---
title: "Voltage Drop Calculator: AS/NZS 3008.1.1 Cable Voltage Drop for Australia"
url: "https://scaleset.com.au/calculator/voltage-drop"
description: "Free AS/NZS 3008.1.1 voltage drop calculator: checks cable Vd against the AS/NZS 3000 Clause 3.6 5% limit (11.5 V / 20 V). Single & 3-phase, Cu and Al."
updated: "2026-10-13"
standards:
  - "AS/NZS 3008.1.1:2025 (Selection of Cables: Clause 4.3 maximum voltage drop and Clause 4.5 load power factor methods, Table 3.1 conductor operating temperatures, a.c. resistance Tables 4.5, 4.7, 4.9 and 4.10, reactance Tables 4.1 and 4.2)"
  - "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)"
author: "Wisam Tozah (B.Eng (Electrical), MIEAust, CPEng, NER, NSW DBP, NSW PRE, APEC, IntPE(Aus))"
site: "ScaleSet"
license: "https://scaleset.com.au/terms"
usage: "Cite and link. Do not reproduce or train on this content."
---

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

Source: https://scaleset.com.au/calculator/voltage-drop

Free, browser-based voltage drop calculator built for Australian and New Zealand electricians, designers and electrical engineers. Calculates cable voltage drop from the AS/NZS 3008.1.1:2025 a.c. resistance Tables 4.5, 4.7, 4.9 and 4.10 and reactance Tables 4.1 and 4.2: at worst case by the AS/NZS 3008.1.1 Clause 4.3 maximum-drop method, Vc = K × √(Rc² + Xc²), or for a known load power factor by AS/NZS 3008.1.1 Clause 4.5, Vc = K × (Rc·cosφ + Xc·sinφ), with K = 2 for single-phase and √3 for balanced three-phase. AC resistance is read at the normal operating temperature of the insulation from AS/NZS 3008.1.1 Table 3.1 (75 °C for PVC, V-90 included, 90 °C for X-90 XLPE and R-90 elastomeric, 110 °C for X-HF-110 and R-HF-110), so the result reflects a fully loaded cable, not a cold textbook value. Supports single-phase (230 V) and three-phase (400 V) a.c. circuits, copper (standard and flexible) and aluminium conductors, multicore cable with circular or shaped conductors and single-core cables in trefoil, flat touching or flat spaced, the 1 to 630 mm² size range wherever the tables publish a row, load power factor, and busbar trunking with the manufacturer's resistance and reactance. Returns the voltage drop in volts and as a percentage of nominal voltage, a within-limit or over-limit check against the share of 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) set for the cable, and a branded PDF report citing the tables, the resistance and reactance used and the insulation's operating temperature: 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%.
- The calculator checks one cable against the Max Drop you set for it. Within limit means this cable fits its share: add the drop on the mains and submains upstream to check the AS/NZS 3000 Clause 3.6.2 total.
- A busbar trunking (busway) run has no AS/NZS 3008 table: switch the conductor to busbar trunking and enter the manufacturer's resistance and reactance per metre (AS/NZS 61439.6 Table 102). The AS/NZS 61439.6 Annex AA load-distribution factor k then scales the drop: 1 for a load at the end of the run, (n + 1) / 2n for a load spread evenly over n tap-offs.

## 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 4.3 maximum voltage drop and Clause 4.5 load power factor methods, Table 3.1 conductor operating temperatures, a.c. resistance Tables 4.5, 4.7, 4.9 and 4.10, reactance Tables 4.1 and 4.2)
- 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 does

