What is the maximum allowable voltage drop in Australia?

AS/NZS 3000:2018 Clause 3.6 limits total voltage drop from the point of supply to any load to 5% of nominal supply voltage. For 230 V single-phase, that is 11.5 V; for 400 V three-phase, 20 V. Final subcircuits commonly target a 2.5% allowance.

How is voltage drop calculated for AC cables?

Voltage drop is calculated using Vd = (K × I × L × Z) / 1000. K is 2 on single-phase, because the current returns through the neutral, and √3 on three-phase. I is the load current in amps, L is the one-way run length in metres, and Z is the cable impedance in ohms per kilometre from AS/NZS 3008.1.1, taken at the cable operating temperature.

Does cable temperature affect voltage drop?

Yes: conductor resistance rises with temperature. AS/NZS 3008.1.1 tables list impedance at the maximum operating temperature for each insulation type (75 °C for V-75/PVC, 90 °C for X-90/XLPE). The ElecAS calculator applies the correct value automatically.

What is the difference between voltage drop and voltage rise?

Voltage drop occurs on cables supplying loads (consumer to load). Voltage rise occurs on cables exporting from generation (e.g., solar inverter back to the point of supply) and is governed by AS/NZS 4777.1 with a 2% inverter-path limit.

What is the maximum permitted voltage drop in Australia?

AS/NZS 3000:2018 Clause 3.6.2 limits total voltage drop from the point of supply to the point of utilisation to 5% of the nominal voltage when supplied at the nominal voltage: that is 11.5 V on a 230 V single-phase circuit or 20 V on a 400 V three-phase circuit. The 5% is a global limit that includes consumer mains, submains and final subcircuits combined.

How do I calculate voltage drop in a three-phase cable?

For balanced three-phase circuits Vd = √3 × I × L × Zc / 1000, with L the one-way length in metres and Zc the cable impedance in ohms per kilometre from the AS/NZS 3008.1.1:2025 Section 4 tables. By default the calculator uses the worst-case impedance Zc = √(Rc² + Xc²); turn Worst Case PF off and it uses Zc = Rc·cosφ + Xc·sinφ from the power factor you enter. Either way the resistance is taken at the cable operating temperature.

Why do my voltage drop results differ from a 20 °C calculation?

AS/NZS 3008.1.1:2025 publishes AC resistance at the cable operating temperature: 75 °C for V-90 PVC, 90 °C for X-90 XLPE. A 20 °C value (sometimes used in textbook examples) under-estimates real-world drop by 18–28 % for a fully loaded circuit because conductor resistance rises with temperature.

When do I need to include cable reactance Xc?

You do not need to decide: this calculator always includes reactance, and a cable with no reactance value in the tables is treated as missing data rather than zero. As a rule of thumb, reactance is negligible on small cables (AS/NZS 3000 Appendix B4.3 allows it to be ignored at or below 35 mm² where the conductors run close together) and becomes significant on large cables and at low power factor.

Does AS/NZS 3008.1.1:2025 change the voltage drop methodology from 2017?

The voltage drop method is unchanged. The 2025 revision renumbered the impedance tables into the Section 4 series (4.1 to 4.10), updated a number of entries (notably aluminium AC resistance for some sizes) tightened the temperature correction factors and added entries for high-temperature 110 °C insulations. The ElecAS calculator uses the 2025 table values.

Voltage drop vs voltage rise: what is the difference?

Voltage drop is the reduction in voltage as current flows from the source to the load (most installations). Voltage rise is the increase in voltage as current flows from a distributed generator (typically a rooftop solar inverter) back to the point of supply. AS/NZS 4777.1 Clause 3.3.3 limits voltage rise to 2% along the whole path from the point of supply to the inverter a.c. terminals (not just the inverter-supply cable). The ElecAS voltage rise calculator covers that case.

Does the calculator handle multiple cables in parallel?

Not on this page: the voltage drop calculator sizes one cable at a time. For parallel runs use the Cable Selection calculator, which has a Parallel Runs stepper and divides the design current between the runs. AS/NZS 3000 Clause 3.6.3 says the voltage drop of a parallel set is the drop in one conductor carrying the circuit current, divided by the number of conductors in parallel.

