Home › Builds › Light with one switch

Light with one switch

Bench build · Power, transformers and three-phase · Beginner · about 20 minutes

One 9 W LED bulb on a 1-way wall switch, fed from a 10 A breaker. The simplest lighting circuit in a house: breaker → wall switch → lamp → back on the neutral. The switch must break the LINE (L), never the neutral, so the lamp holder is dead when the switch is off and you can change the bulb safely.

Light with one switch: the finished build running on the simulator's bench

Build it in the labGuided build, test sheet and fault finding, free in your browser.

Parts list

Test procedure

Each test has an expected value and a pass range, like a factory test sheet:

  1. Switch on: the lamp lights at its rating
  2. Switch off: the lamp is off
  3. Switch off: the lamp holder is dead (the switch breaks L, not N)
  4. Breaker off: the whole circuit is dead
  5. Cable sized for the breaker

How it works

What it does: One 9 W LED bulb on a 1-way wall switch, fed from a 10 A breaker.

Build it (guided or ready-made), then run its test procedure below. Every test has an expected value and a pass range, just like a factory test sheet.

Background

Every room starts here. A switch in the neutral still turns the lamp off, which is why the mistake goes unnoticed until someone touches a "dead" bulb socket and finds it live at 220 V.

More builds: power, transformers and three-phase