My son’s house has five switches controlling the same stairway light. One in each bedroom, one in the upstairs hall and one at the bottom of the stairs. How is this done? I know how a “3-way” switch (which I always called an upstairs/downstairs switch) works, but I can’t quite figure this out.
Is it truly 5-way (each switch can turn the on light off and the off light on no matter how any other is set) or are they parallel or series (all have to be on, or all have to be off, or one is a master, some override, etc.)?
They make 3 and 4 way switches and I believe there’s a way to use a combination of them to expand above 4 switches controlling one load.
How new is the house? If it, or the wiring, is new enough that it’s not a typical switch where you’re actually opening and closing a circuit but rather using wifi switches or low voltage switches (that control relays, which in turn control the lights) you can probably do just about anything you want to do.
If these are indeed hardwired switches, then two of the switches are 3-way switches and three of the switches are 4-way switches. You can add an arbitrary number of 4-way switches between two 3-way switches. Lots of extra wiring, though.
In my current house I was able to use “smart” switches so that the outside lights are controlled from four switch locations.
You can control a light from as many switches as you like. Your electrical supply house will sell you 2 3 way switches to control a single light, and as many 4 way switches switches as you like to add. Those are sometimes called SPDT (single pole dual throw) and DPDT (double pole dual throw), although it really doesn’t match the electronics use of the DPDT term. Pretty simple, actually:
The trick is that the 4 way just switches two leads coming in one side with the two leads on the other side. At each end you have the 3 ways that switch a single wire on one side between two other leads.
Just as compelling is, “Why?” My brother’s house has a switch at the bottom and one at the top of the stairs, which has always sufficed quite nicely. Why a gazillion switches?
The typical reason is to be able to turn on the stairwell light no matter where you start from, thus avoiding having to stumble around in the dark. I have also seen setups involving timer switches (push a button outside your apartment door and the light switches on for a certain period of time).
In a small single story I have a hallway light controlled from 3 switches, which is reasonable - one switch in the living room, one in the master bedroom at the other end of the hallway, and one by the front door which enters on to the hallway. Five does seem a bit excessive, although I note that mine doesn’t allow you to switch the hallway light on from the other bedrooms which are along the hallway.
Perhaps it was just an electrician showing how smart he was…
The stairs are likely the most dangerous place in your house (maybe second-most-dangerous after the kitchen). Reducing the need to approach them in the dark when you’re half-asleep might be one of the more safety-conscious design decisions you could make.
Wikipedia is your friend:
Actually quite simple when you see the schematics.
Thanks. I answer to some of the questions raised, the house was built in 2010 and, yes, the stairway light can be turned on and off from any one of the five locations. And it means not having to stumble down an unlit (okay there is a small night light on a baseboard) hallway. Quite convenient really.
I will really have to study those wiring diagrams in the wiki article more carefully.
We have two switches for the stairs between the first and second floors, and it would be nice to have additional ones on the first floor. When you turn off the lights on the first floor, you have to first go over and turn in the stairs light, then go back to the other light switches to turn them off. Otherwise you are just walking in the dark. Depends on the other lights, it can make sense.
I have outside flood lights that are controlled from 4 locations. There are switches located at each outside doorway as well as in the master bedroom. I’ll admit thst I didn’t wire it myself.
Tangentially… you can now get these little plug-in light-sensitive LED night lights that take negligible amounts of power. I put them all around my house, so there’s a candlelight glow throughout the house at night, plenty enough to walk around without stumbling.
I’ve only done three switches to control one light at most.
Your son is great.
Three r̶i̶n̶g̶s̶ switches for the Elven-kings under the sky,
Seven for the Dwarf-lords in their halls of stone,
Nine for mortal men doomed to die,
One for the Dark Lord on his dark throne;
In the Land of Mordor where the shadows lie.
Sorry 
We’ve got a similar set-up at our house - the lights for the downstairs hallway / stairs have a switch at either end of the downstairs hall (including one just inside the front door) and one at either end of the upstairs hall, so four switches in all for the same lights. It’s quite convenient, and as noted it’s a safety feature.
That’s what your phone is for. One of my apps (K9 mail, but it doesn’t really matter) has a mostly white screen and loads very quickly. It’s perfect for lighting up my walk to bed after turning off all the lights, and it’s not as blinding as the flashlight.
Wired light switches are very ‘last season’ as far as technology is concerned.
These days you don’t need a power cable running through a switch to a light to control it. A modern wall switch only needs power to send a very weak radio signal to a switch built into the light. This makes it trivial to have lots of switches controlling the same light and many other possibilities such as a master switch to turn off all or some of the lights when you sleep or the house is empty.
If you don’t need a power cable to each switch, this saves a ton of wiring work in a building and everything can be controlled from switches located in any convenient location or from a smartphone app. Elaborate wiring schemes will become a thing of the past.
However, I suspect electricians are not overly keen on the prospect of reduced costs for the household installations. :dubious: