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 = (I × L × Z) / 1000, where I is load current (A), L is one-way cable length (m), and Z is the cable impedance per metre from AS/NZS 3008.1.1 (combining Rc and Xc adjusted for power factor and 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 × (Rc·cosφ + Xc·sinφ) where Rc is the AC resistance in mΩ/m at the cable operating temperature from AS/NZS 3008.1.1 Table 30, Xc is the reactance from Table 31, L is the one-way circuit length in metres and cosφ is the load power factor. The ElecAS voltage drop calculator does this with the correct operating-temperature resistance automatically.

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

AS/NZS 3008.1.1 Table 30 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?

Include Xc whenever the cable cross-sectional area is 16 mm² or larger, or whenever the load power factor is below about 0.85. For small (≤10 mm²) cables at high power factor (≥0.95) the reactance term contributes less than 5% to the total and can be approximated as zero, but the AS/NZS 3008.1.1 Clause 4.4 formula always includes it.

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

The Clause 4.4 voltage drop formula is unchanged. The 2025 revision updates a number of Table 30 and Table 31 entries (notably aluminium AC resistance for some sizes), tightens the temperature correction factors, and adds new 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?

Yes. Enter the number of cables per phase and the calculator divides the per-cable current accordingly and applies the parallel AC resistance and reactance per AS/NZS 3008.1.1 Clause 4.4 Note 3. Parallel cable installations also require attention to grouping derating (AS/NZS 3008.1.1 Table 22) which the ElecAS cable selection calculator handles.

ElecAS

Voltage Drop Calculator

Calculate cable voltage drop using Australian cable data, installation methods and load inputs.

Why this page matters

Calculate cable voltage drop using Australian cable data, installation methods and load inputs. This static content is published so the canonical route has meaningful crawlable HTML even before the interactive application hydrates.

Who this page is for

Electrical designers checking voltage performance against supply and final subcircuit limits.

Relevant standards

AS/NZS 3008

What this tool helps with

Estimate voltage drop from cable impedance, load current and circuit length.
Compare installation methods and conductor selections for Australian projects.
Use results alongside cable sizing and maximum demand calculations.

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 from AS/NZS 3008.1.1 Table 30 at the matching operating temperature (75 °C, 90 °C or 110 °C) and reactance from Table 31.
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 AS/NZS 3008.1.1 Table 30 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 Table 30 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.

Reviewed by

Wisam Tozah — Associate Electrical Engineer. B.Eng (Electrical), MIEAust, CPEng, NER, NSW DBP, NSW PRE, APEC, IntPE(Aus). 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 = (I × L × Z) / 1000, where I is load current (A), L is one-way cable length (m), and Z is the cable impedance per metre from AS/NZS 3008.1.1 (combining Rc and Xc adjusted for power factor and 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 × (Rc·cosφ + Xc·sinφ) where Rc is the AC resistance in mΩ/m at the cable operating temperature from AS/NZS 3008.1.1 Table 30, Xc is the reactance from Table 31, L is the one-way circuit length in metres and cosφ is the load power factor. The ElecAS voltage drop calculator does this with the correct operating-temperature resistance automatically.
Why do my voltage drop results differ from a 20 °C calculation?: AS/NZS 3008.1.1 Table 30 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?: Include Xc whenever the cable cross-sectional area is 16 mm² or larger, or whenever the load power factor is below about 0.85. For small (≤10 mm²) cables at high power factor (≥0.95) the reactance term contributes less than 5% to the total and can be approximated as zero, but the AS/NZS 3008.1.1 Clause 4.4 formula always includes it.
Does AS/NZS 3008.1.1:2025 change the voltage drop methodology from 2017?: The Clause 4.4 voltage drop formula is unchanged. The 2025 revision updates a number of Table 30 and Table 31 entries (notably aluminium AC resistance for some sizes), tightens the temperature correction factors, and adds new 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?: Yes. Enter the number of cables per phase and the calculator divides the per-cable current accordingly and applies the parallel AC resistance and reactance per AS/NZS 3008.1.1 Clause 4.4 Note 3. Parallel cable installations also require attention to grouping derating (AS/NZS 3008.1.1 Table 22) which the ElecAS cable selection calculator handles.