ElecAS

Voltage Drop Calculator: AS/NZS 3008.1.1 Cable Voltage Drop for Australia

Free, browser-based voltage drop calculator built for Australian and New Zealand electricians, designers and electrical engineers. Calculates cable voltage drop straight from the AS/NZS 3008.1.1:2025 impedance tables (Tables 4.1–4.10) using the Clause 4.4 method (Vc = √3 × (Rc·cosφ + Xc·sinφ) for balanced three-phase, 2 × (Rc·cosφ + Xc·sinφ) for single-phase, and the resistance-only form for DC) with AC resistance taken at the correct conductor operating temperature (75 °C for V-90 PVC, 90 °C for X-90 XLPE, 110 °C for high-temperature insulations) so the result reflects a fully loaded cable, not a 20 °C textbook value. Supports single-phase (230 V) and three-phase (400 V) circuits, copper and aluminium conductors, multi-core and single-core constructions, the full AS/NZS 3008.1.1 installation method library, the 1–630 mm² cable size range, load power factor and parallel cables per phase. Returns the voltage drop in volts and as a percentage of nominal voltage, a pass/fail check against the AS/NZS 3000:2018 Clause 3.6.2 5% limit (11.5 V on 230 V single-phase, 20 V on 400 V three-phase), and a branded PDF report citing the clause, table and resistance value used: ready for the design submission record.

Key facts

AS/NZS 3000 Clause 3.6 limits total voltage drop to 5% from the point of supply to the furthest point: 11.5 V on a 230 V supply, 20 V on 400 V.
Voltage drop is calculated from AS/NZS 3008.1.1 conductor resistance and reactance at operating temperature.
Vc = K × Z, with K = 2 for single-phase circuits and √3 for balanced three-phase circuits.
The drop is apportioned across consumer mains, submains and final subcircuits; the sum must stay within 5%.

Who this page is for

Electrical engineers, designers, estimators and licensed electricians checking cable voltage performance for consumer mains, submains and final subcircuits against the AS/NZS 3000 Clause 3.6 5% voltage drop budget on residential, commercial and industrial installations across Australia and New Zealand.

Relevant standards

AS/NZS 3008.1.1:2025 (Selection of Cables: Clause 4.4 voltage drop method, Tables 4.1–4.10 conductor R and X impedance values)
AS/NZS 3000:2018 (Wiring Rules: Clause 3.6.2 maximum 5% voltage drop from the point of supply to the point of utilisation)
AS 60038 (Standard Voltages: 230 V / 400 V nominal voltage the 5% limit is expressed against)

What this tool helps with

Applies the AS/NZS 3008.1.1:2025 Clause 4.4 voltage drop method: Vc = √3 × (Rc·cosφ + Xc·sinφ) for balanced three-phase, 2 × (Rc·cosφ + Xc·sinφ) for single-phase, and the resistance-only form for DC circuits.
Checks the result against the AS/NZS 3000:2018 Clause 3.6.2 limit: 5% of nominal voltage from the point of supply to any point of utilisation (11.5 V on 230 V single-phase, 20 V on 400 V three-phase) with a clear pass/fail pill.
Reads AC resistance Rc and reactance Xc directly from the AS/NZS 3008.1.1:2025 impedance tables (Tables 4.1–4.10) at the conductor operating temperature, not a 20 °C value that under-estimates real drop by 18–28%.
Temperature-correct by insulation type (75 °C for V-90 PVC, 90 °C for X-90 XLPE and 110 °C for high-temperature cross-linked cables) selected automatically from the chosen cable.
Single-phase (230 V) and three-phase (400 V) circuits, copper and aluminium conductors, multi-core and single-core constructions across the standard 1 mm² to 630 mm² cable size range.
Full AS/NZS 3008.1.1 installation method library and single-core arrangement (trefoil, flat-touching, flat-spaced) feeding the reactance, so the calculated drop matches the real install.
Load power factor and parallel-cables-per-phase support: the calculator divides per-cable current and applies the parallel impedance per AS/NZS 3008.1.1 Clause 4.4.
Branded PDF voltage drop report showing the voltage drop in volts and percent, the governing clause and table, the resistance value and operating temperature used: ready for the design submission and verification record.
Built and reviewed by a Chartered Professional Engineer (CPEng, NER, NSW DBP, NSW PRE, APEC, IntPE Aus): see the Verification page for the testing and review process.

