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HTINews Feature Article

Which One Should I Use - Part III 120/240v Residential Coupling by Phil Kingery

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 http://members.tripod.com/~edward_cheung ... 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 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 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).

Now 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. You 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. Oh 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 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". In figure 7 the CP000 has been installed (next to the breaker panel in a 2x4 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. Well, 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.

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 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. The 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 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...

Which One Should I Use, Part IV
(Complex Residential Coupling with Considerations for Dim/Bright)

As always, comments and suggestions are always welcome. Email me at actpccpek@aol.com .

Phillip Kingery is the representative of Advanced Control Technologies, Inc.
and teaches X-10 related classes around the country.
Upcoming classes include: Dallas, Los Angeles, New York City and Atlanta.