Description

A detailed engineering guide on cable selection as per IEC 60364-5-52, IEC 60287, IEC 60949 and IEC 60502. Covers ampacity, derating factors, voltage drop, short-circuit withstand and installation requirements.

Keywords

IEC cable sizing, IEC 60364-5-52 cable selection, IEC 60287 ampacity calculation, IEC 60949 short-circuit rating, IEC cable derating factors, voltage drop limits IEC, cable installation methods IEC, IEC 60502 LV/MV cable requirements, conductor class IEC 60228

Table of Contents

  1. Introduction
  2. IEC Standards Used for Cable Selection
  3. Step-1: Determining Current-Carrying Capacity (IEC 60364-5-52 & IEC 60287)
  4. Step-2: Applying Derating Factors (Temperature, Grouping, Thermal Insulation)
  5. Step-3: Voltage Drop Compliance (IEC 60364-5-52)
  6. Step-4: Short-Circuit Withstand (IEC 60949)
  7. Step-5: Conductor Material & Class Selection (IEC 60228)
  8. Step-6: Insulation & Sheath Requirements (IEC 60502-1 / 60502-2)
  9. Step-7: Fire Performance Requirements (IEC 60332, 60754, 61034)
  10. Step-8: Mechanical & Installation Requirements (IEC 60364-5-52)
  11. Engineering Checklist
  12. FAQs

1. Introduction

Cable selection under IEC standards ensures that the cable is capable of:

  • Carrying load current continuously
  • Withstanding short-circuit stresses
  • Maintaining voltage within acceptable limits
  • Performing reliably under installation conditions
  • Remaining safe under fire and mechanical conditions

The following IEC standards form the basis for the correct selection and sizing of LV/MV cables:

  • IEC 60364-5-52 — Selection & Erection of Wiring Systems
  • IEC 60287 — Thermal Current-Carrying Capacity Calculations
  • IEC 60949 — Short-Circuit Thermal Withstand
  • IEC 60502-1/2 — Construction & Tests for LV/MV Cables
  • IEC 60228 — Conductor Classes
  • IEC 60332 / 60754 / 61034 — Fire and Smoke Performance

2. IEC Standards Used for Cable Selection

StandardRelevant ClausesPurpose
IEC 60364-5-52Clauses 522, 523, 524, 525, 526Installation, current rating, voltage drop, mechanical requirements
IEC 60287Part 1–3Thermal ampacity calculation
IEC 60949Clause 3Short-circuit thermal withstand
IEC 60502-1/2Clauses 5–8Cable construction (LV/MV)
IEC 60228Clause 4Conductor class definition
IEC 60332 / 60754 / 61034Test proceduresFire propagation, halogen acid gas, smoke density

3. Step-1: Determining Current-Carrying Capacity

IEC 60364-5-52 — Clause 523

Defines the selection of current-carrying capacity based on:

  • Installation method
  • Insulation type
  • Ambient temperature (air/soil)
  • Thermal resistivity of soil
  • Cable grouping
  • Conductor material

Reference Installation Methods

Annex A & B provide standard installation methods (A–F).
Examples:

  • Method C — On wall
  • Method D — Underground
  • Method E — In buried ducts

IEC 60287 — Thermal Model Calculation

Used when:

  • Manufacturer data is unavailable
  • Non-standard installation
  • High current applications

IEC 60287 considers:

  • Conductor losses
  • Dielectric losses
  • Thermal resistances
  • Ambient conditions

4. Step-2: Applying Derating Factors (IEC 60364-5-52)

4.1 Temperature Correction — Clause 523.4

Correction factors must be applied for:

  • Ambient air temperature
  • Soil temperature
  • Soil thermal resistivity

4.2 Grouping Factors — Clause 523.7

Multiple circuits installed together reduce heat dissipation, requiring derating.

