Electricity and three way switches

I know enough that I can probably debug with enough time, but I am hoping these symptoms are common enough that the answer is well known so I can save time.

Disclaimer: Please stay on topic. Do not tell me that I don't need three way switches, that I don't need a light in my room, that light bulbs are only for people not manly enough to use candles, that nothing good happens when it's dark enough outside to warrant lighting of any kind, or any other silliness.

I have two separate situations. Let's start in the kitchen:

There are three switches which light the same light. It's now a fan with a remote, so I can use it to decide if I want the fan and/or the light. When I installed the fan, the first thing I did is to turn off the three switches and pull the old light out. When I did I found that there was 24Vac on the line. Flipping any one switch on (I think) makes 48Vac or so. Only when two switches are flipped do you get 120Vac. The light works even with one switch on, and my meter is fine.

Next we go into the den. In the den there are two switches which control the same light. Both of these have to be on to make the light come on. In logic parlance, this is an AND gate rather than an OR gate. I am guessing that one of these switches is either nit a three way switch, or not wired as a three way switch. I have not put a meter on this one... yet.

Den first- you've got a 3 way switch wired wrong...

First, look at the switches. If they have the words "On" or "Off" on the toggle, they are not 3 way switches. They are double pole.

If both are 3 way switches, time to look inside. Kill the power, and unscrew the faceplate and switches. You should see 3 terminals on EACH switch for the common and travelers. Next, you should see 3 conducters (usually white black and red) coming into the box. If you don't have 3 conductors, it will NOT be possible to make the switches work as 3 ways (they can't be an "OR gate").

So, now you know you've got the right switches and wiring. Next thing is the connections. There are a couple of ways to wire a 3 way (depending on where the power line source is- the fixture, or the switch). I suggest printing a wiring diagram off Google, and tracing the wires carefully.

For the kitchen... it's the same procedure, except you can't do it with 3 way switches. You need (2) 3 way switches and a 4 way- the 3 ways will have 3 terminals, the 4 way will have 4 terminals. Again, you will need a wiring diagram (and some patience).

As far as the voltage- I'm clueless.

BTW, I am not sure what you mean by "ON". If you mean the switch is in the up position, that's not necessarily on. A 3 way switch reverses when the current is routed through the opposite switch- sometimes up is "ON", and sometimes down is "ON".

SVreX wrote: BTW, I am not sure what you mean by "ON". If you mean the switch is in the up position, that's not necessarily on. A 3 way switch reverses when the current is routed through the opposite switch- sometimes up is "ON", and sometimes down is "ON".

If you are referring to the kitchen, I had Tunawife flip all switches up and down while I watched the meter. It was... entertaining.

Making a light come on from either of two switches was not done until the early 1970s. This is because it was easier to put a man on the moon than figure it out! NASA Engineers, still buzzing from their space-travel accomplishment, said "OK, let's tackle the hard stuff now!"

(it is possible that I have incorrectly wired this several times and have decided that I like the dark better)

The low voltage is concerning. I'd be very worried that something internal to one of the switches was misbehaving. Are you sure one of them isn't trying to turn off the ground or something silly like that?

When measuring the voltage were you measuring between the leads, or between the leads and ground?

You may have a floating ground or you neutral isn't at 0v.

See if the 24v is still there with the circuit braker for those lights turned off.

mazdeuce wrote: The low voltage is concerning. I'd be very worried that something internal to one of the switches was misbehaving. Are you sure one of them isn't trying to turn off the ground or something silly like that?

I haven't dived in yet. I know the schematic, and I know how to operate the switches, but in between is a big fat "?". I was hoping someone would say "oh yeah that happens when the one four way switch is installed upside down and the wires blah blah blah" like you'd answer if I was a non-car-guy and asked why my TPMS went off when it got cold outside.

jstand wrote: When measuring the voltage were you measuring between the leads, or between the leads and ground? You may have a floating ground or you neutral isn't at 0v. See if the 24v is still there with the circuit braker for those lights turned off.

Between the leads.

There was 0 with the breaker off.

When I find myself in that situation, I unwire everything, chase all the wires out, label them, and start from scratch. Even standing there with the meter in hand, unless you know exactly which wire goes where, straightening out someone else's mess is a PITA.

