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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/Lighting Circuits

lesson · 8min · Lesson 12 of 39

One-way switching: full diagram

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

One-way switching: full diagram

Domestic Wiring · Lesson 12 · Beginner

BeginnerReview: professional review pending

Purpose

Trace a complete one-way lighting circuit and distinguish functional switching from isolation.

Before you beginLighting wiring methods · Line and neutral

Learning objectives

  • Draw the current path
  • Place a one-pole switch in line
  • Identify switched line
  • Plan polarity and continuity checks

A one-way circuit controls one lighting load from one position. Its simplicity makes it the reference case for understanding polarity, switching, and conductor identification.

One-way lighting circuit with the switch in the line conductorONE-WAY LIGHTING CIRCUITpermanent lineone-pole switchlampneutral returnswitched line

Core theory

The protective device supplies the circuit permanent line and neutral; a one-pole functional switch interrupts the line conductor feeding the load.

The switched-line conductor is a line conductor and must be identified as such even when a multicore cable uses a core colour normally associated with another function.

Verification includes protective-conductor continuity, insulation resistance, polarity, protective-device/RCD checks, functional operation, and required circuit documentation.

Terms, symbols, and units
TermMeaningSymbolUnit
One-way switchSwitch controlling a load from one positionNot applicableNot applicable
PolarityCorrect connection of line, neutral, and protective conductorsNot applicableNot applicable
Worked exampleTrace conventional current when a one-way switch is closed.

Assumptions: Healthy circuit; One lamp.

  1. Line path: Origin line passes through protection, permanent line, closed switch, and switched line to the lamp.
  2. Load: Current transfers energy in the lamp or driver.
  3. Return: Current returns on neutral; the CPC carries no normal load current.

The closed switch completes the line path; neutral completes the return path.

Reasonableness check: Opening the line path stops normal current while leaving protective conductors intact.

Common mistakes
  • Switching neutral instead of line
  • Calling switch-off isolation
  • Failing to identify a repurposed core

Where this appears in practice

One-way circuits appear in rooms, cupboards, external lights, and control inputs.

SafetyNever infer dead from lamp state or switch position. A failed lamp, borrowed neutral, incorrect polarity, or open conductor can mislead.
Local code checkThis lesson uses UK lighting-circuit conventions. Verify the current BS 7671 edition and amendments, equipment standards, manufacturer instructions, fire-separation requirements, Approved Document P applicability, and local notification rules before design or work.

Knowledge check

Which conductor should an ordinary one-pole light switch interrupt?

The line conductor. Correct polarity avoids leaving the load holder connected to line when switched off.

Answer: The line conductor. Correct polarity avoids leaving the load holder connected to line when switched off.

Practical exercise

Annotate a paper one-way diagram with test points for CPC continuity and polarity; do not perform live measurements.

Summary

  • One position controls one load
  • The switch belongs in line
  • Switch-off is not isolation

Sources and review

  • Best Practice Guide 9: Safe installation of retrofit LED lamps: Electrical Safety First; Current online issue; United Kingdom
  • Mythbuster #5: Will any old terminal block do?: IET Wiring Matters; 2020; United Kingdom
  • Electrical safety: Approved Document P: UK Government; Current online edition; England
  • 16AX switches and intermediate switch installation manual: Hager; WGML1XX/WGCXL1XX, April 2019; Manufacturer wiring instructions; accessed 2026-09-02

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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