As easy as they are to use, the many plug-in and hard-wired X-10 compatible devices have caused more than one of us to ask the question, “Which one should I use?”. Before we can choose the right X-10 device, however, we need to know a little more about the load we are wanting to control and how the circuit is wired.

Technically speaking, we can categorize the various loads in your home into two neat groups: linear and non-linear. Electronically speaking, a linear load is purely resistive, having no (or a negligible amount of) inductive or capacitive impedance. Conversely, non-linear loads have a degree of inductive or capacitive impedance.

Linear loads used to be the most prevalent, by far. From the earliest days of Thomas Edison, electricity in our homes was used for only two purposes. The first was to power Mr. Edison’s new incandescent light bulbs. The other was to heat coils of wire for warming our houses or cooking our food. Occasionally, we used electricity for an inductive load, like a transformer or a motor.

Today, however, non-linear loads far outweigh the linear ones. We have televisions, radios, the electronic timers in our coffee makers, our electronic digital clocks, our computers, alarm panels and anything else you can think of. Even my wife’s sewing machine now has a microprocessor inside it.

Sometimes, we may think that a light bulb is a linear load when it really isn’t. Halogen bulbs come in a variety of types and styles. Some are 120v bulbs and since they have tungsten filaments, they are linear loads. Some halogen lights are really 24v and so are powered by a transformer or electronic power supply. In those instances, the entire load is non-linear.
Figure 1Another consideration is the circuit itself. If this is to be a retrofit situation, we may be limited in our choices simply by how the circuit is wired. We often think of a circuit as being wired from the panel, to the switch, then to the load (as in Figure 1). Because of the electrician’s prerogative and what was convenient at the time, it is also common to find that the circuit was wired from the panel, to the load and then to the switch.

Figure 2Figure 2 shows, what is commonly called a “switched loop” circuit. As far as the electrons are concerned, they pass through the switch before going to the load in both cases. The only difference is the arrangement and order of the junction boxes.

Our confusion begins when we try to replace a standard mechanical wall switch with an electronic X-10 switch. A regular mechanical wall switch gets it’s “power” from your finger. Even though it is connected to a wire that has 120v on it, the old mechanical switch does not “use” that power. When you want to “switch” on the load, the power to do that, comes not from the wire, but from your finger. The purpose of that mechanical switch is to complete the circuit or interrupt the circuit depending on which you desire, but it is not an electrical load in and of itself. The same is also true of most of the standard, hardware-store-variety, dimmer units. You supply the power to turn the knob.
Figure 3Most “do-it-yourself”-ers are fortunate enough to have begun their journey into the world of X-10, remote control and home automation, by plugging a table lamp into a “lamp module”. Later we may have replaced a mechanical wall switch with an X-10 brand or Radio Shack “electronic” wall switch (figure 3) on a simple lighting load circuit. These work especially well in those instances where there are only 2 wires in the box.

We might have been disappointed to learn that we could turn it “on” and “off” locally, but had to use a transmitter to do any dimming. (Only later did we discover that we could open it up and restore the local dimming feature.)
Figure 4Only a few of us noticed that the Radio Shack or X-10 wall switch had only “two” wires and wondered why it did not require a connection to neutral. After all, it was an electronic gizmo and as such, did it not need its own supply of electricity? Even ACT’s own RD130 (figure 4) is a 2-wire dimmer. It is very close in design to the standard X-10 or Radio Shack units. All of them are made mostly for those retrofit situations where the installer wants to replace a standard mechanical wall switch.
Figure 5Since they are the simplest of the X-10 receivers, they can be used in both circuits types. A switched “loop” circuit (figure 4) has no neutral wire. Oh sure, there is a white wire (I use yellow in my illustrations) but if the electrician followed code, he used a marker, paint or tape to color the wire end “dark” to signify that it was now being used as a switched line wire. When used in a switched line circuit (figure 5) a true neutral is available but in this case, its isn’t used.

These 2-wire X-10 dimmers connect to only line and switched line (or hot and switched hot) and operate from the trickle current through the load. In other words, even when the light bulb (resistive linear load) is “off”, there is still a little current through it to keep the 2-wire dimmer operating.

Only a few unlucky DIY’ers discovered the problems when they tried using one of these 2-wire dimmer units on a circuit with a radio or TV on it. Not only did the receiver not work, the radio or TV was probably damaged.

While these 2-wire dimmers (intended only for use with incandescent or “linear” loads) seem to be the most prevalent of the hard-wired devices, they suffer from one deficiency that occasionally results in unreliable operation. Not only does their operating voltage come through the light bulb, the X-10 signal must also do the same. If the signal strength is high, then there is usually more than enough signal that gets through. Sometimes, however, the X-10 signal is just barely high enough for the receiver to turn “on”. Once “on” the signal is partially blocked by the bulb and there is now too little signal to turn it “off” again.

