How do I find the main load switch in a 3-way switch set-up?

[swc69]

Greetings all,

I'm trying to install some switchlincs to replace some 3-way switches in my house.

The installation requires that I install the master switch at the load control point, and the slave switch at the other point.

How do I figure out which switch is the load control switch?

I pulled both switches out of the wall, and used a simple voltage tester on the leads on the side of each switch. Depending on which switches were on or off, I could detect voltage on either one.

If I disconnect the HOT from one switch, and the lights still work, then is that the slave switch? (Or vice-versa - if I disconnect the hot and the lights don't work is that the master?)

Or should I just disconnect the red traveller wire? Whichever switch works after that that is then the load?

Is there a better way to tell?

Thanks!

Steve C.

[swc69]

OK - unhooked the red traveller wire - and then the lights didn't work at all.

So that's not the solution.

Any suggestions?

Steve C.

[NutsyHome]

"Usually" there's a White-Black-Red conductor cable that connects the two switches. The switch with the live incoming feed will have another White-Black cable coming into the box, which would be your "Hot" main power supply.

If yours isn't based on simple, apparent wiring, you may need to do the more complicated method. . . Disconnect all the wires from both switches. Then use a meter to find the single White/Black pair that's hot.

^^ All of the above assumes you're following proper electrical safety measures, turning off breakers when appropriate, etc, etc.

[swc69]

Hmm - it just so happens that both the swtiches I'm replacing are in a dual box with a second adjacent switch that controls something completely different. (So there's a lot of wires coming into/out of each box. )

If I was to disconnect all the wires, what pair would I test for voltage?

Or, to be more specific - am I looking for voltage across the random black wires or do I need to test the black wires against a neutral (white) wire?

Thanks for your help.

Steve C.

[pete@malibubeach.com]

Some months ago, I posted a picture showing the two possible ways 3-ways are wired:

http://board.homeseer.com/showthread.php?t=114667

The first diagram is nuch more common (and, in fact, may be the only legal way these days). As you see, you do not necessarily have the hot wire and the load in the same box. Most switch boxes will have a common (white) wire. If both have a common, then you can use either for the master. If only one has a common, then you need to use it for your master. Since there are two travellers (generally any color other than black or white), you can use one of them as the signalling wire between the slave and the master switch and the other to get the missing signal across: that is, if you put your master in the box with the hot, use the second traveller to get the switched load over to the other box where the wire to the actual light fixture is; and if you put your master in the box with the wire to the fixture, then use the second traveller to get the hot (black) over to it (assuming there is no hot in that box already).

If you are in an older house with the second wiring approach, then you have a different problem: while you have a hot, a common and a wire to the load in each box, you do not have a traveller to carry the switching signal from the remote to the master. Really, the only solution here is to use two masters coupled together with links (in the UPB world) or their equivalent in Insteon or Z-wave worlds. This will mean creating a dummy device and then either let the technology do the coupling of the devices (links) or let Homeseer do it (detect a command from one and echo it to the other).

Hope this helps,
Pete

[swc69]

Pete - thanks for the info.

My house is only a few years old so I'm assuming that I have the more current/common configuration. I also scoured many other web sites that are very clear on how the 3-ways are wired in general, but I've still found nothing that helps my actually tell which one is the master.

I think my issue is complicated by the fact that box one currently contains a single and a three way switch, with three cables coming in, and box two contains two 3-way switches, with four cables coming in. So for me, its not intuitive as to which sets of wires constitute the main Hot or Load wires.

Lets go back to nutsyhome's suggestion about testing the wires for voltage:

I assume I need to connect my tester across a pair of wires to detect voltage. Should I be testing among all the black wires? or should I test each black wire across a white (neutral) wire?

If someone can help me with that question then I should be all good to go to figure out the rest of it.

The smarthome manuals shows testing the wires using some device that only requires a single contact point. I wasn't aware such a device existed (i.e. - seems like you'd have to have two contact points to create a path to test for voltage).

In addition to my $5 110V two-prong tester, I also have a volt/ohm meter - is there some way to use that to test voltage on a single wire? (instead of a pair of wires?)

Thanks all,

Steve C.

[joeslat]

Remove the existing switches and leave all those wires hanging separately (I hope I'm not over-simplifying and you know how dangerous this all is and you are careful). Then test all the non-white (black or red) against a ground wire. There should be only one that tests out 110 v. That's the 'hot.' It might be coming directly into the gang box or it might be coming off a wire nut if there wasn't enough slack or there are more than one switch in the box. When you find it, trace it back to the entry point, because 'usually,' your electrician may have used a standard, like "hot always comes into the box from the top left.' Not always the case, but I've found it to be a good guide and it saves a little time next time you do this.

