IEC standards behind the calculations
Every calculator on this site implements the method of a published standard. These pages explain what each standard covers, which quantities it defines, and which clause and formula a calculation actually uses — so a number produced here can be traced back to the document it came from and defended in a design review.
Written up in full
- 60909 IEC 60909 — short-circuit current calculation The equivalent voltage source, the voltage factor c of Table 1, transformer correction KT, I″k by Formula (33), peak current by the three methods of 8.1.2, thermal equivalent current, and why the minimum current is a different calculation.
- 60364-5-52 IEC 60364-5-52 — wiring systems, cable selection and voltage drop Maximum operating temperatures of Table 52.1, the reference installation methods of Annex A, the current-carrying capacity tables of Annex B, the correction factors, and the voltage-drop formula and limits of Annex G.
- 60287 IEC 60287 — continuous current rating of cables The thermal model: the temperature-rise equation of clause 1.4, conductor a.c. resistance, dielectric and sheath losses, and the thermal resistances T1 to T4 of Part 2-1.
- 60947-2 IEC 60947-2 — circuit-breakers The ratings a fault current is compared against: Icu, Ics, Icw with the minimum values of Table 3, the making capacity, and selectivity categories A and B.
Also implemented in the calculators
These standards are used by the tools and cited inside them; their own pages are being written.
| Standard | Subject | Used by |
|---|---|---|
| IEC 60364-4-41 | Protection against electric shock; disconnection times of Table 41.1 | #012 |
| IEC 60364-5-54 | Earthing arrangements and protective conductors | #SDK |
| IEC 60228 | Conductors of insulated cables — resistance classes | #004, #001 |
| IEC 60502-2 | MV cables 6 kV to 30 kV | #001, #004 |
| IEC 60949 | Short-circuit current rating of cables, adiabatic and non-adiabatic | #004 |
| IEC 60076 (−1, −5) | Power transformers: loss tolerances, impedance bands | #010 |
| IEC 60034-1, 60034-30-1 | Rotating machines: site conditions, efficiency classes IE1 to IE4 | #009 |
| IEC 60072-1 | Preferred machine output ratings | #009 |
| IEC 60831, IEC 61921 | Shunt capacitors and capacitor banks | #005 |
| IEC 61869-2, IEEE C57.13 | Current transformers | #006 |
| IEC 62305 (−1, −2) | Lightning protection and risk management | #013, #003 |
| IEC 62548, IEC 61215 | PV array design; module qualification | #011 |
| IEC 60721, IEC 60826 | Environmental classes; extreme-value method for design conditions | #014 |
| IEEE Std 80 | Substation earthing: touch and step voltage | #003 |
The standards applied as an algorithm
A standard tells you what a cable has to satisfy. It does not tell you in which order to apply the checks, or which of them will bind. These four pages do: one flowchart per voltage class, with every decision node cited to the clause it comes from.
- LV LV cable selection algorithm, up to 1 kV IEC 60364-5-52, 60364-4-43, 60364-4-41 and 60364-5-54 in one sequence.
- MV MV cable selection algorithm, 1 to 36 kV IEC 60502-2, 60183, 60287, 60949, 60986 and 61936-1.
- HV HV cable selection algorithm, above 36 kV IEC 60840, 62067, 60183, 60287, 60853 and 60071-1.
- DC DC cable selection algorithm, PV and battery IEC 62548, 60364-7-712, 60364-5-52 and 60287.
How to read these pages
Each standard page answers the same questions in the same order: what the standard is, when it applies, which quantities it defines, the formula for each one with its clause number, what input data the calculation needs, the workflow, a worked example where the standard publishes one, and the calculators that implement it.
What these pages deliberately do not contain is the text of the standards. A standard is a copyrighted document, and a summary is no substitute for it — if you calculate for a living, buy the document from IEC or IEEE. What is quoted here are clause numbers, formula numbers and the individual values a calculation needs, so you can check them against your own copy.
How the implementations are checked against the standards' own published values is on the validation page; the rules every engine follows are on the methodology page.