Two-way Switching
Two switches controlling one lamp — top and bottom of the stairs.
● Line● Neutral● Earth
Tap any wire, switch or device to see what it is.
Useful Information
Line enters SW1 COM; two strappers link L1–L1 and L2–L2; SW2 COM feeds the lamp.
Flipping either switch changes the lamp state.
Important to know
- Use 3-core & earth between switches; sleeve grey and black cores brown (514.3.2).
- Conversion method: 3-core between switches, twin & earth drop at one switch.
- All cores in a switch drop must be from the same circuit (521.8.1 / 314.4).
Common faults
- Lamp only works in some combinations — COM and strapper swapped at one switch.
- Works from one switch only — open-circuit strapper.
Testing tips
- Continuity: test with both switches in all four positions.
- Polarity: lamp holder centre contact must be the switched line.
BS 7671:2018+A4:2026 references
514.3.2521.8.1643.6
Study notes paraphrased — check against your copy of BS 7671.