What standards does the ElecAS cable size calculator use?

AS/NZS 3008.1.1:2025 supplies the current carrying capacity tables (Tables 3–21), derating factors (Tables 22–29), conductor R and X values for voltage drop (Tables 30–39) and short-circuit k-values (Table 52). AS/NZS 3000:2018 drives compliance — Cl. 2.5.3.1 protection coordination, Cl. 3.4 minimum sizes, Cl. 3.6.2 voltage drop limits (5% from the network, 7% from an on-site substation), Cl. 5.7.2 disconnection times, Appendix B4.5 simplified Zs method, Table 5.1 earth conductor sizing and Table 8.1 maximum Zs. AS/NZS 3013 covers fire-rated wiring systems and AS 60038 sets the 230 V +10% / -6% voltage envelope.

What checks does the cable size calculator run?

Six checks on every result: (1) current carrying capacity after k1·k2·k3·k4 derating; (2) protection coordination Ib ≤ In ≤ Iz per AS/NZS 3000 Cl. 2.5.3.1; (3) voltage drop against your per-segment limit and the Cl. 3.6.2 envelope; (4) device breaking capacity against the prospective fault current; (5) the adiabatic I²t ≤ k²S² short-circuit thermal withstand check on both the active and the earth conductor using AS/NZS 3008.1.1 Table 52 k-values; and (6) earth-fault loop impedance using the AS/NZS 3000 Appendix B4.5 simplified resistance method against the Cl. 5.7.2 disconnection time.

What voltage drop limit applies to consumer mains in Australia?

AS/NZS 3000 Cl. 3.6.2 does not publish a separate limit for consumer mains — the 5% total (or 7% from an on-site substation) applies from the point of supply to the load. Designers conventionally hold the mains segment to roughly 1.0% so the submain and final subcircuit downstream still have room to comply. The calculator checks whatever per-segment allowance you enter and the result still has to satisfy the appliance operating-voltage range once it is combined with the rest of the path.

Does cable temperature affect voltage drop?

Yes — copper resistance rises about 0.4% per °C, and AS/NZS 3008.1.1 publishes its impedance Tables 30 to 39 at the maximum continuous operating temperature of each insulation class. The calculator picks the correct row automatically once you select the insulation: 75 °C values for V-75 PVC, 90 °C values for X-90 XLPE and R-90 elastomer, and 110 °C values for X-110 XLPE and R-110 elastomer. Voltage drop on a fully loaded XLPE cable is therefore a few percent worse than the same conductor sized in PVC because the conductor is hotter at design current.

Should I use worst-case PF or the actual power factor for voltage drop?

AS/NZS 3008.1.1 publishes two methods and the calculator offers both via the Worst Case PF toggle. With it on (the default) the cable component is the full impedance Zc = √(R² + X²) — conservative and bounded regardless of the load plant that ends up connected, suitable for distribution boards, mains and mixed loads. With the toggle off the calculator uses the actual-PF projection Vc = R·cosφ + X·sinφ from the entered power factor; real loads at lagging PF give a smaller drop than the worst-case envelope, allowing tighter sizing where the load PF is known and stable (a single dedicated motor, VFD or large fixed plant).

How is voltage drop calculated for single-phase vs three-phase cables?

The base formula is the same: Vd = (L × Ib × Vc) / 1000, with L in metres, Ib in amps and Vc the cable’s mV/A·m factor. What changes is the multiplier baked into Vc to account for the loop. On single-phase circuits the current returns through the neutral, so Vc = 2·Z. On three-phase line-to-line drop the geometry gives Vc = √3·Z. The calculator picks the correct factor automatically from the Phases selector at the top of the configuration panel.

What size cable do I need for a 32A circuit in Australia?

For a 32 A circuit, 4 mm² copper V-75 may be suitable under common installation conditions — for example single-phase, Method M5 (enclosed in conduit on a wall) at reference ambient and grouping — but this is not universal. A three-phase 32 A circuit derates further because three conductors are loaded, and longer runs or tighter voltage-drop allowances often push the result up a size. Re-run the calculator for your actual phasing, length, ambient temperature and grouping, then verify short-circuit withstand and Zs against the upstream device.

What size cable do I need for a 63A circuit?

Reference: copper, three single-cores in conduit on a wall (Method M5). V-75 PVC copper typically lands at 16 mm² for capacity; X-90 XLPE copper can drop to 10 mm² subject to terminal temperature ratings. Buried installations do not automatically mean smaller cables: direct-buried (M9) only outperforms M5 at the AS/NZS 3008.1.1 reference soil resistivity of 1.2 K·m/W and shallow burial. Most Australian soils sit at 1.5–2.5 K·m/W which derates buried capacity significantly, and buried-in-enclosure (M10) ratings are often similar to or lower than M5. Re-run the calculator with your actual soil resistivity, depth and grouping.

What size cable do I need for a 100A submain?

A 100 A copper submain typically falls around 25–35 mm² depending on installation method, insulation type, conductor arrangement and derating. Three single-core copper V-75 cables in conduit on a wall (Method M5) at reference conditions usually land at 35 mm² for capacity. Aluminium will generally require a larger size (around 70 mm² in the same scenario since 50 mm² aluminium does not meet 100 A in M5). Voltage drop becomes the governing constraint on long runs or where the upstream allowance is tight.

What size cable for a 200A consumer mains?

Reference: three single-cores in conduit on a wall (Method M5). Copper V-75 PVC lands at 95 mm² for capacity; copper X-90 XLPE can drop to 70 mm² subject to terminal temperature ratings; aluminium V-75 PVC steps up to 150–185 mm² (120 mm² aluminium falls short of 200 A in M5). Voltage drop on long mains often governs — keep this segment to about 1% allowance to leave room for the submain and final subcircuit.

When does grouping derating apply?

Grouping derating from AS/NZS 3008.1.1 Tables 22 to 24 applies whenever multiple loaded cables run in close proximity — bunched in a conduit, on a tray, in an enclosed run or tied together — because each cable raises the temperature of its neighbours and reduces the heat the conductor can dissipate. Switch on the Grouping sub-toggle, set the Number of Circuits to the actual number of loaded circuits in the group, and pick the matching arrangement (bunched in air, single layer on a tray, multilayer, or buried) — the calculator pulls the correct factor and folds it into k2. Spacing of at least one cable diameter between adjacent cables avoids the derating entirely on most installation methods.

Why does soil thermal resistivity matter for buried cables?

A buried cable dissipates the heat from its losses through the surrounding soil. The higher the soil’s thermal resistivity, the more poorly it conducts that heat away, and the hotter the cable runs at any given current. AS/NZS 3008.1.1 publishes the entire buried current carrying capacity table at a reference resistivity of 1.2 K·m/W; Table 28 gives the k3 correction for any value above or below that. Most moist Australian soils sit around 1.5 K·m/W, dry sandy soils run from 2.0 to 2.5 K·m/W, and crushed-rock backfill or thermally enhanced sand can go below 1.0 K·m/W. Use the geotechnical report value or 1.5 K·m/W as a conservative default.

Which AS/NZS 3008.1.1 installation method should I select?

