Breaker Off

Breaker Off / Light switches

Smart switch on a switch loop with a neutral

One 3-wire cable in the switch box (black, red, white and bare), and two cables in the light box.

Where the power comes in

At the switchtwo cables in the switch boxAt the light, no neutralone 2-wire cable at the switchAt the light, with neutralone 3-wire cable at the switch

What goes in the box

SwitchDimmerSmart switch

The breaker is off: every wire is dead and safe to work on. Tap a switch in the drawing to flip it.

PanelLight boxSwitch boxLight fixtureSmart switch14/2 NM-B14/3 NM-B BREAKER NEUTRAL BAR GROUND BARLINELOAD
PanelLight boxSwitch boxLight fixtureSmart switch14/2 NM-B14/3 NM-B BREAKER NEUTRAL BAR GROUND BARLINELOAD

How to tell this is your box

This is a switch loop with a neutral: power reaches the light first, and the 3-wire cable brings the neutral to the switch box, which is what newer homes have and what smart switches need.

The job, in order

  1. In the light box, join the black from the panel to the black going down to the switch.
  2. Connect the red wire coming back from the switch to the fixture's black lead.
  3. Join both whites with the fixture's white lead.
  4. In the switch box: black to LINE, red to LOAD, white to the smart switch's neutral (or capped if the switch has no neutral terminal).

Every connection, box by box

Read from the same circuit the drawing is made from. A simulator checked it in every switch position: the light turns on exactly when they should, nothing shorts, and every device is grounded.

At the panel

  • The black wire to the light goes to the breaker.
  • The white wire to the light goes to the neutral bar.
  • The bare copper wire to the light goes to the ground bar.

In the light box

  • The black wire from the panel and the black wire to the switch join under one wire nut.
  • The red wire to the switch goes to the fixture's black lead.
  • The white wire from the panel and the white wire to the switch join under one wire nut with a short pigtail to the fixture's white lead.
  • The bare copper wire from the panel and the bare copper wire to the switch join under one wire nut with a ground pigtail to the fixture's ground.

In the switch box

  • The black wire from the light goes to the LINE terminal.
  • The red wire from the light goes to the LOAD terminal.
  • The white wire from the light goes to the NEUTRAL terminal.
  • The bare copper wire from the light goes to the ground terminal.

Parts for this box

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Other boxes on this circuit