How to calculate voltage drop under AS/NZS 3008.1.1:2025

Enter the load current: Enter the design current Ib in amperes: the worst-case continuous current the cable will carry (after applying diversity for max-demand calculations).
Set the circuit type: Pick single-phase 230 V, three-phase 400 V balanced, or DC. The calculator applies factor 2 × L for single-phase / DC and √3 × L for balanced three-phase per AS/NZS 3008.1.1 Clause 4.4.
Enter the cable run length: Enter the one-way circuit length in metres. The factor of 2 or √3 in the formula accounts for the return path automatically: do not double the length manually.
Pick the cable conductor and insulation: Choose copper or aluminium, conductor cross-sectional area, and insulation (V-90 PVC, X-90 XLPE, X-90-HT). The calculator reads AC resistance and reactance from the AS/NZS 3008.1.1:2025 Section 4 tables (4.1 to 4.10) at the matching operating temperature (75 °C, 90 °C or 110 °C).
Enter the load power factor: For motor loads use the nameplate cosφ; for typical lighting / electronic loads with PFC use 0.95–0.99. Power factor enters the formula as Rc·cosφ + Xc·sinφ.
Review the result and check against the 5% Clause 3.6 limit: The calculator displays the voltage drop in volts and as a percentage of the nominal voltage, and flags any result above the AS/NZS 3000:2018 Clause 3.6 5% limit. Export the branded PDF for the design submission record.

Complete guide to voltage drop calculation under AS/NZS 3008.1.1:2025

What does AS/NZS 3000:2018 say about voltage drop?

Clause 3.6.2 of AS/NZS 3000:2018 limits the total voltage drop between the point of supply and any point of utilisation to 5% of the nominal voltage when supplied at the nominal voltage. This is the single design limit most Australian and New Zealand electrical installations work to: 230 V × 5% = 11.5 V maximum drop on a single-phase circuit, or 400 V × 5% = 20 V on a three-phase circuit.

The 5% allowance is a global ceiling: it includes consumer mains, submains and final subcircuits combined. Most consulting practice budgets 2% to consumer mains, 1% to submains and 2% to final subcircuits, but the split is a design choice as long as the total stays below 5%.

The exact voltage drop formula from AS/NZS 3008.1.1:2025

AS/NZS 3008.1.1:2025 Clause 4.4 gives the voltage drop per ampere per metre as Vc = √3 × (Rc·cosφ + Xc·sinφ) for three-phase circuits or Vc = 2 × (Rc·cosφ + Xc·sinφ) for single-phase. Rc and Xc are the AC resistance and reactance in mΩ/m taken from the AS/NZS 3008.1.1:2025 impedance tables (Tables 4.1–4.10), evaluated at the cable operating temperature.

For DC circuits the reactance term drops out entirely and Vc = 2 × Rc with Rc taken at the operating temperature. For LV three-phase balanced circuits with cosφ near unity the formula collapses to Vd ≈ √3 × I × L × Rc: the form most engineers use as a sanity check.

Why operating temperature matters

AC resistance in the AS/NZS 3008.1.1:2025 Section 4 tables (4.1 to 4.10) is published at 75 °C for V-90 PVC cables, 90 °C for X-90 XLPE cables and 110 °C for high-temperature cross-linked types. Voltage drop calculated at 20 °C ambient resistance under-estimates real-world drop by 18–28 % for a fully loaded V-90 circuit.

The ElecAS voltage drop calculator picks the correct operating temperature from the cable insulation type automatically and applies the matching Section 4 table entry. The PDF report shows the resistance value, the temperature and the clause used so the calculation can be re-traced.

Single-phase, three-phase and DC: when each applies

Use the single-phase formula (factor 2 × L) for any 230 V single-phase circuit and for any 400 V three-phase circuit operating with an unbalanced load that returns through the neutral. Use the three-phase formula (factor √3 × L) for balanced three-phase circuits (motors, three-phase final subcircuits with balanced lighting).

For DC circuits (solar string DC, EV charger DC link, battery banks) use 2 × L and ignore the reactance term. AS/NZS 4777.1 (Clause 3.3.3) sets a separate 2% maximum voltage rise from the point of supply to the inverter a.c. terminals on the AC side of grid-connected inverters; the ElecAS voltage rise calculator handles that case separately.

Key terms

Voltage drop (Vd): The reduction in voltage along a cable under load. AS/NZS 3000 Clause 3.6 limits the total from the point of supply to the furthest point of the installation to 5% of nominal voltage.
Vc (mV/A·m): The voltage drop per ampere of load current per metre of route length, in millivolts, derived from the cable's resistance and reactance in the AS/NZS 3008.1.1 tables.
Operating temperature: The conductor temperature used to read resistance from AS/NZS 3008.1.1; a loaded conductor at 75 or 90 degrees Celsius has a higher resistance than at 20 degrees Celsius, so using the cold value understates the drop.
Route length: The one-way cable run length used in the voltage drop formula. The single-phase factor K = 2 already accounts for the return conductor.

