The other three switch puzzle: how to wire them all to a singe light



There isn't, but in the UK, we use an "intermediate" switch which can do this. You can control a light from a pair of 3-way switches and any number of intermediate switches. (Note that outside the US, a changeover switch is called a 2-way switch, not a 3-way switch, as it has 2-ways.) See the following for diagrams: ttp://www.tlc-direct.co.uk/Technical/DataSheets/MK/WiringDiagrams.pdf
In other European countries, this is more commonly done by using any number of momentary push buttons and an impulse relay (changes state every time the coil is operated), which is uually fitted in the panel.
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Andrew Gabriel wrote:

Your "intermediate" switches are what we commonly call 4-way switches, which are internally cross wired DPDTs. They are also called "reversing switches" from their use in motor wiring.
When I first saw this puzzle, I thought the basis of the "tail-gunner's heater" problem might carry over, but I haven't gotten anywhere with it.
Jerry
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Andrew Gabriel wrote:

I think I finally see why in America a SPDT switch is called a three-way. A double-throw knife switch would have had three possible states. Is that a reasonable explanation?
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Doghouse...

No, I think that it's much simpler than that. In the UK an SPDT is called a two-way switch because one input is switched between two ways. In the US it's called three-way because it has a total of three terminals - or "ways". Likewise a DPDT switch internally wired as a cross-over (or "intermediate") switch has four terminals and hence in US parlance it's a four-way switch. The problem is that "way" does not mean the same thing on both sides of the Atlantic.
David
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David Lee wrote:

Well, I've been dealing with toggle switches for <mumble> years, and the only classifications I ever heard of were 1/2/3 Pole single/double throw, with double throw possibly modified by center-off. Some throws could be momentary. Make before break is unusual, but make after break is usual (and generally safer).
SPST, SPDT, DPST, DPDT, 3PST, 3PDT ...
all can have momentary action. DT can have optional center off. Another rarity is triple throw, ie. DP3T. P counts common connections, T output connections per pole.
Rotaries are another story.
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proclaimed to the world:

The terms "three way" and "four way" are used in the home electrical wiring industry only. My father learned electricity through apprenticeship and in turn I started out as a kid learning the common terms that electricians used. Back when he started most all electrical work was what we now call residential and industrial electricity was just beginning to use a different set of terms. For 99 out of a 100 "electricians" those terms were unheard. Most of the terms that have become standard now come from the industrial side where the guys making the drawings were those that learned terminology from going to college. In turn, those that taught the courses often were recruited from the current workforce and blended in some of the old terms with the more proper ones.
I had a discussion with my father a few days ago about a freezer that I have that is on the blink. He is 82 and sometimes forgets that I know anything at all. I explained to him that I checked the starting capacitor and relay. He then asked me if I checked the condenser. Condenser was used as a term for capacitor in the auto industry and ac motor field for a long time, still is but most people will give a blank stare if I call something a condenser. I used to know the history behind that term, but now it eludes me. My mind needs some cobwebs blown out.
Another leftover from the past is seen when you buy common house wiring. Two conductor with ground used to be known as three conductor. If you asked the clerk for three conductor wiring you will now get a four conductor, three hot wires and a ground.
I stated earlier in this tread that I had seen the solution to this puzzle somewhere in the past but could not remember exactly what it was. I have been trying to jog my memory and doodle on paper a bit to see what that might show. In trying to make a circuit, I see again what keeps it from being possible and do now remember more about the solution. You can't do it with just three SPDT switches. There was something more and it might have had to do with terminology.
I did come up with one configuration that works but you have to reset the breaker in one switch position. I don't think that counts. <grin>
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Paul M wrote:

Your reminiscence reminds me of a Saturday afternoon in 1946 when my father brought me to work. He was primarily there to let in the electrician who was to wire a large* shears, but busied himself with estimating a job, leaving me to wander through the shop on my own. The shears' size led its designer to power it with a motor at each end of the four-inch-diameter shaft that powered it, in order to limit shaft windup. Instead of the usual industrial motor starter with push buttons for on and off, this installation was controlled by a pair of relay starters to ensure that both motors operated together. The relays were operated in parallel by ordinary three-way residential light switches.
The electrician was directed to install a switch at each end of the behemoth. He soon returned to my father's office to say he was done. My father went to the shop floor and turned on the shears. Then he walked to the other, flipped the switch, and nothing happened: the switches were in parallel. He carefully explained that the motors had to go on from either end and off from either end -- that was the reason for having three switches.
Not long after, the electrician returned. My father flipped one of the switches and nothing happened: the switches were in series. Mt father explained again. The electrician got mad. "You can connect them either in parallel or in series. You can't do both!" My father got madder. He growled, "Let my kid show you." (I was 13.) One of my prouder moments! :-)
Here's another tricky switch use. The filaments of high-voltage gas rectifier tubes need to be fully warmed before the high voltage is applied. Unless a time delay is used, two switches are provided, and the operator know enough to wait. What they sometimes forget is, which switch is which. A fairly common amateur-radio practice used two DPDT switches so wired that either would turn on the filaments but both weer needed to turn on the plate supply. Clever, but not especially tricky.
________________________________ * It could cut ten-foot-wide quarter-inch-thick steel. That's LARGE!
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Jerry Avins wrote:

Three-WAY switches. ARRGH!
Jerry
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proclaimed to the world:

My brain translated automatically. There are lots of slips in this thread.
Or we stutter a lot.
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Yeah, I could only make it work with two 2-way SPST and 1 double pole DPDT changeover switch (crossover).

Yeah, I found that one as well. :)
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Clive Mitchell
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On Thu, 02 Nov 2006 12:49:57 -0500, Doghouse

I think it might just be that it has three terminals, unlike a "normal" switch with only two.
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Nick Atty wrote:

I just noticed, a 4-way switch has only 4 terminals, so it isn't simply DPDT.
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Doghouse wrote:

It's a DPDT with the NO of each pole internally wires to the NC of the other.
Jerry
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Jerry Avins wrote:

I wonder if they sell regular DPDT wall switches. Would they be called 6-way?
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There's a "Two circuit switch", but that's not it. That's equivalent to a DPDT with two contacts missing:
W C D Z
A google search reveals that you can get DPDT wall switches, called exactly that. I found one from Hubbell Wiring Devices for $75 which seems a bit excessive. It also appears you can get some called "Two Circuit Three Way", which should be the same thing.
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Here's your DPDT:
W X C D Y Z
Wire X to Y, and W to Z, and you have a four-way. XY and WZ are the inputs, C and D are the outputs.
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Yeah, but by bridging the two diagonally opposing pairs of contacts on a typical DPDT switch it becomes a crossover switch.
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Doghouse wrote:

No. Open both ways in not the third item. It is called a three-way switch (for better or for worse) because it has three terminals.
Jerry
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On Thu, 02 Nov 2006 12:49:57 -0500, Doghouse

No. The US three-way switch has no center off position.
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The Karnaugh map for this is
C C c c B b B b A 1 0 0 1 a 0 1 1 0
where a = not A, b = not B, c = not C
As you can see, any change in input A, B, or C inverts the output. There's also no simplification that I can see from the map.
Put in equation form gives
A ( BC + bc ) + a ( bC + Bc )
It's too hard to draw the resulting switching diagram using ascii, but I did it on paper, and the result I got was you need the following as a minimum:
switch A = single pole double throw switch B = double pole double throw switch C = double pole double throw
I don't see how it can be done with less.
dave y.
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