4.3 Thermal Insulation — Clause 523.9

Cables surrounded by thermal insulation may need:

  • Larger CSA
  • Reduced loading
  • Free airspace consideration

5. Step-3: Voltage Drop Requirements (IEC 60364-5-52)

Clause 525 — Voltage Drop

Defines:

  • Permissible voltage drop
  • Calculation method
  • Use of R & X under operating conditions

Typical IEC limits:

Load TypeMaximum Voltage Drop
Lighting3%
Other Loads5%
Motor StartingHigher allowance based on manufacturer

Calculation (Clause 525.2)

Uses:

  • Resistive component (R)
  • Reactive component (X)
  • Load current
  • Power factor

Both AC single-phase and three-phase formulas are defined.

6. Step-4: Short-Circuit Withstand (IEC 60949)

Clause 3 — Short-Circuit Equation

For short-circuit duration t and fault current Ik:

Where:

  • A = conductor cross-section (mm²)
  • Ik = prospective short-circuit current (kA)
  • t = clearing time of protective device (s)
  • k = material constant based on conductor & insulation type

This ensures the cable can withstand:

  • Thermal stress
  • Electromechanical forces

7. Step-5: Conductor Material & Class (IEC 60228)

IEC 60228 — Clause 4 defines:

  • Class 1 — Solid
  • Class 2 — Stranded
  • Class 5 — Flexible
  • Class 6 — Extra flexible

Selection Guidelines

ClassApplication
1Fixed wiring, non-flexible
2LV/MV power cables
5Control cables, flexible applications
6Special flexible applications

8. Step-6: Insulation & Sheath Requirements (IEC 60502-1 / 60502-2)

IEC 60502-1 — LV Cables

Covers:

  • Conductor (Clause 5)
  • Insulation (PVC/XLPE — Clause 6)
  • Sheath (Clause 7)
  • Tests (Clause 8)

IEC 60502-2 — MV Cables

Adds:

  • Metallic screening requirements
  • Dielectric strength
  • Short-circuit constraints of screens

9. Step-7: Fire Performance Requirements

IEC 60332-1 (Single Cable Flame Test)

Test for flame propagation on individual cables.

IEC 60332-3 (Bundle Fire Test)

Fire spread test for grouped cables.

IEC 60754

Halogen acid gas emission test.

IEC 61034

Smoke density test.

Engineering Requirement

For commercial/industrial installations:

  • Prefer FRLS or LSZH cables
  • Mandatory for evacuation paths
  • Mandatory for data centres, hospitals, hotels

10. Step-8: Mechanical & Installation Requirements (IEC 60364-5-52)

Clause 522 — Mechanical Requirements

Specifies:

  • Minimum bending radius
  • Tensile strength considerations
  • Vibration conditions
  • Mechanical protection (trays, conduits, armour)

Clause 526 — Connections & Terminations

Requirements for:

  • Crimping
  • Ferrules
  • Lugs
  • Glands
  • Jointing methods

11. Engineering Checklist (IEC-Compliant Cable Selection)

Determine installation method — IEC 60364-5-52 Annex A/B

Select ampacity — Clause 523

Apply derating factors — Clauses 523.4, 523.7, 523.9

Verify voltage drop — Clause 525.2

Confirm short-circuit withstand — IEC 60949 Clause 3

Choose conductor class — IEC 60228

Select insulation & sheath — IEC 60502-1/2

Ensure fire performance — IEC 60332 / 60754 / 61034

Verify mechanical conditions — IEC 60364-5-52

Document calculations and installation conditions

12. FAQs

1. What is the main IEC standard for cable sizing?

IEC 60364-5-52 is the primary standard for selecting current ratings, voltage drop, derating, and installation requirements.

2. When should IEC 60287 be used?

When manufacturer data is insufficient or a thermal model is required for high-capacity or non-standard installations.

3. What short-circuit rating must cables meet?

As per IEC 60949, the cable must withstand the expected fault current for the protective device’s clearing time.

4. What is the allowable voltage drop for lighting?

Typically, 3%, as recommended by IEC 60364-5-52.

5. Are LSZH cables mandatory?

LSZH is mandatory in critical areas like escape routes, tunnels, hospitals, data centres, and recommended for all commercial buildings.