# 3 way switches shows 2 hot wires

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• posted on February 26, 2012, 12:31 am
I measured a 3 way switch and I got two wires on 2 different screws measuring 120 volts. I thought only one should be hot??? I'm in a rush so I can't write a lot but if looking at the switch with screws were like this
c where c is the black screw
a b
I got voltage at "a" and "c" so I'm confused. I'll google later if that will help me but does this make any sense? I will try to explain more later as necessary. I may take the wires off the switch and just measure from the wires rather than from the screws on the switch, if that matters. I want to explain more but gotta run.
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<%-name%>
• posted on February 26, 2012, 12:37 am

I could take a stab at it but I don't have time to polish my crystal ball and see what you realy have.
cb
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<%-name%>
• posted on February 26, 2012, 1:05 am
On 2/25/2012 7:31 PM, Doug wrote:

If you are trying to diagnose a mis-wired set of 3 way switches, you need to take the wires off of the switches first.
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<%-name%>
• posted on February 26, 2012, 9:23 am

Well it's a 3-way (that is double-throw) switch. Which is the common screw? If it's c, it will be connected to a or b at all times. So ift's conneected to a, you'll have the same votage at a and c.
If you didn't know this, you should do some reading before you fiddle with this stuff. About switches, electricity, voltage, etc.

They weren't miswired when he started, 3 threads ago. He's putting in some kind of timer, but doesn't say if he's done that yet, or if he rewired any of the switches t hat were there.
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<%-name%>
• posted on February 26, 2012, 1:28 am
wrote:

You will ALWAYS have 2 hots on a 3 way switch. You have power in and power out. There is no "off" on a 3 way switch. They are just wired that depending which way the switches are set neither "ON" of each switch is connected to the load. Switching either switch to the other position means ONE "ON" is connected to the load.
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<%-name%>
• posted on February 26, 2012, 2:17 am
wrote:

Based on what I read elsewhere (correct me if I'm wrong please) if I measure the voltage at the switch screws with wires fasten to them, I might get 2 hot wires but if I remove those wires and check the voltage just at the wires, I will get one hot wire.
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<%-name%>
• posted on February 26, 2012, 4:13 am
On 2/25/2012 9:17 PM, Doug wrote:

That is correct. With wires connected, one of the two switches will always have two hot terminals, and the other switch could have one or two hot terminals, depending upon the position of the handle.
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<%-name%>
• posted on February 26, 2012, 3:11 pm
On 2/25/2012 10:13 PM, RBM wrote:

I agree if the switches are working.
If the switches work and the terminals at one end are X, Y, Z; X and Y are hot. Flip the switch and Y and Z are hot. Then this is the switch connected to power - Y connects to power (and is the "common" terminal) and X and Z are "travelers" to the other switch.
With terminals T, U, W; T and U are hot and the light is on. Flip the switch and T is hot and the light went out. U connects to the light (and is the "common" terminal).
Or, more simply if the switches work - at one switch the "common" terminal will be hot in either switch position. That is the hot feed wire.
One switch the "common" terminal will be hot only in the switch position where the light is on. That terminal connects to the light.
If you really understand how 3-ways work it isn't real hard to diagnose a problem without disconnecting all the wires. Disconnecting the wires makes it easier. (Then you run into a Carter circuit or California 3-way.....)
--
bud--

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<%-name%>
• posted on February 26, 2012, 3:30 pm
On 2/26/2012 10:11 AM, bud-- wrote:

Jeeze, just when I was beginning to understand it, you throw in California and Carter!!
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<%-name%>
• posted on February 26, 2012, 3:43 pm
On 2/26/2012 9:30 AM, RBM wrote:

When I do commercial wiring with three way and four way switches, I use blue and yellow wire for the travelers. It really freaks out some other electricians. I know some electricians who are clueless when it comes to installing three and four way switches. o_O
TDD
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<%-name%>
• posted on February 26, 2012, 9:30 am
wrote:

Do you mean with no wires connected to the switch? Yes.
But at the top you were talking about screws, not wires.
But the question you ask now is just a part of a whole, and if you understood what you were doing, you could have answered the question yourself. You should read austerity's url and study every wiring situation until you understand each one of them, even if you're only goin gto use one this time . And you should probably read more than that.
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<%-name%>
• posted on February 26, 2012, 12:05 pm
wrote:

Micky, believe me, I read a lot before I even started this job and thought I understood my 3 wire switch. Obviously I was wrong but as I wrote here, I was also reading. I do owe a lot GRATITUDE for the people here who were quick to help me. I will take your advice and read austerity's url . Thank you.
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<%-name%>
• posted on February 26, 2012, 12:13 pm
wrote:

I might add to my earlier reply that I'm sure glad I bought a multitester when I did (a couple weeks ago) in preparation for this job. I don't know how I could have done this job without it.
I'm still not done as I'm waiting for daylight before I mess with the leg end of this 3 way switch to unwire it again and test just the wires for voltage. I know I can do this job that's why I refuse to hire an electrician as my wife keeps asking me. Besides, this job is making me learn 3 way switches. I still need to wire up a timer on a 2 way switch but that's easy and I chose to do this 3 way first to challenge myself.
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<%-name%>
• posted on February 26, 2012, 7:09 pm
wrote:

Loads of people try, it seems. Since you can't see electricty except when it's sparking (not desired) , it sure is better to have a meter.

You'll figure it out. I had a head start on you, starting with my electric train when I was about 8.

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<%-name%>
• posted on February 26, 2012, 4:00 am
Doug wrote:

http://www.homeimprovementweb.com/information/how-to/three-way-switch.htm
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<%-name%>
• posted on February 26, 2012, 12:57 pm
Mr. Austerity wrote:

We are going to get this damn thing working yet,..... Here's how it works, this ought to help you understand just how simple the wiring really is,

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<%-name%>
• posted on February 26, 2012, 1:08 pm
On Sun, 26 Feb 2012 06:57:21 -0600, "Mr. Austerity" <"PrintMo.Money "> wrote:

Thanks !!!! Don't worry, I won't give up. Just glad I have a multitester to simplify. I mean if I know which wire is hot, there are only so many combinations before it has to work. Of course I'm not trying to discount the idea of learning the theory of a 3 way switch either. I want to learn the theory and with your help, others and google, I know I will. Thanks again.
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<%-name%>
• posted on February 26, 2012, 2:21 pm
On 2/26/2012 8:08 AM, Doug wrote:

What exactly, are you trying to do?
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<%-name%>
• posted on February 26, 2012, 9:10 pm

Trying to wire in a Intermatic ST01 timer on a 3 way circuit. I've farted around 1/2 the day and still no luck even tho I could have sworn I followed the instructions. My daughter said to me earlier that the reason it didn't work is because the installer had a few loose wires so I gave her the look. Anyway, that's what I'm checking for now at the main (hot) end because I think the remote (leg) end is tight. Keeping my fingers crossed.
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<%-name%>
• posted on February 26, 2012, 11:44 pm
On 2/26/2012 4:10 PM, Doug wrote:

Well, your daughter sounds like a wise woman. FYI, that timer doesn't wire like a standard 3 way switch. When installing the timer itself, you only need to know the common wire of the circuit. It gets attached to the black wire of the timer. The other two wires of the circuit go to the blue and red wires of the timer. This end of the circuit is done. Now you need to install the jumper on the other switch. You need to remove the common wire and one of the other wires from the switch, wire nut them together along with the small jumper wire. Once the 3 wires are connected together, you install the other end of the jumper on to the common terminal of the switch. Note: you will only have two wires connected to this switch. Now it should work.