Three-Way Switch Circuits

Which One Should I Use, Part VI:
Three-Way Switch Circuits
by Phil Kingery

Oh no! How will Captain Coupling get out of this one? Unfortunately, he was ambushed by Dan Rather and a 60 Minutes camera crew where he was discovered engaging (*g*a*s*p*) in a "3-way" ! (If you know what I mean, wink, wink, nudge, nudge!)

Email Uncle Phil

Well, hello again, you gluttons for punishment. I can only imagine all the nice email you have been sending me but, unfortunately, I have not been able to see it since my old address is now kaput. Fear not, for I have a new email address. It is pkingery@act-solutions.com . Now that we here at ACT now have our own web site I don’t want you to completely abandon my friend Bob here at HTI (Home Toys Inc.).

At the end of the last installment of this (seemingly never ending) series, I wasn’t sure if I should continue with complex coupling or if I should let that rest for a while. For months I have been promising to give you an article on "X-10 Three-Way Switch Circuits". I guess this is as good a time as any. (For you surfers who have discovered this section of HTINews for the first time, I urge you to back up and review a few of the earlier chapters or this one won’t make a lot of sense.) Therefore, this section is entitled:

I need to get a few things off my chest before I get into this. Of all the technical calls we get in my office, the overwhelming majority have to do with 3-ways (and I don’t mean the kind that Captain Coupling was caught doing). Usually the underlying problem is that the installer doesn’t understand standard 3-way circuits, let alone X-10 3-way circuits. Often the caller will become angry at us because it seems that we are incapable of visualizing what he needs. I have had more than one installer yell at me saying, "...you are supposed to be the experts and you can’t tell me how to install this?!?". We may be the experts, but we can’t see through the phone in order to tell what kind of 3-way circuit he has. There are many variations in standard 3-way wiring and in most cases the installer has no idea which one he has. It is unfortunate that he assumes that there is only one kind. Believe me, nothing could be further from the truth. The many variations in 3-way circuits dictate which X-10 3-way receivers will work and which ones will not.

Before we talk about "X-10" 3-way circuits, we need to talk about "standard mechanical" 3-way circuits. Have you ever wondered why they are called "3-way circuits" when there are only 2 switches? Well, it has to do with the number of "drop points" and not the number of switches in the circuit. You see back in the early days of electrical wiring, back in the days of Thomas Edison, the vocation of "electrician" was brand new. These new electricians would base their cost estimates partly on the number of "drop points" on each circuit. A drop point could be a switch, a load or any junction point. In a sense a circuit with only 1 switch and 1 load would be a "2-way". I suppose this was because the wires had to go "two different ways". A circuit with 2 switches and 1 load would be "3-way". Incidentally, a circuit with 1 switch and 2 loads would also be a 3-way, but over the years, the label of "3-way" has evolved into meaning any circuit with 2 switches in it.

It is rare indeed to find any house in North America that does not have at least one 3-way circuit. Perhaps it is at the top and bottom of a stairway or at both ends of a long hall. In any case, it enables the user to turn on or off the load (usually a light) from either location. It sometimes seems confusing that the switches are made so that "on" can be either "up" or "down" depending on the position of the other switch. How are these wired? Let’s look at a standard mechanical 3-way circuit. Figure 1 shows a typical 3-way circuit. This is what I think of when I think of a 3-way circuit: 2 switches with the load at the end.

This diagram is pretty good but it was a pain to draw. Besides it’s hard to see where the wires go. Since I don’t want to draw complex drawings every time, and I want you to be able to see where the wires go, I am going to simplify all the diagrams from here on. Figure 2 is a much more practical drawing for the purpose of this article.

(Let me get one more thing off my chest. Just because this drawing starts with the breaker panel on the left, then the switches, and then the light on the right, does not mean that yours will always be in this "left-to-right" pattern. Yours may be left-to-right or right-to-left, up-to-down or down-to-up. As long as the circuit is wired in this progression, it is the same. Got that? I had a guy tell me one time that his circuit was different because his panel was on his right and the light was on his left. It’s a good thing I wasn’t close enough to strangle him....)

Look closely at the diagram. Please notice that the current for the light

bulb must travel through both switches. If you remember nothing else from this article, please remember this:

How do X-10 3-way master receivers work? Some X-10 3-way master receivers are standard 2-wire dimmers with a third "control" wire (figure 3). If you hook up just the line (black) wire and the load (blue) wire, it would work just like a standard X-10 dimmer receiver.

