DIY Home Improvement Forum banner
1 - 20 of 24 Posts

·
Registered
Joined
·
197 Posts
Discussion Starter · #1 · (Edited)
I know there are a lot of these threads...but I'm going to try to write this like I would have needed it when I was looking for help.

Not being an electrician but being handy enough; I'm able to wire an entire room with multiple circuits back to the panel with outlets, multiple lights on their own switch without a problem...but 3 & 4-way switches have always boggled my mind until now.

I had a hard time finding a simple diagram or written instructions that didn't use seemingly ambiguous trade lingo. So I figured it out myself and now I'll try to write it out in as simple layman's terms as possible.

---------

What started this is that I replaced the switches in my basement hallway, swapping the wires from the old switch to the new switch by position. Of course nothing worked right when I turned the power back on.

FIRST LESSON: Don't do this, get an electrician or go through the steps below to DETERMINE WIRE FUNCTION and wire that way. Unless you're lucky it won't be right.


GENERAL CONFIGURATION

4 way switches work by having a 3 way switch on either end of the switch circuit and 4 way switches in the middle. Let's look at the circuit in parts:

Part 1This is the first 3 way and has a live input and two "travelers" as outputs (call them A and B). These two travelers go out to the next part.

Part 2This is a 4 way switch. The travelers from part 1 come here and connect to the switch and then more travelers leave and go to part 3. Delete part 2 if you only have two switches in your switch circuit, add another part two if you have 4 or more switches in your switch circuit. Just remember that the end switches are always 3 ways.

Part 3This is the last 3 way and has two travelers coming into it and one final wire going out to the light.


HOW THE WIRES ARE CONNECTED

For all the switches to turn on and off the lights independently, is should be wired like this. Depending on if you're wired live at the light, one of the switches, or like I was at the 4 way switch box then to the first 3 way through the 14/3 wire, etc...this part can be confusing. The key is to leave wire-nutted wires alone, only disconnect the wires attached to the switches...then continue on with this lesson fully before starting. If you're wiring a 4 way switch circuit from scratch then you should know enough that this guide you're reading is completely elementary...if it's not...call an electrician and save yourself a few days of headaches.

Part 1Live wire (hopefully black) to the black "COM or COMMON" screw, outgoing travelers to the other two brass screws (one each, doesn't matter which)

Part 2Incoming travelers to the terminals marked "IN" (one each), outgoing travelers to the wires marked "OUT" (one wire each)

Part 3Incoming travelers to the brass screws (one each, doesn't matter which), outgoing wire to the "COM or COMMON" or black screw.


HOW THE CIRCUIT WORKS

Part 1The first 3 way switches live voltage to one or the other wire...it's never off, only just making one or the other travelers live.

Part 2The 4 way switch just switches the top screw of the "IN" to either the top or bottom screw of the "OUT" and vice versa for the bottom "IN". (ie: switch up: top IN - top OUT, bottom IN - bottom OUT. switch down: top IN - bottom OUT, bottom IN - top OUT.) It just reverses the path from crossed to straight if you were able to look through the switch.

Part 3The last 3 way switch takes the travelers and switches between them to the "COM or COMMON" screw to the light.

The end result is every switch has a live and a dead traveler leaving it and/or coming into it. This is why every switch can turn the light on/off independently because each switch acts like a simple on/off switch but also affects the live and dead travelers to all other switches to make them all act in concert.

Take a moment to ponder this...draw it out if you have to...it's the most fundamental part you need to know to understand this entire lesson. Your drawing might look something like:

<live> _/ = <travelers> =x= <travelers> =\_ <light>

This will help:
http://users.wfu.edu/matthews/misc/switches/4WayAnimation.gif

DETERMINE WIRE FUNCTION

If you're comfortable doing this, do so but be careful. Notify all people in the household and keep children away if you do. It's okay to be nervous but not okay to be careless or rushed.

  1. Turn off the power
  2. Pull off all the switches disconnecting only the wires attached to the switch
  3. Situate the wires out in the open air far away from everything and each other but keep access to a part of the box open
  4. Find your multimeter
  5. Turn on the power
  6. CAREFULLY find the only live wire at one of the 3 way switch boxes. It will have full voltage. The other might have a smaller amount of voltage on them but ignore this (this is called "induced" voltage I think and is due to not having a neutral in the switch loop) Do this by setting your multimeter to AC volts, touching the black probe to the box metal, and touching the red probe to the wires you're testing.
  7. Note this live wire
  8. Turn off the power
  9. Connect this wire that was live to the black "COM or COMMON" screw on the switch and the other two "travelers" to the other two brass screws (doesn't matter which)
  10. Put the switch in the box, place the cover on. You're done with this switch.
  11. Confirm your other wires at the other locations are still out and not touching anything.
  12. Turn on the power
  13. CAREFULLY find the live wire at one of the 4 way switch locations. Note this wire.
  14. Turn off the power
  15. Connect this wire (traveler) and the other wire that runs with it in the same cable to the "IN" side of the 4 way switch (one each, doesn't matter which order)
  16. Connect the other wires (travelers) to the "OUT" terminals (one each, doesn't matter which order)
  17. Put the switch in the box and put the cover on, you're done with this switch.
  18. Repeat the above 7 steps for any other 4 way switches or delete them if you don't have any 4 way switches
  19. Confirm your last 3 way box is still safe to energize with wires in safe open positions
  20. Turn the power on
  21. Find the live wire, this is one of the travelers. Note this wire.
  22. Go to the last switch you finished wiring in and flip it
  23. Back at the last 3 way box, find the live wire. This should be different now and is the other traveler. Note this wire.
  24. Turn the power off
  25. Connect the two traveler wires to the two brass screws (one each, doesn't matter what order)
  26. Connect the last wire to the black "COM or COMMON: terminal.
  27. Put the switch in the box and put the cover back on. You're done with the switches.
  28. Turn the power on.
  29. Confirm that all switches turn the lights on and off independently (should work regardless of what position any other switch is in).


