Why are those switches that work in pairs and allow you to turn on/off lights from either end of a hallway called “3-Way” switches? Why not “2-Way”?
I know how they work. I just want to know why they’re called “3”. They operate from 2 different places. There are 4 possible switch settings. The only thing I cxan think of is that each switch has 3 contacts.
So, why 3-Way ?
That’s it. There are three terminals where current can flow. The term ‘way’ is a bit misleading. In hydraulics or pneumatics it’s also used to describe the number of ports used to provide fluid flow in a solenoid. For instance, a 5-way solenoid has 5 ports through which fluid flows at some point during normal operation. I’m not sure how the term way came to be used in this manner. I’d like to know though.
I call them “SPDT” switches.
heretic!
If it helps, there are 4-way switches. If you count the terminals there are four. Ground is not included since it isn’t supposed to carry current during normal operation.
Like many electrical terms its so the average Joe get confused and decides to call an electrical rather then do it himself.
When I wanted to know how to wire one, I googled “upstairs/downstairs switch” and got loads of hits. Including one with detailed wiring instructions.
There are a lot more ways to wire one of those than you’d think. It’s a question on one of our labs, and it seems like every year or two, some creative student who hasn’t seen the standard wiring diagram manages to come up with a new way to do it. I think I’ve seen five different methods, plus a sixth that would get the desired behaviour out of the light bulb but which would be a short when turned off.
Chronos, you’re absolutely right. Unfortunately, each of those combinations has been tested by a homeowner somewhere. I had a co-worker ask me to look at their basement to see why their switch would only work in one position. I found they had used 14/3 wire and were determined to use every conductor. I was measuring a dead short in some positions with the power off. I couldn’t believe they hadn’t tripped the breaker but then found that was wrong too. It was funny after the fact.
Ok, why do I have a bathroom switch that is not binary? Up is light and fan, down is fan, and off is this frustrating little slice of middle. I have trouble with it as an adult; I doubt young kids could literally use it.
Interesting. I’ve never seen that; having a separate switch for the fan is so much better, because then you need only turn it on when you’re clearing the room.
I’ve got a hallway light that can be operated from three different switches. At any of the switches, turning the switch up or down will turn the light on or off, reversing whatever the previous state was. I wonder what kind of switches those are, and how the wiring works.
And somebody commonly buys a 4-way switch when they want to have 3 switches to control their light, continuing the N-1 places phenomenon noted by the OP. Of course, they can actually stick as many 4-ways as they like between the two three-ways as per that diagram and have an arbitrary number of switches for the light.
ETA:
suranyi, your post crossed this one - look at the provided link on the four way switch.
That’s a ‘four-way’ switch. Link.
I like a separate switch better too. Even better again, to me, is to have the fan on a timer so you don’t need to go back and switch it off and you can let it run for a good chunk of time.
Yes, but only one of those led to shorts. I mean that there were five different circuits that worked and didn’t produce shorts. They do all have their flaws (there’s a reason the standard is the standard), but they all worked. Several of them, for instance, would end up reversing the hot and neutral at the bulb in the two different “on” positions, and I suspect all of them would end up using more length of wire in a real house situation.
This thread showed up just as I was grappling with my own 3-way switch problem. We had company this weekend, staying in the basement bedroom. We have three switches wired to the basement lights and somehow, our guests manged to use all three of them to turn the lights on and off. Now we have switches in both the up and down position and I can’t figure out what order to flip them, so the lights are off and all three switches are in the down position. Help?
Put all the switches in the down position in any order. If that configuration previously corresponded to lights off, it will again. The switches have no memory.
Ah! I logically deduced some time ago that our hall light worked that way, but I’ve never seen the working parts of a 4-way, or one on sale, or any documentation. (I wired a pair of 3-ways, or “2-ways” in Brit parlance, a while back: the load to L1 and L2 of one switch, and 3-core+earth between the corresponding terminals of the two switches. Each switch can connect either L1 or L2 to C, but not both, so the circuit makes only when either switch is connecting L1 to C, and the other C to L2. Obviously, for a third switch to work, it must go between them and connect L1 and L2 either straight through or crossed - if it’s wired for C at all this must be a pass-through.)
In our jurisdiction it is illegal to have a separate light-only switch if there is no openable external window in the room. The light switch must also turn on the fan.
Stupid law, but there you go.