- Applies AS/NZS 3008.1.1:2025 Clause 4.3, the maximum drop Vc = K × √(Rc² + Xc²), by default, or AS/NZS 3008.1.1 Clause 4.5, Vc = K × (Rc·cosφ + Xc·sinφ), when you enter a known load power factor, with K = 2 for single-phase and √3 for balanced three-phase a.c. circuits.
- Checks the cable against the share of the AS/NZS 3000:2018 Clause 3.6.2 limit you set for it, with a within-limit or over-limit pill. The clause allows 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), so the drop upstream of the cable is added to check it.
- Reads a.c. resistance Rc from AS/NZS 3008.1.1:2025 Tables 4.5, 4.7, 4.9 and 4.10 at the conductor operating temperature and reactance Xc from AS/NZS 3008.1.1 Tables 4.1 and 4.2. In AS/NZS 3008.1.1 Table 4.7(A) copper resistance is about 20% higher at 75 °C than at 25 °C and about 25% higher at 90 °C, so a cold value understates the drop of a loaded cable by that much.
- Temperature-correct by insulation type, from the normal operating temperatures of AS/NZS 3008.1.1:2025 Table 3.1: 75 °C for PVC (V-75 and V-90 alike), 90 °C for X-90 XLPE and R-90 elastomeric, and 110 °C for X-HF-110 and R-HF-110, 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.
- Cable arrangement selector (multicore with circular or shaped conductors, single-core in trefoil, flat touching or flat spaced at one diameter) picks the reactance row of AS/NZS 3008.1.1 Table 4.1 or 4.2, with the AS/NZS 3008.1.1 Table 4.1(A) Note 1 spacing correction for spaced cores from 25 mm², so the calculated drop matches how the cores are run.
- Busbar trunking as well as cable: switch the conductor to busbar trunking, enter the manufacturer's resistance and reactance per metre (AS/NZS 61439.6 Table 102), and the AS/NZS 61439.6 Annex AA load-distribution factor is applied for a load at the end of the run or spread over its tap-offs.
- 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

1. **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).
2. **Set the circuit type** — Pick single-phase 230 V or three-phase 400 V. The calculator applies K = 2 for single-phase and √3 for balanced three-phase (AS/NZS 3008.1.1:2025 Clauses 4.3.2 and 4.3.3). For an unbalanced three-phase circuit, enter the current of the heaviest-loaded phase with the three-phase setting, the conservative check of AS/NZS 3008.1.1 Clause 4.6.
3. **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.
4. **Pick the cable conductor and insulation** — Choose copper (standard or flexible) or aluminium, the conductor size, the insulation class (PVC at 75 °C for V-75 and V-90, X-90 XLPE or R-90 elastomeric at 90 °C, X-HF-110 or R-HF-110 at 110 °C) and the arrangement (multicore circular or shaped, single-core trefoil, flat touching or flat spaced). The calculator reads a.c. resistance from AS/NZS 3008.1.1:2025 Tables 4.5, 4.7, 4.9 and 4.10 at that operating temperature and reactance from Tables 4.1 and 4.2.
5. **Set the power factor** — Leave Worst Case on for the maximum drop of AS/NZS 3008.1.1 Clause 4.3, Zc = √(Rc² + Xc²), which holds whatever the load power factor. Untick it and enter the load displacement power factor (cos φ), the motor nameplate figure for a motor, only where it is known and consistent: AS/NZS 3008.1.1 Clause 4.5 then takes Zc = Rc·cosφ + Xc·sinφ.
6. **Review the result against the Max Drop for this cable** — The calculator displays the voltage drop in volts and as a percentage of the nominal voltage, and flags any result above the Max Drop you set for this cable. Add the drop on the mains and submains upstream to check the AS/NZS 3000:2018 Clause 3.6.2 5% total. 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. A common split is 1% to 2% on the consumer mains, 1% to 1.5% on submains and 2% to 2.5% on final subcircuits, but the split is a design choice as long as the total stays within 5%.

