How to reverse a three way switch?

Question

I have a set of lights that are controlled by two different switches. Flipping either switch at any time always changes the state of the lights (on to off or off to on).

I have OCD and so I want both switches to be in the down position when the lights are off. Right now the lights are off whenever the switches are pointed in different directions, and the lights are on whenever both switches are in the same direction.

I remember playing a "game" as a kid with three-way switches (that controlled the stairway lights) where by running up and down the stairs I could change the order for which the lights would turn on. Is there an "algorithm" for the order with which to flip the switches in order to get to my desired state (both switches down = off), or do I need to physically go and remove the wall plate to rotate one of the switches? If so, which one?

Currently:

Switch A	Switch B	Lights
DOWN	UP	OFF
UP	UP	ON
UP	DOWN	OFF
DOWN	DOWN	ON

Desired:

Switch A	Switch B	Lights
DOWN	DOWN	OFF
UP	DOWN	ON
UP	UP	OFF
DOWN	UP	ON

If this is a better question for StackOverflow, please let me know.

Answer 1

Don't make it harder than it is lol.

Pick either switch. Flip it over.

3-way switches are symmetrical. They do not have an "on" and "off" legend.

So no wiring is needed. Remove the cover plate, remove the 2 screws attaching it, feel to see which direction it will flip the easiest given the wires attached, flip and screw it back on. Be careful that the ground wire doesn't hit the side screws.

Only flip one switch.

I have OCD and so I want both switches to be in the down position when the lights are off.

Me too. This is how I deal with it.

Answer 2

Swap the travelers at one end

Pick one of the two switches involved, and with the power off, swap the two traveler wires so they land on the other traveler terminal on the switch compared to when you started. This will fix your "cross-ways" three-way switch. (Just don't mess with the wire connected to the differently colored hot screw on the switch, as that's a common wire, not a traveler.)

Answer 3

Two approaches:

1. On the switches you SHOULD have two terminals in one color and one terminal in another color. Not all switches are built this way. But if you do, just on one switch swap the two wires connected to the same-colored terminals. (Ignoring the ground terminal, that might be green or brass, and will have a green or bare copper wire attached or no wire attached. IE, besides that one, there should be three more and two of them might be the same color.)

2. Physically turn one switch upside down. Hopefully you can do it without disconnecting any wires, but if any are too short or too awkward to twist around the rest, disconnect only what you must to be able to turn the switch upside down, then reconnect them to the same place they were. In case your switches are marked with a "Top" and you wonder if that matters, this Question might help (but not very much).

Answer 4

To explicitly answer your question here:

Is there an "algorithm" for the order with which to flip the switches in order to get to my desired state (both switches down = off)

No. Here's why:

Let's call down D and up U. We can represent each state of the combined two-switch system as a node in a graph:

• DD (on)
• UD (off)
• UU (on)
• DU (off)

From any state, either switch can be flipped to cause a state transition (eg. DD–>DU or DD–>UD). Likewise, after flipping either switch, one can flip that same switch again to transition back to the original state (eg. DD–>DU–>DD). This makes the graph a symmetric directed graph. So, if the nodes as listed above are arranged clockwise on the corners of a square, then the graph's edges trace the edges of that square.

Your problem asks to starts at a state in {DD, UU} and perform an even number of transitions to reach a state in {DU, UD}, so that the original on/off state will be preserved by the end of the sequence. Note that both {DD, UU} and {DU, UD} are states at opposite corners of that square. I'll skip a formal proof, but this should make it obvious that any sequence of such transitions will take an odd number of steps, and thus the on/off state cannot be preserved without changing some wiring.

Answer 5

Each switch is known as a "single pole, double throw" or SPDT. This means that the centre common terminal can be switched between the other two, known as L1 and L2.

Wikipedia has a good diagram:

As earlier answers have said reversing the connections to L1 and L2 on one switch will result in your light being off when both switches are down. However it will also be off when both are up and the light will only illuminate when the switches are positioned differently. The annoying positioning is unavoidable if you want two way switching without "something" remotely moving the distant switch.

Answer 6

I solved this by using impulse switches and a impulse relay at the lamp.

This can also be a tremendous simplification of wiring, as there is only a single 'switched' line common for all switches.

I don't know if it's legal or otherwise acceptable in NA though.

Answer 7

That is easy,

On a 3 way switch there are wire 1, wire 2, and common terminals. For two switches, if you connect wire 1 to wire 1, wire 2 to wire 2 it will work as shown in the first table.

If you connect the two switches as wire 1 to wire 2 and wire 2 to wire 1 it will work as shown in the second table.

Alternatively, connect as 1-1/2-2 and mount one switch upside down.