Others have a neutral wire. These are usually called "3-wire" dimmer receivers. You may have inadvertently misread that last sentence. I didn’t say "3-way", I said "3-wire" receivers. These are not the same thing but if you are scratching your head right now, you should go back to the earlier chapter "Which One Should I Use?" and possibly "Which One Should I Use - Part 2" to see what I’m talking about. A 3-wire dimmer with a fourth wire (control) is a 3-wire, 3-way dimmer receiver. Again, if one of these are wired using just the line (black) wire, the neutral (white) wire and the load (blue) wire, it would work just like a standard X-10 dimmer receiver. So what makes them a 3-way master? If voltage is applied to their control lead they will change state. That’s where the slave switch comes in.

Figure 3 also shows how the "slave" switch (or "auxiliary" switch if you want to be politically correct) is connected to the 3-way master. All the 3-way masters use the same slave switch. (We here at ACT sell five different 3-way masters: RD101, RD161, RD123, RS101 and the RS301). If you are only familiar with mail-order X-10 or Radio Shack slaves switches, they still do the same job but they may look different. The X-10 and Radio Shack versions have wires while our slave switch (part number AS001) has screw terminals (like our 3-way relay receivers, RS101 and RS301, shown in figure 4).

Slave switches (oh, all right, "auxiliary" switches -- happy now??) are just high voltage momentary push buttons. They are, in a sense, fancy doorbell buttons. When the button is pressed, line voltage is applied to the control lead (but please don’t try to use a doorbell button, okay?).

The single biggest mistake made by installers trying to retrofit a pre-existing 3-way, is that they don’t know which kind of 3-way circuit they have. (Most may not even know that there are different kinds.) In order to change an existing 3-way into a X-10 3-way, the installer must first identify how the circuit was originally wired. Once that is done, choosing and installing the appropriate X-10 3-way receiver is relatively simple. In this installment, I am going to present four different ways that a standard 3-way might be wired. (There are a few more but four is all I’m going to tackle in this edition.)

A standard 3-way circuit can not be converted to an X-10 3-way circuit by replacing only one switch. Sorry, that simply does not work. (Believe me, I have seen people try that.)

If a dimmer receiver is designed to work without a neutral connection (it only needs "line" and "load" wires) then I call it a "2-wire" dimmer. While it’s true that the control lead makes it a total of 3 wires, I still consider it a "2 wire" dimmer. We at ACT sell these under our part number RD101. (And yes, Leviton has similar units but since I work for ACT, I’m only giving you our part numbers.)

If a dimmer receiver is designed with a neutral connection (it needs "line", "neutral" and "load" wires) then I call it a "3-wire" dimmer. While it’s true that the control lead makes it a total of 4 wires, I still consider it a "3-wire" dimmer. We at ACT sell these under our part number RD161 (and our 2400 watt version, RD123). I know that this is somewhat confusing but that’s the way it is.

Also, please note that in many of the diagrams that follow, the wire colors seems to change color. Believe me, they will not magically change colors as you connect them to various X-10 units. I simply chose the wire colors to show those most commonly used in standard 3-way wiring scenarios and then I changed them to show the wire colors of the X-10 receivers.

Look back at figure1 and especially figure 2. (This article is already so long that Bob would kill me if I duplicated the same diagrams again so you’re just going to have to scroll up and look at them....[The editor gremlin makes Phil happy by adding a quick link back to the figures :-)] Good, now you’re back.) To convert this version to an X-10 3-way, simply replace the first mechanical switch with a slave switch (as shown), then replace the second mechanical switch with the appropriate X-10 3-way Master. (Figure 5.)

If the load is incandescent and less than 500 watts, a 2-wire dimmer (I know, 3 wires if you count the control lead) can be installed. If you have read my previous words of wisdom, you know that when ever there is a neutral wire available, I always recommend a 3-wire dimmer. They just work better. In this example, we are extremely lucky to have a neutral connection available in the j-box, so I suggest a 3-wire dimmer (our RD161). If the load is greater than 500 watts, or is something that you just don’t want to "dim", then a relay receiver (ACT’s RS101, for instance) can be installed. Both the relay receiver (RS101) and the 3-wire dimmer (RD161) require a neutral connection.

Figure 6 shows another common method of wiring a 3-way circuit. In this version the switches are at both ends of the circuit run and the load (a light, in my example) is in the middle j-box. To convert this to an X-10 3-way, simply replace the first mechanical switch with a slave switch (as shown in figure 7), then replace the second mechanical switch with a 2-wire, 3-way master dimmer receiver (like the ACT RD101).

