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Wiring diagram shows how the electrical power enters the ceiling light electrical box and then a two conductor cable is installed to the switch without a neutral conductor

Smart Light Switch Wiring Diagrams

Dear Mr. Electrician:  What is the correct light switch wiring diagram I should use to control ceiling lights?  I also want to add a WiFi smart switch to the circuit. Answer:  There is no set method of wiring lights and switches.  The choice of materials and wiring diagrams is usually determined by the electrician who does the electrical work, and by the electrical and building codes in force at the time of construction. In commercial and industrial construction the wiring methods and materials are sometimes determined by the architects and engineers who designed the project.  Below are some of the possible light switch wiring diagrams that could be used.  For WiFi smart switches you must adhere to the manufacturer's wiring instructions.  NOTE: Text links below go to applicable products on Amazon.com A recent update to the National Electrical Code (NFPA 70, 2020) in article 314.27(C) now requires that all ceiling light electrical boxes in habitable rooms at likely fan locations, be rated for ceiling fan support. Choices of Light Switch Wiring Diagrams The photo above depicts the wiring diagram of a ceiling light and light switch with the power from the circuit breaker panel entering the ceiling electrical box.  From the ceiling a three conductor cable with a grounding conductor is used to send power to a light switch.  The grounding conductor is not shown in order to simplify the wiring diagram. It is required by the National Electrical Code (NFPA 70) that a neutral conductor be available in each light switch electrical box.  See Article 404.2(C).  This is for the use of electronic dimmers, timers, and WiFi smart home devices that can be installed instead of an ordinary light switch.  All of article 404 pertains to the installation of switches. The two conductor wiring diagram at the top of this page is from older homes and is likely not used much anymore depending on which code book is in force in each jurisdiction.  The two conductor cable from the ceiling box to the light switch is supposed to have the white conductor re-identified with another color because it is not being used as a neutral, but as a hot wire. Although that is the code requirement, it has not been put into practice as much as it should.  Consequently it is quite common to find a white wire in a switch box that is the hot LINE and the black wire is the switch leg connected to the LOAD.  You cannot connect a receptacle outlet to this switch wiring, but you can at the ceiling electrical box, assuming there is enough room for the extra wires. It is very important to follow the electrical code and other building codes for the safety and protection of your home and family. It is easy to to supply power to more than one light fixture as the wiring diagram above shows.  You just install a cable or conduit from a ceiling box to the next ceiling box.  The main thing to watch out for is having too many wires in one...