Voltage Tester

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  #1  
Old 01-25-11, 05:59 PM
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Voltage Tester

I have plans to install a motion sensor switch on my stairwell lights. It's wired as a 3-way where there is a light switch at the top and bottom of the stairs. I am trying to figure out which wire is the hot one. So, I bought a non-contact voltage tester but when I touch any of the wires at the top and bottom switch the voltage tester makes a noise and turns red. Based on the instructions, that means that wire is hot. I have it hard to believe that all wires are hot. Why is it beeping when I touch all the wires? Am I using the wrong tool for this project?

I have other questions on the wiring of the motion sensor switch but let's deal with this first issue first. Thank you!
 
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  #2  
Old 01-25-11, 06:08 PM
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Because they don't detect voltage. They detect electromagnetic fields. To detect voltage you need a test light, multimeter, or solinoid tester. If you get a volt meter unless you get an expensive one they will show ghost voltage. Best to get an analog.

It's wired as a 3-way where there is a light switch at the top and bottom of the stairs. I am trying to figure out which wire is the hot one.
It will be one of the two commons. Does the motion sensor require a neutral. Is the motion sensor designed for a 3-way?
 
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Old 01-26-11, 04:40 AM
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If you install the motion sensor at the light, you will have a neutral. You will need to leave the lights "on" all the time for it to work, however. You don't need to worry about the switch wiring if you are locating it at the lamp itself. You will need to turn the power off to the circuit prior to working on it, however.
 
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Old 01-26-11, 09:07 AM
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Before I deal with the motion light switch I need to find out which wires are hot. Is my non-contact voltage tester incorrect since it is beeping all the time?
 
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Old 01-26-11, 10:35 AM
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Originally Posted by MikeyBoy View Post
Before I deal with the motion light switch I need to find out which wires are hot. Is my non-contact voltage tester incorrect since it is beeping all the time?
Yes. As stated they only detect the presence of an electromagnetic fields not necessarily usable voltage. For most purposes except a quick double check to see if a line is dead they are useless.

You can probably visually determine the hot just by looking. The hot and neutral you need is from a 2-conductor cable either at the light or in one of the switch boxes. Open the light box and determine if you have a switch loop. If you have two or more 2-conductor cables and you have a black from one cable connected to a white from another cable 99% chance you have a switch loop. If only a single 2-conductor cable chances are power comes in at one of the switch boxes.

Please note if you have a switch loop and the sensor requires a neutral you will not be able to connect it at a switch box with out rewiring.

My opinion of a non-contact voltage detector does not necessarily reflect the opinion of the forum or other forum members.
 
  #6  
Old 01-26-11, 10:44 AM
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Originally Posted by MikeyBoy View Post
Before I deal with the motion light switch I need to find out which wires are hot. Is my non-contact voltage tester incorrect since it is beeping all the time?
My Greenlee tester is not too sensitive. It will discern a hot from neutral on a 12/2 NM. It will also detect the hot side of a recept. successfully. Otherwise, Ray offers the best use for the gadgets; detecting voltage in the area. And, you want to test it on a known live wire immediately preceeding.
 
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Old 01-26-11, 11:16 AM
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And to keep the electromagnetic field effect, disconnect the power, then remove the two wires which are attached to the andonized screws and separate them from the mix so they don't touch anything. Restore power and check with your non contact device. Turn the power back off and reattach the wires.
 
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Old 02-06-11, 06:51 AM
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I finally bought two different voltage testers at Home Depot with the red and black wires just to make sure both give me the same results.

I have a 3-way light with a switch at the top and bottom of the stairs. I followed the instructions on the the voltage testers and nothing lit on the voltage tester when testing it at both top and bottom switch. I alternated the red and black wires all possible combinations and still nothing.

I took the voltage testers and inserted it in an electrical outlet and it lit. I was also able to make it light at a different light switch as well. So, what is wrong with the 3 way light switch I am trying to test this with? Does this mean the hot wires are at the light fixture? If yes, will this prevent me from installing a motion sensor switch at the top and bottom switches?
 
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Old 02-06-11, 07:22 AM
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To test for voltage at a switch you need to check to ground or a neutral if available in the back of the box.

You power should be on the odd colored screws, not the two screws of the same color.
 
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Old 02-06-11, 07:41 AM
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From the voltage tester, I touched the red wire to the ground wire in the switch and moved the black wire on the remaining white, red and black wires in the switch and nothing lights up.
 
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Old 02-06-11, 09:27 AM
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You should be looking for power at a 2-conductor cable usually not the three conductor cable.
 
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Old 02-06-11, 02:05 PM
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Both switches at the top and bottom of the stairs both have 3 cables: white, red and black.
 
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Old 02-06-11, 03:30 PM
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Originally Posted by MikeyBoy View Post
Both switches at the top and bottom of the stairs both have 3 cables: white, red and black.
Then your power cable is probably at the light.
 
  #14  
Old 02-09-11, 09:35 PM
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To clarify what ray said: In order to have a usable neutral in the switch boxes, there must be both a 3-wire cable and a 2-wire cable in *both* switch boxes. Hot and neutral in, neutral and two travelers out/in, and switched hot/neutral out. If you were to draw it it'd start on one side and end on the opposite. If it's wired as a loop, then one box will have only one 3-wire set, and the other will have two 2-wire cables. This is a loop setup: hot-travelers-second switch, then switched hot going back the other way. If you have a loop setup there is no neutral in the loop box... and the ground might be faulty. Just to make it uglier, if one switch box has just a 3-wire and the other has the 3-wire and a single 2-wire, you have a loop from one of the light fixtures. Have to start taking apart the lights to find where the switch loop starts. Use the neutral in that box to test.
 
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