Switch Connections and the Neutral at Switch Boxes

Always switch the hot, never the neutral — that way the fixture is dead when the switch is off. Since the 2011 cycle, a neutral has to be present at most switch boxes.

That neutral rule caught a lot of people off guard, but it is forward-looking: smart switches need power to run, and without a neutral they used to steal it through the ground.

When it applies

This covers how switches are wired, and it now touches almost every switch box in a new dwelling. Switches must break the hot conductor, not the neutral, and most switch locations must have a neutral present so smart switches, timers and electronic dimmers have a place to draw their small operating current.

Common mistakes

• Switching the neutral instead of the hot, which leaves the fixture energized even when it looks off.
• Wiring a switch loop the old way with no neutral, then leaving the next person unable to install a smart switch.
• Using the equipment ground as a substitute for the missing neutral — never do this.

In the field

I run a neutral to every switch box now even when the current device does not need one. Homeowners upgrade to smart switches constantly, and pulling that extra conductor during rough-in saves them from opening walls later.