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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 · 10min · Lesson 13 of 39

Two-way switching: staircase wiring

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 · 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

Two-way switching: staircase wiring

Domestic Wiring · Lesson 13 · Beginner

BeginnerReview: professional review pending

Purpose

Explain two-way switching as two changeover devices selecting between a pair of strapper conductors.

Before you beginOne-way switching · Changeover contacts

Learning objectives

  • Identify common and strapper terminals
  • Trace all four switch states
  • Avoid terminal-label assumptions
  • Preserve conductor identification

Two-way switching controls one load from two locations. Each switch changes its common terminal between two strapper paths.

Two-way lighting circuit with two changeover switches and two strappersTWO-WAY CHANGEOVER CIRCUITpermanent lineCOML1L2strapper 1strapper 2L1L2COMswitched line to lamp

Core theory

One common is associated with permanent line and the other with the switched line to the load; the two strapper conductors link the changeover terminals.

The circuit is complete when both switches select a continuous strapper path and open when they select different paths.

Terminal arrangements vary by product, so COM/L1/L2 markings and the manufacturer diagram take precedence over memorised physical positions.

Terms, symbols, and units
TermMeaningSymbolUnit
CommonMoving contact terminal of a changeover switchNot applicableNot applicable
StrapperOne of two conductors linking changeover switchesNot applicableNot applicable
Two-wayControl from two positionsNot applicableNot applicable
Worked exampleSwitch A common selects strapper 1 and Switch B common also selects strapper 1. Is the lamp path complete?

Assumptions: Strapper continuity is healthy.

  1. A: Permanent line is connected to strapper 1.
  2. B: Strapper 1 is connected to the switched line.
  3. Path: A continuous line path reaches the load.

Yes; matching selected strappers complete the path in this convention.

Reasonableness check: Operating either switch changes one selection and therefore toggles the load state.

Common mistakes
  • Assuming L1 is physically identical on every product
  • Mixing a common with a strapper
  • Losing core identification during replacement

Where this appears in practice

Two-way switching commonly serves stairs, halls, and rooms with two entrances.

SafetyMultiple switch boxes can contain permanent line even when the lamp is off. Isolate the whole circuit and prove dead at every relevant conductor.
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

What electrical function does each two-way switch perform?

Single-pole changeover. Its common connects alternately to one of two strapper terminals.

Answer: Single-pole changeover. Its common connects alternately to one of two strapper terminals.

Practical exercise

Build a four-row truth table for the two switch positions and mark when the lamp path is complete.

Summary

  • Two changeovers select strapper paths
  • Either switch toggles the result
  • Use actual terminal markings

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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