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Educational use: ElectraCore supports learning and preliminary checks. It does not replace a competent electrician or engineer. Verify results, equipment data, and current local regulations before installation or live work.
Courses/Domestic Wiring/Cables & Containment

lesson · 8min · Lesson 28 of 39

Trunking, conduit and dado systems

Course syllabusCourse overview
01Consumer Unit Design
  1. ReadConsumer unit layout and components
  2. ReadMCBs: types, ratings, and selection
  3. ReadRCDs vs RCBOs: when to use which
  4. ReadSplit load vs dual RCD boards
  5. quizModule quiz
02Ring Final Circuits
  1. ReadHow ring circuits work: the topology
  2. ReadCable selection for ring finals
  3. ReadSpur outlets: fused and unfused
  4. ReadRadial circuits: when to use them
  5. exerciseWiring practice problems
03Lighting Circuits
  1. ReadJunction box vs loop-in wiring methods
  2. ReadOne-way switching: full diagram
  3. ReadTwo-way switching: staircase wiring
  4. ReadIntermediate switching for long runs
  5. ReadDimmer circuits and LED compatibility
  6. quizLighting circuit quiz
04Earthing & Bonding
  1. ReadTypes of earthing: TN-S, TN-C-S, TT
  2. ReadMain protective bonding
  3. ReadSupplementary bonding requirements
  4. ReadEarth electrode installation for TT
  5. quizBonding quiz
05Special Locations
  1. ReadBathroom zones: Zone 0, 1, 2
  2. ReadKitchen wiring requirements
  3. ReadGarage and outbuilding circuits
  4. ReadGarden power: outdoor sockets and lighting
06Cables & Containment
  1. ReadTwin-and-earth cable construction
  2. ReadInstalling in walls: notching and chasing
  3. ReadTrunking, conduit and dado systems
  4. ReadCable in ceilings and floor voids
  5. quizDepths and zones quiz
07Fault Finding
  1. ReadSystematic fault finding process
  2. ReadOpen circuits: symptoms and finding them
  3. ReadShort circuits and cross-connections
  4. ReadRCD nuisance tripping
  5. exerciseFault finding case studies
08Wiring Regulations
  1. ReadBS 7671 structure and using the regs
  2. ReadNotification, certification and sign-off
  3. ReadPart P and building control
  4. quizFinal assessment
Lesson · 8min
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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

Trunking, conduit and dado systems

Domestic Wiring · Lesson 28 · Beginner

BeginnerReview: professional review pending

Purpose

Select and size trunking, conduit, and dado containment through capacity, bend, segregation, earthing, support, fire, and environmental checks.

Before you beginCable selection · Concealed routes

Learning objectives

  • Compare containment systems
  • Plan fill and cable installation
  • Maintain segregation
  • Coordinate metal containment with protection

Containment organises and protects wiring, but it also changes heat dissipation, pulling forces, accessibility, and fault paths.

CABLE ROUTE AND CONTAINMENTCABLE ROUTE AND CONTAINMENTROUTEisolate · protect · identifydevice / pointtrace every conductor path

Core theory

Trunking offers accessible grouped routes; conduit offers enclosed routes with bends and draw-in constraints; dado systems integrate power/data accessories but require compatible partitions and fittings.

Fill is not just geometric area: apply current maximum-fill guidance, bend radius, pulling tension, conductor damage, grouping/thermal factors, and future additions.

Metal containment may need verified protective continuity and bonding/earthing appropriate to its role; lids, couplers, joints, entries, bushings, supports, and fire-stopping must form a complete system.

Terms, symbols, and units
TermMeaningSymbolUnit
ContainmentSystem enclosing, supporting, or routing wiringNot applicableNot applicable
SegregationSeparation of circuits/services to control hazards or interferenceNot applicableNot applicable
Draw-in pointAccessible point assisting cable installationNot applicableNot applicable
Worked examplePower and data cables are proposed loose in one unpartitioned dado compartment. What checks arise?

Assumptions: No cable voltage ratings or system declaration supplied.

  1. Segregation: Check required separation or equivalent insulation for the circuit categories.
  2. Capacity: Verify fill, grouping, bend, and termination space.
  3. System: Use compatible partitions, boxes, lids, supports, and fire-stopping.

Do not approve the shared compartment without verified segregation and complete-system data.

Reasonableness check: One physical enclosure can create both electrical hazard and interference paths.

Common mistakes
  • Filling containment to visual capacity
  • Relying on a loose metal lid for CPC continuity
  • Mixing circuit categories without assessment

Where this appears in practice

Containment is common in workshops, offices, garages, utility spaces, and refurbishments.

SafetySharp cut edges and damaged entries can abrade insulation. Deburr, bush, support, earth as designed, and inspect before energisation.
Local code checkApply the current BS 7671 edition and amendments plus the applicable national Building Regulations, DNO requirements, product instructions, structural/fire/acoustic rules, and local notification process. Dimensions or methods in this lesson are concepts, not site approval.

Knowledge check

Why is percentage area alone insufficient for conduit selection?

Bends, pulling forces, grouping, damage risk, and current rules also matter. Treat the route as an installation system.

Answer: Bends, pulling forces, grouping, damage risk, and current rules also matter. Treat the route as an installation system.

Practical exercise

Compare conduit, trunking, and dado for a fictional mixed power/data route and state why each may be accepted or rejected.

Summary

  • Containment changes installation conditions
  • Segregation must be proven
  • Use a complete compatible system

Sources and review

  • BS 7671:2018+A4:2026 model EICR schedule: IET; Amendment 4:2026; United Kingdom
  • Wiring Regulations Help: Electrical Safety First; Current online technical guidance; United Kingdom
  • Electrical safety: Approved Document P: UK Government; Current online edition; England
  • Structure: Approved Document A: UK Government; Current online edition; England

Editorial review date: 2026-08-21. 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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