IEC Cable Verification Reference Sheet

01 · DECISION MAP

One cable, five technical gates

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Cable verification engineering decision map showing installation, ampacity and protection, voltage drop, short-circuit thermal withstand, and economic review.

02 · CORE EQUATIONS

Keep each check separate

Ampacity / protectionIb ≤ In ≤ Iz

Corrected cable ampacity must support both the design current and the selected protective-device rating.

Corrected ampacityIz = Iz,ref × kT × kG × kOther

Start from the correct reference method and apply only factors valid for that rating basis.

Voltage drop3φ: ΔU = √3 · I · (R cosφ + X sinφ)

Use one-way length, conductor temperature and project/manufacturer R/X assumptions consistently.

Short-circuit thermalI²t ≤ k²S²

Use prospective current + clearing time or verified total-clearing device I²t.

A pass in one box does not prove the cable is adequate. The final technical minimum is governed by the largest section required by all applicable checks.

03 · WORKED EXAMPLE

Why a cable can pass ampacity and still fail overall

Example basis: 400 V, 3-phase, 52 A design current, Cu XLPE, method C, 65 m one-way length, 40 °C ambient, two grouped circuits, 63 A protective device, 6 kA prospective fault and 0.20 s clearing time.

Candidate16 mm² Cu XLPE

Corrected ampacity69.9 APASS

Protection52 ≤ 63 ≤ 69.9 APASS

Voltage drop1.75 %PASS

Short-circuit minimum18.76 mm²FAIL

Technical minimum25 mm²SELECT

This example is deliberately multi-constraint: the 16 mm² cable is not rejected by continuous load or voltage drop. It is rejected by the adiabatic short-circuit thermal check.

Reproduce this example interactively

04 · REVIEW CHECKLIST

Before design release

05 · LIMITS

What this reference sheet does not decide

It does not reproduce or replace IEC current-carrying-capacity or correction-factor tables.
It does not select a protective device from time-current curves or prove selectivity.
It does not model every sheath, armour, harmonic, soil or thermal-installation effect.
It does not replace project specifications, manufacturer data, local regulations or engineer-of-record review.
Economic upsizing is a lifecycle decision after technical compliance, never a substitute for it.

06 · REFERENCE SCOPE

Standards context

IEC 60364-5-52:2009+AMD1:2024 — wiring systems, current-carrying-capacity context and voltage-drop scope.

IEC 60364-4-43:2023 — protection against overcurrent.

IEC 60949 — thermally permissible short-circuit currents including non-adiabatic considerations.

IEC 60287-3-2:2012 — economic optimization concept for power cable size.

The resource explains the engineering workflow and original calculations. It intentionally does not reproduce protected standards tables.