Don’t ya love it when you’re learning
about something and things, just, click?
Like a light switch!
Clicky switches are pretty fun.
But why do switches make noise?
What’s the point of all that clacking?
Well, it has to do with the fact that you’ve
been lied to.
Uhh, but let’s not get too conspiratorial
just yet, first let’s look at some of the
switches that don’t click because there
This electronically controlled dimming module
turns the lights on completely silently.
No clicking there.
Then again, this other one that’s not a
dimmer makes a pronounced clicking sound.
[pronounced clicking sound ]
And I didn’t even touch it!
Well, the dimming module is using a solid-state
device known as a triac to actually turn the
lights on and off, so it’s not quite what
I mean by a switch.
This standard thing goes on or off module
does in fact use a type of real switch to
do its work, so you hear a click.
Same with this toggle light switch.
This rocker switch.
This rotary switch.
This lamp cord switch.
This power button.
[softer, double click]
The rocker switches
on this studio light.
[four clicks in a row]
Oh, and the big one,
[a somewhat softer click]
[a click that’s Automatic Beyond Belief]
The mode selector on this space heater.
[clicking as it turns]
Even its thermostat
makes a distinct click.
[soft, repetitive click]
Why be so clicky clacky all the time?
To start to answer this question, we first
need to answer a simpler question;
what is a switch?
Well, a switch is a handheld game –
A switch is a mechanism used to divert rail
cars fr –
A switch is the simplest mechanism that can
control the flow of electricity.
Say you have a simple table
lamp and want to connect it up with the power grid.
Well, we simply take its bare wires and carefully
touch them to these live wires and voila!
Let there be light.
Now to turn the light off, all we need to
do is carefully pull those wires apart, and
hope the live ones don’t t–
But this is pretty dangerous.
Even Edison knew that.
So we designed electrical sockets which contained
live wires behind an insulating barrier and
we designed plugs that would, depending on
your country, somewhere between somewhat safely
and completely safely allow you to make and
break electrical connections.
But this isn’t the most convenient way to
turn something on or off.
And most importantly, using them that way
isn’t good for your plug or your receptacle.
See, if I take this lamps and plug it into this outlet, it lights up no problem!
And if I simply unplug it, it goes out, also
without a problem.
But watch what happens if I take this space
heater and unplug it while it’s running.
Ooh, that was quite a spark!
Let’s do it again!
Let’s do it again.
Let’s do that again!
Let’s do… let’s do that again!
[VOICEOVER]: While this specimen continues
to be amused by the sparks,
we’ll move on to the next jump cut.
When the heater is running, a lot of electricity
is flowing into it through this cord.
1,500 watts, in fact.
To stop that flow of current, all we need
to do is put an insulator between the contacts
of the receptacle and the pins of the
Which of course we can do simply by unplugging
But when we unplug it, it doesn’t just stop
the current flow right away.
There’s a brief moment where that current
manages to jump out from the outlet, and the
result is a spark.
The same thing happens if you plug in the
heater with it turned on, right before the
pins of the plug and the receptacle first
make contact, but the spark usually isn’t
as large as when an active connection is broken.
And this is where you’ve been lied to.
See, when you were little, you were probably
taught about electrical conductors, like the
wires in this cord, and electrical insulators,
like the plastic insulation surrounding that wire.
If you had a really nerdy teacher you might
have learned about semiconductors, but lots
of us were sorting things into the two categories
of insulators and conductors.
The lie is that, just like most things in
the real world, the electrical conductivity
of any given substance exists on a spectrum.
Everything conducts electricity when you try
Now we rely on the resistance of air all the
Electrical transmission lines are typically bare aluminum
and are held up in the air by stacks of insulating discs.
The higher the voltage of the line the more
of these discs you need because even they
aren’t perfect insulators.
Nothing’s a perfect insulator!
And that’s the problem.
Air’s pretty good, and when you unplug something
from an electrical outlet you do disconnect
it from the power grid and stop the flow of
electricity to it precisely because there’s
air now between the pins of the plug and the
conductors in the receptacle.
But, when you pull that plug out of the wall,
there will be a brief moment when there’s
only a tiny bit of air between the plug and
the socket, and this is not good.