The Installation Method selector matches the AS/NZS 3008.1.1 method codes to the physical install. Pick Unenclosed in air (Methods M1 to M4) for cables on a tray, ladder or clipped direct to a wall, with sub-options for spaced or touching arrangements; Enclosed in conduit (Methods M5 to M8) for surface or in-wall conduit and trunking; Buried direct (Method M9) for cables laid in a trench with controlled backfill; and In underground enclosure (Methods M10 to M11) for cables drawn into buried conduits or ducts. Buried installations do not automatically mean smaller cables — buried direct only outperforms an in-air install at reference resistivity and shallow burial.

Copper vs aluminium — which conductor should I size with?

Copper is the default in Australia. It has higher conductivity for the same cross-section, better mechanical and fatigue strength, and terminates cleanly into standard lugs without specialist preparation. Aluminium is genuinely useful on large mains and submains (typically 70 mm² and above) where lower weight and cost outweigh the drawbacks, but it has only ~60% of copper’s conductivity (one or two sizes larger for the same current), cold-flows under terminal pressure demanding torque-controlled lugs and anti-oxidation paste, oxidises with a poorly-conducting oxide layer, and reacts galvanically with copper so any aluminium-to-copper joint needs a bimetallic lug. The calculator restricts the insulation menu to V-75, X-90 and R-90 when aluminium is selected because the 110 °C products are only manufactured in copper.

V-75 (PVC) vs X-90 (XLPE) — which insulation should I pick?

V-75 PVC runs at 75 °C and is the cheapest construction; the calculator’s Auto rule selects V-75 for any size up to 16 mm². X-90 XLPE runs at 90 °C, carries roughly 25 to 30% more current in the same cross-section, and has a higher Table 52 k-value (143 vs 115 for copper) — Auto selects X-90 once the resolved cable is larger than 16 mm². The deciding factor in practice is termination temperature: most MCBs, switch-disconnectors and lug terminals are rated for 75 °C terminations, so even an X-90 cable has to be sized off the 75 °C column at those devices.

What is cable insulation and what does it do?

The insulation is the dielectric layer surrounding each conductor. It prevents leakage between conductors and to earth at the operating voltage, sets the maximum continuous conductor temperature (which together with the installation method fixes the AS/NZS 3008.1.1 current carrying capacity), and sets the short-circuit k-value used in the Table 52 adiabatic check. The five Australian insulation classes are V-75 (PVC 75 °C), X-90 (XLPE 90 °C including X-90UV and X-HF-90 halogen-free variants), R-90 (Elastomeric 90 °C including R-EP-90, R-CPE-90 and R-HF-90), X-110 (XLPE 110 °C, X-HF-110 form), and R-110 (Elastomeric 110 °C, R-HF-110 and R-E-110 forms — the fire-rated option). The 110 °C options are only available with copper conductors.

How do I select the right cable insulation?

Leave the Insulation selector on Auto and the calculator resolves V-75 PVC for any cable up to 16 mm² and X-90 XLPE above 16 mm² — the same convention most contractors and suppliers default to. If the section is flagged as essential safety, Auto resolves to R-110 elastomeric instead. Pick V-75 manually for general dry fixed wiring at 40 °C indoor ambients. Pick X-90 when capacity is tight, ambient is elevated, the run is heavily grouped, or you want the ~25 to 30% capacity uplift. Pick R-90 elastomeric for industrial, vibration-prone or harsh-environment runs. Pick X-110 when 90 °C XLPE is still capacity-limited. Pick R-110 for fire-rated and critical-service circuits. Always verify the terminal temperature rating of the upstream and downstream device.

How do I choose the number of cores for a cable?

The Construction selector filters automatically once you set Phases. Single-phase offers four constructions: 2C+E (active, neutral, integral earth), 2C (active and neutral with a separate earth), 2x1C+E and 2x1C single-cores. Three-phase offers six: 4C+E (three actives, neutral, integral earth — for any submain or consumer main feeding single-phase loads), 3C+E (three actives plus earth — balanced three-phase loads such as motors), 4C (separate earth), and the corresponding single-core layouts (4x1C+E, 3x1C+E, 4x1C). Auto resolves to multi-core up to 95 mm² and single-core from 120 mm² upwards, with the earth integral by default.

Single-core vs multi-core cables — which should I pick?

Multi-core cables carry every conductor inside one outer sheath, which is easier to install, identify and terminate, fits cleanly through conduits, and ensures the conductors take the same path. The calculator’s Auto rule picks multi-core for any cable up to 95 mm². Single-core cables run each conductor in its own jacket — Auto switches to this from 120 mm² upwards because multi-core becomes physically unwieldy at those sizes and parallel runs (which AS/NZS 3000 Cl. 3.4.3 only allows on identical single-cores) become more common. For single-cores the Cable Arrangement selector lets you pick trefoil, flat-touching or flat-spaced; the calculator pulls the correct R and X values from the matching AS/NZS 3008.1.1 impedance table.

What is the WS classification on a cable, and what does it mean?

WS stands for Wiring System under AS/NZS 3013, and the code summarises three combined tests applied to the entire system rather than the cable alone. The W component is the fire test (subscript X = no fire, Y = lower-temperature exposure, Z = full 1100 °C exposure), the S component is the water-spray test, and the trailing numeral is the mechanical impact rating. Common designations on Australian projects include WS51W and WS52W (1100 °C fire combined with water spray and mechanical impact, longer duration on WS52W) and WS3X (mechanical impact only, no fire). The project’s fire engineering report specifies the required WS rating per circuit, and the cable, support system, cleats and terminations all have to meet or exceed that rating.

When is short-circuit thermal withstand the limiting factor?

Short-circuit withstand tends to govern when prospective fault currents are high (close to the supply transformer or downstream of a large on-site substation) and the upstream protection has a relatively slow clearing time. The calculator’s Source Fault Current field carries the prospective Isc at the location of the cable, and Fault Clearing Time is the duration the protection takes to interrupt that fault — typical presets are about 10 ms for an HRC fuse, 20 ms for a current-limiting MCB, 40 ms for a standard MCCB, 80 ms for an electronic-trip MCCB and 100 ms for an ACB. The check is the adiabatic equation I²t ≤ k²S² on both the active and the earth conductor, with k from Table 52: 115 for copper PVC, 143 for copper XLPE/elastomer, 76 for aluminium PVC and 94 for aluminium XLPE.

How does the calculator check earth-fault loop impedance under AS/NZS 3000?

The calculator follows the simplified resistance method in AS/NZS 3000 Appendix B4.5. The cable contribution is Zint = ((Ra + Re) × L) / 1000, where Ra is the active conductor resistance and Re the earth conductor resistance per kilometre at operating temperature, and L is the route length in metres. The total loop impedance is Zs = Ze + Zint, with Ze the external impedance of the supply (default 0.35 Ω for residential or 0.02 Ω for an on-site substation). The pass condition is Zs ≤ U₀ / Ia with U₀ = 230 V and Ia from the linked Schneider Electric breaker database — Im for MCBs and thermal-magnetic MCCBs, Ii for electronic-trip MCCBs and ACBs, with a generic fuse fallback. The disconnection time required by Cl. 5.7.2 is 0.4 s for socket outlets up to 63 A and portable equipment, and 5 s for fixed and distribution circuits.