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

AS/NZS 3008.1.1:2025 gives the drop from circuit impedance as Vd = K × I × L × Zc / 1000, with K = 2 for single-phase (AS/NZS 3008.1.1 Clause 4.3.2) and √3 for balanced three-phase (AS/NZS 3008.1.1 Clause 4.3.3). AS/NZS 3008.1.1 Clause 4.3 takes Zc = √(Rc² + Xc²), the maximum drop, reached when the load power factor equals the cable's own. Where the load power factor is known and consistent, AS/NZS 3008.1.1 Clause 4.5 uses Zc = Rc·cosφ + Xc·sinφ, so Vc = √3 × (Rc·cosφ + Xc·sinφ) for three-phase and 2 × (Rc·cosφ + Xc·sinφ) for single-phase. Rc is the a.c. resistance from AS/NZS 3008.1.1 Tables 4.5, 4.7, 4.9 and 4.10 and Xc the reactance from Tables 4.1 and 4.2, both in Ω/km, which is numerically mΩ/m.

AS/NZS 3008.1.1 Clause 4.4 lets a lightly loaded cable be read at a lower temperature than its insulation allows; the calculator does not take that reduction and reads the normal operating temperature. For balanced three-phase circuits with cosφ near unity the AS/NZS 3008.1.1 Clause 4.5 form collapses to Vd ≈ √3 × I × L × Rc / 1000: the form most engineers use as a sanity check.

### Why operating temperature matters

AS/NZS 3008.1.1:2025 publishes a.c. resistance (AS/NZS 3008.1.1 Tables 4.5, 4.7, 4.9 and 4.10) in conductor temperature columns from 25 °C to 110 °C, and the column a cable is read at is the normal operating temperature of its insulation in AS/NZS 3008.1.1 Table 3.1: 75 °C for PVC (V-75 and V-90 alike), 90 °C for X-90 XLPE and R-90 elastomeric, and 110 °C for X-HF-110 and R-HF-110. In AS/NZS 3008.1.1 Table 4.7(A) copper resistance is about 20% higher at 75 °C than at 25 °C, about 25% higher at 90 °C and about 33% higher at 110 °C, so a drop worked from a cold resistance understates a fully loaded cable by that much.

The ScaleSet voltage drop calculator picks the operating temperature from the cable insulation type automatically and reads the matching column. The PDF report shows the resistance and reactance values, the tables they came from and the insulation with its operating temperature, so the calculation can be re-traced.

### Single-phase or three-phase: which factor applies

Use the single-phase factor (2, AS/NZS 3008.1.1 Clause 4.3.2) for any 230 V single-phase circuit: the drop is in the active and the neutral. Use the three-phase factor (√3, AS/NZS 3008.1.1 Clause 4.3.3) for balanced three-phase circuits such as motors and three-phase final subcircuits with balanced loads. For an unbalanced three-phase circuit, AS/NZS 3008.1.1 Clause 4.6 gives a conservative check: treat it as balanced at the current of the heaviest-loaded phase, which is what entering that current with the three-phase setting does.

The calculator covers a.c. circuits only: it has no d.c. setting, so a solar string, battery or other d.c. circuit is not checked on this page. 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 ScaleSet voltage rise calculator handles that case separately.

### Worked example 1: a 20 A single-phase final subcircuit

A 20 A socket-outlet circuit runs 25 m from the distribution board in 2.5 mm² copper V-90 twin and earth, clipped direct. From AS/NZS 3008.1.1:2025 Table 4.7(A) the AC resistance of 2.5 mm² copper at 75 °C is 9.01 Ω/km and from AS/NZS 3008.1.1 Table 4.1(B) the reactance is 0.102 Ω/km, so the worst-case impedance is Zc = √(9.01² + 0.102²) = 9.01 Ω/km and the single-phase voltage drop per ampere-metre is Vc = 2 × 9.01 = 18.02 mV/A·m.

Vd = Vc × I × L / 1000 = 18.02 × 20 × 25 / 1000 = 9.01 V, which is 3.92% of 230 V. That passes the 5% installation limit on its own, but it leaves less than 1.1% for the consumer mains and submain ahead of it, so on a real job it fails a 2.5% final-subcircuit budget. Going to 4 mm² (Vc = 11.22 mV/A·m) brings the same run down to 5.61 V, or 2.44%, which is why 4 mm² is the usual answer for a long 20 A circuit.

