Need to wire a 3-way switch. Any help?

**HiredGoon** · February 22nd, 2009, 06:04 PM

I'm trying to attempt what should be a simple little project and need some help.

Want to install a motion detector wall switch in a hallway. This is a 3-way switch with a switch at the top and at the bottom of the stairs, both controlling one ceiling light.

I have installed single switches before, but not a 3-way.

The original switch was installed about 45 years ago and has two black wires on one side and one white wire on the other. No separate ground wire at all.

The new switch has a green ground wire, and a red, black and brown wire.

I have the instructions for the new switch. The old switch is not marked anywhere for "common" as they sometimes are, I guess.

The new switch also says to use a jumper wire from the common to the traveller.

And no, I don't have any electrical testing gear

So is there a way to figure out which is the common...other than trial and...ZAP...error?

I did take some pics of the wiring if that will help. The 2 blacks are on the left side looking in and the white on the bottom right.

Any help appreciated. Yes, I did have the breaker off while checking this

Thanks!

**gnbrotz** · February 22nd, 2009, 06:15 PM

Go to your local home improvement store and spend $20 for a multi-tester?

I'd let ya borrow mine, but it's a heck of a drive.

**Don T.** · February 22nd, 2009, 06:23 PM

There can be a number of different ways they're hooked up. This guy's site should provide some help & easy to read schematics. http://www.electrical-online.com/wiringdiagrams.htm

+1 on the multi-tester. I never leave home without it!

**MrBi11** · February 22nd, 2009, 07:06 PM

Typically the common connection on the switch will have a different color screw [1 silver vs 2 brass], it'll most likely be the one with the white wire connected to it, but that depends on the person who wired it.

[by the national electric code that white wire needs to be marked to be used as a hot wire as it is being used]

To test, remove one wire from the switch [carefully] making sure it makes no contact with anything, turn on the power, if you can make the light work from the other switch it's not the common one. Shut off power, replace wire and try a different one. when you get the one that you can't turn on the light, it'll be the common terminal.

Disclaimer: your personally safety is your responsibility

**HiredGoon** · February 22nd, 2009, 09:38 PM

Originally Posted by MrBi11

Typically the common connection on the switch will have a different color screw [1 silver vs 2 brass], it'll most likely be the one with the white wire connected to it, but that depends on the person who wired it.

[by the national electric code that white wire needs to be marked to be used as a hot wire as it is being used]

To test, remove one wire from the switch [carefully] making sure it makes no contact with anything, turn on the power, if you can make the light work from the other switch it's not the common one. Shut off power, replace wire and try a different one. when you get the one that you can't turn on the light, it'll be the common terminal.

Disclaimer: your personally safety is your responsibility

Thanks for the replies guys

The screws all look black and there seems to be nothing to indicate common. As I said it originally was wired about 45 years ago and not touched since. Maybe I can try and clean off the screws and see if I can make out a color. Power off of course.

Thanks for the tip on removing one wire at a time...that helps. I'll see what I can figure out tomorrow.

**HiredGoon** · February 23rd, 2009, 01:35 PM

Hey...my 3 way went very well

Oh and I got the 3 way switch installed just fine also. It has a motion sensor on it which is nice. I set the light to go out after 1 minute of inactivity...just what I needed.

Thanks again guys.

**MrBi11** · February 23rd, 2009, 04:33 PM

kewel, and you learned a new trick for testing besides

**HiredGoon** · February 23rd, 2009, 05:06 PM

One funny thing to pass on... I had just come back upstairs from turning off the correct breaker, went to the open switch box, touched a copper wire and...saw a little spark

I was like... WTF!!!

I knew I hit the correct breaker.... then I realized I had picked up some static electricity from walking across the carpet and.... a small ZAP... ha ha ha

Yeah...that white wire was my common, so that tip worked great the first time.

Now on to installing a single pole remote-control dimmer in another room and I am done with my electrical work for the rest of the year probably