What is the smallest cable allowed under AS/NZS 3000?

Minimum conductor sizes depend on the circuit type, conductor material, wiring system and mechanical protection. From AS/NZS 3000:2018 Table 3.3 and common Australian practice: lighting final subcircuits are typically 1.0 mm² copper minimum, and socket-outlet final subcircuits are typically 2.5 mm² copper minimum. Signal and relay control circuits can drop to 0.5 mm² and flexible cords to 0.75 mm²; aerial wiring is 6 mm² copper or 16 mm² aluminium. Submains and consumer mains are not in Table 3.3 — their size is driven by capacity, voltage drop, short-circuit withstand and Zs, but practical minimums still apply (consumer mains typically not less than 16 mm² copper or 25 mm² aluminium under most utility service rules). The calculator’s standard size set runs from 1 mm² to 630 mm² in the AS/NZS 3008 preferred series.

How do I size a cable for a three-phase motor?

Take the motor full-load current from the nameplate (not the locked-rotor or starting current — protection device coordination handles those transients) and enter it into the Design Current field. For continuous-duty motors a common convention is to size on roughly 1.25 × FLA to allow for sustained running, but the actual design current depends on duty cycle, overload protection, starting method, installation conditions and the AS/NZS 3000 Section 4 motor requirements. Set Phases to 3 and Construction to 3C+E or 3x1C+E (no neutral for a balanced three-phase motor). Voltage drop on the longest motor run is usually the governing constraint, especially for soft-started or VFD-fed motors where excessive volt drop also worsens torque output and starting performance.

Which MCB protective device curve should I use — B, C or D?

The MCB curve sets the magnetic instantaneous trip threshold the calculator uses for its earth-fault loop impedance check. Curve B trips at 3–5× In and suits resistive loads and lighting. Curve C trips at 5–10× In and is the general-purpose default. Curve D trips at 10–20× In and is reserved for transformers, motors and other loads with high inrush that would nuisance-trip a C curve. The compliance trade-off comes through Ia in Zs ≤ U₀ / Ia: a higher curve raises Ia, which lowers the maximum permissible Zs and tightens the earth-fault loop impedance constraint. If a C-curve passes Zs and a D-curve does not, you usually need to drop a curve, increase the cable size to lower Zs, or switch to an electronic-trip device.

Does the calculator handle four-core cables and neutral derating?

Yes. The Construction selector covers four single-phase layouts (2C+E, 2C, 2x1C+E, 2x1C) and six three-phase layouts (4C+E, 3C+E, 4C, 4x1C+E, 3x1C+E, 4x1C). For a balanced three-phase load with no neutral — most three-phase motors — pick a 3C+E or 3x1C+E construction; for any submain feeding single-phase loads downstream pick a 4C+E or 4x1C+E so a neutral is included. The calculator counts loaded conductors when it pulls the AS/NZS 3008.1.1 capacity table — three loaded actives in a 4C+E cable are rated lower than two loaded actives in a 2C+E. Where the load is harmonic-rich (LED lighting, drives, IT equipment), AS/NZS 3008.1.1 requires the neutral to be treated as a current-carrying conductor; keep a 4C construction and accept the four-loaded-conductor rating.

Is the ElecAS cable size calculator free?

Yes — the AS/NZS 3008.1.1:2025 cable size calculator runs entirely in your browser, with no account required for the standard workflow, and the cable selection report exports as a PDF you can attach to the project documentation. Project metadata (project name, number, address, designer, revision) is captured at the top of the page and flows into the exported report so the PDF is ready to issue.

ElecAS

Cable Size Calculator — AS/NZS 3008.1.1:2025 Cable Sizing for Australia

Free, browser-based AS/NZS 3008.1.1:2025 cable size calculator built for Australian electrical engineers, designers, electricians, estimators and contractors. Enter your design current, supply phase, conductor material, insulation, construction, installation method, route length and protection device — the calculator returns the smallest compliant cable size after running every check that AS/NZS 3000 and AS/NZS 3008.1.1 require: current-carrying capacity with k1 ambient, k2 grouping, k3 soil thermal resistivity and k4 depth-of-burial derating; protection coordination Ib ≤ In ≤ Iz; voltage drop against your per-segment limit and the AS/NZS 3000 Clause 3.6.2 envelope (5% from the network or 7% from an on-site substation); device breaking capacity against the prospective fault current; the I²t ≤ k²S² adiabatic short-circuit withstand check on both the active and the earth conductor using AS/NZS 3008.1.1 Table 52 k-values (115 Cu/PVC, 143 Cu/XLPE, 76 Al/PVC, 94 Al/XLPE); and earth-fault loop impedance using the Cl. B4.5 simplified resistance method, with the trip current Ia pulled directly from the linked Schneider Electric circuit protection database (Im for thermal-magnetic MCBs and MCCBs, Ii for electronic-trip MCCBs and ACBs). Three conductor types — Copper (Cu), Copper Flexible, Aluminium (Al) — and five insulation classes — V-75 PVC, X-90 XLPE, R-90 elastomeric, X-110 XLPE and R-110 elastomeric (the calculator's essential-safety / fire-rated option per AS/NZS 3013) — are supported, along with the full AS/NZS 3008.1.1 Table 3 installation method library M1 to M11. Auto-size mode resolves V-75 up to 16 mm² and X-90 above, multi-core construction up to 95 mm² and single-core from 120 mm² upward, and R-110 when the section is flagged as essential safety. Built-in support for parallel runs, separate earth-conductor sizing per Table 5.1, full project metadata capture and a branded PDF cable selection report you can drop straight into a design submission.

Why this page matters

Who this page is for

Electrical engineers, designers, electricians, estimators and contractors sizing copper, copper flexible or aluminium conductors for consumer mains, submains, final subcircuits, motor circuits and essential / fire-rated services under AS/NZS 3000:2018, AS/NZS 3008.1.1:2025, AS/NZS 3013 and the National Construction Code (NCC).

Relevant standards

AS/NZS 3008.1.1:2025 (Cable Selection — Tables 3–21, 22–29, 30–39, 52)
AS/NZS 3000:2018 (Wiring Rules, including Clauses 2.5.3, 3.4, 3.6, 5.7.2 and Appendix B4.5)
AS/NZS 3000 Table 5.1 (Earthing Conductor Sizing)
AS/NZS 3000 Table 8.1 (Maximum Earth-Fault Loop Impedance)
AS/NZS 3013 (Fire-Rated Wiring Systems — WS Classification)
AS 60038 (Standard Voltages — 230 V +10% / -6%)
National Construction Code (NCC) — essential services

