Switches and dimmers
The simplest X-10 receiver is a plug-in appliance module, such as the Radio Shack module shown in Figure 9. It requires no special wiring concerns, and because it is either on or off, with no dimming capability, it can control any type of load up to its rated capacity.
The type of load you connect to a module is important for all other kinds of receivers. Resistive loads, such as heaters and lamps, do not respond to variations in the AC waveform. Reactive loads have capacitive and/or inductive components, in addition to the resistive load, that make the loads unsuitable for control by triac semiconductor devices that modify the AC waveform.
FIGURE 9: Appliance module
A triac is a three-terminal semiconductor device used by all modern dimmers to control an AC line.Two of the terminals form a path for the load current, while the third terminal turns the device on (the triac turns off at every zero crossing of the AC waveform). If the control terminal is always on, you get a standard AC sine wave. If there is a delay after the zero crossing before the control terminal turns on, you get a truncated AC waveform such as in Figure 10. Triacs replaced rheostats in dimmers because they’re smaller and generate far less heat.
The frequency analysis in Figure 11 (derived from Figure 10) shows the problem the triac output waveform creates for reactive loads. The solid line is the fundamental frequency, while the dashed lines show the additional frequency components introduced by the waveform truncation. Reactive loads respond to those additional frequency components, and not necessarily in a good way.
FIGURE 10: Dimmer waveform output
FIGURE 11: Dimmer output frequency analysis
The net result you need to remember from Figure 11 is that you must only use a dimmingcapable X-10 module with a resistive load. Reactive loads — essentially anything but an incandescent lamp — require appliance modules rated for the more complex load. Even halogen lamps may have transformers in their circuitry, making them a reactive load and unsuitable for dimming.
Most X-10 light switches can dim, although the dimming function may only be accessible from a remote controller and not from the switch itself. Some, but definitely not all, can report their on/off status back to the controller. Modules capable of replacing a single, standard light switch are not suitable for use in threeway or one-way configurations. Special module sets (Figure 12) are available for that purpose, and must be paired in a master/slave configuration.
FIGURE 12: X-10 three-way light switch set