As I work on the basement finishing (thanks for the great help in the previous thread) I have come to the thing that I have dreaded most: I need to install a three way switch where currently there is a single switch, and I don’t know the route of the existing wiring.
I do understand how a three way works, and I have wired them before, but here is the situation:
I have fixtures at the top and bottom of a stairway, both controlled by a single switch at the top of the stairs. As you probably know, there should be a second switch at the bottom of the stairs. I can see the wiring for the light at the bottom. That fixture has one wire that disappears into the wall and I THINK it goes up to the upper fixture, and then on to the switch. There is another wire (here, wire = nm 14-2) that disappears into a wall and I don’t know where it goes. So I don’t know where the circuit is powered from.
The switch at the top of the stairs is in a finished wall*, but since I will be sheetrocking the stairway (was unfinished, and I will finish it), if I had to do a little exploratory surgery it would not be the end of the world.
Once I know what wires go where, I think I can wire it up correctly, so I guess I am asking for suggestions on how I can determine this.
Sorry if that’s rambling and incoherrent.
Thanks
The stairway walls are finished down to the landing, unfinished below that. The treads and risers are that classic “builder’s staircase”
is the other wire (the unknown) that disappears into the wall at the top or bottom?
how many cables and wires go into the switch box at the top of the stairs? is the switch at the top of the stairs a single or three way? turn off that circuit, remove the cover plate and gently loosen or remove the switch so that you can see.
there may have been a 3-way circuit in place at one time depending on what you find. if there was and the wires are still good and correct then you might just need to add a switch, maybe extend wiring if needed.
if it wasn’t previously a 3-way circuit you will need to add cable to join the switches.
treat all wires as live until you test them to be off.
Seems a bit incoherent to me, but I was never good at word problems. Bottom line is: you need a hunk of 3-conductor romex to go to the 3-way switch at the bottom. Two of the wires are travelers, the other is either the feed from the panel, or the feed to the light fixtures. The two switches have to be linked together with the travelers for the switches to function properly. At present, you’ve got a single pole at the top of the stairs, which is only going to have line in, switch leg out. So it sounds to me like you’ve got to do more than just exploratory surgery.
First, IANAE, but I would procede thus… You need to be sure which way the feed comes. It might enter at the light fixture or the switch, could be either. If you are O.K. wirh electrical work, shut off the power, pull out the light so you can see how many conductors are connected. If you have just one cable into the box (black and white wires and bare ground), then the power feed is at the switch. At any rate, as already mentioned, you will need a three conductor cable to make connections. If you are happy with doing drywall you might open the wall below the switch, unstaple the present cable, and use that to pull through the new one. I believe the three way switches will have a diagram in the box to help figure out the terminals
To determine if the switch at the top is a three way switch not, just look at the switch does it have on and off on the handle, if ye it is not a three way.
You are probably going to have to pull some wire. You need to determine if the power comes into the switch box or the light fixture. As stated locate breaker and turn off, then check for power to be sure circcuit is dead. Then it is just a normal wirring job.
To clarify, you can’t run a two-switch configuration without a third wire. If you are lucky enough to have both ends of the wire (white/neutral and black/hot) in each switch box, you can likely make it work, but what typically comes into a switch box is just the switched (black/black) loop. There’s no way to convert that connection to three-way switching.
Along with what’s said above, another way to trace the wires: Turn off the power and use an automotive continuity light. It will have to have a very long lead, i.e. you’ll have to use an extra piece of wire. Also make sure any wire you test is completely disconnected, only test bare end to bare end otherwise the circuit can travel outside that length of wire.