3-Way Switch Wiring

MrBill_DIY · 09-05-2008, 08:10 PM

Many years ago a tenant in my townhouse condo took it upon himself to replace one of the 3-way switches (the one in the basement rec room) with a dimmer switch, which no longer dims. Last week I took out the old dimmer switch and tried to replace it with an ordinary 3-way switch. Of course, I didn't know how the circuit was originally supposed to be wired. When I opened up the box, the old dimmer was connected by three wires (red, black, and white) by pigtails to wires of the same color. There were three cables going into the box, but I didn't disturb any of the wires except for the three already connected by pigtails to the old dimmer switch. The example in my how-to wiring book seemed to suggest that the black wire, which is from a two-wire cable, should go to the common terminal of the 3-way switch, and that the other two wires (which I assume are also hot wires) could be interchangeably connected to the two traveler terminals. When I tried this, the switch (which is downstairs) will work only if the switch at the top of the stairs is left in the "down" position. Similarly, the upstairs 3-way switch will work only if the new downstairs switch is left in the "up" position.

I'm wondering whether just switching the red and white wire connections might fix this, although I thought these are traveler wires that are interchangeable. Could that work?

Here's another thought: My townhouse condo is in a large neighboorhood of hundreds of nearly identical units, all wired at the same time in 1974. I'm guessing that they are wired the same way, according a single electrical diagram, even down to the wire color that goes to each switch. If this is true, my next-door neighbor can tell me how his downstairs switch is wired and I can get the right answer that way, without getting into voltage testing and all that. Can I assume that two otherwise identical houses are wired identically?

220/221 · 09-05-2008, 08:28 PM

It could be wired several different ways. Assuming that he didn't mess with the other 3 way it should be easy. Even if you dont have a voltage tester, there are only 3 possibilities.

ONE of those 3 wires goes to the common terminal. The other two can go on either of the remaining two terminals. Try black as common, then white, then red. If it still doesn't work properly there is another issue.

darren · 09-05-2008, 11:41 PM

You said your complex was built in the mid 70s. Check and see if you have aluminum wireing, if you do this would make it more complex them simply swapping switches(unless there rated for aluminum)

SD515 · 09-05-2008, 11:50 PM

For your use as a reference and understanding of 3 ways.

3 way switch wiring:

White from the source goes directly to the load.

Black from the source goes to the common terminal of one of the 3 way switches.

Black of the load goes to the common terminal of the other 3 way switch.

The travelers get hooked to the remaining terminals.

If you have to use a white as 'hot', it has to feed a switch and be taped black at both ends.

What it sounds like you may have is the wrong wire on the common term. Not your fault, probably done that way by someone before you. Try what 220 suggested...I'm putting my money on the white being the common. I would have tried to avoid that, but I've seen it before.

220/221 · 09-06-2008, 04:18 AM

Quote:

Check and see if you have aluminum wireing, if you do this would make it more complex them simply swapping switches(unless there rated for aluminum)

Quote:

the old dimmer was connected by three wires (red, black, and white) by pigtails to wires of the same color

Quote:

all wired at the same time in 1974

Pigtailed aluminum.

MrBill_DIY · 09-06-2008, 12:52 PM

It's definitely not aluminum wiring. I was surprised that the white white wasn't marked black, since I know that's required for a white wire that's hot (which I still assume it is).

I'll try putting the white wire on the common terminal, as soon as this hurricane blows over.

darren · 09-06-2008, 11:35 PM

It is a requirement to change the white to a different colour(either black or red). I don't beleive I have ever seen it or have done it myself. In my defence, any electrician that takes off a switch and see a white wire on the switch will know that it is the hot.

SD515 · 09-07-2008, 11:15 AM

Quote:

Originally Posted by darren

It is a requirement to change the white to a different colour(either black or red). I don't beleive I have ever seen it or have done it myself.

I've seen it done. The source and the load entered the same sw box, and they tied the white (and didn't re-identifiy it) of the 14/3 to the 'hot'. They didn't put the source on the common at the first sw, and tie the 14/3 black to the load (as would be typical in my area).

Quote:

Originally Posted by darren

In my defence, any electrician that takes off a switch and see a white wire on the switch will know that it is the hot.

That's the way it should be done...but I never assume anything someone else has wired.

Wildie · 09-07-2008, 06:53 PM

Quote:

Originally Posted by SD515

I've seen it done. The source and the load entered the same sw box, and they tied the white (and didn't re-identifiy it) of the 14/3 to the 'hot'. They didn't put the source on the common at the first sw, and tie the 14/3 black to the load (as would be typical in my area).

That's the way it should be done...but I never assume anything someone else has wired.

If a white conductor is used as a 'hot' lead it should be re-colored, unfortunately this requirement did not apply in the 'good' old days!
Bet there's millions of houses out there, that have 'white' conductors.