In the 120V circuits of homes and offices, the grounded conductor is the same as the neutral. Typically, when wiring a switch for a 120V load (e.g., a light) only one wire comes to the switch and only one wire leaves the switch. You need to make sure this is the hot, not the neutral [NEC Sec. 404.2(B)].
This doesn’t mean the neutral can never be disconnected by a switch or breaker. It can, if all circuit conductors (in a 120V branch circuit, both the hot and neutral) are simultaneously disconnected. And it can be disconnected under another scenario; the device is arranged so the neutral can’t be disconnected until the hot wire is.
For lighting circuits in occupancies, install the neutral at the location where the switch controls the lighting loads. If multiple switch locations control the same lighting load (and certain conditions apply), you need a neutral at only one location [NEC Sec. 404.2(C)]. Some exceptions apply, for example where a switch controls a receptacle load. You must also supply a neutral to any switching device that requires line-to-neutral voltage to operate.