If the load is socket-outlets or lighting spread along the circuit, AS/NZS 3000:2018 Clause 3.6.2 Exception 1 lets the check use half the protective device rating: at 10 A the 2.5 mm² run drops 4.51 V (1.96%) and passes the same 2.5% budget without upsizing.

### Worked example 2: a 63 A three-phase submain at 0.85 power factor

A 63 A submain to a distribution board runs 40 m in 16 mm² four-core copper X-90 on a perforated tray. AS/NZS 3008.1.1 Table 4.7(A) gives 1.47 Ω/km at 90 °C, the X-90 operating temperature, and AS/NZS 3008.1.1 Table 4.1(B) gives 0.0805 Ω/km. With a mixed motor and lighting load at 0.85 lagging, the AS/NZS 3008.1.1 Clause 4.5 form is Vc = √3 × (Rc cos φ + Xc sin φ) = √3 × (1.47 × 0.85 + 0.0805 × 0.527) = 2.24 mV/A·m.

Vd = 2.24 × 63 × 40 / 1000 = 5.64 V, or 1.41% of 400 V. Checking the same cable at worst case (AS/NZS 3008.1.1 Clause 4.3, Zc = √(Rc² + Xc²), the default on this page) gives 2.55 mV/A·m and 6.43 V, or 1.61%. On 16 mm² the gap between the two is almost all power factor: the reactance term adds 0.042 Ω/km of the 1.29, about 3%. Its share grows with the conductor, because resistance falls with size and reactance barely changes. On 240 mm² copper at 90 °C and 0.8 power factor, Xc·sinφ is about 35% of Zc for multicore cable (AS/NZS 3008.1.1 Table 4.1(B), 0.0709 Ω/km), about 38% for single-core cables in trefoil (AS/NZS 3008.1.1 Table 4.1(A), 0.0818 Ω/km) and about 42% for single cores flat touching (0.0970 Ω/km): a third or more of the answer, though not most of it, and more again when single cores are spaced apart. That is why the calculator never drops Xc.

A 1.4% to 1.6% submain leaves about 3.4% for the consumer mains and the final subcircuits downstream, which is comfortable. The same run in 25 mm² would sit at 0.91% (1.02% at worst case); that is the size to pick if the board is going to feed long final subcircuits of its own.

### Maximum cable run length for voltage drop

### Splitting the 5% between consumer mains, submains and final subcircuits

### Aluminium versus copper for voltage drop

Aluminium has about 1.6 times the resistivity of copper, so an aluminium conductor needs roughly 1.6 times the cross-section for the same voltage drop. On a 160 A, 60 m three-phase submain at 0.9 power factor in X-90 multicore cable read at 90 °C, 70 mm² copper drops 5.67 V (1.42%). The nearest aluminium sizes are 95 mm² at 6.68 V (1.67%) and 120 mm² at 5.38 V (1.35%), from AS/NZS 3008.1.1 Table 4.7(B). The larger aluminium conductor, the larger conduit and the bimetallic terminations all have to be carried through the rest of the design.

The calculator reads the aluminium tables directly: pick aluminium as the conductor and it switches from AS/NZS 3008.1.1 Table 4.7(A) to Table 4.7(B) for multicore resistance (AS/NZS 3008.1.1 Table 4.5(B) for single-core). Every insulation class stays available, because the 2025 aluminium tables publish a 110 °C column, and aluminium sizes start at 16 mm².

### What the 5% limit does not apply to

AS/NZS 3000 Clause 3.6.2 has a note and four exceptions that change the check. Note 1 excludes motor starting, solenoid closing and similar transient currents from the 5% limit: the transient dip is a motor-performance question (AS/NZS 3000 Clause 4.13 and the motor manufacturer's minimum starting voltage), not a wiring-rules limit, so the calculator is run at the motor's full load current, not its locked-rotor current. Exception 2 excludes high voltage and extra-low voltage circuits, which have their own rules in AS/NZS 3000 Clauses 7.6 and 7.5.

