Switches: 3-Way/4-Way Wiring, Neutral at the Switch, and Grounding

Switches control the ungrounded conductor — never the neutral — and modern code now wants a neutral present in the box. Here are the rules that trip people up on the exam.

1. Switch the hot, not the neutral (404.2(A)/(B))

• All switching must be done on the ungrounded (hot) conductor. (CEC 404.2(A))
• A switch generally must not open or disconnect the grounded (neutral) conductor. (CEC 404.2(B)) (Otherwise you could turn a light "off" while the fixture stays energized.)

2. 3-way and 4-way switching

• A 3-way switch pair controls one load from two locations. The two wires running between the two 3-way switches are the travelers.
• To control from three locations, add one 4-way switch between the two 3-ways. Each additional location adds another 4-way.

3. Neutral required at the switch — 404.2(C)

Most lighting switch locations must now have a grounded (neutral) conductor present in the box. (CEC 404.2(C)) The reason: modern electronic switches and occupancy sensors draw a small line-to-neutral standby current even when "off," and older switch boxes had no neutral. (There are exceptions — e.g., raceway wiring, boxes accessible for future cable, or automatic controls.)