What this tool helps with

Runs every AS/NZS 3000 and AS/NZS 3008.1.1:2025 cable selection check in one pass — current carrying capacity (with full k1·k2·k3·k4 derating), Ib ≤ In ≤ Iz protection coordination, voltage drop, breaking capacity, I²t ≤ k²S² thermal withstand on the active and the earth conductor, and earth-fault loop impedance.
Applies the four AS/NZS 3008.1.1 correction factors automatically from Tables 22–29 — ambient air or soil temperature (k1), grouping (k2), soil thermal resistivity (k3) and depth of burial (k4) — and shows the resulting Total Derating Factor in the configuration panel.
Three conductor options — Copper (Cu), Copper (Flexible) and Aluminium (Al) — with calculator-aware impedance values for fine-stranded flexible cores and the aluminium-specific insulation restrictions.
Five insulation classes — V-75 PVC, X-90 XLPE, R-90 elastomeric, X-110 XLPE, and R-110 elastomeric (the essential-safety / fire-rated option for fire pumps, mechanical essential boards, fire-mode lifts and fire detection / EWIS per AS/NZS 3013).
Auto-size mode picks V-75 PVC up to 16 mm² and X-90 XLPE above, multi-core construction up to 95 mm² and single-core construction from 120 mm² upward, and R-110 elastomeric when the section is flagged as essential safety — the same conventions used on Australian commercial and industrial installations.
Ten construction layouts covering single-phase and three-phase: 2C+E, 2C, 2x1C+E, 2x1C, 4C+E, 3C+E, 4C, 4x1C+E, 3x1C+E and 4x1C — with the calculator counting loaded conductors when it pulls the AS/NZS 3008.1.1 capacity table.
Full AS/NZS 3008.1.1 Table 3 installation method library — unenclosed in air (M1–M4), enclosed in conduit (M5–M8), buried direct (M9) and in underground enclosures (M10–M11) — with single-core arrangement options (trefoil, flat-touching, flat-spaced) feeding the impedance lookup.
Voltage drop calculated by the impedance method Z = √(R² + X²) per AS/NZS 3008.1.1, with a one-toggle switch to the actual-PF projection Vc = R·cosφ + X·sinφ for tighter sizing on known-PF loads, and the per-segment limit checked against your design split (typically 1% mains, 1.5–2% submains, 2–2.5% final subcircuits inside the 5% Cl. 3.6.2 envelope, or 7% from an on-site substation).
Earth-fault loop impedance computed using the AS/NZS 3000 Cl. B4.5 simplified resistance method Zs = Ze + ((Ra + Re) × L) / 1000, with the trip current Ia pulled from the linked Schneider Electric circuit protection database (Im for MCB / thermal-magnetic MCCB, Ii for electronic-trip MCCB / ACB) and a fuse fallback when no breaker record applies.
Native parallel-runs support per AS/NZS 3000 Cl. 3.4.3 with a separate earth conductor stepper, automatic AS/NZS 3008.1.1 Table 5.1 earth sizing, and a project metadata block (project name, number, address, designer, revision) that flows into the exported PDF cable selection report.
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 size a cable under AS/NZS 3008.1.1 and AS/NZS 3000

Enter design current (Ib) — Enter the maximum continuous design current the circuit will carry. For motors use the nameplate full-load current; for distribution circuits use the maximum demand from AS/NZS 3000 Section 2.
Select phases and protection device — Set Phases to 1 or 3 and pick the upstream protective device (MCB curve B/C/D, MCCB, ACB or fuse). The device rating In must satisfy Ib ≤ In ≤ Iz per AS/NZS 3000 Cl. 2.5.3.1.
Choose conductor, insulation and construction — Pick Copper (Cu), Copper Flexible or Aluminium; pick V-75, X-90, R-90, X-110 or R-110 insulation (or leave Auto); pick a multi-core or single-core construction with the appropriate number of cores for the loading.
Choose AS/NZS 3008.1.1 installation method — Select Method M1–M4 (unenclosed in air), M5–M8 (enclosed in conduit), M9 (buried direct) or M10–M11 (in underground enclosure) to match the physical install.
Apply derating factors — Switch on Apply Derating and enter ambient temperature, number of grouped circuits, soil thermal resistivity and depth of burial. The calculator pulls k1·k2·k3·k4 from AS/NZS 3008.1.1 Tables 22–29 automatically.
Set route length and voltage drop budget — Enter the cable route length in metres and the per-segment voltage drop allowance — typically 1% for consumer mains, 1.5–2% for submains and 2–2.5% for final subcircuits, inside the AS/NZS 3000 Cl. 3.6.2 5% (or 7%) envelope.
Enter fault current and clearing time — Provide the prospective short-circuit current Isc at the cable origin and the upstream device clearing time so the calculator can run the adiabatic I²t ≤ k²S² check on the active and the earth conductor.
Set external impedance Ze for Zs check — Enter the supply external impedance Ze (default 0.35 Ω for residential or 0.02 Ω for an on-site substation). The calculator computes Zs = Ze + ((Ra + Re) × L)/1000 and verifies Zs ≤ U₀/Ia against the AS/NZS 3000 Cl. 5.7.2 disconnection time.
Review pass/fail pills and export the PDF report — Each compliance check shows a pass/fail pill. When every check passes, fill in the project metadata block and export the branded PDF cable selection report for submission.

Cable sizing under AS/NZS 3008.1.1:2025 — practical guide

Standards and methodology

The ElecAS cable size calculator reads tabulated values directly from the current Australian/New Zealand standards — no rules of thumb and no interpolation beyond the published data. AS/NZS 3008.1.1:2025 is the dominant reference: current-carrying capacity comes from Tables 3 to 21 selected by the chosen installation method, conductor and insulation; voltage drop uses the impedance values published in Tables 30 to 39 (R and X per kilometre at the conductor operating temperature); derating factors come from Tables 22 to 29; and short-circuit k-values for the adiabatic check come from Table 52.

AS/NZS 3000:2018 (the Wiring Rules) drives the compliance checks. Clause 2.5.3.1 sets protection coordination Ib ≤ In ≤ Iz. Clause 3.4.1 and Table 3.3 fix minimum conductor sizes. Clause 3.4.3 governs parallel runs. Clause 3.6.2 sets the voltage drop limit (5%, or 7% where the consumer’s point of supply is at an on-site substation). Appendix B4.5 gives the simplified earth-fault loop impedance method the tool uses for Zs. Clause 5.7.2 sets disconnection times (0.4 s for socket outlets and portable equipment, 5 s for distribution and fixed equipment). Table 5.1 fixes the minimum earthing conductor and Table 8.1 publishes the corresponding maximum Zs values. AS 60038 sets the nominal voltage envelope (230 V +10% / −6%) that the 5% drop limit feeds into.

The six compliance checks

Cable selection requires more than one check. The calculator verifies current-carrying capacity with correction factors, voltage drop, short-circuit thermal withstand and earth-fault loop impedance/disconnection time. It also verifies protection coordination per AS/NZS 3000 Cl. 2.5.3.1 (Ib ≤ In ≤ Iz) and short-circuit breaking capacity at the device. Each check is reported with its own pass/fail pill in the result summary.

Capacity is the cable’s tabulated rating after the four derating factors are applied (ambient temperature k1, grouping k2, soil thermal resistivity k3 and depth of burial k4). The thermal withstand uses the adiabatic equation I²t ≤ k²S² on both the active and the earth conductor with the Table 52 k-value matched to the resolved insulation. The earth-fault loop impedance check computes Zs using the Cl. B4.5 simplified resistance method Zs = Ze + ((Ra + Re) × L) / 1000 and verifies Zs ≤ U₀ / Ia for the disconnection time required by Cl. 5.7.2.

