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About Bruce Grant
Expertise
I can answer any questions about residential electrical wiring and most questions about commercial wiring. In my own business, I insist on using best practices in all work we do (which to me means "to Code" or BETTER, using the most recommended ways to do things).
Experience
I'm 65, but learned wiring basics as a teenager. I only used this knowledge for myself, friends and family until early 2002, when economic downturns suddenly made my 30 years in IT irrelevant. Through the Internet, I bought many books on wiring and electrical code and switched careers, becoming an unlicensed electrical contractor, carpenter, and handyman. I now know, after 7 years in the industry, everything I need to get a California C-10 License except some of the Industrial wiring stuff (which I'll probably never use, but need to pass the test). The main reason I haven't yet obtained the License is lack of funds to pay for it and the required insurance. Eventually, I'll get it.
Education/Credentials
* BS in Physics and Mathematics from Oregon State University, 1967
* Primarily self-taught from books written for electrical and construction pros, but also informal training from more experienced pros
Past/Present Clients
homeowners and small businesses in the San Francisco Bay Area, mainly on the S.F. Peninsula
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You are here: Experts > Home/Garden > Home Improvement/Repair > Electrical Wiring in the Home > Wiring a motion sensor light switch
Expert: Bruce Grant - 11/2/2009
Question
Hello, I have a motion sensor light switch that I got from work. They were going to throw them away, so I got 1. It has 3 wires on the back of it. They are green, blue and black. I assume the green is ground and needs to be connected to the ground wire. Does the blue need to be hooked to the hot wire and the black go to the neutral? I hooked it up this way and got nothing. I tried it at work and it worked, but not when I got home. I am not too sure that I have a good ground from my house wiring though. Any thoughts would be great. Thank you very much!
Answer
Scott,
This is an easy one if you follow my logic.
== First, you were probably right in using the Green for Ground, as that matches Code (Ground can only be Green or bare copper), however some manufacturers use that as a Neutral connection with no Ground connection intended (see middle and top diagrams, attached), since older Codes did not require a Ground wire in switch boxes.
== Secondly, you were half right about the other two wires. One of them, probably the Blue connects to the Hot input, but the other (Black) connects to the Hot terminal of the light fixture (I may have the colors reversed, but that's easy to test). You should have had two Black wires or a Black and another color (usually Black or Red, but any color other than White*, Gray, or Green) in the switch box, and those are the Hot input and the Hot output to the fixture. The objective of the switch is to allow the interruption or connection of a Hot wire to a device (see bottom diagram, attached).
* Note the asterisk on White above. There is an exception in the National Electrical Code which allows the use of NM-2 cable ("Romex") which has one Black, one White and one bare copper wire, for a switch loop. In that case the Hot input wire would be the White wire, but it must be marked with Black paint or tape at both ends.
I hope this solves your problem. Good luck.
Bruce
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