How Does A Light Switch Work
Most of us use light switches every single day to set or adjust the level of lighting we want. Our recessed fixtures, pendant lights, chandeliers and wall sconces are usually turned off and on by flipping a switch that is on a wall somewhere. More often than not we do not give the switch itself much thought. But the kind of wall switch we use, and knowing the way each kind works and needs to be connected, can be essential if we want to make some changes or improvements to the way our lighting works.
There are only three sorts of wall switches which can be used to manage light fixtures: An On/Off switch, a 3-way switch, and a 4-way switch. Choosing which one you need depends upon the way you wish to be able to control your lights. Light switches also come in several different styles, including toggle (Manufacturer’s Site), rocker (Manufacturer’s Site) and push button (Manufacturer’s Site). You possibly can choose the style and color to match your decor. The important thing is to decide on a switch that’s made to do what you need it to do.
An On/Off switch is one which just turns the lights off or on from one location. For that reason, they’re sometimes known as single location switches.
The technical, or proper, name of an On/Off light switch is a single-pole, single throw (SPST) switch. Single-pole signifies that just one “hot wire” will be connected to it. Single-throw signifies that whenever you switch it, it only connects to 1 other wire — the wire going to your light.
Inside an On/Off switch, there is a spring-loaded gate. When you alter the switch to On, that gate snaps closed. It closes the circuit and lets the power flow through the switch to the light. When you change it to Off, the switch snaps open. It opens the circuit and interrupts the flow of power to the light.
A 3-way switch is a single pole, double-throw (SPDT) switch. Single-pole, again, signifies that only one “hot wire” is connected to it. It also has two other wires connected to it, and double-throw signifies that if you switch it, instead of opening and closing the circuit, a 3-way switch changes the connection of the “hot wire” back and forth between two other wires.
Those other two wires are called the “travelers.” They are connected, ultimately, to a second 3-way switch, and that second switch is connected to the wire that carries the facility to your light.
Internally, a 3-way switch looks like a “V.” The point of the V is the terminal where the recent wire coming from your breaker or fuse panel, or the load wire — the one going to the sunshine — is connected. The two traveler wires are connected to the 2 open points of the V. The point of the V is known as the common, or point terminal. It’ll look different, usually because it can have a dark, almost black, screw. The open points of the V are called the traveler terminals, and they will usually have bright brass screws.
Here is why, by installing a pair of 3-way switches, you may turn a light on or off from two different locations:
On one of many switches, the facility coming from the panel is connected to the common terminal. Internally, that terminal is connected to one of the switch’s two traveler terminals, which takes it to one among the 2 traveler terminals on the second switch. If the second switch just isn’t set to connect that traveler terminal to its common terminal, the sunshine is off. If you happen to flip one of the switches either one –, then both of the switches can have their common terminal connected to the identical traveler. The facility will likely be connected to the sunshine, and it’ll come on.
Similarly, you probably have a pair of 3-way switches controlling a light and that light is on, then both of those switches are set so that both of their common terminals are connected to the same traveler wire. When that’s the case, flipping just one of the switches will connect that switch’s common terminal to its other traveler terminal.
The new feed will not be connected all the way through, and the light will go off.
A 4-way switch is a double-pole, double throw switch. Double-pole implies that two “hot,” or potentially hot, wires are connected to it. Those are the two traveler wires from the 3-way switch that’s connected to the facility from the panel. It also has the 2 traveler wires from the 3-way switch that is connected to the wire that carries the ability to the light. Double-throw means that when you switch a 4-way switch, it changes the connections between the 2 pairs of traveler wires.
Internally, a 4-way switch might be regarded as both an “X” and a pair of parallel lines — either “||” or “=.” In a single position a 4-way switch connects the terminals which can be diagonally opposite each other. That is the “X.” When you change the switch, it disconnects the X and connects the terminals which might be either next to one another — “||” — or the ones which might be across from each other — the =.
Certainly one of the 2 traveler wires coming from the 3-way switch that is connected to power will likely be hot. If the 4-way switch is about in order that that wire is connected to the traveler that’s disconnected at the second 3-way switch the sunshine will probably be off. Changing any of the three switches will turn it on.
If you happen to flip the three-way switch that has power connected to it, you are changing which of its two travelers is carrying power. The facility will now come into the 4-way switch on the terminal that it has connected to the traveler that the other 3-way switch has connected to the light to the wire and the light will come on.
In case you flip that switch back and switch the sunshine off, you possibly can go to the 4-way switch and flip it. That may change its internal connections so that the traveler with power on it’s connected to the traveler that the second 3-way has connected to the wire going to the light, and the light will come on.
Finally, for those who flip the 4-way switch again, so that the light is off, and also you flip the second 3-way switch, that switch will disconnect its common terminal from the traveler that doesn’t have power on it and connect it to the one which does — and the sunshine will come on.
Two Things to remember
If you want to replace one in all your existing switches with a new switch, a timer or a dimmer, the new control needs to have the same functionality because the switch it’s replacing. That’s, you will want a single-location, or single-pole, single throw, switch, timer or dimmer to replace a single-location on/off switch, and you will need a 3-way switch, timer or dimmer to replace a 3-way switch. An on/off switch, timer or dimmer will not work where a 3-way control is needed. A 3-way switch, timer or dimmer can usually be made to work as an on/off control, but it may be tricky to get it connected, and a single-location device will usually cost less.
There aren’t any hard-wired 4-way timers or dimmers, so it is advisable to plan on replacing one of the two 3-way switches if you’d like so as to add timing or dimming to a switch circuit that has greater than two switches.
The other thing to keep in mind that the power is rarely off in a switch circuit. It means, of course, that you simply need to show the facility off on the breaker before you start to work on any switch. It also means that you might want to turn the facility off at the breaker even if you are only going to replace a light bulb or two. That may eliminate the chance that someone might turn the ability to the fixture back on by flipping one of the 2 or three switches.