This may be oversimplified but I think it needs to be for complete understanding. If any electricians or other more experiences people find problems with this lesson, please let me know and I'll fix or delete it.

Thanks.
 

·
Remodel and New Build GC
Joined
·
10,138 Posts
I don't think you were oversimplified at all.... and will probably help alot of people.... (I did not study all the steps...leave that to someone else).

Only suggestion might be to toss in a wiring schematic to help some understand,..,. there are plenty out there somewhere in internet.

I would comment that I don't know that all four ways are as clearly marked as in/out. I could swear last one I put in was marked somewhat funny (can't remember exactly... maybe with A's and B's or something). I had to just check my continuitys in the switch.)

Best
 

·
Rob
Joined
·
1,036 Posts
Do you think you could shorten it a lot and make it so a 60 year old could read it. Maybe I will read it when I go through my third childhood:thumbup:.
 

·
A "Handy Husband"
Joined
·
13,146 Posts
That explanation works when the power is connected at the first 3 way and the load (light) is connected at the last 3 way. But there are other methods of wiring. The concept is the same but the wiring connections vary.

Power is connected at the light

Power and light are connected in the first (or last) 3 way.

Power is connected at the 4 way.
 

·
Registered
Joined
·
197 Posts
Discussion Starter · #6 ·
Thanks for the comments. And true, there are other configurations. For example mine had the line cable and the light cable in the 4 way box. The power went to the first 3 way via the black wire of the 14/3 cable with the travelers and the final switched conductor came back to the 4 way box via the black conductor from the last 3 way with those travellers.

So all kinds of different ways... But hopefully people trying this have enough of that basic knowledge to figure it out from there.

Please feel free to post additional common (or less common) configurations... I'd be interested to hear them.
 

·
A "Handy Husband"
Joined
·
13,146 Posts
The problem with 3/4 way configurations (in the US) is the NEC now requires a neutral in every switch box and that further middies the water. Often 4 wire cables are required to meed this requirement.
 

·
Registered
Joined
·
9,837 Posts
The other might have a smaller amount of voltage on them but ignore this (this is called "induced" voltage I think and is due to not having a neutral in the switch loop) Do this by setting your multimeter to AC volts, touching the black probe to the box metal, and touching the red probe to the wires you're testing.
It is not likely to be "induced" voltage. It is more likely "phantom" voltage. Neither is impacted by a switch loop, or having a neutral in the box.

Do you think the color of the probe makes a difference when looking for AC voltage ?
Perhaps a bigger issue might be "what do I do when my box happens to be plastic?".
 

·
Registered
Joined
·
197 Posts
Discussion Starter · #9 · (Edited)
Oso, no i don't think colour matters. Just old habit for writing procedures for automotive DC voltage ;-)

And I should have added to use the ground wire if the box is not metal.

Thanks!

Also: "phantom" voltage is what i meant by induced voltage. Are the two used interchangeably? 30 feet of open wire running next to a wire with line voltage will read voltage on it due to the pulsing magnetic field running through it (one of the few high school physics lessons I remember)
 

·
Remodel and New Build GC
Joined
·
10,138 Posts
Hey Guys.... Come to think of it, (I haven't done anything new under permit since new code, is it as simple as a neutral EVERY SWITCH), regardless of whether we have a hot feed. (3 and 4 ways?)

TIA
 

·
a sparky
Joined
·
92 Posts
The way I hear it the answer is a simple "yes".
( 'cept conduit, as a neutral can be inserted )
Unless localities have not adopted this one.
 

·
Remodel and New Build GC
Joined
·
10,138 Posts
It is not likely to be "induced" voltage. It is more likely "phantom" voltage. Neither is impacted by a switch loop, or having a neutral in the box.

Do you think the color of the probe makes a difference when looking for AC voltage ?
Perhaps a bigger issue might be "what do I do when my box happens to be plastic?".
Use the plastic part of the probe....:wink:
 

·
a sparky
Joined
·
92 Posts
Thanks for the comments. And true, there are other configurations. For example mine had the line cable and the light cable in the 4 way box. The power went to the first 3 way via the black wire of the 14/3 cable with the travelers and the final switched conductor came back to the 4 way box via the black conductor from the last 3 way with those travellers.

