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Courses/Cable Sizing & Installation/Current-Carrying Capacity

lesson · 10min · Lesson 4 of 28

Reference methods C, E, F, G

Course syllabusCourse overview
01Current-Carrying Capacity
  1. ReadHow CCC tables work: Appendix 4
  2. ReadReference method A: enclosed in conduit
  3. ReadReference method B: clipped direct
  4. ReadReference methods C, E, F, G
  5. exerciseCCC selection problems
02Derating & Correction Factors
  1. ReadAmbient temperature correction (Ca)
  2. ReadGrouping correction factor (Cg)
  3. ReadThermal insulation factor (Ci)
  4. ReadDepth of burial correction (Cs)
  5. exerciseApplying multiple correction factors
03Voltage Drop Calculations
  1. ReadWhy voltage drop matters: Reg 525
  2. ReadmV/A/m tables and how to use them
  3. ReadCalculating voltage drop for single-phase
  4. ReadThree-phase voltage drop
  5. exerciseVoltage drop problems set
04Armoured Cables
  1. ReadSWA construction: layers and materials
  2. ReadUnderground cable installation methods
  3. ReadSWA as protective conductor?
  4. ReadXLPE vs PVC insulation
  5. exerciseSWA sizing exercise
05Mineral Insulated (MICC) Cable
  1. ReadMICC construction and applications
  2. ReadFire performance cables: FP200, LSOH
  3. ReadCable selection for life safety systems
  4. quizFire cable quiz
06Full Cable Sizing Design
  1. ReadEnd-to-end cable sizing: worked design
  2. ReadDocumenting the cable schedule
  3. ReadCommon errors and how to avoid them
  4. quizFinal assessment
Lesson · 10min
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In this lesson

PurposeCore theoryWorked exampleKnowledge checkSources

In this lesson

PurposeCore theoryWorked exampleKnowledge checkSources
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ElectraCore lesson handout

Reference methods C, E, F, G

Cable Sizing · Lesson 4 · Intermediate

IntermediateReview: professional review pending

Purpose

Distinguish current reference-method families C, E, F and G without collapsing their geometry.

Before you beginCCC table structure

Learning objectives

  • Compare surface and free-air arrangements
  • Distinguish multi-core and single-core data
  • Recognise spacing effects
  • Choose exact columns

C, E, F and G are not a ladder of automatically improving ratings. They represent different cable constructions and arrangements whose heat transfer and electromagnetic effects differ.

CURRENT-CARRYING CAPACITY WORKFLOWCURRENT-CARRYING CAPACITY WORKFLOWIbloadIndeviceIzIt × applicable factorsphysical method · exact table · declared conditions · all design gates

Core theory

Method C is associated with specified direct-on-surface arrangements. E and F commonly cover free-air arrangements for multi-core and touching single-core cables respectively; G commonly addresses spaced single-core arrangements. Confirm the exact edition and table wording.

For single-core AC circuits, formation, spacing, transposition, magnetic enclosure and phase grouping affect impedance, heating and forces. A thermal column cannot be transferred between formations.

The chosen table must match conductor material, insulation, cable construction, loaded conductors and arrangement. Manufacturer data may be required outside standard assumptions.

Terms, symbols, and units
TermMeaningSymbolUnit
Free airSpecified ventilated installation with stated support/spacing conditionsNot applicableNot applicable
Touching formationSingle-core cables arranged in contact as declaredNot applicableNot applicable
Spaced formationSingle-core cables separated by a declared spacingNot applicableNot applicable
Worked exampleThree single-core AC cables are shown spaced one cable diameter apart, but the calculation uses a touching formation column.

Assumptions: Both columns exist in the supplied current table.

  1. Compare: The declared geometry differs from the selected column.
  2. Check: Confirm spacing is maintained along the full relevant route and supports/enclosure comply.
  3. Select: Use the exact matching spaced-formation data or redesign.

The touching-column calculation is not evidence for the spaced installation.

Reasonableness check: Formation changes heat transfer and AC behavior.

Common mistakes
  • Treating free air as any visible cable
  • Mixing multi-core and single-core tables
  • Ignoring formation changes

Where this appears in practice

Large feeders need coordinated thermal, impedance, short-circuit force and support design.

SafetySingle-core high-current circuits can produce severe heating and electromagnetic forces; engineered containment and isolation are essential.
Local code checkUse the current standard, exact cable construction and manufacturer data, declared installation geometry, conductor loading, ambient or ground conditions, and competent design procedure. The numbers in worked examples are supplied fictional table data, not universal ratings. Cable work must be isolated, proved dead, tested and certified as required locally.

Knowledge check

Can a Method G value be used merely because it is larger?

No. Its precise spaced single-core conditions must actually be met.

Answer: No. Its precise spaced single-core conditions must actually be met.

Practical exercise

Match supplied C/E/F/G sketches to supplied table descriptions and state every qualification.

Summary

  • Methods encode geometry
  • Cable construction matters
  • Use the exact matching column

Sources and review

  • BS 7671:2018+A4:2026 Requirements for Electrical Installations: IET/BSI; Current edition and corrigenda must be confirmed; United Kingdom
  • Guidance Note 6: Protection Against Overcurrent: IET; Current edition must be confirmed; United Kingdom
  • Electricity at Work Regulations 1989: HSR25: Health and Safety Executive; Current online edition; Great Britain

Editorial review date: 2026-08-22. Professional electrical review is pending.

Educational material for learning and preliminary checks. Verify current local requirements and exact equipment instructions. This lesson does not replace competent professional work.

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