![]() ![]() Two, 2-wire cables run between each light fixture after that and 3-wire cable runs from the last light to SW2.Īt the beginning of the circuit the hot source is connected to the common terminal on SW1. Here the source is at the first switch, SW1, and 3-wire cable runs from there to the first light, L1. In this circuit, two light fixtures are shown but more can be added by duplicating the wiring arrangement between the fixtures for each additional light. Wiring a 3 Way Switch with Multiple Lights Check below for more details about these circuits and some troubleshooting tips. There are many possible three-bit gray codes, each represented by a unique traversal of all eight states in the state diagram.The diagrams on this page illustrate connecting multiple lights in 3 way and 4 way switch circuits. (You’ll note that that’s the order in which I listed the switch states in the diagrams above). For example, a three-bit gray code - known as the binary reflected gray code - is 000, 001, 011, 010, 110, 111, 101, 100. A gray code is an ordering of binary numbers such that only one bit changes between adjacent numbers. But in a light circuit, no toggling sequence of the eight states can result in binary counting order, because only one switch can change at a time (I’m not counting two or three people toggling switches at the same time!). In this order, multiple bits can change between two adjacent numbers for example, two bits change from 001 to 010. As listed, that is the counting order for the binary integers zero through seven. If each switch is viewed as a bit - I’ve labeled up as ‘1’ and down as ‘0’, by convention - then there are eight binary values: 000, 001, 010, 011, 100, 101, 110, 111. The light toggles from off to on or from on to off with each change of switch position. You can go indirectly to any other state by traversing a path through the diagram. From each state you can go directly to three other states. Each arrow represents the change of position of one switch - to up or down. ![]() This state machine captures the logic of any switching sequence: State Machine Diagram for a Three-Switch Circuit Of the eight states, half close the circuit and turn the light on, and half open the circuit and turn the light off. ![]() Here are the same states, but shown with the position of the light switches (the switches are of course separate, but I’ve drawn them together): All Eight States of a Three-Switch Circuit Here are all eight states of a three-switch light circuit: All Eight States of a Three-Switch Circuit In a multiple-switch circuit, the position of an individual switch does not correlate with the state of the light - turning a switch up or down can turn the light on or off, depending on the position of the other switch(es). (You can see the pattern - with n switches, there are 2 n states.) With three switches, there are 2 3 = 8 different switch states. (I’m assuming arbitrarily that “up” is the direct connection and “down” is the crossed connection I don’t know what it actually is, but it doesn’t matter.) When the 4-way switch is in the down position, the traveler connections are crossed, inverting the state of the circuit for example: Example State of a Three-Switch Circuit For example, here’s a three-switch circuit, with both 3-way switches in the down position and the 4-way switch in the up position: Example State of a Three-Switch Circuit To control a light from three or more locations, you need one or more 4-way switches sandwiched between two 3-way switches, with a pair of traveler wires connecting each switch. Since there are two switches that can each be in two positions, there are 2 2 = 4 switch states in all. For example, here’s a two-switch circuit, with both 3-way switches in the down position: Example State of a Two-Switch CircuitĮach switch can be up or down, connecting a single wire to one of two other wires. To control a light from two locations, you need two 3-way switches, connected by two “traveler” wires. In a one-switch circuit, the position of the switch correlates with the state of the light for example, up will mean on, and down will mean off. Essentially, the switch takes two ends of a wire and connects or disconnects them. The switch either closes the circuit, in which case the light goes on, or it opens the circuit, in which case the light goes off. To control a light from one location, all you need is a simple on/off switch. Example Switching Sequence of Three Light Switches I’ll share my thoughts and diagrams with you in this article. I drew some diagrams, including a state machine. While installing it, I thought about the binary properties of my three-switch circuit: I saw powers of two, binary logic, and binary gray code. Recently I had to replace a 4-way switch, an electrical component that lets you turn a light on or off from three or more locations. ![]()
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