What has happened is that when “off”, most of the (differential) signal voltage is across the receiver, but when on, more of the signal is across the bulb. When ever the installer has a neutral in the wall box, I always suggest using a 3-wire dimmer (figure 6) so that the receiver circuit always has its own connection to line and neutral and no longer has to rely on trickle current to operate (figure 7).
Figure 6 Figure 7

There is another interesting and often confusing aspect of home automation, and that is, “speed” control. I am constantly amazed by just how easily we all associate “dimming” with motor control. As I said earlier, incandescent lights are resistive loads while motors and transformers are inductive loads.

What really gets confusing is when a triac based dimmer unit is used on inductive loads. Most modern dimmers, including all X-10 compatible dimmer units, have a triac output. A triac dimmer does not attenuate the 60Hz sine wave, instead it cuts out varying chunks of the sine wave. Since the output is non-sinusoidal, the motor in a ceiling fan, for instance, begins to exhibit some unpleasant side effects. Sometimes the fan begins to hum or buzz. It may also run hotter than normal since it is no longer receiving a smooth sinusoidal wave as its power source.

Receivers like the RD140, from ACT (figure 7), is not only a 3-wire dimmer, it is also rated for non-linear loads. Many users find satisfactory operation using this dimmer in those applications where speed control of a ceiling fan, or a transformer is desired. Giving the dimmer its own connection to line and neutral makes it possible to have a power source that is unaffected by the on/off condition of the load. This will also make sure that the X-10 signals do not have to squeeze through the load (the motor, in this case) in order to get to the dimmer unit.

I know of many people who have attempted to use a two-wire dimmer with a motor (or transformer for low-voltage lighting) and discovered that if it works at all, it is very intermittent. Either it will not stay on, will not stay off, or they can not turn it on and/or off remotely.

However, just because the RD140 is rated for non-linear loads does not automatically mean that your non-linear load wants to be controlled by a triac based dimmer. We all know that we will damage a television or radio if we try to control them with a dimmer unit. Trying to control a television’s picture brightness or a radio’s volume with a dimmer is like trying to control your car’s speed by how fast you fill the gas tank. The same is true for some “non-linear” loads like fluorescent lights, low-voltage lighting systems and motors.
Figure 8Some non-linear loads just should not be controlled with a dimmer at all. Even when the dimmer is full on, it is still not a true sine wave and therefore causes the load to hum, buzz, run hot, or worst case, burn out. In these cases, a switch that uses a relay instead of a triac is required (figure 8). A relay, of course, is either on or off: it isn’t a variable output.
Figure 9These kinds of receivers are known as “hard-contact” receivers and are also available from ACT as our part numbers RS120. Since these have a relay as their output device, they can carry much larger amounts of current than a comparably sized dimmer unit. Our industrial grade devices are rated at 20 amps. They will require their own connection to line and neutral, (figure 9) and so they will not work in wall boxes where there are only two wires.

While the question of “which one should I use?”, has been only partially answered in this article, I hope that the next time you want to replace an old mechanical light switch, you will be able to make a more informed choice.

To all of you who enjoyed and benefited from my other articles, thank you for your nice emails. This one is a continuation of my first “Which One Should I Use?” If you have not read the first one, it is a good prerequisite to this installment: Use the index at the left to go to the December Issue or use this link (

In that first article I made this statement:

“Some non-linear loads just should not be controlled with a dimmer at all. Even when the dimmer is full on, it is still not a true sine wave and therefore causes the load to hum, buzz, run hot, or worst case, burn out.”

That one sentence motivated many of you to email asking for more information. Well, get comfortable, here it is.

There is an interesting and often confusing aspect of home automation, and that is, “speed” control. I am constantly amazed by just how easily we all associate “dimming” with “speed control”. On more than one occasion , when I have had a particularly bad day, I have been asked about using dimmers for ceiling fan speed control, to which I sarcastically respond, “Yes, when you dim a ceiling fan, it begins to disappear until eventually you can’t see it at all. You can feel the breeze but you don’t know where its coming from.” (Most people don’t seem to appreciate my sarcasm.) Let’s begin by looking at the basic differences between dimming and speed control.

As you probably know, incandescent lights are resistive loads, which means that, electrically speaking, they have no (or insignificant amounts of) inductive or capacitive reactance. In other words, as far as the electricity is concerned, incandescent lights “feel” like big resistors. More importantly, as standard X-10 dimmers are concerned, incandescent lights “feel” like big resistors and not capacitors nor inductors. Most modern dimmers, including all X-10-based dimmer units, are triac based. A triac dimmer does not attenuate the 60 Hz sine wave, as we might expect.

