to Connection Point; approved calculation basis applies |
| NEC Informational Note 210.19 / 215.2 | USA | Branch circuit and feeder combined | Informational guidance: 3% branch and 5% combined; not a universal fixed 2% feeder or generation-rise limit |
| IEC 60364-5-52 | International | Building wiring final circuits | IEC guidance distinguishes lighting and other loads and public/private supply; 5% is not a universal allowance |
| EN 50160 | Europe | Public LV supply voltage quality | Public-network supply-voltage characteristics; not a cable-rise allowance |
| IEEE 1547-2018 | USA | Distributed energy resources | DER control capabilities and voltage/time-dependent ride-through; activation/settings follow applicable requirements, not a universal ±10% cable limit |
Illustrative Resistance-Only Cable-Length Example
As an illustration, assume 5 kW at 230 V, unity power factor, current rounded to 21.7 A, two equal conductors, and an assumed 2% (4.6 V) voltage-rise budget. The resistance budget is approximately 4.6 V / 21.7 A = 0.212 ohms. One-way run = 4.6/(21.7 × 2 × Vd), using the listed approximate 20°C DC coefficients. These lengths illustrate the resistance-only model and do not establish installation compliance.
| Conductor | Vd (mV/A·m) | Max One-Way Run (m) | Max One-Way Run (ft) |
|---|---|---|---|
| 12 AWG Copper | 5.20 | 20.4 | 67 |
| 10 AWG Copper | 3.27 | 32.4 | 106 |
| 8 AWG Copper | 2.06 | 51.5 | 169 |
| 6 AWG Copper | 1.29 | 82.2 | 270 |
| 6 AWG Aluminum | 1.99 | 53.3 | 175 |
| 4 AWG Aluminum | 1.25 | 84.8 | 278 |
Possible design remedies include larger conductors or a shorter run, assessed against all installation requirements. Inverter control settings must follow approved installer and network requirements. Volt-VAR behavior depends on the equipment, configured settings and network impedance; this resistance-only calculator does not model it.
High local voltage can cause inverter curtailment or disconnection. The response depends on regional settings, network conditions and the installation. There is no universal trip voltage, production-loss percentage or PV-penetration threshold. Use the applicable network requirements and measured site conditions.
