International Cable Sizing Calculator

Method & Assumptions

Cable sizing determines the minimum conductor cross-section that carries the design current (Ib) without exceeding the conductor's rated maximum temperature. The derated ampacity must satisfy:

Ib ≤ Iz′ = Iz × Ca × Cg

Where:

  • Iz — tabulated base ampacity at reference conditions (A)
  • Ca — ambient temperature correction factor
  • Cg — grouping (bunching) derating factor

Supported standards:

  • IEC 60364-5-52:2009 — International, reference ambient 30 °C. Ampacity tables from Annex B (Tables B.52.2–B.52.9). Temperature correction from Table B.52.14. Grouping factors from Table B.52.17.
  • BS 7671:2018 (18th Edition) — UK wiring regulations. Base ampacity tables are identical to IEC 60364-5-52 Annex B (Tables 4D1A–4E4A in Appendix 4). Reference ambient 30 °C.
  • AS/NZS 3008.1.1:2017 — Australia and New Zealand. Independent ampacity tables at reference ambient 40 °C (Tables 7, 8). Temperature correction from Table 27.

Installation methods:

  • B2 — Multicore cable in conduit on wall or surface trunking. Grouping factor from enclosed-conduit table.
  • C — Single layer multicore cable clipped direct to a non-metallic surface (wall, structure).
  • E — Multicore cable in free air on a ventilated cable tray.
  • F — Single-core cables touching in trefoil in free air.

Aluminium conductors: available in 16 mm² and above only. Values are from the published standard tables and are typically 75–82% of equivalent copper ratings.

Limitations: This tool covers the single-cable ampacity check. Voltage drop, short-circuit withstand, and protection coordination require separate analysis. Ground burial (Method D1/D2) and harmonic derating are not included in this calculator. Values are representative — always verify against the current edition of the applicable standard before final design.

Citations: IEC 60364-5-52, BS 7671:2018, AS/NZS 3008.1.1

See also: Cable Schedule, Tray Fill.

Standard & Installation Method

Select the standard that governs cable sizing for your project jurisdiction. IEC 60364 is the international baseline; BS 7671 applies in the UK; AS/NZS 3008 applies in Australia and New Zealand.

How the cable is installed affects heat dissipation and therefore rated current. Method C (clipped) and E (free air) allow more current than B2 (in conduit). Refer to the Method & Assumptions panel above for detailed definitions.

Three-phase circuits carry 3 current-carrying conductors; single-phase circuits carry 2. Balanced three-phase neutral currents are zero and are not counted.

Conductor Parameters

Aluminium conductors are approximately 78–82% of the equivalent copper rating. Aluminium is only available from 16 mm² upwards.

90 °C thermosetting insulation (XLPE or EPR) allows higher continuous current than 70 °C thermoplastic (PVC) for the same conductor size.

Design Conditions

The maximum continuous operating current the cable must carry. For motors, use the full-load current. For feeders, use the maximum demand current.

Higher ambient temperatures reduce the allowable cable current. Leave blank to use the standard reference temperature.

Number of cables or circuits bundled together in the same conduit, tray, or trunking. Each additional circuit reduces the allowable current due to mutual heating. Enter 1 for a single isolated cable.

Calculation Mode