Cable Size Calculator Australia AS/NZS 3008:2026

Q: What is the formula for cable size calculation?

Minimum cable size based on current ≥ load current / correction factors, and voltage drop ≤ allowable. Use Vd = (2 × I × L × R)/1000 for single-phase and (√3 × I × L × R)/1000 for three-phase.

Q: How do I choose cable size for a 3-phase motor?

Calculate full load current (I = P / (√3 × V × PF)). Pick cable with ampacity ≥ I, then check voltage drop (max 5%). Use our 3 phase cable size calculator for instant results.

Q: What cable size for 12V solar panels?

Use a 12v cable size calculator – for 20A over 10m, at least 6mm² copper to keep voltage drop < 3%. Higher currents require 10mm² or larger.

Q: Is the calculator compliant with Australian standards?

Yes, it follows AS/NZS 3008.1 ampacity tables and voltage drop methodology updated for 2026. Always get final approval from a licensed electrician.

Q: How to calculate earth cable size?

Earth wire size is based on active conductor size and fault current. Typically for final subcircuits, earth size = active size up to 16mm², then half for larger cables.

Q: Does cable length affect ampacity?

Indirectly – longer cables increase voltage drop, which may force you to upsize the cable even if ampacity is sufficient. Our tool automatically checks both criteria.

Accurate electrical cable sizing for 12V DC, 240V single-phase & 415V three-phase systems. Voltage drop & ampacity compliant with Australian standards.

Cable Sizing Tool – 2026 edition

Enter your installation parameters. We calculate minimum cable size (mm²) based on current-carrying capacity and voltage drop (AS/NZS 3008).

System type

Voltage (V)

Conductor

Load (choose one) or

Cable length (m) - one way

Max voltage drop (%)

Power factor (AC only)

Ambient temp factor (optional)

Recommended cable size: — mm²

Voltage drop: — %

Current capacity of selected size: — A

⚡ Estimate based on AS/NZS 3008 (PVC insulated, 75°C). Always verify with a licensed electrician.

How to calculate cable size accurately (2026 guide)

Selecting the correct cable size calculator is critical for safety, efficiency, and compliance with Australian Wiring Rules (AS/NZS 3000 & 3008). Whether you’re wiring a shed, installing solar panels, or sizing a three-phase motor, this guide walks you through the cable sizing calculation formula, voltage drop constraints, and practical examples.

Step-by-step cable sizing method

Determine design current (I_b) – from load power or nameplate current.
Select installation reference method (enclosed, clipped direct) → affects current rating (Iz).
Apply correction factors – ambient temp, grouping (C_a, C_g).
Choose cable size where tabulated current rating ≥ I_b / (C_a × C_g).
Check voltage drop ≤ 3% (lighting) or 5% (power) per AS/NZS 3000.

Standard copper cable ampacity table (PVC 75°C, reference Method B – conduit)

Cable size (mm²)	Current rating (Cu) A	Current rating (Al) A	Resistance (Cu) Ω/km @50°C
1.5	14	11	15.0
2.5	18.5	14.5	9.0
4	25	19.5	5.6
6	32	25	3.7
10	43	34	2.2
16	57	45	1.41
25	75	58	0.90
35	92	72	0.64
50	120	94	0.45
70	151	118	0.32

Voltage drop formula – 3 phase & single phase

Single-phase / DC: Vd = 2 × I × L × R_c / 1000
Three-phase: Vd = √3 × I × L × R_c / 1000
R_c = conductor resistance (Ω/km) at operating temp.

Using our cable size calculator Australia automates these complex calculations. For 12V systems, voltage drop is especially critical: we recommend 12v cable size calculator ensures less than 3% drop to avoid appliance under-voltage.

Exclusive 2026 insight: Solar & EV charger cable sizing trends

With the rise of rooftop solar and EV chargers in Australia, proper DC cable size calculator and AC cable sizing have become essential. For solar arrays, use our tool with "DC" mode and ensure voltage drop < 1% for maximum efficiency. For 3-phase EV chargers (22 kW), we recommend 3 phase cable size calculator with at least 6 mm² copper for 30m runs, depending on current. Always apply derating when cables are bundled in roof spaces (40°C+).

