Understanding S.P.S.T and 2-Way Switches for Home Wiring

[biferi]

In Home Wiring the Switch that is used to tun on and off just one light is called a S.P.S.T Switch.

Now when you have one light that has two Switchs that can turn it on and off the Switchs are 2 way Switchs. But are they called S.P.D.T Switchs?

 

[Integral]

SPST stands for Single Pole Single Throw. I think the 3 way switch is a SPDT, Single Pole Double Throw.

 

[wirenut]

Integral is correct a s.p.s.t., or more commonly a single pole switch, is just an on/off switch. A 3 WAY switch is a s.p.d.t. and the ones used in homes/offices have 1 terminal either a different color or the word common in the plastic near the terminal. They are called 3 way because you have 3 different combinations of positions- on/on , on/off , off/off- and each position change on EITHER switch will change the load state. There is also a 4 way switch which when toggled will change from [top right connected to bottom right ] and [top left connected to bottom left] to {top right connected to bottom left} and {top left connected to bottom right}. These are 4 terminal devices and can be installed in any number between (2) 3 way switches to allow control from any location. (Do not confuse a 4 way switch with a 2 pole switch (2 single pole switches in 1 handle[ D.P.D.T]) , they look identical)

I've been an electrician for approx 25 yrs and know some more experienced guys who can't wire a 3 way or 4 way setup. Troubleshooting and replacing them is the most confusing home project you will encounter (including rough framing, drywall finishing and plumbing.)

 

[biferi]

OK thanks for all the help and yes I do know how one switch connects to one Light.

And I do know how two switchs connect to one Light.

But there is one thing I never could understand.

When you see a Light with a Fan and one switch I do understand how this connects.

But I do not understand how they connect two switchs to a Light with a Fan.
You know when one switch turns the Fan on/off and the other switch turns the Light on/off.

I did a google search for photos of wiring and they are not that good.

Can you show me a good photo or diagram of how they connect?

 

[etudiant]

OK thanks for all the help and yes I do know how one switch connects to one Light.

And I do know how two switchs connect to one Light.

But there is one thing I never could understand.

When you see a Light with a Fan and one switch I do understand how this connects.

But I do not understand how they connect two switchs to a Light with a Fan.
You know when one switch turns the Fan on/off and the other switch turns the Light on/off.

I did a google search for photos of wiring and they are not that good.

Can you show me a good photo or diagram of how they connect?

Not sure I understand the question.
Is that not simply one switch for the light, one switch for the fan, each with a separate circuit?

 

[biferi]

Well whenever I look at how they wire two switches to a Fan with a Light they are very very diferant.

Can you maybe post a link to a photo?

 

[biferi]

Thank you for all the help I am getting it now.

But I would like to go over the diferant switches to see if I have it right.

A way switch is called a S.P.S.T

The two switches in a Hallway that connect to one light are called D.P.S.T

Now you may see three switches connected to one light. And the first and last switch are D.P.S.T but the middle switch is one with Four Screws so am I right this is called D.P.D.T ?

 

[wirenut]

Biferi, the two switches are S.p,D.t. and the third can only be described as a [straight through / criss cross] switch (It is NOT a D.P.D.T- that switch has 6 terminals).
In one position the terminals go straight through (top right to bottom right) and (top left to bottom left), and in the other position the criss cross (top right to bottom left) and (top left to bottom right). Sorry, I can't draw on a computer to save my life so I can't help with a diagram.

 

[OmCheeto]

Thank you for all the help I am getting it now.

But I would like to go over the diferant switches to see if I have it right.

A way switch is called a S.P.S.T

The two switches in a Hallway that connect to one light are called D.P.S.T

Now you may see three switches connected to one light. And the first and last switch are D.P.S.T but the middle switch is one with Four Screws so am I right this is called D.P.D.T ?

I wired up my house with three switches controlling one light, about 25 years ago. I think it involved a special "4-wire conductor": 3 hots/neutrals, plus that inevitable "Ground".

The magic isn't in the number of screws on your switch, it's the "black box" circuitry inside the switch.

Learn boolean logic.

 

[biferi]

Just to see if I have what you tell me right.

The two switches that work one light are called DpSt

Now I am watching a video


And it has three switches and one light.

The first and last switch are a DpSt switches.

And the middle switch is just a Pass through you say.

Please watch the video and tell me if I am right I thought it may have a name?

 

[wirenut]

They are not DpSt(double pole single throw) they are SpDt (single pole double throw). Please reread my above post. The switch in the middle is called a 4 way switch.

 

[OmCheeto]

A quick google search clears it all up:

Multiway switching
...
a "3-way" switch is a Single-Pole, Double-Throw (SPDT) switch.
...
A "4-way" switch is a Double-Pole, Double-Throw (DPDT) switch
...

A quick look at switches:

Switch
...
The number of "poles" is the number of separate circuits which are controlled by a switch.
...
The number of "throws" is the number of separate positions that the switch can adopt.
...

indicates to me that I'm drunk, as there should be no such thing as a single throw switch.

I would call that a wire...

 

[biferi]

Thanks for all the help but what I ment was there is
S.P.S.T switches.
S.P.D.T switches.

And then the 4 way switches.

But don't the 4 way switches have a name?

 

[OmCheeto]

Thanks for all the help but what I ment was there is
S.P.S.T switches.
S.P.D.T switches.

And then the 4 way switches.

But don't the 4 way switches have a name?

Do you not trust wiki?

A "4-way" switch is a Double-Pole, Double-Throw (DPDT) switch

I don't after what they said.

This makes more sense:

Dummies...
...
Throw: The number of throws indicates how many different output connections each switch pole can connect its input to.
...

It has been many decades...

I really did used to know all this stuff.

 

[Averagesupernova]

A 4 way switch is in fact a DPDT switch with the 2 sets of throws (can they be called that?) criss-crossed and tied together.

 

[biferi]

Thanks for all the help again.

But I have one more Link to a video I was watching and I just wanted to know if I am looking at it right.



On a 4 Way Switch are the Top 2 Screws Brass and the Bottom 2 Screws Black?

 

[Averagesupernova]

Colors and position may vary from switch to switch. I usually just check continuity. What the vid says makes good sense though. One set of colors going one direction and the other set going the other direction.