Another NM cable connects from this dimmer box to the light fixture box. Both line and neutral travel from the switch box to the light fixture box.
Diagrams shown on this page are simplified for clarity. Electrical outlet boxes can have numerous NM cables going in and out. See Actual Switch Box Wiring.
Ground connection diagram is shown separately.
In the diagram below, a 2-
The common terminal of the 3-
The white neutral wires are connected together in each switch box.
Dimmer Switch Wiring