What I do from here may be a little unconventional, but I've never been able to figure it out unless I do this. I'm searching for which is the load and which is the traveler, and colors haven't been reliable, or I don't remember.

In the gang box where the 'hot' isn't coming in, (remembering that all wires are currently disconnected), I connect one of the two non-white wires to a neutral. Then go back to the hot and tap it on the remaining non-white wires. After the spark and noise and your wife screaming, your light should have come on and you have found which wire is the "LOAD."

Here is another idea. You could take out the light bulb and do a continuity test across the two suspect wires to figure out which one is load and which one is traveler. For example, get a bunch of wire and spread it from one gang box to the other, and connect one end to the red (or black or blue or whatever), then use your ohm tester to test continuity and see if you get a signal. If the light bulb is out, you won't get be able to complete the circuit. Test it again with the light bulb in. That's how I figure out traveler v. load.

I've also had a situation where the wires in the light fixture weren't wired consistently, so, although the light 'works,' the traveler and load wires were not configured right. Hard to explain, but in this case I had to ultimately use the 'virtual 3-way' approach, using 2 primary x10 switches, where one acted as the switch and the other simply acted as a transmitter.

Hope I don't get you electricuted.

Joe

[pete@malibubeach.com]

Once you've found the hot, it is really pretty easy --- the other two are the travellers; they go to the traveller contacts on the other switch. And the last wire coming from the common contact on the other switch has to go to the load. To confirm this (WITH THE POWER TURNED OFF), disconnect all the wires (three from each switch). Your ohmmeter should measure a resistance on the load to ground (won't be zero, but it also won't be infinite---the amount depends on what is on you r load). The take out the light bulb(s) and measure again. This should move the resistance to infinite.

Another thing I've done to identify which traveller is which is (again with all wires disconnected) measure the resistance at each end of the traveller (each switch box). This is actually pretty eay if you have a long extension cord: run the extension cord from one box to the other and connect the traveller to it at one end--now, at the other end you can measure the resistance. Note that alternatively, you can (this time with the wires connted as they originally were to the switches) turn the power on and measure voltages at both switches. Again, I recommend removing the loght bulbs, as you can get spurious voltages floating around that may confuse you (if you see any voltage other than 120VAC, assume it is zero -- not saying to touch the wire, but in most cases you PROBABLY could.

Finally, it doesn;t sound like enough wires in your boxes: you need three wires to each 3-way (two travellers and either power or load) and two for the regular switch (power and load). Obviously the power can be shared between the 3-way and regular switch. But you don't describe enough wires (unless, by 'cable' you mean 2-conductor Romex or something like that). But if you truly have as few wires as you indicate, there may not be a common (white) wire, in which case you are in trouble in terms of installing UPB (or anything except X-10).

Last, in terms of mearuing voltage: you should measure between the wire in question and ground or common. If your junction boxes are metal, they are gorunded and you can measure to them. If not, you need a white or (common) or green (ground) wire to test against.

Pete

[joeslat]

Pete, I'm amazed at how similar our replies were, and by the times it looks like you hadn't seen my post. Is that true? Funny, of all the 100's of 'how to wire 3-way' posts here, I've never seen these methods mentioned, and here we are roughly saying the same thing about testing with ohmeter and removing light bulbs and such. I guess I'm just happy that my methods weren't so crazy after all, considering I'm just an HA geek with no electronics background.


Joe

[pete@malibubeach.com]

Actually, I probably typed that in about the same time you did, but it sat for 45 or 60 minutes before I finished it and posted it. Except for the touching hot wires to find the load, I agree with you completely (and, to be honest, I would probably do what you said, just not sure I would suggest it to anyone else!!).

But i have always found the easiest way to trace the runners to be an ohmmeter and a long wire (usually an extension cord is the most convenient) that I can run from one switch to the other.
Pete

[tman1]

If your travelers are clearly color coded you can use one of them for the "extension" cord in the above suggestion. It runs (probably) to the box your testing between. WITH POWER OFF. Attach one lead to the travler and one to the wire your are "pinging" for. Go to the other box and touch the marked traveler to each of the wires your unsure of and when your "assistant" hears the meter beep, BINGO. This method can also work using the ground wire or nuetral to find your first "known" wire. Rewired an outbuilding ran in all conduit once, the owner agreed to pull the wires and I would do the finish work. He ran it all in the same color. What a mess!

Later, hope this helps. Terry