Figure 1If we were to use a big variable resistor or a variable transformer, the entire sine wave could be reduced in amplitude (see figure 1). Variable resistor dimming is what was used in stage lighting back in the first half of this century. This, however, is a very inefficient and expensive method of dimming. Today, we have solid state dimmer units that will reduce the light’s output not by attenuating the entire sine wave but instead, by quickly turning the sine wave “on and off”. Think of it like this. If you were fast enough to flip a switch on and off again, so that only a part of each half-sine wave was allowed to pass through to the light bulb, it would glow only a fraction of its normal brightness. That is what the triac does. Instead of being a variable resistor, it cuts out varying sized chunks of the sine wave. To really see what the output of a triac dimmer looks like you need to look at it like an oscilloscope.

Figure 2Figure 2 shows a couple of sine waves as they would appear on the output side of a standard X-10 dimmer. You will notice that the leading edge of every half-sine wave has a chunk removed from it. Interestingly, even when the X-10 dimmer is “full on”, the light is never really at 100%. Instead it is only allowing about 96% of the power to flow through it to the light bulb. You may have noticed (or thought it was just your imagination) that as soon as you installed your X-10 dimmer, the light doesn’t seem as bright as it used to be. There is a very good reason for that. It isn’t. It is about 4% lower than it would be with a standard mechanical switch. This is done by design.

It is common, especially in older homes, to find that there are only two wires in the wall box. That means the circuit was originally wired with the line and neutral wires going from the breaker panel to the load junction box, and then two-conductor wire (with ground wire, I hope) extending from that box to the wall box where the switch was installed. Those two wires are not line and neutral, they are really line and switched-line (or hot and switched-hot, colloquially speaking). In order to have a dimmer that will work in this instance, most X-10 dimmers (and those from Radio Shack) have only two wires and are meant to operate on the trickle current “through” the light bulb’s filament to power the dimmer circuitry (see figure 3).

Since incandescent lights are “linear” loads, the two-wire X-10 dimmer receives a steady and “linear” amount of current on which to operate. When the light appears to be “off”, the filament still allows enough current to flow to keep the X-10 unit alive. Even when the light is supposed to be full “on” the X-10 unit keeps about 4% of the power for itself. If it were to allow all 100% of the power to flow to the light, there would be none left for its own circuitry. That is why in figure 2, there is a small chunk of each half cycle left out. That is the 4% that is being used by the dimmer unit. This also explains why X-10 dimmers must have a minimum load. Using a 400 or 500 watt load allows for more than enough current to keep the X-10 circuitry working. Using a 40 watt or 60 watt light bulb will still allow sufficient current to flow. However, if the load is too small, like a small wattage night light, then there will be too little current to keep the dimmer unit alive. It will stave to death (and you don’t want that on your conscience, do you).

There is another greater benefit to that 1.1 milli-second gap. That creates a clean space in which the X-10 pulses will appear (see figure 4). Having such an abrupt and instantaneous “switching” action going on twice each cycle has a very definite downside. In that instant in time where the electron flow is trying to go from nothing to full on, that abrupt transition causes a lot of electrical “noise”. The X-10 engineers, therefore, designed the X-10 dimmers to always leave the first little section clear so that the units would be able to receive the X-10 signals.

The 3-wire dimmers (those which require their own connection to neutral) really don’t need to keep that 4% for their own use, since they have their own source of power (see figure 5). Even so, they will also always leave the first 1.1 milli-seconds blank so that they can receive clear signals.

What really gets confusing is when an X-10 dimmer unit is used on inductive loads. Inductive loads are typically motors and transformers. Since the output of a triac based, X-10 dimmer is non-sinusoidal (that means its not really a sine wave), the motor or transformer tends to be “unhappy” with it. Inductive loads are designed to use clean, smooth sine waves. They don’t like it when their source of power is all chopped up. If you do use an X-10 dimmer with an inductive load, you will most likely notice that it (the motor or transformer) begins to hum or buzz.

Now, lets talk about motors. A standard AC motor relies on the flux lines created around the stator at 60Hz to cause a mechanical rotation in the rotor. A “synchronous” motor is the least tolerant of speed variations due to load. It will attempt to maintain exact speed (in relation to the supply frequency) by drawing more current to increase its torque. Since most AC motors rotate in relation to their supply power, the most widely used method of commercial speed control is the “variable frequency drive”. These units are usually abbreviated “VFD’s” or “VSD’s” (for variable speed drives). These electronic speed control drive units will control the speed of the motor by actually changing the frequency of the power to the motor. To have the motor run slower, the drive supplies power below the standard frequency of 60 Hz. For the motor to run faster than normal, the drive will supply power at a frequency greater than 60 Hz.