Voltage drop split across the path

AS/NZS 3000:2018 Cl. 3.6.2 limits the total drop from the point of supply to any load to 5% of nominal when the supply comes from the network — 11.5 V on a 230 V single-phase circuit and 20 V line-to-line on a 400 V three-phase circuit. Where the point of supply is at a consumer-owned on-site substation the limit becomes 7%.

The total is a budget for the whole path. A conservative allocation that gives sensible headroom at the final outlet is roughly 1.0% on consumer mains, 1.5% to 2.0% on submains, and 2.0% to 2.5% on final subcircuits. The calculator’s Maximum Voltage Drop field is the per-segment limit you want this cable checked against.

Conductor, insulation and construction choices

Copper is the default in Australia. Aluminium is offered for large mains and submains (typically 70 mm² and above) where weight and cost favour it, but it has only ~60% of copper’s conductivity, cold-flows under terminal pressure, oxidises and reacts galvanically with copper. The calculator restricts the insulation menu to V-75, X-90 and R-90 when aluminium is selected because the 110 °C products are only manufactured in copper.

V-75 PVC is the calculator’s default for lighting, general power and small submains; the Auto rule selects V-75 for any size up to 16 mm². X-90 XLPE carries roughly 25–30% more current in the same cross-section with a higher Table 52 k-value (143 vs 115); Auto selects X-90 once the resolved cable is larger than 16 mm². The deciding factor in practice is termination temperature — most MCBs, switch-disconnectors and lug terminals are rated for 75 °C terminations, so even an X-90 cable has to be sized off the 75 °C column at those devices.

R-110 elastomeric is the calculator’s fire-rated option (R-HF-110 / R-E-110 halogen-free elastomeric circuit-integrity cables). When the section is flagged as essential safety the Insulation Auto rule resolves to R-110 directly. Construction Auto resolves to multi-core up to 95 mm² and single-core from 120 mm² upwards, with the earth integral by default.

Derating and installation methods

Switch the Apply Derating toggle on and the four AS/NZS 3008.1.1 correction factors fold in automatically: k1 for ambient air or soil temperature (Tables 25 and 27), k2 for grouping of circuits (Tables 22 to 24), k3 for soil thermal resistivity on buried cables (Table 28), and k4 for depth of burial (Table 29). Their product is the Total Derating Factor shown in the configuration panel — typically between 0.5 and 1.0 in real installations.

AS/NZS 3008.1.1 publishes the entire buried current carrying capacity table at a reference resistivity of 1.2 K·m/W. Most moist Australian soils sit around 1.5 K·m/W, dry sandy soils run 2.0 to 2.5 K·m/W, and crushed-rock or thermally enhanced sand can go below 1.0 K·m/W. Use the geotechnical report value or 1.5 K·m/W as a conservative default.

The Installation Method selector matches the AS/NZS 3008.1.1 method codes to the physical install. Unenclosed in air (M1–M4) covers tray, ladder or clipped direct; Enclosed in conduit (M5–M8) covers surface or in-wall conduit; Buried direct (M9) covers cables in a trench; and In underground enclosure (M10–M11) covers cables in buried conduits or ducts. Buried installations do not automatically mean smaller cables.

Short-circuit thermal withstand and earth-fault loop impedance

Short-circuit withstand tends to govern when prospective fault currents are high and the upstream protection has a relatively slow clearing time. Typical clearing-time presets are about 10 ms for an HRC fuse, 20 ms for a current-limiting MCB, 40 ms for a standard MCCB, 80 ms for an electronic-trip MCCB and 100 ms for an ACB. The adiabatic equation I²t ≤ k²S² is applied to both the active and the earth conductor with k from Table 52: 115 for copper PVC, 143 for copper XLPE/elastomer, 76 for aluminium PVC and 94 for aluminium XLPE.

For earth-fault loop impedance the calculator follows the AS/NZS 3000 Appendix B4.5 simplified resistance method. Zint = ((Ra + Re) × L) / 1000, Zs = Ze + Zint, and the pass condition is Zs ≤ U₀ / Ia with U₀ = 230 V. The trip current Ia is read from the linked Schneider Electric circuit protection database — Im for MCBs and thermal-magnetic MCCBs, Ii for electronic-trip MCCBs and ACBs, with a generic fuse fallback when no breaker record applies.

Earth conductor sizing and parallel runs

The minimum copper protective earthing conductor comes from AS/NZS 3000 Table 5.1: 1, 1.5 and 2.5 mm² actives keep an earth equal to the active; from 4 to 10 mm² the earth steps down; from 16 mm² upwards the earth is roughly half the active CSA rounded to the next standard size, capped at 120 mm² up to a 630 mm² active. The earth still has to pass the adiabatic check I²t ≤ k²S², which the calculator runs automatically and escalates the size if it fails.

For parallel runs, set the Parallel Runs stepper to the number of identical sets and the design current per run becomes Ib / n. AS/NZS 3000 Cl. 3.4.3 requires every run to be no smaller than 4 mm² and identical in length, cross-sectional area, conductor material and installation method. Parallel single-core runs are usually grouped and may also need the AS/NZS 3008.1.1 Table 22 grouping factor.

Fire-rated and essential-services cables

A fire-rated cable keeps circuit integrity for a specified period under fire exposure so the load it feeds keeps operating from the mains during evacuation. AS/NZS 3013 publishes the wiring system (WS) classification — e.g. WS52W combines a 1100 °C fire test with water spray and mechanical impact.

Fire rating is required where the load has no autonomous backup and must keep drawing mains power during the fire — fire pumps and sprinkler controls (AS 2941, AS 4214), mechanical services essential boards, emergency / fire-mode lifts, fire detection and EWIS / sound systems where the head-end has no on-board battery (AS 1670, AS 7240), and any other circuits the NCC designates as essential (Specification E1.5 / E2.2). Emergency and exit luminaires (AS/NZS 2293) and the FIP have integral batteries and do not require fire-rated cables.

The support system has to hold the cable in place for the full WS-rated duration. AS/NZS 3013 calls for stainless-steel ties or metallic clips, reduced fixing spacings of about 350 mm or less, tested fire-rated cleats matched to the cable family, and heavy-gauge steel trays with documented fire test results. Penetrations through fire-rated walls or floors must use a tested seal.