This is where the plot thickens. If the load exceeds 500 watts, or is non-resistive, we have a problem. Look closely at figure 7. Neutral is available only in the first two j-boxes. The 3-way master is sitting in the third box and there is no neutral wire there. Can you swap the slave and the master in order to use a 3-wire dimmer or a relay receiver? Nope! There aren’t enough wires. You are stuck. If you are trying to convert this kind of pre-existing 3-way circuit to an X-10 3-way, you are limited to using a 2-wire dimmer. If your load is greater than 500 watts or is something other than a regular incandescent light, you must abandon the use of a true X-10 3-way and instead use a single relay receiver (like the ACT RS121) in the first position and a wall-mount transmitter (like the ACT TB100 with a keypad) in the last position (as shown in figure 8). Also please note that you will have to get up on a ladder and do some rewiring in that middle box to accommodate the electrical needs of these devices.

If dimming is desired, yet the use of a 2-wire dimmer (RD101) is inappropriate, a 3-wire dimmer (RD161) can not be used in place of the 2-wire dimmer (in figure 7) since there is no neutral. You can, however, use a 3 wire dimmer or a relay receiver (figure 8) but not as a true 3-way masters. There are not enough wires from one j-box to the others.

Okay, we’re half way there. Figure 9 shows another wiring version of a standard 3-way circuit. In this example, the load (or light) is first and then the two switches are in the second and third positions. If you thought the last one was difficult, this one is a killer. Since neutral exists only in the first j-box, the choices of X-10 master receivers is limited only to the 2-wire dimmer versions since they operate on the trickle current through the load.

To convert this version to an X-10 3-way, simply replace the first mechanical switch (second position) with the 2-wire, 3-way master (like the ACT RD101) and then replace the second mechanical switch (third position) with the slave switch (AS001) as shown in figure 10. The load must be incandescent and 500 watts or less. Can you imagine how frustrating it can be for an installer who orders a 3-way relay receiver and a slave switch and then tries to install them into this kind of a circuit? Sorry, it won’t work. (Of course, then he calls me and wants me to "fix it" over the phone.)

If the load exceeds 500 watts, or is non-resistive, then the only option is to abandon the use of a true 3-way and install a fixture receiver and two transmitters (as shown in figure 11). It ain’t pretty but it’s the only option I can give you for this one. In commercial buildings we can pull more wires through the conduit, but in a house, you are usually stuck with whatever is already there.

4. Standard 3-way with the load at the beginning of the run and the switches split.

This is the last one we will do in this edition. Look at figure 12 and you will see a 3-way circuit where the light is actually in the first j-box and then the 2 switches are split off on either end. Unlike most of the previous examples, converting this type of 3-way will require significant wiring changes in the load j-box.

Since neutral exists only in the first j-box, the choices of X-10 3-way master receivers is limited to the 2-wire variety since they operate on the trickle current through the load. To convert this version, simply replace either mechanical switch with a 2-wire, 3-way dimmer (like the RD101) then replace the other mechanical switch with the slave switch (as shown in figure 13). The load must be incandescent and less than 500 watts.

If the load exceeds 500 watts, is non-resistive, or the use of a 2-wire type dimmer is inappropriate, the installer must then abandon the use of a true X-10 3-way and instead use a relay receiver and a wall mount transmitter (as shown in figure 14). Remember, with this version, a significant amount of rewiring will be required in the load j-box to accommodate the electrical needs of these devices.

BIG NOTE: All electrical work should be done by a qualified and licensed electrician adhering to all national and local electrical codes. Although circuit breakers are not shown, appropriately sized breakers are required on all circuits. ACT’s RD101 dimmer is rated for 500 watts, incandescent only. The RD161 is also rated for 500 watts, for resistive and non-linear loads. Both the RS101 and the RS121 are rated for 20 amps on 120v. ACT’s RF100 fixture receiver is also rated for 20 amps on 120v. This article was written for the Home Automation market in mind and so it implies only 120v circuits, however, ACT also offers a 277v version of the RS101. It is the RS301. The AS001 is rated for 277v and 120v. And most importantly, Never use the ground wire for anything other than ground!

Well, we have come to the end of another chapter in this "Which One Should I Use" series. I knew when I started this one that it would be big and I was right. In the next chapter (February 1998) we will look at two more 3-way wiring scenarios (one is the most complicated one I have ever seen, the other is the easiest) plus 4-way wiring. If time permits, we will also get into some 3 & 4-way troubleshooting.

Like everyone else who puts their work out on the web, I love to hear your comments. (It strokes my ego.) If you have any questions on this or any previous article in this series, please email me. If you have any suggestions for future discussions, please let me know. Have a nice Christmas and New Year and I hope to see you at the Consumer Electronic Show in Las Vegas in January . I will be teaching a class there so please stop by and say "Hey".

Phillip Kingery is the representative of Advanced Control Technologies, Inc. and teaches X-10 related classes around the country. Email him at pkingery@act-solutions.com