Other AC motors will “slip” as the load increases because their available torque can no longer keep up with the demand of the load. Some AC motor controls take advantage of this relationship by limiting the current to a motor, thereby limiting the torque. As the torque is reduced, the motor slows because it simply can no longer maintain its speed. There are also AC/DC motors whose speed can easily be controlled with a simple variable transformer. That is somewhat how an X-10 dimmer unit controls the speed of some motors.

Aside from the receiver section, the X-10 unit is a basic triac type dimmer. Its triac chops out greater and greater chunks of the sine wave as it dims the light. When set for 50% brightness, its triac “holds back” the first half of every half cycle (see figure 6).

And of course, when the light bulb is nearly out, the triac is cutting out nearly all of each half sine wave (see figure 7).

This same reduction in power can be used to control the speed of some motors. The frequency remains the same although it is no longer a true, smooth sine wave. Ceiling fans are the most common motorized load for which a home owner (or home automation installer) wants speed control. Unfortunately, ceiling fans use a wide variety of motors. Some manufacturers will even use a different type of motor every other month on the same model fan. Some fans can be controlled by a standard dimmer. It is well known that “shaded pole” and “permanent split capacitor” type motors are the best candidates for use with triac based (X-10) dimmers.

There are still some drawbacks to using triac dimmer units (regular or X-10) even with the most compatible of motors. The motor may run hotter than normal since it is no longer receiving a smooth sinusoidal wave as its power source. Being a “non-linear” load, what may be listed as a 1/5hp fan, may appear to be far greater than that to the dimmer triac. For a few milli-seconds each sine wave, the triac may “think” it is connected to a dead short. For those few milli-seconds the triac is being asked to deliver far more current than it was designed to handle, and so it burns up. Even if the triac based dimmer is capable of delivering the current for those short durations, the motor and the associated circuitry inside the fan may not be able to handle it and so they burn up. Don’t be discouraged, however. Many times they work fine but we will get into that later.

Now, let’s discuss transformers. When someone says “halogen lights” they often mean “low-voltage” halogen lights. In order to tightly wind the filament into a compact space, many decorator lamps used 24v bulbs. That means that the power to run them must come from something that will reduce the regular house power of 120v down to 24v. That used to mean a “transformer”. (Now, it may more likely be a low-voltage electronic power supply, but let’s talk about transformers first.)

A transformer is, of course, an inductive load and its basic design has not changed much since Edison’s day. In simple terms a transformer is a primary coil of wire that allows the flow of current, whose flux lines induce a voltage into a secondary coil of wire. In this case a 120v 60 Hz primary power, induces a secondary 24v 60 Hz power (see figure 8). These coils of wire are wound very close together and are kept apart by “laminates”. As long at the transformer is powered by smooth sine waves (remember those back in figure 1), they induce a smooth output in the secondary side. Unfortunately, should the input power “not” be smooth, the transformer may not like it. The same problems that occur when a chopped up sine wave is supplied to a motor also occur when a chopped up sine wave is given to a transformer. Cheap transformers will literally come apart. I have seen a few instances where a triac based dimmer was being used with an old, cheap transformer. The adhesive holding the layers of wire and laminate were so poorly bound that the transformer buzzed like a 2 pound bumblebee. It finally began to tear itself apart. More expensive transformers will do better because their physical construction tolerates the stresses caused by the irregular power.

Even with all of that, there is another problem with many X-10 designed dimmer units (at least in this application). Back in “PART I”, we discussed the occasional problem of using a 2-wire dimmer whose supply of power “and” signal must come through the load before it reaches the receiver (see figure 9). Sometimes, a user will notice that a newly installed unit will operate locally but he can not remotely send an “OFF” command to it. Once it is turned off manually, he can send an “ON” command, but once on, he can not get it to go off again. This is caused by the slight change in signal strength seen by the dimmer in the two states. When the light bulb is off, the receiver has nearly the full 120v differential across its two wires as well as the nearly full amount of available X-10 signal, but when the light bulb is on, the signal is divided and the dimmer unit will not receive quite as much. Although this situation is rare, it happens occasionally when the signal level is marginal to begin with.

This effect is greatly exaggerated when a two-wire dimmer is used with a non-linear load, like a low-voltage transformer (see figure 10) or a ceiling fan motor. I know of many people who have attempted to use a two-wire dimmer with a transformer and discovered that if it works at all, it is very intermittent. Either it will not stay on, will not stay off, or they can not turn it on and/or off remotely.

With all of these potential problems what then are you supposed to do? Well, there are ways to get around most of these problems. First, giving the dimmer unit its own connection to line and neutral makes it possible to have a power source that is unaffected by the on/off condition of the load (see figure 11). This does not mean that somehow you can use a 2-wire dimmer by some wiring trick. This means that you will have to purchase a real 3-wire dimmer. Using a 3-wire dimmer will make sure that the X-10 signals do not have to squeeze through the load (the transformer, in this case) in order to get to the dimmer unit. These 3-wire dimmers are usually constructed to operate with non-linear loads. They have better circuitry that helps them withstand the severe current fluctuations associated with inductive loads.

