Neutral wire required at light switches
Where switches control lighting in bathrooms, hallways, stairways, habitable rooms or occupiable spaces, the code generally requires a neutral wire at the switch location so smart switches can work. The 2023 NEC removed the exemption for boxes that could take a new cable later.
What the code requires
A grounded (neutral) conductor must be provided at switch locations that control lighting in bathrooms, hallways, stairways, and habitable rooms or occupiable spaces, when that lighting is fed by a general-purpose branch circuit with a neutral. If several switch locations control the same lights and the whole floor area can be seen from them, only one of those locations needs the neutral.
Under the 2023 NEC, the neutral is not required in four cases: a raceway with room for a neutral enters the box; snap switches with integral enclosures are used under 300.15(E); the lighting is controlled by automatic means; or the switch controls a receptacle rather than lighting.
Where a switch needs line-to-neutral voltage to power its electronics in standby, the neutral must be connected to it, under 404.22.
On the job
- Switch loops with no neutral in bedrooms, bathrooms and hallways are a common correction.
- Smart switches that need a neutral must have one connected; installing them without it is a frequent problem.
- The neutral is required at rough-in even if standard switches go in. Since 2023, an accessible box that could take a new cable later no longer excuses it.
Exceptions that matter
- For replacement or retrofit switches in locations wired before your area adopted this rule, where a neutral cannot be extended without removing finish materials, electronic control switches without a neutral connection are allowed, limited to 5 per branch circuit and 25 per feeder.
What changed in 2023
The 2023 NEC deleted the exemption for a switch box that could be reached to add a cable later without removing finish materials.
Related sections
- NEC 404.22
- NEC 300.15(E)
- NEC 200.2(B)
- NEC 404.9(B): Grounding switches and metal cover plates
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