Home Tags Smart Switches

Tag: Smart Switches

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

Light Switch Wiring Diagrams

Dear Mr. Electrician:  What are the choices of light switch wiring diagrams to wire a light switch to a ceiling light? Answer:  Light switch wiring diagrams are below.  The choice of materials and wiring diagrams is usually determined by the electrician who installs the wiring, and by the electrical and building codes in force at the time of construction.  NOTE: Text links below go to applicable products on Amazon or EBay. If you are planning to install a ceiling fan, visit my Ceiling Fan Wiring Diagrams post. In commercial and industrial construction the wiring methods and materials are sometimes determined by the architects and engineers who designed the project.  Light switch wiring diagrams are sometimes furnished to the contractors doing the installation. For WiFi smart switches you must adhere to the manufacturer's wiring instructions. 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 ceiling fan locations, be rated for ceiling fan support. CHOICES OF LIGHT SWITCH WIRING DIAGRAMS The above two conductor switch wiring diagram 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. Re-identifying a wire is done using colored electrical tape.  Some electricians use a permanent marker. Although re-identifying a wire 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 type of switch wiring because there is no neutral wire in the switch box, but you can at the ceiling electrical box, assuming there is enough room for the extra wires. 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).  The neutral is needed for the use of electronic dimmers, timers, and WiFi smart home devices that can be installed instead of an ordinary light switch.  This is why the above wiring diagram is not used much anymore.  All of article 404 pertains to the installation of switches. It is very important to follow the electrical code and other building codes for the safety and protection of your home and family. 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 easy to supply power to more than one...