“What’s a 3-way switch...?”

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sw_ross

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Me- “You know, like a fixture that is turned on-off from 2 (or more) locations...”

Homeowner- “Why is it called a 3-way switch?”

Me- “Uh... I don’t know... It just is...”

I’m to the point where I don’t use terms like 3-way and 4-way switches with HO’s unless they say it first.

By the way, why is it called 3-way switching and 4-way switching?
 
sw_ross said:
Me- “You know, like a fixture that is turned on-off from 2 (or more) locations...”

Homeowner- “Why is it called a 3-way switch?”

Me- “Uh... I don’t know... It just is...”

I’m to the point where I don’t use terms like 3-way and 4-way switches with HO’s unless they say it first.

By the way, why is it called 3-way switching and 4-way switching?
Click to expand...
Slang that came a long time ago is what it is I think.

A three way switch is a single pole double throw switch.

A four way switch is a two pole device that reverses polarity when operated.
 
The answer, my friend, is blowing in the wind.

Literally. It's been lost to time.

My theory is Appleton had them listed as 3-point switches 100 years ago in their catalog.
 
kwired said:
Slang that came a long time ago is what it is I think.

A three way switch is a single pole double throw switch.

A four way switch is a two pole device that reverses polarity when operated.
Click to expand...
So, in the trivial case of a standard light switch, it's a 2-way?
 
sw_ross said:
Me- “You know, like a fixture that is turned on-off from 2 (or more) locations...”

Homeowner- “Why is it called a 3-way switch?”

Me- “Uh... I don’t know... It just is...”

I’m to the point where I don’t use terms like 3-way and 4-way switches with HO’s unless they say it first.

By the way, why is it called 3-way switching and 4-way switching?
Click to expand...

It has to do with the quantity of terminals on the switch itself. A simple (single pole/single throw) switch only has 2 terminals. The 3-way switch has three terminals on the device, and is a single pole / double throw switch (SPDT). Pole = number of blades within the switch, "throw" = number of connection points to which you can send the blade. Call the terminals, A, B, and C. C is the common terminal with the "hinge" of the switch blade, while the blade can either be thrown to A or B.

The 4-way switch, used as a third or greater intermediate switch in the travelling switch circuit, has four terminals, which I'll call A, B, C, and D. It either has the switch state where connections are between AB and CD, or the cross switch state where connections are between AD and BC.
 
480sparky said:
Then why is a 2PST switch not called a 4-way?
Click to expand...

Because it isn't used in the application of travelling switch circuits, where the terminology is needed to distinguish the switch from ordinary switch. The 2PST switch is used as an ordinary switch for switching circuits of 2 ungrounded wires. Its purpose is just like the ordinary 1PST switch, except with a circuit containing both the black and red wire.
 
Carultch said:
It has to do with the quantity of terminals on the switch itself. A simple (single pole/single throw) switch only has 2 terminals. The 3-way switch has three terminals on the device, and is a single pole / double throw switch (SPDT). Pole = number of blades within the switch, "throw" = number of connection points to which you can send the blade. Call the terminals, A, B, and C. C is the common terminal with the "hinge" of the switch blade, while the blade can either be thrown to A or B.

The 4-way switch, used as a third or greater intermediate switch in the travelling switch circuit, has four terminals, which I'll call A, B, C, and D. It either has the switch state where connections are between AB and CD, or the cross switch state where connections are between AD and BC.
Click to expand...
I can just see trying to tell a HO that...!🙄
 
I find the best answer is
"It is what it is. The trades evolved their own jargons, which don't necessarily have any basis in reality, and are often obsolete."

Deep down inside, a 4-way is a DPDT with the throws cross-wired.

reversing-dpdt-color.png
reversing-dpdt-linedrawing.jpeg
 
drcampbell said:
I find the best answer is
"It is what it is. The trades evolved their own jargons, which don't necessarily have any basis in reality, and are often obsolete."
Click to expand...

Case and point, the entire name of the trade of plumbing. It is no longer even legal to use plumbum in any plumbing of drinking water, for good reason because of how toxic lead is known to be. It should really be called cupring, if its name reflected at least one of the materials we use for pipe construction today.
 
When I was in my early 20s, which was a long time ago, I bought a new Atlas 6" metal lathe. The motor and especially the reversing switch from the company seemed at the time to be very expensive. And so I was thinking about how I could get around this with more commonly available parts. Info was not so easy to get like today with internet search engines, and so I had to think about what must be inside the switches I could find in a hardware store. That's when I realized that a 4-way must act like a reversing switch to perform the way it does in lighting circuits. I also had to take apart the relatively cheap motor that I had to access both sides of the starting winding and then connect it to the 4-way switch. It wasn't a fancy single lever controI for on/off and reversal, but it worked fine for my purposes.
I still have that lathe.
 
Cell phones, wi-fi access points, and other wireless devices commonly use double-balanced passive mixers which are really just 4-way switches, but are being switched at GHz rates (a little too fast for a toggle switch :)). Such mixers are used in both receivers and transmitters.

www.semanticscholar.org

Figure 4 from A H-band double balanced passive down-conversion mixer in a 65 nm bulk CMOS | Semantic Scholar

Fig. 4. Core of the double-balanced passive mixer - "A H-band double balanced passive down-conversion mixer in a 65 nm bulk CMOS"
www.semanticscholar.org www.semanticscholar.org
 
synchro said:
... a 4-way must act like a reversing switch to perform the way it does in lighting circuits. ...
Click to expand...
Well, not exactly the way it does in lighting circuits.

Starting with only one traveler being energized at a time, and nothing bad happening if both travelers are connected to each other for a moment during the switch's transition, and little or no inductive or starting-inrush current.

There are a zillion and one subtleties of switch design.
Make-before break or break-before make is an important one.
The very best selection for a motor-reversing switch is a hesitation switch. A mechanical interlock prevents it from being switched directly from "forward" to "reverse". It will only switch as far as the center-off position, after which you need to release pressure on the handle and hesitate for a moment before it will switch from "off" to "reverse".

Vehicle controls, rockers, toggle switches, and indicators | Eaton

www.eaton.com www.eaton.com
 
drcampbell said:
Well, not exactly the way it does in lighting circuits.

Starting with only one traveler being energized at a time, and nothing bad happening if both travelers are connected to each other for a moment during the switch's transition, and little or no inductive or starting-inrush current.
Click to expand...
That's why I had a separate switch to turn the motor ON or OFF. The reversing switch was only toggled when the power switch was off. Also, when the motor was up to speed the centrifugal switch disconnected the starting winding. It wasn't foolproof, but nothing really is when running a lathe.
If I was wiring it today I would have something better.
 
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