Exception 3 raises the limit to 7% where the point of supply is the LV terminals of a substation on the premises and dedicated to the installation, because the distributor's share of the drop has been taken out of the picture. Exception 4 lets a stand-alone system to AS/NZS 3000 Clause 7.3 run to a total of 11% below nominal at the equipment terminals, source regulation and cable drop together. Both are a design decision to record, not a default: the calculator checks 5% unless the limit field is changed.

## 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.

## Frequently asked questions

### What is the maximum allowable voltage drop in Australia?

AS/NZS 3000:2018 Clause 3.6.2 limits the voltage drop from the point of supply to any point in the installation to 5% of the nominal voltage: 11.5 V on a 230 V single-phase circuit and 20 V on a 400 V three-phase circuit. The 5% is one limit for the whole path, shared between the consumer mains, submains and final subcircuits, so a common split is 1% to 2% on the mains, 1% to 1.5% on submains and 2% to 2.5% on final subcircuits. On this page the Max Drop field is the share for the one cable you are checking, and it starts at 2%.

### What is the voltage drop formula in AS/NZS 3008.1.1?

Vd = K × I × L × Zc / 1000, in volts, where K is 2 for single-phase (active and neutral) and √3 for balanced three-phase, I is the current in amps, L is the one-way route length in metres and Zc is the cable impedance in ohms per kilometre. AS/NZS 3008.1.1:2025 Clause 4.3 takes Zc = √(Rc² + Xc²), the maximum drop, reached when the cable and load power factors are equal; AS/NZS 3008.1.1 Clause 4.5 uses Zc = Rc·cosφ + Xc·sinφ for a known load power factor. K × Zc is Vc, the drop in mV/A·m. The calculator reads Rc at the cable operating temperature from the AS/NZS 3008.1.1 a.c. resistance Tables 4.5, 4.7, 4.9 and 4.10 and Xc from AS/NZS 3008.1.1 reactance Tables 4.1 and 4.2, and uses the worst-case form unless you untick Worst Case and enter a power factor.

### Does cable temperature affect voltage drop?

Yes. Conductor resistance rises with temperature, so a cable at full load drops more than a 20 °C figure suggests: copper resistance is about 22% higher at 75 °C and about 27% higher at 90 °C. AS/NZS 3008.1.1:2025 publishes a.c. resistance in temperature columns up to 110 °C, and the calculator reads the column for the insulation's normal operating temperature from AS/NZS 3008.1.1 Table 3.1: 75 °C for PVC (V-90 as well as V-75), 90 °C for X-90 XLPE and R-90 elastomeric, and 110 °C for X-HF-110 and R-HF-110. That is the fully loaded case. AS/NZS 3008.1.1 Clause 4.4 allows a lower temperature for a lightly loaded cable; the calculator does not take that reduction.

### What is the difference between voltage drop and voltage rise?

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 ScaleSet voltage rise calculator covers that case.

### How do I calculate three-phase voltage drop?

For a balanced three-phase circuit Vd = √3 × I × L × Zc / 1000, with I the line current, L the one-way length in metres and Zc in ohms per kilometre, and the percentage is taken against 400 V. Example: 63 A over 40 m of 16 mm² four-core copper X-90 has Rc = 1.47 and Xc = 0.0805 ohms per kilometre at 90 °C, so at worst case Vc = √3 × 1.472 = 2.55 mV/A·m and Vd = 2.55 × 63 × 40 / 1000 = 6.43 V, or 1.61%. At a 0.85 power factor it is 5.64 V, or 1.41%. Single-phase uses 2 in place of √3 and 230 V. Where the phases are unbalanced, AS/NZS 3008.1.1:2025 Clause 4.6 allows the conservative check of treating the heaviest-loaded phase as a balanced load: enter that phase's current with the three-phase setting.

