Q. Is a neutral conductor allowed to be switched for 3-way or 4-way switching?
A. Wiring for 3-way and 4-way switching must be done so that only the ungrounded conductors are switched [404.2(A), as shown in the Figure below. In other words, the neutral conductor must not be switched. The white insulated conductor within a cable assembly can be used for single-pole, 3-way, or 4-way switch loops if it's permanently re-identified to indicate its use as an ungrounded conductor at each location where the conductor is visible and accessible [200.7(C)(2)].
If a metal raceway or metal-clad cable contains the ungrounded conductors for switches, the wiring must be arranged to avoid heating the surrounding metal by induction. This is accomplished by installing all circuit conductors in the same raceway in accordance with 300.3(B) and 300.20(A), or ensuring that they're all within the same cable.
About the Author
Mike Holt
Mike Holt is the owner of Mike Holt Enterprises (www.MikeHolt.com), one of the largest electrical publishers in the United States. He earned a master's degree in the Business Administration Program (MBA) from the University of Miami. He earned his reputation as a National Electrical Code (NEC) expert by working his way up through the electrical trade. Formally a construction editor for two different trade publications, Mike started his career as an apprentice electrician and eventually became a master electrician, an electrical inspector, a contractor, and an educator. Mike has taught more than 1,000 classes on 30 different electrical-related subjects — ranging from alarm installations to exam preparation and voltage drop calculations. He continues to produce seminars, videos, books, and online training for the trade as well as contribute monthly Code content to EC&M magazine.