Smart appliance switches refer to the unit that uses a combination of control board and electronic components with programming to achieve intelligent control of circuit smart appliances. Switch control, also known as BANG-BANG control, is adopted in many household appliances and lighting controls due to its simplicity and ease of implementation. However, conventional switch control cannot meet the requirements for further improving control accuracy and energy saving.
Most of the smart appliance switches on the market require a neutral wire because any US houses built after the 1980s should have a neutral (white) cable connected to the light switch box. In this way, the smart appliance switch is connected between the neutral wire and the hot wire, so it consumes power in the usual way. The electronic equipment of the smart appliance switch itself can easily obtain power from the power line and the neutral line as needed. In this configuration, the smart appliance switch will control the power of the lamp through the load hot (red) wire. Only when the switch is turned on (physically or through intelligent function), the circuit will be complete and power will flow to the lamp. Otherwise, the circuit will be broken and the lamp will not light up.
However, as long as there is no neutral wire, a simple two-wire circuit can be used to provide power to the lamp. The hot and ground enter the switch, and the hot is called the power hot, which is a permanent charged power supply from the main power source of the house. Then, the switch connects another hot cable (called a load hot wire or switch branch) to the light fixture. The switch completes the circuit: when it is turned on, the circuit is completed, and the hot load provides the charged power to light up the bulb.
When the switch is turned off, the circuit is disconnected, and no power flows. This works overall, but it can cause problems for smart appliance switches, which must provide their own (small) power source to make smart functions work properly. Since there is no neutral wire to cut off the power, the smart appliance switch is installed in series with the bulb. The difficulty here is that the load wire is not designed to provide power to the smart appliance switch, so the smart appliance switch needs to "steal" (or leak) some electricity from the bulb. This is done by using the dimming function of the switch/bulb, which draws a small amount of power from the charged load cable.
In summary, smart appliance switches without neutral wires have become an important part of the market, but they also rely on some necessary "hacks" to provide power for their smart functions, which have some limitations.