Section 404.2/Switch Connections (Neutral at Switch Locations)
NEC 404.2(C) requires a grounded (neutral) conductor at lighting switch locations for occupancy sensors and electronic switches.
Section 404.2(C) requires a grounded (neutral) conductor at switch locations that control lighting loads. The neutral conductor must be provided in the switch box or be accessible from a raceway system. This requirement ensures that occupancy sensors, timers, dimmers, and other electronic switches that require a neutral for their internal electronics can be installed without rewiring. The grounded conductor must not be connected to the switching device unless listed and identified for use with the conductor. Exceptions exist for switches controlling receptacle loads, where the box is accessible for rewiring, and certain snap switches.
Why this section exists
Traditional toggle switches interrupt only the hot (ungrounded) conductor and do not need a neutral. Modern electronic switches (occupancy sensors, programmable timers, smart switches, dimmers) require a small amount of power to operate their electronics, which requires a neutral connection. Before this requirement, retrofitting a manual switch with an occupancy sensor often required pulling a new neutral conductor through finished walls. The neutral-at-switch requirement ensures every switch box is ready for electronic devices without costly rewiring.
What plan reviewers look for
Plan reviewers check the electrical drawings for switch leg wiring details. They verify that lighting switch boxes include a neutral conductor (either connected to the switch or available in the box). For switches in conduit systems, they check the wire count to confirm a neutral is pulled to the switch location. They verify the exceptions where a neutral is not required.