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To understand how the X-10 protocol works, you need to know the basics of household electrical wiring. (Keep in mind that you should always consult with a licensed electrician before performing electrical work.) In the United States, household power is 120-volt AC and, unlike DC, works on a sine wave. While DC provides a solid stream of power -- 12-volt DC will constantly supply 12 volts--AC power output rises and falls from -170 volts to 170 volts, which averages at 120 volts. A sine-wave cycle will complete once every 1/60 of a second, or at 60 Hz. In a typical U.S. household, all the power lines terminate in a centrally located circuit-breaker box.

Power is brought in from the utility pole via three wires: One is ground, and the other two are hot wires containing 120 volts of electricity each, 180 degrees out of phase. The hot wires' voltage levels change with respect to the ground wire. Typical household appliances use 120 volts and are connected to one hot wire. The other wires in the receptacle are neutral and ground. Remember that the two 120-volt lines entering the house are 180 degrees out of phase? If you look at the graph of y=sin(x) and y=sin(x + pi), below, you'll see that when one sine wave is descending, the other is rising. Large appliances, such as clothes dryers and hefty air conditioners, require 240 volts. These receptacles are equipped with two hot wires -- one to each of the 120-volt lines entering the house. This lets you use 240-volt appliances.

If you look at your circuit breaker, you'll notice two rows of circuits: The left row is connected to one of the 120-volt lines supplied from the pole, and the right side links to the other 120-volt line. If you were to disconnect one of the 120-volt lines, half your house and all the 240-volt appliances would lose power, while the other half would remain active. Because of this separation, X-10 signals theoretically can talk to one side or the other but not both. Because the X-10 signal travels in between the power cycles, there is no physical connection from the left side to the right and, even if there were, the signals would be out of phase anyway. This could cause multiple headaches, especially if you want to control the entire household from one console device or have circuits from each side in the same room. Fortunately, there are some easy solutions, such as installing a 240-volt piggyback bridge on any 240-volt outlet, perhaps where you plug in the dryer. This option is the simplest -- no rewiring is required; you're just routing the X-10 signals between the two hot wires. However, the approach is not ideal because it requires added distance for the signals to travel, and that could affect performance and quality. A better option is to install the bridge inside the circuit-breaker box between the two 120-volt hot pole lines. Because of the danger associated with approaching two high-energy hot lines, you should have a certified electrician perform this operation.