Cable Size Calculator (IEC 60364-5-52)
Inputs
Result
Smallest metric size that covers the loadHow the size was chosen
- Reference installation methodCRef: IEC 60364-5-52:2009, Table B.52.5 (air, 30°C reference)
- Tabulated capacity of 4 mm² at the reference conditions40 ARef: IEC 60364-5-52:2009, Table B.52.5 (air, 30°C reference)
- Ambient temperatureCorrection factor x 1 (reference 30°C, air).Ref: IEC 60364-5-52, Table B.52.14
- GroupingGrouping factor x 1 for 1 circuits.Ref: IEC 60364-5-52, Table B.52.17
- Corrected capacity40 A
- Load to cover32 A
Export
The PDF contains your inputs, the result, the verdict, the formula with the values substituted, and the code reference for every step. No signup, no watermark, nothing held back.
Tabulated capacities with the ambient temperature and grouping corrections applied. Values are taken from IEC 60364-5-52:2009. The 2024 consolidated edition has not been checked for changes to these tables — verify against the edition in force where the installation will be inspected.
The installation method decides the answer
The same cable carries noticeably less current in insulation than it does clipped to a masonry wall, because heat has nowhere to go. The reference methods name those situations, and the standard assigns one from the actual installation rather than letting you pick the flattering one. Choosing a method one step too generous is the most common way a metric cable size comes out too small.
| Method | In plain terms |
|---|---|
| A1 | Insulated conductors or single-core cables in conduit inside a thermally insulated wall |
| A2 | Multicore cable in conduit inside a thermally insulated wall |
| B1 | Insulated conductors or single-core cables in conduit on a wooden or masonry wall |
| B2 | Multicore cable in conduit on a wooden or masonry wall |
| C | Single-core or multicore sheathed cable fixed directly to a wooden or masonry wall |
| D1 | Single-core or multicore cable in an underground conduit or duct |
| D2 | Sheathed single-core or multicore cable laid direct in the ground |
The A and B cases differ by what is carrying the heat away, and each pair splits on whether the cable is a single-core conductor or a multicore cable — which is why the same nominal size appears twice with different numbers. If you work to BS 7671 you will know the buried cases as reference method D; the IEC tables split that into D1 and D2, so check which one your installation matches before reading a value.
Two further corrections sit on top of the tabulated value: ambient temperature, and grouping when several loaded circuits share a route. Both are applied here for cables in air, so a PVC cable at 45 degrees, or six circuits bunched together, is selected several sizes larger than the same cable on its own at 30 degrees.
Buried installations use a different pair of tables. The temperature correction is taken from the soil table rather than the air one — at 30°C soil the PVC factor is 0.89, against 1.00 in 30°C air; the 0.94 figure is the 35°C air factor — and the grouping correction depends on how far apart the buried circuits are laid, with separate tables for D1 and D2. The tabulated values assume a soil thermal resistivity of 2.5 K·m/W and a burial depth of 0.7 m. If the ground is drier, sandier or hotter than that, the real capacity is lower and even the corrected result here is optimistic.
Voltage drop is a separate check. The standard's guidance (clause 525 and the table in Annex G) is 3% for lighting and 5% for other loads on an installation supplied from the public low-voltage network, and 6% and 8% where the supply is from a private source. A cable that satisfies the tabulated capacity can still fail on a long run.
What this tool will not do
- It will not convert an NEC ampacity into an IEC capacity, or the other way round. The two tables rest on different assumptions.
- It will not estimate a value outside the range that has been checked. The standard tabulates some aluminium sizes below 16 mm²; this tool has not checked those cells, so they are unavailable rather than guessed. Grouping beyond the tabulated circuit counts is treated the same way.
- It will not guess outside the tables. A soil temperature or a circuit spacing that the standard does not tabulate comes back as no answer, not as an estimate.
- It will not decide the installation method for you. That comes from the run itself, not from the load.
Frequently asked
- What is the difference between an IEC current rating and an NEC ampacity?
- They are not interchangeable. An IEC tabulated capacity depends on the reference installation method, the insulation and the number of loaded conductors, and assumes air at 30 degrees with a single circuit. An NEC ampacity starts from a base table for the conductor and insulation, then applies ambient and conductor-count adjustment factors before the termination limit caps it. The two systems also step through different size series. Use the table that belongs to the standard your installation is inspected against.
- Which reference installation method should I choose?
- The method is assigned by the installation, not chosen for convenience. A1 and A2 cover conductors or cables enclosed in thermal insulation, B1 and B2 cover conduit or trunking on a wall, and C covers cable clipped direct. Two runs that look similar can fall under different methods — for example a cable in a conduit buried in insulation is not the same as the same cable in conduit on a masonry wall — and the tabulated capacity can differ by 30% or more.
- Are ambient temperature and grouping corrections applied?
- Yes, from whichever table matches the installation. In air the ambient factor comes from the air table — 1.00 at 30 degrees, about 0.79 at 45 degrees on PVC — and the grouping factor from the arrangement and the number of circuits, where six bunched circuits cost 43% of the capacity. Buried methods use the soil table for temperature, which is not the same curve, and the buried grouping tables, which depend on the spacing between circuits and differ between D1 and D2. Where a temperature or a spacing is outside the tabulated range the calculator refuses to answer rather than extrapolate.
- What voltage drop does the IEC standard expect?
- Clause 525 refers to a table in Annex G that suggests 3% for lighting and 5% for other loads where the installation is supplied directly from the public low-voltage network, rising to 6% and 8% where the supply comes from a private source. The note adds that final circuits should stay within the lower figures where possible, and allows a small relaxation on main runs longer than 100 m. These are recommendations rather than mandatory limits, so a specification can be tighter.
- Why does the calculator refuse to answer for some combinations?
- Because only the combinations that have been cross-checked against the published tables are offered. IEC 60364-5-52 Tables B.52.2 to B.52.5 do tabulate some aluminium sizes from 2.5 mm², but this calculator includes aluminium only from 16 mm² upward. Smaller aluminium sizes, and grouping beyond the tabulated circuit counts, are reported as unavailable rather than guessed.
Related
Educational information only — not professional engineering advice. Tabulated values are taken from the published IEC tables and are pending review against the edition in force in your area.