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 standards does the ElecAS cable size calculator use?: AS/NZS 3008.1.1:2025 supplies the current carrying capacity tables (Tables 3–21), derating factors (Tables 22–29), conductor R and X values for voltage drop (Tables 30–39) and short-circuit k-values (Table 52). AS/NZS 3000:2018 drives compliance — Cl. 2.5.3.1 protection coordination, Cl. 3.4 minimum sizes, Cl. 3.6.2 voltage drop limits (5% from the network, 7% from an on-site substation), Cl. 5.7.2 disconnection times, Appendix B4.5 simplified Zs method, Table 5.1 earth conductor sizing and Table 8.1 maximum Zs. AS/NZS 3013 covers fire-rated wiring systems and AS 60038 sets the 230 V +10% / -6% voltage envelope.
What checks does the cable size calculator run?: Six checks on every result: (1) current carrying capacity after k1·k2·k3·k4 derating; (2) protection coordination Ib ≤ In ≤ Iz per AS/NZS 3000 Cl. 2.5.3.1; (3) voltage drop against your per-segment limit and the Cl. 3.6.2 envelope; (4) device breaking capacity against the prospective fault current; (5) the adiabatic I²t ≤ k²S² short-circuit thermal withstand check on both the active and the earth conductor using AS/NZS 3008.1.1 Table 52 k-values; and (6) earth-fault loop impedance using the AS/NZS 3000 Appendix B4.5 simplified resistance method against the Cl. 5.7.2 disconnection time.
How much voltage drop is allowed under AS/NZS 3000, and how do I split it across consumer mains, submain and final subcircuit?: AS/NZS 3000:2018 Cl. 3.6.2 limits the total drop from the point of supply to any load to 5% of nominal when the supply comes from the network — 11.5 V on a 230 V single-phase circuit and 20 V line-to-line on a 400 V three-phase circuit. Where the point of supply is at a consumer-owned on-site substation the limit becomes 7%. The total is a budget for the whole path, not a per-segment limit. A conservative allocation is roughly 1.0% on consumer mains, 1.5% to 2.0% on submains, and 2.0% to 2.5% on final subcircuits. The calculator’s Maximum Voltage Drop field is the per-segment limit checked against this cable.
What voltage drop limit applies to consumer mains in Australia?: AS/NZS 3000 Cl. 3.6.2 does not publish a separate limit for consumer mains — the 5% total (or 7% from an on-site substation) applies from the point of supply to the load. Designers conventionally hold the mains segment to roughly 1.0% so the submain and final subcircuit downstream still have room to comply. The calculator checks whatever per-segment allowance you enter and the result still has to satisfy the appliance operating-voltage range once it is combined with the rest of the path.
Does cable temperature affect voltage drop?: Yes — copper resistance rises about 0.4% per °C, and AS/NZS 3008.1.1 publishes its impedance Tables 30 to 39 at the maximum continuous operating temperature of each insulation class. The calculator picks the correct row automatically once you select the insulation: 75 °C values for V-75 PVC, 90 °C values for X-90 XLPE and R-90 elastomer, and 110 °C values for X-110 XLPE and R-110 elastomer. Voltage drop on a fully loaded XLPE cable is therefore a few percent worse than the same conductor sized in PVC because the conductor is hotter at design current.
Should I use worst-case PF or the actual power factor for voltage drop?: AS/NZS 3008.1.1 publishes two methods and the calculator offers both via the Worst Case PF toggle. With it on (the default) the cable component is the full impedance Zc = √(R² + X²) — conservative and bounded regardless of the load plant that ends up connected, suitable for distribution boards, mains and mixed loads. With the toggle off the calculator uses the actual-PF projection Vc = R·cosφ + X·sinφ from the entered power factor; real loads at lagging PF give a smaller drop than the worst-case envelope, allowing tighter sizing where the load PF is known and stable (a single dedicated motor, VFD or large fixed plant).
How is voltage drop calculated for single-phase vs three-phase cables?: The base formula is the same: Vd = (L × Ib × Vc) / 1000, with L in metres, Ib in amps and Vc the cable’s mV/A·m factor. What changes is the multiplier baked into Vc to account for the loop. On single-phase circuits the current returns through the neutral, so Vc = 2·Z. On three-phase line-to-line drop the geometry gives Vc = √3·Z. The calculator picks the correct factor automatically from the Phases selector at the top of the configuration panel.
What size cable do I need for a 32A circuit in Australia?: For a 32 A circuit, 4 mm² copper V-75 may be suitable under common installation conditions — for example single-phase, Method M5 (enclosed in conduit on a wall) at reference ambient and grouping — but this is not universal. A three-phase 32 A circuit derates further because three conductors are loaded, and longer runs or tighter voltage-drop allowances often push the result up a size. Re-run the calculator for your actual phasing, length, ambient temperature and grouping, then verify short-circuit withstand and Zs against the upstream device.
What size cable do I need for a 63A circuit?: Reference: copper, three single-cores in conduit on a wall (Method M5). V-75 PVC copper typically lands at 16 mm² for capacity; X-90 XLPE copper can drop to 10 mm² subject to terminal temperature ratings. Buried installations do not automatically mean smaller cables: direct-buried (M9) only outperforms M5 at the AS/NZS 3008.1.1 reference soil resistivity of 1.2 K·m/W and shallow burial. Most Australian soils sit at 1.5–2.5 K·m/W which derates buried capacity significantly, and buried-in-enclosure (M10) ratings are often similar to or lower than M5. Re-run the calculator with your actual soil resistivity, depth and grouping.
What size cable do I need for a 100A submain?: A 100 A copper submain typically falls around 25–35 mm² depending on installation method, insulation type, conductor arrangement and derating. Three single-core copper V-75 cables in conduit on a wall (Method M5) at reference conditions usually land at 35 mm² for capacity. Aluminium will generally require a larger size (around 70 mm² in the same scenario since 50 mm² aluminium does not meet 100 A in M5). Voltage drop becomes the governing constraint on long runs or where the upstream allowance is tight.
What size cable for a 200A consumer mains?: Reference: three single-cores in conduit on a wall (Method M5). Copper V-75 PVC lands at 95 mm² for capacity; copper X-90 XLPE can drop to 70 mm² subject to terminal temperature ratings; aluminium V-75 PVC steps up to 150–185 mm² (120 mm² aluminium falls short of 200 A in M5). Voltage drop on long mains often governs — keep this segment to about 1% allowance to leave room for the submain and final subcircuit.
How do I derate a cable for grouping and ambient temperature?: Switch the Apply Derating toggle on and the calculator pulls all four AS/NZS 3008.1.1 correction factors at once: k1 for ambient air or soil temperature (Tables 25 and 27), k2 for grouping of circuits (Tables 22 to 24), k3 for soil thermal resistivity on buried cables (Table 28) and k4 for depth of burial (Table 29). Their product is the Total Derating Factor shown in the configuration panel — typically between 0.5 and 1.0 in real installations. The calculator sizes the cable so Iz_actual = Iz_table × k1 × k2 × k3 × k4 stays at or above the design current Ib.
When does grouping derating apply?: Grouping derating from AS/NZS 3008.1.1 Tables 22 to 24 applies whenever multiple loaded cables run in close proximity — bunched in a conduit, on a tray, in an enclosed run or tied together — because each cable raises the temperature of its neighbours and reduces the heat the conductor can dissipate. Switch on the Grouping sub-toggle, set the Number of Circuits to the actual number of loaded circuits in the group, and pick the matching arrangement (bunched in air, single layer on a tray, multilayer, or buried) — the calculator pulls the correct factor and folds it into k2. Spacing of at least one cable diameter between adjacent cables avoids the derating entirely on most installation methods.