Should you wish to control a ceiling fan, the manufacturer of the fan should be contacted to be sure that their motor is compatible with “triac based” dimmers (don’t ask them about X-10 dimmers, they usually don’t know what you are talking about.). The one-speed fans do the best. If the fan you are trying to control is already a multi-speed fan, then set it to the highest speed using its pull-chain switch. Now the 3-wire dimmer can be used to control the speed through a wider range. (See figure 12.) Don’t expect to get reliable low speed operation. There is so little torque at low speeds the fan will most likely stall. Also expect the fan to hum a little at the lower to middle speed where the sine-wave chopping is most severe. If you are lucky, the hum will be so slight it won’t be noticeable. Surprisingly, it’s the cheapest ceiling fans that usually do the best.

Home Automation Systems can supply you with 3-wire dimmers from Advanced Control Technologies, under the part number RD160. However, just because the RD160 is made for non-linear loads does not automatically mean that your non-linear load wants to be controlled by a triac based dimmer. We all know that we will damage a television or radio if we try to control them with a dimmer unit. Trying to control a television’s picture brightness or a radio’s volume with a dimmer is definitely not a good idea. The same is true for some “non-linear” loads like some fluorescent lights, low-voltage lighting systems and motors.

If X-10 dimmers cause inductive loads like motors and transformers to buzz and hum, why don’t all speed controls? That is a complex question and I can only give you part of the answer. Some triac based dimmers are modified for use with inductive loads by adding capacitive loads (big capacitors) in parallel with inductive load. This makes the overall load appear more “linear” to the dimmer unit. These capacitors help absorb the wild voltage swings present at that moment in time where the triac “switches on” (see figure 13). This helps smooth out the power and so the motor (or transformer) is not so shocked by the abrupt transitions. There is a project in the works to develop a modified X-10 dimmer that will also have a capacitor dampening circuit.

In those cases where dimming is just not a good idea, a switch that uses a relay instead of a triac is required. A relay, of course, is either on or off: it isn’t a variable output and as such, will deliver a full 100% of the sine wave to the load. These receivers are known as “hard-contact” receivers and are available from ACT as our part numbers RS120 (for a single unit) or RS100 (for a master unit that can be used in 3-way installations with a slave switch). Since these are industrial/commercial grade devices, both are rated at 20 amps. They will also require their own connection to line and neutral, and so, they will not work in wall boxes where there are only two wires.

Here ends “Which One Should I Use – Part II” and I hope this has shed some light on the use of dimmers with fans and transformers.

Bob has been very generous in letting me write about whatever I want but I think I will ask your help for the next piece. I received a lot of great email from the non-technical article on “Lucky Lindy Meets My Grandmother” ( ), so much that because of it, I have been asked to speak at two upcoming conventions. Now I need your feedback. Please help me choose one of the following subjects for the continuing saga of “Which One Should I Use – Part III”.

Will it be:
1. – Basic Coupling (Passive Couplers and Repeaters)
2. – Three and Four-Way Switch Circuits (Why are There so Many Ways to Wire Them)
3. – Noise and Filtering (What is Noise Pollution, What Causes It, How to Stop It)

Well, actually, before we get to “which one should I use (“part trey”), we have some unfinished business to discuss.

First, in the April HTI issue, I gave you information on the use of X-10 receivers with non-linear loads (Which One Should I Use, Part II). For those of you who yearned for more I have some additional information for you.

Many of you who read the “comp.home.automation” newsgroup will recognize the name Edward Cheung, Ph.D. (We call him Doc Ed in the newsgroup.) He is a frequent contributor and very well respected in the group and in the industry. He, too, was disappointed with the humming and buzzing associated with using X-10 dimmer receivers with non-linear loads, especially, ceiling fans, so he put his considerable metal powers to bear and came up with a solution. He has designed an add-on device that makes an X-10 dimmer work better with motors. He calls it his “Not ho-hum but no-hum ceiling fan speed control”. You may have to do some surfing to get to the exact page, but I strongly suggest that you begin at his home URL of … and work your way down through his home automation section and then to the dimmer page. Most electronic tinkerers should be capable of building his do-it-yourself project.

Next! Thanks to all who sent me the nice emails and voted for their preference on the subject of this part of the series, “Which One Should I Use?” I especially want to thank Dwight Hapeman who said (in part):

“Your articles are, as usual, very informative and entertaining. ACT better be paying you at least $150,000/ yr. (That was for you to show to the boss.)”.

