What Is Packet Switching and How Does It Work
Throughout your home, there are a variety of switches that are used. Some are used for lighting, while others are used to disconnect power for servicing, like in the case of a garbage disposal. Besides the typical switches that turn things on and off, there are specialized switches that dim lighting and are adjustable for controlling things like fan speed.
Probably the most widely used switches are the single-pole switches. They control lighting from one location and are also used on things like furnace disconnects, garbage disposers, and small motor disconnects, like taco pumps used in outdoor wood burning boilers. They are also used in the form of adjustable switches that can be turned on and off, but also turned from bright to dim. As mentioned above, single-pole switches are also used for fan controls, and with the right type switch, speed is controlled with this switch.
Switches to Control Lighting
Another widely used switch is the three-way switch. These are used in combinations of two switches to control lighting from two locations in most circumstances. They may be used in hallways, staircases, any number of rooms like living rooms, or garages. In the latter case, the lighting may be for the garage itself or the outdoor lighting associated with the garage and front door lighting, being switched in both the home and garage entrance doors.
The four-way switch is not used on its own, but in addition to a combination of switches. A three-way switch connects traveler wires from that switch to one side of the four-way switch, while the other side is connected to the other three-way switch, and the three-way switch is then connected to a light. When connected properly, a simple flip of any of the switches will turn on the light.
What Are Traveler Wires?
Traveler wires run between switches to offer multiple ways to complete the circuit. In other words, they allow you to send power to a light from more than one switch.
4-Way Switches
Four-way switches are used to control lighting from three or more locations. Four-way switches are used in combination with three-way switches. There are four terminals that provide two sets of toggle positions on a four-way switch. Each set of terminals is one of the toggle positions. When the switch is in the up position, the current can flow through two terminals. In the down position, the current flows through the other two terminals. Many times, four-way switches will come with two brass-colored terminal screws and two darker-colored terminal screws. A green ground terminal is also on a four-way switch.
Ohm Meter
To find out which terminals go together, you can use an ohm meter to test the terminals and the toggle positions, or take a quick look at the manufacturer's instructions, which should outline the pairings. Each set of terminals will connect to the traveler wires from each of the three-way switches. When connected properly, you'll be able to turn lights on from either of the three-way switches or the four-way switch. In the event that you need to switch lighting from more than three locations, simply add additional four-way switches between the two three-way switches.
Four-way switches can come in handy in large rooms that have many door openings or exits. Each opening from which you can enter or leave a room should have a switch that controls the lighting within that room. For example, if you have a living room that has three openings you need a four-way switch in order to control the lighting in the room. Say the hallway is in the shape of a "T' also needing the use of a four-way switch—by placing a three-way switch at two different locations and the four-way switch at the third location, the lighting can be switched from each location. This is why, for lighting control in three or more locations, four-way switches are the answer.
Tip
In this scenario, the four-way switch must be placed electrically between the two three-way switches via 14/3 or 12/3 wiring, depending on the ampacity of the circuit you are working with.
What Is Packet Switching and How Does It Work
Source: https://www.thespruce.com/what-is-a-four-way-switch-1152400