Reviewed by

Wisam Tozah: Associate Electrical Engineer. B.Eng (Electrical), MIEAust, CPEng, NER, NSW DBP, NSW PRE, APEC, IntPE(Aus). See how these calculations are verified. LinkedIn.

Frequently asked questions

What is the maximum allowable voltage drop in Australia?: AS/NZS 3000:2018 Clause 3.6 limits total voltage drop from the point of supply to any load to 5% of nominal supply voltage. For 230 V single-phase, that is 11.5 V; for 400 V three-phase, 20 V. Final subcircuits commonly target a 2.5% allowance.
How is voltage drop calculated for AC cables?: Voltage drop is calculated using Vd = (K × I × L × Z) / 1000. K is 2 on single-phase, because the current returns through the neutral, and √3 on three-phase. I is the load current in amps, L is the one-way run length in metres, and Z is the cable impedance in ohms per kilometre from AS/NZS 3008.1.1, taken at the cable operating temperature.
Does cable temperature affect voltage drop?: Yes: conductor resistance rises with temperature. AS/NZS 3008.1.1 tables list impedance at the maximum operating temperature for each insulation type (75 °C for V-75/PVC, 90 °C for X-90/XLPE). The ElecAS calculator applies the correct value automatically.
What is the difference between voltage drop and voltage rise?: Voltage drop occurs on cables supplying loads (consumer to load). Voltage rise occurs on cables exporting from generation (e.g., solar inverter back to the point of supply) and is governed by AS/NZS 4777.1 with a 2% inverter-path limit.
What is the maximum permitted voltage drop in Australia?: AS/NZS 3000:2018 Clause 3.6.2 limits total voltage drop from the point of supply to the point of utilisation to 5% of the nominal voltage when supplied at the nominal voltage: that is 11.5 V on a 230 V single-phase circuit or 20 V on a 400 V three-phase circuit. The 5% is a global limit that includes consumer mains, submains and final subcircuits combined.
How do I calculate voltage drop in a three-phase cable?: For balanced three-phase circuits Vd = √3 × I × L × Zc / 1000, with L the one-way length in metres and Zc the cable impedance in ohms per kilometre from the AS/NZS 3008.1.1:2025 Section 4 tables. By default the calculator uses the worst-case impedance Zc = √(Rc² + Xc²); turn Worst Case PF off and it uses Zc = Rc·cosφ + Xc·sinφ from the power factor you enter. Either way the resistance is taken at the cable operating temperature.
Why do my voltage drop results differ from a 20 °C calculation?: AS/NZS 3008.1.1:2025 publishes AC resistance at the cable operating temperature: 75 °C for V-90 PVC, 90 °C for X-90 XLPE. A 20 °C value (sometimes used in textbook examples) under-estimates real-world drop by 18–28 % for a fully loaded circuit because conductor resistance rises with temperature.
When do I need to include cable reactance Xc?: You do not need to decide: this calculator always includes reactance, and a cable with no reactance value in the tables is treated as missing data rather than zero. As a rule of thumb, reactance is negligible on small cables (AS/NZS 3000 Appendix B4.3 allows it to be ignored at or below 35 mm² where the conductors run close together) and becomes significant on large cables and at low power factor.
Does AS/NZS 3008.1.1:2025 change the voltage drop methodology from 2017?: The voltage drop method is unchanged. The 2025 revision renumbered the impedance tables into the Section 4 series (4.1 to 4.10), updated a number of entries (notably aluminium AC resistance for some sizes) tightened the temperature correction factors and added entries for high-temperature 110 °C insulations. The ElecAS calculator uses the 2025 table values.
Voltage drop vs voltage rise: what is the difference?: Voltage drop is the reduction in voltage as current flows from the source to the load (most installations). Voltage rise is the increase in voltage as current flows from a distributed generator (typically a rooftop solar inverter) back to the point of supply. AS/NZS 4777.1 Clause 3.3.3 limits voltage rise to 2% along the whole path from the point of supply to the inverter a.c. terminals (not just the inverter-supply cable). The ElecAS voltage rise calculator covers that case.
Does the calculator handle multiple cables in parallel?: Not on this page: the voltage drop calculator sizes one cable at a time. For parallel runs use the Cable Selection calculator, which has a Parallel Runs stepper and divides the design current between the runs. AS/NZS 3000 Clause 3.6.3 says the voltage drop of a parallel set is the drop in one conductor carrying the circuit current, divided by the number of conductors in parallel.