Well Dwight, I did show your email to my boss. He said that it must be a misprint. It should have read, “$15,000”. (…oh well, we tried…)

Third! What did I choose as the subject for this installment? Well, it wasn’t easy. From the very beginning, “Basic Coupling” took an early lead in the votes with “Three and Four-Way Circuits”, a close second. Then as more and more votes came in, the order did not change but it looked like it was going to be a photo finish as “Basic Coupling” and “Three and Four-Way Circuits” were running almost neck and neck with “Noise and Filtering” a very close third. I may have subliminally influenced the voting by listing them in that order.

Thinking that “Basic Coupling” was still going to win, I began working on “Part III” with that as my subject. Well, here I am, putting the finishing touches on the piece and it now appears that “Three and Four-Way Circuits” has won by a nose. One of the later votes was from John Diamant (thank you, John) who sent me an email. Not only did he cast his vote for “Three and Four-Way Switch Circuits”, but he lobbied heavily for his choice with:

“The reason I suggest this subject over the other two choices is that both of the other two are covered fairly extensively in various other sources, whereas I’ve never seen a good discussion on 3 and 4 way switch wiring.”

In light of his, plus a few other votes, I feel a little deceptive in presenting this next segment in the series. Unfortunately, I have already done too much work on “Basic Coupling” to jump to the another horse. To all who voted, thank you very much. To all who voted for “Three and Four-Way Circuits”, I promise that I will write that one after this one is finished.

Did you notice how cleverly I worded that last sentence? “…after this one is finished”. You see, the problem is that as I started writing this one, I realized that it was such a large subject that I couldn’t do it justice in one small section. Bob Hetherington, here at HTI, has been very generous in allowing me to write about whatever I wanted and as much as I wanted, but I have to be realistic. None of you want to stay on-line to read “Gone With The Wind”. So this one will be “Which One Should I Use, Part III – 120/240v Residential Coupling” and later I will do the next section, “Which One Should I Use, Part IV – Complex Residential Coupling with Considerations for Dim/Bright”. After that I will do my best to do the “Three and Four-Way” piece. For all you who voted for “Noise and Filtering”, I will most likely do that a way down the road but don’t worry, I won’t forget you.

Okay, I think we are all finally ready for…….

Which One Should I Use, Part III
(120/240v Residential Coupling)

Most of us started in the X-10 world using Radio Shack stuff. We would buy a plug-in lamp module and a desk-top transmitter and once home eagerly rip them out of the bubble pack and rush to plug them in and try them out. At that time we had no idea how they worked (sure we had heard some stories about signals on the line) but we didn’t care. Most of the time we were lucky and they “did” work. If we had just happened to plug the transmitter and receiver into outlets on the same circuit, they nearly always worked. If we were lucky enough to plug them into outlets that were on different circuits but on the same “leg” of the transformer, they still nearly always worked.

Figure 1Figure 1 shows a greatly simplified diagram of the wiring hidden inside a home. Here in North America, we use 60Hz, 120/240v split-single phase power as the standard in nearly all of our residential systems. (I have to be careful to specify that since I know that HTI gets some readers from other countries.) When we plugged our Radio Shack desk-top transmitter into that outlet, and then the lamp module into the other outlet, we probably had no idea that they were on the same “side” (or “leg”) of the breaker panel. The X-10 signal that was generated by the transmitter did not have very far to travel. It simply went upstream to the breaker panel and from there, it went out to every circuit that it could go to. Some of that signal found its way onto the nearby circuit that had our lamp module on it. Press the button and bingo!, the lamp came on.

So, we went back to Radio Shack to buy some more “X-10 Powerhouse” stuff. This time, however, we didn’t happen to pick an outlet that was on the same “side” of the panel as the one before. No matter. The house is not very large and so the signal still makes it from there to here. Figure 2Figure 2 shows the path the signal must now take to go from the transmitter to the receiver. Somehow it has to pass from one side of the panel to the other side of the panel. In some houses, like my own, there is sufficient “natural” coupling for the signal to travel back and forth from one side to the other. Either it goes through some phase-to-phase loads (electric 240v water heater or stove, for instance) or it goes “through” the transformer (figure 3).

Figure 3Now bear in mind that the signal is like water pressure, it actually goes everywhere it can. Just because there is no X-10 receiver on that circuit in the living room doesn’t mean that the signal doesn’t go there. Don’t give that X-10 signal any anthropomorphic qualities. It can’t “decide” where it will go and where it won’t. Believe me, it just goes anywhere it can.

