You’ve probably seen thousands of light switches throughout your life, and yet,
have you ever seen the inside of a light switch? Also, have you ever wondered how two, three,
or more light switches can be wired together and used to control the same set of lights,
such as in the case of light switches positioned at the top and bottom of a stairway?
Well in this video we’re going to explore the engineering inside the humble light switch,
as well as how multi-way light switches work. So, stick around, and let’s jump right in.
Here’s a basic light switch. When you flip the switch from OFF to ON, this circuit becomes
closed, a path for electricity to flow is created, and the light turns on. When you flip the switch
OFF, the path breaks open, and the light turns off. The part that you flip up and down is called
the toggle switch or handle, and when you flip it to ON, a plastic leg at the bottom of the
toggle switch releases the metal contact bar or track. This metal contact bar springs upward
thereby allowing the two contact points to touch and electricity to flow from one screw terminal to
the other, thus closing the circuit and powering the light. However, when the toggle is flipped
OFF, the plastic leg at the bottom of the toggle switch presses against the metal contact bar
and separates the electrical contacts, thus disrupting the flow of electricity,
opening the circuit, and turning OFF the light. There are a few other key components that enable
this light switch to function properly. First, there’s a spring in the center which presses on
the bottom of the plastic toggle switch. This spring is positioned so that it’s compressed
when the toggle is in the middle of the ON and OFF positions. The spring applies a force to the
bottom of the toggle switch which ensures that when the switch is not being flipped,
it’s either fully in the ON position or fully in the OFF position and not somewhere in the middle.
The second key component is a pair of bumpers which limit the motion of the toggle switch
and provide a solid surface for the toggle switch to bump into. Finally,
we have the screw terminals for attaching wires, the metal bracket for attaching the
light switch to the electrical outlet box as well as a screw terminal for a ground wire,
the plastic housing that keeps everything contained, and on top of everything is the
face-plate that can be either simple or ornate. With the functionality and components of a basic
switch wrapped up, let’s now take a look at multi-way switches, specifically three-way
switches which are used when we want to have two light switches control a single set of lights.
For example, in my house, we have one three-way light switch at the top of the stairs and another
one at the bottom, and they both are used to control the same stairway light. In contrast to
the basic light switch, three-way switches have a common terminal and two traveler terminals.
Now when the toggle switch is flipped, the common terminal moves from being in contact with
one traveler to being in contact with the other traveler. These travelers are a pair of wires that
travel through the walls in order to connect one light switch to the other. When we flip the toggle
of one of the three-way switches, a path for the electricity to flow to the stairway light is
created, and the light turns ON. However, when we flip the other three-way switch’s toggle, the path
is broken, and the light turns OFF. In general, if both toggles are flipped down or both toggles up,
the lights turn off. To turn the lights on, one toggle needs to be up and the other down.
Let’s take a look inside one of these three-way light switches and see what’s happening inside.
Here we have a metal bar or track connected to the common terminal along with the two traveler metal
bars, each connected to their own separate traveler terminals. When we flip the toggle
switch, one traveler is pushed away from the common by the bottom of the toggle switch while
the other traveler is in contact with the common. Now let’s say we want three or more light switches
to control a single set of lights. To do that we have to use one or more 4-way switches with
a 3-way switch at each end. Here’s the schematic. Instead of a com-mon and two travelers as we saw
in the 3-way switch, 4-way switches use two sets of two travelers. When the toggle is flipped, the
two pairs of travelers on the left change to being connected to the opposite traveler on the right.
Here’s a brief animation showing how the path of electricity is closed or opened
and the light turns on or off depending on the position of each switch.
When we open up the 4-way switch, we find an even more complicated layout,
and yet a familiar set of components. The bottom plastic leg of the toggle switch presses down on
the one contact bar when toggled up and presses down on the other contact bar when toggled down.
As you can see, the path of the electricity is flipped from each pair of traveler terminals
to the other pair when toggling the switch from the up position to the down position.
Light switches are practically everywhere, and as a result there are dozens of different designs,
internal mechanisms, and methods for wiring the light switches together, but unfortunately, we
can’t cover them all. Note that this video isn’t a guide to the installation of light switches which
is why we avoided using the terminology of hot, neutral, and ground. Please do NOT install light
switches unless you’re a professional or you’re fully knowledgeable about what you’re doing.
Light switches are pretty humble, but if you want to build complicated circuits, you’re going to
have to use Printed Circuit Boards or PCBs, which is rather fitting because this video was made
possible by our sponsor PCBWay. PCBWay can quickly manufacture your PCBs with competitive prices
and impeccable standards. They also provide PCB assembly services where they populate and
solder the components to the PCB. Check them out using the link in the description below.
The amount of engineering that goes into a simple light switch
is amazing. We believe the future will require a strong emphasis on engineering education
and we’re thankful to all of our Patreon and YouTube Membership Sponsors for supporting
this dream. If you want to support us on YouTube Memberships, or Patreon, you can find the links in
the description. You can also provide support by subscribing, liking this video, commenting below,
and sharing this video with others. Thank you for watching until the end. This is Branch Education.