### What does mV/A·m mean in voltage drop?

mV/A·m (Vc) is the voltage drop in millivolts for each amp of current over each metre of route. Multiply it by the current and the length and divide by 1000 to get volts: Vd = Vc × I × L / 1000 (AS/NZS 3008.1.1:2025 Clause 4.2). The printed mV/A·m tables (AS/NZS 3008.1.1 Tables 4.14 to 4.31) are three-phase values at the maximum-drop condition; multiply by 1.155 for single-phase. This calculator works Vc out from the cable's Rc and Xc instead, so it can apply your power factor, and the result panel shows Rc, Xc, Zc and the working.

### How do I calculate voltage drop as a percentage?

Divide the drop in volts by the nominal voltage and multiply by 100: %Vd = Vd / Vo × 100, against 230 V for single-phase and 400 V line-to-line for three-phase. AS/NZS 3000 Appendix C writes the same thing in one step as %Vd = L × I × Vc / (10 × Vo). For example, 9.01 V on a 230 V circuit is 3.92%, and 6.43 V on a 400 V circuit is 1.61%. The calculator reports the drop in volts and as a percentage, and checks the percentage against the Max Drop you set for the cable.

### How do I calculate the voltage drop of a busbar trunking or rising main?

AS/NZS 61439.6 Annex AA gives u = k × √3 × (R cos φ + X sin φ) × IB × L for a three-phase run, with R and X the mean resistance and reactance per metre the busbar trunking manufacturer declares at rated current and 35 °C ambient (AS/NZS 61439.6 Table 102). Below 100 A the reactance is deemed negligible. The factor k accounts for where the load sits: 1 when it is concentrated at the far end, (n + 1) / 2n when it is spread evenly over n tap-off units, so a riser feeding four equal floors sees five-eighths of the end-load drop. Choose busbar trunking as the conductor in this calculator and enter those figures; the AS/NZS 3000 5% limit still applies to the total.

### When do I need to include cable reactance Xc?

On this page, always: the calculator includes reactance on every cable, and a size with no reactance value in the tables is treated as missing data rather than zero. Reactance matters more as the cable gets larger, because resistance falls with size while reactance barely changes: at 90 °C, Xc on 16 mm² copper multicore is about 5% of Rc, on 95 mm² about 30% and on 240 mm² about 70%. Xc comes from AS/NZS 3008.1.1:2025 Tables 4.1 and 4.2 and depends on conductor shape and spacing, which is why the single-core arrangement (trefoil, flat touching or spaced) changes the result. AS/NZS 3000 Appendix B lets reactance be ignored at 35 mm² or less, but that is for earth fault-loop impedance, not voltage drop.

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

The voltage drop method is unchanged: the drop from circuit impedance at the maximum-drop condition (AS/NZS 3008.1.1 Clause 4.3), the load power factor form where the power factor is known (AS/NZS 3008.1.1 Clause 4.5), and resistance taken at the conductor operating temperature (AS/NZS 3008.1.1 Clause 4.4). The 2025 edition puts its tables in AS/NZS 3008.1.1 Section 4: reactance in Tables 4.1 to 4.4, a.c. and d.c. resistance in Tables 4.5 to 4.13, and the mV/A·m voltage drop tables in Tables 4.14 to 4.31, and its aluminium a.c. resistance tables carry a 110 °C column. The ScaleSet calculator uses the 2025 table values.

### Does the calculator handle multiple cables in parallel?

Not on this page: the voltage drop calculator checks one cable at a time. For parallel runs use the Cable Selection calculator, whose Parallel Runs stepper divides the design current between the runs. AS/NZS 3000:2018 Clause 3.6.3 takes the voltage drop of a parallel set as the drop in one conductor carrying the circuit current divided by the number of conductors in parallel, so you can check a parallel set here by entering that per-run current against one cable.