So all kinds of different ways... But hopefully people trying this have enough of that basic knowledge to figure it out from there.

Please feel free to post additional common (or less common) configurations... I'd be interested to hear them.
Yep, but people sometimes panic. That clouds judgement and the final picture. I still say your's is a good solid guide.

Just for reference, a graphic I made for another forum, ( no longer a part of because they... well, they no longer were as user friendly ), showing block diagrams of the basic methods for a three way switch. Now with adding just a single four-way, well, it gets a lot more variables. Essentially a four-way switch can be added in any BLUE line and MORE!

Changes to bring it up to present day codes if applicable in your area are;
A. Requires 4-conductor wire in right side blue line.
B. No changes necessary as I understand it.
C. Requires 4-conductor wire instead of 3-conductor
D. Requires 3-consuctor instead or present 2-conductor and 4-conductor instead of present 3-conductor.
E. Requires 4-conducor in place of both 3-conductor wires.

AS a quick count, inserting a four-way into the circuits, I see eight different ways this block diagram could be.
 

Attachments

·
Registered
Joined
·
197 Posts
Discussion Starter · #14 ·
About a year and a half since the last post. Bumping the thread up so it may help some others before it falls into the oblivion of the internets.
 

·
Registered
Joined
·
1 Posts
All of the suggestions provided are excellent. This site was a lifesaver. Using it I realized that the original "electrician" had incorrectly wired the followers at the four way. I found this by doing a continuity test on the followers from the three-ways. This site (users.wfu.edu/matthews/misc/switches/confused4way.html) is also very helpful to troubleshoot 4 way switch problems.

As noted by others, the two follower cable bundles that come into the 4 way box should be connected:
1. to the IN side (two follower wires from one of the 3 way cable bundles) and
2. to the OUT side (the follower wires from the other 3 way's cable bundle)
3. MAKE SURE NEUTRAL WIRES ARE CONNECTED TO NEUTRAL in the box.

The "electrician" who incorrectly wired this 4 way had taken two follower wires (black) from the 3 way follower cable bundles and wire nutted them together inside the 4 way box. He screwed the two follower wires (red) correctly -- one to the IN and the other to the OUT side of the 4 way switch. The "electrician" connected the two cable's NEUTRAL cables (white) to the remaining posts on the 4 way -- one white to the IN and the other on the OUT side of the 4 way! A definite no-no.
:vs_whistle:

Disconnecting the blacks and whites and rewiring the black followers to the proper 4 way posts associated with their respective red (IN or OUT cable bundle), and connecting the whites to neutral fixed the issue.
:vs_cool:

We also found that the "electrician" had incorrectly wired the neutral (white) and a return wire (red) for a washroom fan timer to neutral. :vs_OMG: (OOPS!! INCORRECT).
:glasses:

All boxes have now been checked -- and rewired as necessary. The worst offender: High power circuit to Range was connected below the range, with the wire sitting behind a drawer without a box using electrical tape and painter's masking tape! Love to see this person loose their ticket.
:vs_mad:
 

·
Remodel and New Build GC
Joined
·
10,138 Posts
Sort of associated with this.... but a joke on me in troubleshooting ......

On a flip home of mine I had a F'd up multi switch (2 4-ways) and I knew the previous non-knowledgable HO had replaced a 4-way (he told me).

So naturally I was targeting the 4-ways. I pulled them and the 4 ways can have different nomenclature on their terminals.... so I checked continuitys and installed them back as known correct.

Still did not work.

So I checked the 3-ways.... which were backstabed... and they looked ok....

So I wondered if I missed a box or a wire splice somewhere (hack HO did) and ran continuity checks on the actual wires...... up and down stairs with my long wire tester. They were OK

Well.... the stabs on these 3ways can be tricky located relative to the screw terminals. Finally discovered that the stabs were wrong when I went and redid the stabs to the terminal screws.

Lessen learned.... back stabs can be a little confusing as to terminal when you have multi terminal backstabs.:wink2:
 

·
Registered
Joined
·
561 Posts
3 and 4 way switches always confused me until I read Rex Cauldwell's book "Wiring a House". My key take away lesson from all of this is to be consistent and methodical when wiring. Power in from the left side always, power out from the right side always, special wires labeled every time, and then when you get to something more complicated like a 4 way you don't have as much guessing or remembering to do.
 

·
Remodel and New Build GC
Joined
·
10,138 Posts
I was waiting for you to say the bulb was burned out!
Yea... That would be likely with me also..... sometimes our assumptions,,,, that you don't even realize you assumed, are what get you in trouble.

Many years ago we did a clutch on my sons Ford long bed crew cab old POS.

Involved taking out alot of electrical going thru the console etc.

Got her back together and the battery was dead (took us a week getting some parts) so we tried jumping it and NOTHING.

Naturally we assumed we had missed some harness connection somewhere... but could not find it.

Turned out our jumpers were bad.....
 
1 - 20 of 24 Posts
Top