Difference between revisions of "Phase Coupling"

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[[Noise, Noise Filters and Automatic Gain Control]]
[[Noise, Noise Filters and Automatic Gain Control]]
Key Topics: on, off, noise, circuit, phase, coupler
Key Topics: module, outlet, wiring, phase, electrical, noise, line, interference, circuit, coupler, repeater
'' Written by [[User:Roger1818|Roger H.]] 13:52, 6 April 2006 (PDT) ''<BR>
'' Written by [[User:Roger1818|Roger H.]] 14:29, 6 April 2006 (PDT) ''<BR>

Revision as of 21:29, 6 April 2006

What is Phase Coupling

The vast majority of homes in North America have the electrical power divided into two phases (commercial buildings often have three phases but we will ignore that since I am intending this tutorial for home users). About half of the 110V lights, appliances and outlets use one phase and the rest use the other phase (220 V appliances use both phases and kitchen duplexes typically have one plug on each phase). You don't need to know why your house is set up this way, just trust me that it is.

Phase Coupling is allowing the X10 powerline signals to travel from one phase to another. This is needed so that if the transmitter (transceiver, plug-in controller or 2-way module) is on one phase and the receiver is on the other phase the receiver will hear the X10 signal.

Every home has a small level of coupling between the two phases at the transformer that supplies power to the house. This coupling is inductive which means that the higher the frequency, the more it attenuates (a fancy word for weakens) the signal. When combined with the signal reduction caused by traveling to the transformer and back, it is typically assumed that the signal will be 1/10 as strong on the opposite phase. This would be fine if there wasn’t anything else to weaken the signal or generate noise on the line, but this usually isn’t the case.

Some people will say to test if a problem is due to poor phase coupling by turning on an electric stove or dryer and see if the module starts working. This will sometimes work because a dryer (or stove) provides basically a resistive (yes the motor is inductive, but lets ignore it) load between the two phases. This means that it will attenuate all frequencies by the same amount. The resistance in the dryer is reasonably low, so it will improve the coupling, but it won’t be great. That is why even if the problem doesn't go away when performing this test, a phase coupler may still solve your problem. Every house will benefit from a phase coupler, so I highly recommend installing some type of phase coupler if you want to have more than a couple X10 modules in your house.

Home Grown Solutions

One common technique is to put a 0.1uF, 600VDC capacitor across the phases. A capacitive load is exactly the opposite of an inductive load (the lower the frequency the more it attenuates the signal). With the right capacitor it won’t let the 60Hz power through but the 121kHz X10 signal will be coupled to the other phase with very little attenuation. There are three disadvantages to this solution:

  • It is not approved in the electrical code (if your house burns down, don't blame me),
  • Electrical noise will be coupled between phases along with the X10 signal and
  • 220V modules won’t work (I don’t have time to explain this, but trust me).

Some people make a better phase coupler by putting an 18uH inductor (and a 0.25A fuse) in series with the capacitor (as Ido Bar-Tana describes on his site) to filter out the frequencies above 121kHz. This has two advantages:

  • It will reduce the amount of noise above 121kHz that is coupled
  • It will actually improve the coupling of the 121kHz signal slightly

This is essentially the same as a 2-wire [#Passive Couplers Passive Coupler] but in my opinion, if you are going to this much trouble, you might as well buy a commercial [#Passive Couplers Passive Coupler] which is UL and CSA approved.

Passive Couplers

A Passive Coupler is a device which has been designed and manufactured for the purpose of transferring X10 signals from one phase to another. These are typically CSA and UL approved so that they allowed in the electrical code. They are also typically tuned to pass only 121kHz signals so they will reduce (but not eliminate) the noise that is coupled. There are three types of Passive Couplers (4-wire, 2-wire and plug- in). Each has its own pros and cons.

