One-way Switch (1-gang)
One switch controlling one lamp, wired loop-in at the ceiling rose.
● Line● Neutral● Earth
Tap any wire, switch or device to see what it is.
Useful Information
The line conductor is broken by the switch; neutral goes straight to the lamp.
Most domestic lighting is wired loop-in: supply, onward feed and switch drop all terminate at the ceiling rose.
Important to know
- Single-pole switches must be in the line conductor only (132.14.1, polarity check 643.6).
- Sleeve or tape the blue switch-return core brown (514.3.2).
- Domestic lighting circuits need 30 mA RCD additional protection (411.3.4).
- Safely isolate and prove dead before work (GS38, 537.2).
Common faults
- Lamp always on — line and switch line swapped at the rose.
- Lamp holder live with switch off — switch in the neutral (polarity fault).
Testing tips
- R1+R2 at the rose and switch; polarity with switch on.
- Insulation resistance with lamps removed: ≥1 MΩ at 500 V (Table 64).
BS 7671:2018+A4:2026 references
132.14.1411.3.4514.3.2643.6
Study notes paraphrased — check against your copy of BS 7671.