Switch loop wiring diagram
Light: on
Both conductors in the drop to the switch are in the hot family — one down, one back up — and there is no neutral in that box. Flip the switch and watch the returning conductor go live. The copper highlight is the live path, not a wire colour.
A switch loop controls a light when the supply arrives at the fixture rather than the switch. A two-wire cable drops to the switch: one conductor carries the feed hot down, the switch makes or breaks it, and the other conductor carries the switched hot back up to the lamp. The neutral stays at the fixture.
How this circuit works
Trace the hot from the fixture box. It runs down one leg of the loop to the switch's common. If the switch is closed, it comes straight back up the other leg as the switched hot and feeds the lamp; the lamp returns on the neutral that never left the fixture. Open the switch and the returning leg goes dead — watch the copper drain out of it in the diagram.
The thing to carry away is that both conductors in that drop belong to the hot side of the circuit. There is no neutral in the switch box at all. That surprises people the first time, and it is the whole reason the arrangement has its own name.
Questions people ask
What is a switch loop?
It is the arrangement where the supply and neutral arrive at the light fixture, and only a two-wire drop runs down to the switch. One of those two wires carries the hot down to the switch; the other carries the switched hot back up. The switch itself never sees a neutral.
Why is there no neutral at the switch?
Because the supply landed at the fixture, not the switch. The pair going down to the switch is there only to loop the hot out and bring the switched hot back — both are in the hot family. Older installs left it at that; how the returning conductor must be identified today is a code matter, and the diagram deliberately does not assign colours.
How is this different from a standard single-pole?
The switching is identical — one blade, breaking the hot. The only difference is where the supply enters. Feed it at the switch and it is the textbook single-pole; feed it at the fixture and you get a switch loop. The lamp behaves the same either way.
Related
- Single-pole switch wiring — the same switching, supply fed at the switch.
- Glossary: neutral vs identified conductor
- All wiring diagrams
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