Why does soil thermal resistivity matter for buried cables?: A buried cable dissipates the heat from its losses through the surrounding soil. The higher the soil’s thermal resistivity, the more poorly it conducts that heat away, and the hotter the cable runs at any given current. AS/NZS 3008.1.1 publishes the entire buried current carrying capacity table at a reference resistivity of 1.2 K·m/W; Table 28 gives the k3 correction for any value above or below that. Most moist Australian soils sit around 1.5 K·m/W, dry sandy soils run from 2.0 to 2.5 K·m/W, and crushed-rock backfill or thermally enhanced sand can go below 1.0 K·m/W. Use the geotechnical report value or 1.5 K·m/W as a conservative default.
Which AS/NZS 3008.1.1 installation method should I select?: The Installation Method selector matches the AS/NZS 3008.1.1 method codes to the physical install. Pick Unenclosed in air (Methods M1 to M4) for cables on a tray, ladder or clipped direct to a wall, with sub-options for spaced or touching arrangements; Enclosed in conduit (Methods M5 to M8) for surface or in-wall conduit and trunking; Buried direct (Method M9) for cables laid in a trench with controlled backfill; and In underground enclosure (Methods M10 to M11) for cables drawn into buried conduits or ducts. Buried installations do not automatically mean smaller cables — buried direct only outperforms an in-air install at reference resistivity and shallow burial.
Copper vs aluminium — which conductor should I size with?: Copper is the default in Australia. It has higher conductivity for the same cross-section, better mechanical and fatigue strength, and terminates cleanly into standard lugs without specialist preparation. Aluminium is genuinely useful on large mains and submains (typically 70 mm² and above) where lower weight and cost outweigh the drawbacks, but it has only ~60% of copper’s conductivity (one or two sizes larger for the same current), cold-flows under terminal pressure demanding torque-controlled lugs and anti-oxidation paste, oxidises with a poorly-conducting oxide layer, and reacts galvanically with copper so any aluminium-to-copper joint needs a bimetallic lug. The calculator restricts the insulation menu to V-75, X-90 and R-90 when aluminium is selected because the 110 °C products are only manufactured in copper.
V-75 (PVC) vs X-90 (XLPE) — which insulation should I pick?: V-75 PVC runs at 75 °C and is the cheapest construction; the calculator’s Auto rule selects V-75 for any size up to 16 mm². X-90 XLPE runs at 90 °C, carries roughly 25 to 30% more current in the same cross-section, and has a higher Table 52 k-value (143 vs 115 for copper) — Auto selects X-90 once the resolved cable is larger than 16 mm². The deciding factor in practice is termination temperature: most MCBs, switch-disconnectors and lug terminals are rated for 75 °C terminations, so even an X-90 cable has to be sized off the 75 °C column at those devices.
What is cable insulation and what does it do?: The insulation is the dielectric layer surrounding each conductor. It prevents leakage between conductors and to earth at the operating voltage, sets the maximum continuous conductor temperature (which together with the installation method fixes the AS/NZS 3008.1.1 current carrying capacity), and sets the short-circuit k-value used in the Table 52 adiabatic check. The five Australian insulation classes are V-75 (PVC 75 °C), X-90 (XLPE 90 °C including X-90UV and X-HF-90 halogen-free variants), R-90 (Elastomeric 90 °C including R-EP-90, R-CPE-90 and R-HF-90), X-110 (XLPE 110 °C, X-HF-110 form), and R-110 (Elastomeric 110 °C, R-HF-110 and R-E-110 forms — the fire-rated option). The 110 °C options are only available with copper conductors.
How do I select the right cable insulation?: Leave the Insulation selector on Auto and the calculator resolves V-75 PVC for any cable up to 16 mm² and X-90 XLPE above 16 mm² — the same convention most contractors and suppliers default to. If the section is flagged as essential safety, Auto resolves to R-110 elastomeric instead. Pick V-75 manually for general dry fixed wiring at 40 °C indoor ambients. Pick X-90 when capacity is tight, ambient is elevated, the run is heavily grouped, or you want the ~25 to 30% capacity uplift. Pick R-90 elastomeric for industrial, vibration-prone or harsh-environment runs. Pick X-110 when 90 °C XLPE is still capacity-limited. Pick R-110 for fire-rated and critical-service circuits. Always verify the terminal temperature rating of the upstream and downstream device.
How do I choose the number of cores for a cable?: The Construction selector filters automatically once you set Phases. Single-phase offers four constructions: 2C+E (active, neutral, integral earth), 2C (active and neutral with a separate earth), 2x1C+E and 2x1C single-cores. Three-phase offers six: 4C+E (three actives, neutral, integral earth — for any submain or consumer main feeding single-phase loads), 3C+E (three actives plus earth — balanced three-phase loads such as motors), 4C (separate earth), and the corresponding single-core layouts (4x1C+E, 3x1C+E, 4x1C). Auto resolves to multi-core up to 95 mm² and single-core from 120 mm² upwards, with the earth integral by default.
Single-core vs multi-core cables — which should I pick?: Multi-core cables carry every conductor inside one outer sheath, which is easier to install, identify and terminate, fits cleanly through conduits, and ensures the conductors take the same path. The calculator’s Auto rule picks multi-core for any cable up to 95 mm². Single-core cables run each conductor in its own jacket — Auto switches to this from 120 mm² upwards because multi-core becomes physically unwieldy at those sizes and parallel runs (which AS/NZS 3000 Cl. 3.4.3 only allows on identical single-cores) become more common. For single-cores the Cable Arrangement selector lets you pick trefoil, flat-touching or flat-spaced; the calculator pulls the correct R and X values from the matching AS/NZS 3008.1.1 impedance table.
What is a fire-rated cable, and when is it required?: A fire-rated cable keeps circuit integrity for a specified period (typically 30, 60, 90 or 120 minutes) under fire exposure so the load it feeds keeps operating from the mains during evacuation. AS/NZS 3013 publishes the wiring system (WS) classification — e.g. WS52W combines a 1100 °C fire test with water spray and mechanical impact. Fire rating is required where the load has no autonomous backup and must keep drawing mains power during the fire — fire pumps and sprinkler controls (AS 2941, AS 4214), mechanical services essential boards, emergency / fire-mode lifts, fire detection and EWIS / sound systems where the head-end has no on-board battery (AS 1670, AS 7240), and any other circuits the NCC designates as essential (Spec E1.5 / E2.2). Emergency and exit luminaires (AS/NZS 2293) and the FIP have integral batteries and do not require fire-rated cables. The ElecAS calculator sizes fire-rated cables as 110 °C elastomeric (R-110).
Do I need a fire-rated cable tray or support system?: Yes. When the circuit is fire-rated the support system has to hold the cable in place for the full WS-rated duration — standard galvanised tray or PVC saddles lose structural integrity in minutes and the cable will fall before its insulation fails. AS/NZS 3013 calls for stainless-steel ties or metallic clips (PVC ties are prohibited), reduced fixing spacings of about 350 mm or less, tested fire-rated cleats matched to the cable family, and heavy-gauge steel trays with documented fire test results. Penetrations through fire-rated walls or floors must use a tested seal (intumescent collar, mortar or pillow) so the wall’s FRL is preserved. The fire-resisting integrity is only as good as the weakest link — cable, support, fixing, penetration seal and termination must all carry the specified rating.