Since those cute little house diagrams are so hard to draw, lets use a simpler “schematic” type of diagram to investigate the behavior of the signal as it travels through the electrical distribution system. Figure 4 shows a diagram of just the “A” side of the panel. (Oh, by the way, all my diagrams show neutral as yellow because white just doesn’t show up. Figure 4You should all know that in the real world, at least here in North America, all neutral wires are “white”.) Since both the transmitter and receiver reside on the same side, the signal level is high. (Few things are seldom this simple in the real world but I am pretending that this house has no noise nor “low impedance” problems. Play along with me, okay?) The X-10 signal appears at the zero crossing on the sine wave at a level that is far more than is required for reliable system operation.

Now, however, we have added our second receiver on the opposite side of the panel (figure 5). Even with only natural coupling, there is usually sufficient “bleed-through” of the signal (through 240v loads, or through the transformer) to make it to the second receiver. Figure 5Oh sure, the signal level may only be about 10% as strong, but as long as it is above the published minimum level of 100 milli-volts, it should still work fine. “On” still means “On”. You can’t get anymore “On” than “On” no matter how strong the signal is. The number of “do-it-yourself” residential installations that work fine without any additional coupling is probably in the millions.

Now look back at figure 5. If the signal level on the “A” leg is about 2v and the signal level on the “B” side is about 200mv (at the furthest point), then everything should work. However, what if the house is much larger than the common do-it-yourselfer’s house. What if it has a lot of electronic do-dads that “suck up” the signal like a sponge? What if your neighbors’ have a lot of do-dads that also suck up your signal? You can’t tell your transmitter, “Don’t send your signal that way!”. You still may have enough signal on the “A” side. It may have dropped from 2v to about 400mv but that’s still enough. The problem is on the “B” side where the signal has dropped to about 40mv. Oh sure, sometimes you can get the receiver to go “On”, but it is not reliable. And what’s more, you don’t know why it isn’t reliable and you don’t know how to fix it.

What if you could divide that 200mv that is still on the “A” side and give a chunk of it to the “B” side. You would then have over 100mv on each side, right? There are several ways to do that. First, you could leave you electric stove on all the time. (I have a cute story about a guy who tried turning on his gas stove….but perhaps another time.) Or you could install a capacitor in your breaker panel. You may have read the FAQ (Frequently Asked Questions) in the comp.home.automation newsgroup and found the part that described just such a thing. You may be a little reluctant to do that knowing that a capacitor by itself, is not very frequency selective and not very safe. (I have to admit that it usually works fine, but as a representative of Advanced Control Technologies, Inc. I can not condone it. Actually even if I weren’t a representative of ACT, I still wouldn’t condone it.)

Or you could use a device that has been specifically designed to be a “short cut” for those little pulses of X-10 signal so that they can freely pass from the “A” side to the “B” side and, if needed, back the other way. Figure 6Figure 6 shows the schematic of just such a device. Ours goes by the part number CP000 (and is available from all the usual places). I have to admit that Leviton also has a similar device, but I just hate the term “signal bridge”. Bridges are for people, cars and trains….not high frequency signals. I prefer the more technically accurate term of “passive coupler”.

The “CP000 Passive Coupler” is a twin-tuned circuit that separates the two phases (if it didn’t, there would be one huge flash and your main breakers would pop off) while allowing any high frequency signals to pass through. It is a bi-directional device allowing signal to pass from “A” to “B” and from “B” to “A”. Figure 7In figure 7 the CP000 has been installed (next to the breaker panel in a 2×4 wall box) so that the signal from the transmitter on side “A” can easily flow to side “B”. The signal level on the “A” side is less than it was before but it also higher on the “B” side than it was before.

For most modest sized homes the CP000 is more than sufficient for the job. However (and you knew there was going to be a “however”, didn’t you…), sometimes the addition of a passive coupler merely trades one problem for another.

Figure 8 shows the addition of a 240v, phase-to-phase receiver. Now that there is a passive coupler installed, (1.) – the source leg still has sufficient signal level, (2.) – the “B” leg has improved signal level, (3.) – but for some reason, the phase-to-phase receivers don’t seem to work, or are not reliable. Figure 8Well, here’s what is happening. The X-10 signal is “referenced” to the neutral, so that any amount of signal on one leg is measured “to” neutral. Any amount of signal on the other leg is also measured “to” neutral. But any receiver that is connected phase-to-phase is “not” getting signal referenced to neutral, it is getting its signal (obviously), phase-to-phase.