### How far can I run a 2.5 mm² cable at 20 A before voltage drop is a problem?

On 230 V single-phase, 2.5 mm² copper PVC (V-75 or V-90, read at 75 °C) drops 18.02 mV per ampere-metre on the AS/NZS 3008.1.1:2025 tables, so at the full 20 A it reaches 5% (11.5 V) at 31 m one way and a 2.5% final-subcircuit budget at 15 m. For a socket-outlet or lighting circuit with the load spread along it, AS/NZS 3000 Clause 3.6.2 Exception 1 lets you check at half the breaker rating, which doubles both figures to 63 m and 31 m. A 400 V three-phase circuit at 20 A per phase reaches about 64 m at 5%, because 5% of 400 V is 20 V and the three-phase factor is √3 rather than 2. The Max Run figure in the result gives the length for your own current and Max Drop.

### Can I use half the breaker rating for a voltage drop calculation?

Yes, for one case. AS/NZS 3000:2018 Clause 3.6.2 Exception 1 (added by Amendment 2) allows half the current rating of the protective device to be used for a final subcircuit with a distributed load such as socket-outlets or lighting. It does not apply to a single fixed load, a submain or consumer mains: those are checked at the connected load, the maximum demand or the device rating, whichever is lowest.

### Does the 5% voltage drop include the distributor's network?

No. AS/NZS 3000 Clause 3.6.2 measures from the point of supply of the low voltage installation to any point in that installation, so it is the customer's cables only. The distributor keeps its own supply voltage within the AS 60038 range at the point of supply; the 5% is the allowance the installation may take off whatever arrives there.

### What voltage drop is allowed with an on-site substation?

7%. AS/NZS 3000:2018 Clause 3.6.2 Exception 3 raises the limit from 5% to 7% where the point of supply is the low voltage terminals of a substation located on the premises and dedicated to the installation. On this page, share 7% rather than 5% between the cables when you set each one's Max Drop, and record the exception on the drawing.

### Is motor starting voltage drop covered by the 5% rule?

No. Note 1 to AS/NZS 3000 Clause 3.6.2 excludes motor starting, solenoid closing and similar transient currents from the 5% limit. Check the cable at the motor full load current here, and treat the starting dip as a motor performance question: the starter type, the motor's minimum starting voltage and any supply authority limit on starting current under AS/NZS 3000 Clause 4.13 and the distributor's service rules.

### Is aluminium cable acceptable for voltage drop?

Yes. Aluminium has about 1.6 times the resistivity of copper, so it needs roughly 1.6 times the cross-section for the same drop. On a 160 A, 60 m three-phase run at 0.9 power factor in X-90 multicore cable, 70 mm² copper drops 1.42%, 95 mm² aluminium 1.67% and 120 mm² aluminium 1.35%. Select aluminium as the conductor and the calculator reads AS/NZS 3008.1.1 Table 4.7(B) instead of 4.7(A) for multicore cable (4.5(B) for single-core). Every insulation class stays available, because the 2025 tables publish aluminium resistance up to 110 °C, and aluminium sizes start at 16 mm².

### What is the simplified voltage drop method in AS/NZS 3000 Appendix C?

AS/NZS 3000 Table C8 lists ampere-metres per 1% voltage drop for twelve copper PVC cable sizes from 1 mm² to 95 mm², single-phase at 230 V and three-phase at 400 V, so a run is checked by dividing current × length by the table figure. It is built from the maximum Vc values for PVC cable at 75 °C, so it has no aluminium, XLPE or power factor columns, and it was tabulated against an earlier AS/NZS 3008.1.1 edition. This calculator reproduces AS/NZS 3000 Table C8 to within 1% up to 35 mm² on the 2025 tables and covers everything the table does not.

### What happens if the voltage drop is over 5%?

Equipment may not receive its rated voltage, motors run hotter and draw more current, lighting dims and electronic loads can reset, and the installation does not comply with AS/NZS 3000 Clause 3.6.2. The fixes, in the order they are usually cheapest: shorten the route, move allowance from another section of the budget, go up one conductor size on the longest section, or move the distribution board closer to the load. On a three-phase site, rebalancing a single-phase load across phases also helps because the neutral current falls.

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