What is the WS classification on a cable, and what does it mean?: WS stands for Wiring System under AS/NZS 3013, and the code summarises three combined tests applied to the entire system rather than the cable alone. The W component is the fire test (subscript X = no fire, Y = lower-temperature exposure, Z = full 1100 °C exposure), the S component is the water-spray test, and the trailing numeral is the mechanical impact rating. Common designations on Australian projects include WS51W and WS52W (1100 °C fire combined with water spray and mechanical impact, longer duration on WS52W) and WS3X (mechanical impact only, no fire). The project’s fire engineering report specifies the required WS rating per circuit, and the cable, support system, cleats and terminations all have to meet or exceed that rating.
When is short-circuit thermal withstand the limiting factor?: Short-circuit withstand tends to govern when prospective fault currents are high (close to the supply transformer or downstream of a large on-site substation) and the upstream protection has a relatively slow clearing time. The calculator’s Source Fault Current field carries the prospective Isc at the location of the cable, and Fault Clearing Time is the duration the protection takes to interrupt that fault — typical presets are about 10 ms for an HRC fuse, 20 ms for a current-limiting MCB, 40 ms for a standard MCCB, 80 ms for an electronic-trip MCCB and 100 ms for an ACB. The check is the adiabatic equation I²t ≤ k²S² on both the active and the earth conductor, with k from Table 52: 115 for copper PVC, 143 for copper XLPE/elastomer, 76 for aluminium PVC and 94 for aluminium XLPE.
How does the calculator check earth-fault loop impedance under AS/NZS 3000?: The calculator follows the simplified resistance method in AS/NZS 3000 Appendix B4.5. The cable contribution is Zint = ((Ra + Re) × L) / 1000, where Ra is the active conductor resistance and Re the earth conductor resistance per kilometre at operating temperature, and L is the route length in metres. The total loop impedance is Zs = Ze + Zint, with Ze the external impedance of the supply (default 0.35 Ω for residential or 0.02 Ω for an on-site substation). The pass condition is Zs ≤ U₀ / Ia with U₀ = 230 V and Ia from the linked Schneider Electric breaker database — Im for MCBs and thermal-magnetic MCCBs, Ii for electronic-trip MCCBs and ACBs, with a generic fuse fallback. The disconnection time required by Cl. 5.7.2 is 0.4 s for socket outlets up to 63 A and portable equipment, and 5 s for fixed and distribution circuits.
What size earth conductor do I need?: The minimum copper protective earthing conductor comes from AS/NZS 3000 Table 5.1. The calculator’s Earth Conductor selector defaults to Auto and applies the table directly: 1, 1.5 and 2.5 mm² actives keep an earth equal to the active; from 4 to 10 mm² the earth steps down (a 6 mm² active resolves to 2.5 mm² earth, a 10 mm² active to 4 mm² earth); from 16 mm² upwards the earth is roughly half the active CSA rounded to the next standard size (50 → 25 mm², 95 → 50 mm², 240 → 120 mm²) with the earth capped at 120 mm² up to a 630 mm² active. Above 630 mm² the rule shifts to 25%. Aluminium actives step up one size. Table 5.1 is only the minimum — the earth still has to pass the adiabatic check I²t ≤ k²S², which the calculator runs automatically and escalates the size if it fails.
What is the smallest cable allowed under AS/NZS 3000?: Minimum conductor sizes depend on the circuit type, conductor material, wiring system and mechanical protection. From AS/NZS 3000:2018 Table 3.3 and common Australian practice: lighting final subcircuits are typically 1.0 mm² copper minimum, and socket-outlet final subcircuits are typically 2.5 mm² copper minimum. Signal and relay control circuits can drop to 0.5 mm² and flexible cords to 0.75 mm²; aerial wiring is 6 mm² copper or 16 mm² aluminium. Submains and consumer mains are not in Table 3.3 — their size is driven by capacity, voltage drop, short-circuit withstand and Zs, but practical minimums still apply (consumer mains typically not less than 16 mm² copper or 25 mm² aluminium under most utility service rules). The calculator’s standard size set runs from 1 mm² to 630 mm² in the AS/NZS 3008 preferred series.
How do I size a cable for a three-phase motor?: Take the motor full-load current from the nameplate (not the locked-rotor or starting current — protection device coordination handles those transients) and enter it into the Design Current field. For continuous-duty motors a common convention is to size on roughly 1.25 × FLA to allow for sustained running, but the actual design current depends on duty cycle, overload protection, starting method, installation conditions and the AS/NZS 3000 Section 4 motor requirements. Set Phases to 3 and Construction to 3C+E or 3x1C+E (no neutral for a balanced three-phase motor). Voltage drop on the longest motor run is usually the governing constraint, especially for soft-started or VFD-fed motors where excessive volt drop also worsens torque output and starting performance.
How do I handle parallel cable runs?: Set the Parallel Runs stepper to the number of identical sets and the design current per run becomes Ib / n; the calculator picks a cable that, multiplied back by n, satisfies the loading. AS/NZS 3000 Cl. 3.4.3 (capacity) and Cl. 3.6.3 (voltage drop) require every run to be no smaller than 4 mm² and identical in length, cross-sectional area, conductor material and installation method, which ensures the current actually shares evenly. The earth conductor has its own parallel-runs stepper. Parallel single-core runs are usually grouped and may also need the grouping derating from AS/NZS 3008.1.1 Table 22 — switch on Apply Derating and the calculator pulls the matching factor automatically.
Which MCB protective device curve should I use — B, C or D?: The MCB curve sets the magnetic instantaneous trip threshold the calculator uses for its earth-fault loop impedance check. Curve B trips at 3–5× In and suits resistive loads and lighting. Curve C trips at 5–10× In and is the general-purpose default. Curve D trips at 10–20× In and is reserved for transformers, motors and other loads with high inrush that would nuisance-trip a C curve. The compliance trade-off comes through Ia in Zs ≤ U₀ / Ia: a higher curve raises Ia, which lowers the maximum permissible Zs and tightens the earth-fault loop impedance constraint. If a C-curve passes Zs and a D-curve does not, you usually need to drop a curve, increase the cable size to lower Zs, or switch to an electronic-trip device.
Does the calculator handle four-core cables and neutral derating?: Yes. The Construction selector covers four single-phase layouts (2C+E, 2C, 2x1C+E, 2x1C) and six three-phase layouts (4C+E, 3C+E, 4C, 4x1C+E, 3x1C+E, 4x1C). For a balanced three-phase load with no neutral — most three-phase motors — pick a 3C+E or 3x1C+E construction; for any submain feeding single-phase loads downstream pick a 4C+E or 4x1C+E so a neutral is included. The calculator counts loaded conductors when it pulls the AS/NZS 3008.1.1 capacity table — three loaded actives in a 4C+E cable are rated lower than two loaded actives in a 2C+E. Where the load is harmonic-rich (LED lighting, drives, IT equipment), AS/NZS 3008.1.1 requires the neutral to be treated as a current-carrying conductor; keep a 4C construction and accept the four-loaded-conductor rating.
Is the ElecAS cable size calculator free?: Yes — the AS/NZS 3008.1.1:2025 cable size calculator runs entirely in your browser, with no account required for the standard workflow, and the cable selection report exports as a PDF you can attach to the project documentation. Project metadata (project name, number, address, designer, revision) is captured at the top of the page and flows into the exported report so the PDF is ready to issue.