Pro checklist – before you choose cable size:

✅ Identify load type (motor, resistive, inverter).
✅ Use cable size calculation table for quick reference.
✅ For long runs, upsize cable to reduce voltage drop.
✅ Earth cable size: typically half of active (min 4mm² for main earth).
✅ Always round up to the next standard mm² available.

Real-world example: 3-phase motor cable sizing

Imagine a 15kW, 415V three-phase motor with power factor 0.86, cable length 65 metres, copper conductor, installed in conduit. Full load current ≈ 15,000 / (√3 × 415 × 0.86) ≈ 24.2 A. Using our cable size 3 phase calculator, min ampacity ~ 32A → select 6 mm² copper (32A capacity). Voltage drop check: R = 3.7 Ω/km, Vd = √3 × 24.2 × 65 × 3.7 / 1000 ≈ 10.1 V (2.4% drop). That’s within 5% limit, so 6 mm² works, but for extra efficiency we can upsize to 10 mm² if needed.

Cable sizing formula reference (AS/NZS 3008.1)

The official cable size calculation formula incorporates load current, voltage drop, short-circuit temperature rise, and de-rating factors. Our simplified electrical cable sizing calculator follows the core principles, making it ideal for residential, commercial, and light industrial projects. For high-voltage (HV) or 11kV/33kV systems, professional software is mandatory.

How to calculate cable size for inverters & batteries (12V / 24V)

When using a 12v cable size calculator Australia, always double the current because of low voltage. For a 2000W inverter at 12V, current can exceed 166A. For a 2m run, you’ll need at least 35mm² copper to keep voltage drop under 3% and prevent overheating. Our calculator supports DC mode – just enter voltage (12/24/48) and load.

Quick lookup: Maximum cable length for 3% voltage drop (240V single‑phase, copper)

Current (A)	2.5 mm² max length (m)	4 mm² max length (m)	6 mm² max length (m)	10 mm² max length (m)
10	52	82	124	208
16	32	51	78	130
20	26	41	62	104
32	16	26	39	65

*Values indicative; always confirm with AS/NZS 3008 and your local electrician.

Frequently asked questions – cable sizing

What is the formula for cable size calculation?
The general formula: Minimum cable size based on current ≥ load current / correction factors, and voltage drop ≤ allowable. Use Vd = (2 × I × L × R) / 1000 for single-phase and (√3 × I × L × R)/1000 for three-phase.

How do I choose cable size for a 3-phase motor?
Calculate full load current (I = P / (√3 × V × PF)). Pick cable with ampacity ≥ I, then check voltage drop (max 5%). Use our 3 phase cable size calculator for instant results.

What cable size for 12V solar panels?
Use a 12v cable size calculator – for 20A over 10m, at least 6mm² copper to keep voltage drop < 3%. Higher currents require 10mm² or larger.

Is the calculator compliant with Australian standards?
Yes, it follows AS/NZS 3008.1 ampacity tables and voltage drop methodology updated for 2026. Always get final approval from a licensed electrician.

How to calculate earth cable size?
Earth wire size is based on active conductor size and fault current. Typically for final subcircuits, earth size = active size up to 16mm², then half for larger cables. Refer to AS/NZS 3000 Table 5.1.

Can I use this for HV cable sizing (11kV)?
Our high voltage cable sizing calculator principles apply but HV requires insulation, short-circuit and detailed studies. This tool is intended for LV (low voltage ≤1000V) applications.

Does cable length affect ampacity?
Indirectly – longer cables increase voltage drop, which may force you to upsize the cable even if ampacity is sufficient. Our tool automatically checks both criteria.

Important legal & safety notice

TotalCalcHub provides the cable size calculator as an estimation tool only. All calculations are based on generic PVC-insulated cables and typical installation methods. Actual installations must comply with AS/NZS 3000, AS/NZS 3008, and state regulations. Always engage a qualified electrician before purchasing or installing any electrical cable. We do not accept liability for any damages or losses arising from reliance on these results. Updated for 2026.