A double control switch is a switch with normally open and normally closed contacts (i.e. a pair). Usually, two double-control switches are used to control a lamp or other electrical appliances, that is to say, there can be two switches to control the switches of lamps and other electrical appliances.
How to connect a dual-control switch when one switch is on;
1, in which one duplex line must be directly connected to the middle terminal of two duplex dual-control switches;
2. The other one of the double wires is connected to the upper (or lower) ends of the two switches, one end of the middle lamp is connected to a branch line, and the other end of the lamp is connected to the zero line.
3. Both switches are connected to the live wire, connected to the terminal (or the lower terminal) and not connected to the intermediate terminal.
Wiring characteristics of this circuit:
1, a conductor in the duplex line, and the middle branch line is connected to one end of the lamp. (Traditional dual-control circuits are not allowed to lead out branch lines in dual dedicated lines.)
2. Both switches are connected to the live wire, and can only be connected to the upper end (or lower end), so that the measured voltage from the three terminals of the two switches to the neutral line is 220v when the light is on, that is, the electric probe displays red.