Cable Derating & Sizing Calculator (IEC 60364-5-52)
Full IEC 60364-5-52 cable derating calculator: 12 reference installation methods, ambient/ground temperature correction, soil resistivity, grouping factors for trays/bunched/buried ducts, Annex D curve-fit base ampacities (PVC / XLPE, Cu / Al, 2 or 3 loaded), harmonic derating per Annex E, smallest mm² cross-section and nearest AWG equivalent, with the full factor chain and printable copy.
Cable Derating & Sizing Calculator
Pick the installation method, set the conditions, get the corrected ampacity and the smallest cross-section that carries the load.
Circuit
Installation method
Conditions
Reference is 30 °C
Harmonics and extra factors
Four-core and five-core cables, three loaded conductors
Anything the standard does not cover: tray tiers, enclosure, solar gain
- Required tabulated Iz
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- Total derating
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- Corrected capacity
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- Nearest AWG
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| mm² | Tabulated Iz | Corrected | AWG |
|---|
Base capacities are computed from the curve-fit formula the standard publishes for its own tables, so values may differ from a printed table by a fraction of an ampere at the smallest sizes. Correction factors between tabulated temperatures are interpolated. Voltage drop, short-circuit withstand and protective device coordination are separate checks.
Overview
IEC 60364-5-52 is the European / IEC reference for low-voltage cable sizing. Most of the work is not the cross-section itself — it is the stack of derating correction factors that fold ambient temperature, grouping, burial, soil resistivity and harmonic content back into the tabulated ampacity Iz.
This calculator uses the Annex D curve-fit formulas the standard itself publishes for its own printed tables (PVC 70 °C and XLPE/EPR 90 °C, copper or aluminium, 2 or 3 loaded conductors). Correction factors come from Annex B: ambient or ground temperature (interpolated between tabulated rows), grouping arrangements (bunched / unperforated tray / perforated tray / ladder / cleats, and a separate buried-duct table with clearance), soil thermal resistivity ρ, plus harmonic sizing from Annex E when third-harmonic content exceeds 15 %.
Run it after cable sizing to refine the first estimate into a formally-derated selection, then push the chosen mm² into voltage drop for the Annex G / NEC drop check. Copy button on the result panel produces a single-line summary you can paste straight into a calculation note.
How it works
- 1. Set base circuitDesign current I_B, loaded conductors (2 for single-phase, 3 for three-phase) and choose insulation (PVC 70 °C or XLPE/EPR 90 °C) + material (Cu / Al).
- 2. Pick the IEC reference methodTwelve methods (A1/B1/A2/B2 to C/G2) — for buried and ducts the ground + soil inputs appear automatically, for others it is ambient air.
- 3. Apply grouping and conditionsNumber of grouped circuits (or ducts) and the arrangement (bunched, tray types, ladder, cleats, or buried D1 ducts with clearance); optionally add harmonic h3 and an extra C-extra safety factor.
- 4. Walk standard sizes and copyThe tool walks IEC 60364 nominal sizes 1.5 … 630 mm², finds the smallest Iz · Ct·Cg·Cs·Ch·Cextra ≥ I_B, highlights the row and maps the nearest AWG/kcmil equivalent; use Copy to paste a single-line summary into a calculation note.
FAQ
What does "derating" actually mean here?+
Derating = reducing the table ampacity Iz by a chain of correction factors (Ct·Cg·Cs·Ch·Cextra) to obtain the maximum current the cable is allowed to carry under your real-world conditions. Required Iz to carry your IB is then IB divided by that factor chain.
Why are there 12 reference methods?+
IEC 60364-5-52 references 12 common installation arrangements (direct in wall, buried ducts, touching on perforated tray etc.). Heat escapes differently in each — a cable buried in ductwork sees much worse convection than one on a perforated tray.
Why do you show a size table for every mm² when the answer is one row?+
Because engineers often want to see the margin: one size up, and what you are giving up by stepping down. The full table lets you compare margin, AWG equivalence and corrected capacity across the whole size range at a glance.
Does PVC really drop out above 70 °C?+
At ambient temperatures above 70 °C, 70 °C-rated PVC has no thermal headroom for the ΔT rise it relies on — the standard returns a null factor and we force a warning. Switch insulation type to XLPE/EPR 90 °C for hotter environments.
Why does the grouping table interpolate between 3–6–9 circuits when I enter e.g. 4?+
IEC Annex B grouping tables publish values at integer steps only; the tool uses linear interpolation for intermediate counts, which is the standard engineering convention when a stricter table row is not available.
Harmonic derating: when does this actually kick in?+
Annex E derates when 3rd-harmonic content exceeds 15 % (neutral loaded > phase), then has steps at 33 % and 45 % because the neutral now carries more than the phase current and the installation method matters. Below 15 %, no harmonic factor is applied.