Figure 9 is a visual representation of a silly analogy. If we had 3 wires (just 3 wires, not connected to anything) sitting on our work bench, we could easily see what was happening. The battery represents the transmitter and so there is 1.5vdc when measuring from the first wire to the third wire. With the jumper in place we also measure 1.5vdc from the second wire to the third wire. But when we try to measure the voltage (or signal) from the first wire to the second wire, we get zilch. Now, any electrical engineer worth Pi will tell you that a direct current circuit will not act exactly like a multi-frequency, multi-circuit distribution system, but in this case it is close.Figure 9

Before we try to do something about the phase-to-phase signal cancellation we still have another possibility to consider. Sometimes, especially as the residence gets larger and larger, it eventually comes to the point where there is simply not enough original signal to go around. The output power of a typical X-10 transmitter is actually less than the smallest night light. That is an awfully small amount of power to try and spread out over a large facility. What if the source leg (that side with the transmitter on it) has such a large area to cover, electrically speaking, that the signal level is only about 80mv to begin with. The opposite leg has practically no measurable signal at all. The home owner (or home automation company technician) decides to install a passive coupler only to discover that instead of increasing the signal level on the “B” leg, both sides now quit working. (Then they call me and rant and rave that our passive coupler is a crappy piece of equipment….but that is another story.)

Most of the time it is far more advantageous to use a sophisticated device that actually “recreates” additional signal instead of just trying to spread out the original signal. Figure 10Figure 10 is a block diagram of ACT’s “CR230” coupler/repeater. It does not just allow original signal to pass through it, it actually receives signal and then recreates and retransmits signal. When installed next to a 120/240v breaker panel (figure 11) it will receive signal from either leg and then it retransmits strong signal onto both legs. The CR230, like all of ACT’s eight different X-10 compatible repeaters, was designed by our talented engineers and then built in our production department right here in Indiana.

Don’t misunderstand now. I almost never recommend that a passive coupler and a coupler/repeater be used together. In the overwhelming number of instances they will cancel out each other, or at best, reduce their effectiveness. Figure 11The repeater tries to send signal that it has specifically created for the “A” leg but the passive coupler steals part of it and puts it on the “B” leg where it isn’t needed. Then they get in a big fight and its not a pretty thing to watch. So if you are ever installing a coupler/repeater, remember to take the old passive coupler completely out of the circuit. Don’t think that if one is good, both are better. It doesn’t work like that.

Most “Home Automation” companies used to automatically include a repeater on any house that is 5,000 sq/ft or larger. It’s not that square footage is an absolute measure. Actually, we at ACT have successfully shot signal over 6 miles but I have also seen situations where I couldn’t get signal 20 feet across a room. Its not the square footage, it’s the impedance of the electrical distribution system. The relationship is this: the larger the system, the lower the impedance (usually). Another way to think of it is this: the larger the water pipe system, the more places the water has to go, the more likelihood of small leaks and the harder it is to keep the water pressure high.

As I said, most HA companies used to say that any house larger than 5,000 sq/ft got a repeater, but now many HA companies are lowering that figure to 4,000 sq/ft. As more and more homeowners install more and more home theater systems, computers and other electronic do-dads, the overall high frequency impedance is getting lower and lower (more “leaks”) and so the need for a repeater becomes more prevalent. Not only will the repeater make increased signal available to the regular receivers, it will also fix that bothersome “phase-to-phase signal cancellation” problem.

Okay so how does a coupler repeater work? Figure 12Figure 12 is another one of my silly analogies. The original transmitter sends out its signal, in this case “A1 A1 A-On A-On”. Unfortunately the original signal is not strong enough to get to the receiver. A coupler/repeater, however, is installed midway between the two. It receives the first frame of data (the first “A1) from the transmitter and then retransmits it at the exact same time as the second frame of data (the second “A1”) from the transmitter. The repeater then receives the next frame of data (the first “A-On”) and, as before, retransmits it at the exact same time as the next frame of data (the second “A-On”) from the transmitter. The receiver “hears” (receives) the “A1” and then the “A-On” from the repeater.

Don’t be confused by the term “signal amplifier” that is used by some people in the X-10 industry. In the true electronic sense of the word, the CR230 (like its Leviton counterpart) is not an “amplifier” but a “repeater”. For most users the difference is inconsequential, but I want you to know the difference (…and yes, we at ACT also have true “amplifiers” but they are almost never used in residential applications).

And so, in some small do-it-yourselfer houses, no additional coupling is needed. What natural coupling is present works fine. In larger houses, a passive coupler is usually needed to help that little bit of signal get from one side of the panel to the other. Then, in those big expensive houses, a coupler repeater is needed to “recreate” signal over the entire distribution system.

Ah, I see that some of you have read between the lines and have a few questions, like:

What if the job is on a large estate where even an ACT coupler/repeater is not enough? What do I do then?

If a repeater “repeats” every other frame of data, how does that effect dim and bright commands?

What if I want to take some signal from one distribution system and send it to another distributions system? How do I do that?

When do you use a true amplifier?

What was Spock’s first name?

Why don’t the words comb and tomb rhyme?

Well, those questions (except for the last two) will be answered in the next installment, entitled…

As always, comments and suggestions are always welcome. Email me at .