A new rule will require a neutral conductor at nearly every switch point.

404.2 Switch Connections.

(C) Switches Controlling Lighting. Switches controlling line-to-neutral lighting loads must have a neutral provided at the switch location.

Ex.: The neutral conductor isn’t required at the switch location if:

(1) The conductors for switches enter the device box through a raceway that has sufficient cross-sectional area to accommodate a neutral conductor. (click here to see Fig. 16)

(2) Cable assemblies for switches enter the box through a framing cavity that’s open at the top or bottom on the same floor level or through a wall, floor, or ceiling that’s unfinished on one side.

Note: The purpose of the neutral conductor is to complete a circuit path for electronic lighting control devices.

Analysis: Many lighting control devices (such as occupancy sensors) require that the switch be provided with standby voltage and current at the switch in order to operate. Many electricians don’t include a neutral conductor at switch locations, and the unfortunate result is the equipment grounding conductor being used as the neutral conductor. While the current on the equipment grounding conductor is typically less than 0.50mA, the accumulation of many switches in a building can result in an unacceptable amount of current on the equipment grounding conductors. With this change, gone are the days of using dead-end 3-way switches and two conductor switch loops.

The two exceptions address switch locations that use raceways and those that are at or near unfinished/accessible areas. The use of a raceway obviously allows the installer to pull in a neutral conductor should the need arise (provided the raceway is of adequate size), and the other exception allows for changing the wiring of the switch without resorting to removing drywall and other finish materials.

An Informational Note emphasizes the fact that this provision is for adding a dimmer switch. It’s a bit surprising to see this Informational Note, due to the fact that statements of intent are typically not allowed in the Code.