  • A 4-wire coupler, if designed properly, should allow 220V modules to work, but it requires that you (or an electrician) open up your breaker panel and connect it to two breakers on opposite phases and to the neutral wire.
  • A 2-wire coupler might provide slightly better coupling than a 4-wire coupler, but 220V modules won’t work. It also requires you open up your breaker panel and connect it to two breakers on opposite phases (no neutral wire connection is needed).
  • A plug-in coupler saves you from having to open your breaker panel by letting you plug it into a dryer outlet (you can then plug your dryer into the coupler). The biggest problem with this type is the signals have to travel to your dryer and back. This will increase the signal attenuation depending on how far your dryer is from your breaker panel. Depending on its design it also may be similar to a 2-wire coupler in that 220V modules won't work.

Which one should you get? Well that depends on you. If you feel comfortable opening up your electrical box, you will get better performance from either a 2-wire or 4-wire coupler. If you are like most people and don't use any 220V modules (and don't think you ever will) then a 2-wire Passive Coupler is probably your best bet, otherwise, go with a 4-wire Passive Coupler.

If you don't feel comfortable opening up your electrical box and don't want to hire an electrician, then get a plug-in coupler. Just check if you need a 3-pin or 4-pin plug.


For most people, a Passive Coupler is good enough but if you have a large house (the rule of thumb is over 3000 sq. ft.) and you have a lot of electronic equipment in your house (stereos, TVs, computers, etc) then you might be better off with a Coupler-Repeater. These have their own set of pros and cons.

A Coupler-Repeater uses the fact that most X10 commands are repeated. The Coupler-Repeater will listen for X10 commands on the powerline and then repeat them on both phases at the same time as the transmitter is repeating the command. This is helpful if you have other significant signal loss issues and is typically only needed in larger houses. Since only X10 commands are repeated noise will not be coupled from one phase to the other. 220V modules will work.

The biggest problem with Coupler-Repeaters is they have issues with dimming commands. The number of on (or off) commands is not important, since it will turn on (or off) whether it receives the command 1, 2 or 100 times. However, the number of dim (or bright) commands that the module receives is important as it will effect how bright the light will be. There are some subtle complexities with this that I won't get into (see Phil Kingery’s series of articles for more information), but I will say that different manufacturers of Coupler-Repeaters deal with this problem in different ways. All of them will improve the situation, but none of them are perfect.

Some people like to think that if one is good, two is better. This is not the case with phase couplers. This is especially true with Coupler-Repeaters since they can start to ping-pong commands off of each other. There are situations in large buildings where more than one Coupler-Repeater is needed, and in those cases you must use commercial grade units which can be programmed to handle this. This is well beyond the scope of this tutorial and so I will say you should only install one phase coupler, be it a Passive Coupler or a Coupler-Repeater. If you upgrade to a Coupler-Repeater, be sure and remove the old Passive Coupler.


If most people can get away with a Passive Coupler and only some people need a Coupler-Repeater, an X10 Firewall is overkill for the vast majority of users. If money is no object and you have lots of really noisy equipment or you want a rock solid system then a firewall might be for you.

An X10 Firewall will isolate each circuit that you use for PowerLine Control (PLC). It will monitor each of these circuits for X10 commands and will then transmit this command on all of the other circuits. The Firewall has collision protection which will wait for the line on each circuit to be clear before transmitting a signal on that circuit to insure that no commands are lost. Since each circuit is isolated from all of the other circuits, you get the following benefits:

  • Noise (or signal absorption) on a non-PLC circuit will not be seen on any of the PLC circuits,
  • Noise (or signal absorption) on a PLC circuit will be isolated to that circuit, and
  • Noise (or X10 signals) from outside the house will not be seen on any of the PLC circuits.

The system is expandable in that you can connect multiple firewalls together should you need more than one (or have multiple breaker panels). There are, however some disadvantages to the Firewall:

  • It is very expensive (about $400 for 4 circuits or $700 for 8 circuits),
  • It is difficult to install (you have to route the wires for all PLC circuits through the firewall between the breaker panel and the loads), and
  • The current models (as far as I know, there is only one manufacturer) don't support extended commands.

Related Articles

Phil Kingery’s series of articles
Noise, Noise Filters and Automatic Gain Control

Key Topics: module, outlet, wiring, phase, electrical, noise, line, interference, circuit, coupler, repeater

Written by Roger H. 14:29, 6 April 2006 (PDT)