In reply to tuna55:

i would check between the leads and ground (breaker on and off) just to rule out the neutral being the source of the 24 volts that you measured.

You should check to make sure the ground stake is connected properly along with visually inspecting the wires running to the house.

I'm assuming there are no dimmer switches involved?

BTW, 3-way switches are logically XOR gates (or XNOR, depending on which way you mount the switch), not OR gates.

Presence of that voltage indicates that something is definitely wrong. Should not be getting any readings other than 0 or 120. Could be a bad switch or a wiring mistake. Can't really tell without tracing it all out.

Use SVreX's explanation and Toyman's diagrams to trace it all out.

Den update:

Everything is 96Vac or 0. Weird

The one switch which has a dimmer on it had an unused screw, the one you use with a three way. I found hot and tried to wire it the two ways that make sense but it's still not right.

The switch without the dimmer is red white black. The switch with is red red white. In both cases the white is hot. The dimmer three way has a neighbor used to operate the fan. That one is a two way and is black black black. Not sure why there are three wires. I wonder if the three way needs one of those blacks.

tuna55 wrote: Den update: Everything is 96Vac or 0. Weird

96+24=120

So the the numbers make sense, mathematically.

But the question still remains, where is the 24 volt difference coming from?

You saw 24V when checking the first time and 96V this time, so something that should be at 0v relative to ground is really 24V.

Not to be repetitive, but it sounds like you have a ground issue that is letting the neutral be at 24v relative to ground and causing the funny readings.

Switches are cheap, I would pick up a couple more and wire them in instead to determine if that's what's causing the sneak path.

Putting a dimmer on the power for a fan seems like not a great idea to me.

Sorry guys:

24v was in the kitchen.

96 was in the den

The dimmer is on the den light, not the fan.

Now I feel like you should check the whole house. Something weird is going on. And according to my friend who designs and builds industrial motors for a living, dimmers on motors are a bad idea. They technically work, but they're bad for the motor. (This is for others, I know thst's not how yours is)

This is my new favorite internet mystery. I'm intrigued.

My hypothesis is that somebody added that dimmer, and it's not a 3 way. I'm not sure I've ever seen a 3 way dimmer.

That would explain why you have weird voltages, AND why the switches don't work properly.

(BTW, there's no such thing as a "2 way switch")

Probably doesn't explain the kitchen.

The colors on those switches are meaningless until you trace them. Since they change color, it's almost a certainty that the line comes into the light, then wires the switches from the light. And it's ok if the white is hot on a 3way switch.

mazdeuce wrote: Now I feel like you should check the whole house. Something weird is going on. And according to my friend who designs and builds industrial motors for a living, dimmers on motors are a bad idea. They technically work, but they're bad for the motor. (This is for others, I know thst's not how yours is) This is my new favorite internet mystery. I'm intrigued.

Read above, no dimmer on fan, dimmer on the light which is within the ceiling fan. The fan itself is on the neighbor switch.

SVreX wrote: My hypothesis is that somebody added that dimmer, and it's not a 3 way. I'm not sure I've ever seen a 3 way dimmer. That would explain why you have weird voltages, AND why the switches don't work properly. (BTW, there's no such thing as a "2 way switch") Probably doesn't explain the kitchen.

Dimmer is a three way

It even came with a sticker! (That's how I knew it was wired wrong, because the sticker was untouched and had no wire going to it) I just stuck the sticker on there for the sake of the photo op.

Yup, I got that, this was more of a "for those reading along, don't do that" type of thing. It's absolutely the type of thing I would have tried in my younger days. I'm better now.

I love electrical mysteries. I have been searching the internet for answers to this one since I can't speak from personal experience. Are the den lights and the kitchen lights on separate circuits? If so, does turning one breaker off allow the other one to test normal (no voltage when the switch is off)? This may point to a multi branch circuit with a shared neutral. If I am understanding correctly moving one breaker to the other supply leg would correct the overloaded neutral. I may be way off here...

I'd swap out that dimmer for a $3 three way switch from HD to see what that changes. I've had some very weird failures with dimmers over the years.

In reply to tuna55:

It's not a 3way dimmer if it only has 2 wires connected to it.