When those contacts are close but not quite
touching, the air gap is so small that the
breakdown voltage, that’s the voltage at
which an insulator fails to stay an insulator,
is lower than the voltage of the electrical
This means that the current will actually
jump the gap, and this creates an arc discharge.
That’s the spark you see here.
Now on its own this isn’t particularly bad.
Thanks to the fact that we use AC power, the
voltage crosses the zero point 100 or 120
times per second, so that arc will usually
go out nearly immediately, though it should
be noted that arcs can be sustained on AC
More importantly, the breakdown voltage of
any insulator, including air, is a function
of how thick it is, so once the contacts are
just a millimeter apart, that arc will generally
But here’s the problem.
That arc is hot.
Very, very hot.
So hot, in fact, that it can burn the ends
of the plug and the socket.
So we don’t want to rely on pulling the
plug out of the socket to stop current flow.
What do we do instead?
We use a switch.
All the switch does is create a break in a
There are many different types of switches
but they all do fundamentally the same thing.
There are two electrical contacts, and they’re
either touching, or they’re not.
If they touch, current can flow.
And if they don’t touch, current can’t.
But then, switches do the same thing as unplugging
Don’t they have to worry about arcing?
Yes, in fact even more so.
Electrical arcs damage electrical contacts
in various ways, but among the most significant
ones is that the contacts eventually… melt
See, each time there’s an arc, that plasma
is so hot that the surface of the contact
briefly melts, and that material can sputter
off of it.
Additionally, the high temperature can cause
corrosion of the contacts, and you get lovely
issues like carbon buildup which increases
the electrical resistance of the contacts,
and that’s not good.
Even better, if the arcing is bad enough,
and the surface of the contacts get hot enough,
they can weld together and get stuck closed!
I guess that light’s on forever now…
Since the contacts in a switch are generally
pretty small, we want to minimize the arcing
that can happen because, well, an arc will
warm them up quickly and cause all those problems
I was just going on about.
And how do we do that?
Why, with speed!
Remember that household voltages are low enough
that an arc generally can’t be sustained
once the contacts are just a millimeter apart.
So, if you get them apart quite quickly, any
arc formation that does occur will be very
brief and unlikely to cause significant damage.
And that is why switches click.
Switches are designed with mechanisms
to ensure the contacts open and close very quickly,
quickly enough to prevent an arc
from lasting more than maybe a millisecond or so.
Effectively the contacts are meant to slam
together and then get yanked apart, and that
makes an audible click.
The mechanisms that accomplish this are often
Many times it’s just a spring cleverly integrated
into a pivot.
Let’s take a look at a simple household
This switch is nice and clicky.
[repetitive, rapid clicking]
Who needs a fidget clicker
when you can just run to the hardware store
and get one of these?
This design is almost devilishly simple.
Below the faceplate are three pieces of brass,
two of which are the same ones you attach
wires to on the outside.
The smaller one holds an electrical contact,
and the larger one serves as a pivot point
for a small swinging piece that holds the
If there’s a torque applied to the swinging
piece in this direction, the contact does
not touch the other one, and no current can
flow through the switch.
But, apply a torque in the other direction,
and now the contacts touch.
Current flows into the switch through this
terminal, through the basket thing,
into the swinging thing, through the two contacts,
and out the other terminal.
All it takes to ensure the swinging contact
moves quickly is a spring.
See, the rocker paddle that you touch is in
fact the same thing moving the contact.
These grooves hold onto the edge with a little
play, and when the rocker rocks back and forth,
so does the contact below.
But thanks to the spring, the rocker (and
more importantly the contact) wants to stay
in either position.
The spring gets increasingly compressed as
the rocker meets the apex, and once it passes it…
bam, the spring expands and pushes the
contact it in the other direction.
The result is a swift action in both directions,
Unfortunately, though, this switch design
In fact, many (if not most) switches on sale
See, you can actually move the contact a bit
before the spring takes over.
If you carefully apply pressure on the switch,
you’ll see that the light goes out before
it clicks into the off position.
Listen carefully and you can actually hear
arcing going on inside the switch.
[faint arcing sound]
This… isn’t really
great, especially if you have a lot of lights
on the circuit you’re controlling.
In fact you can see on these contacts that
they have been slightly damaged, and this
isn’t a very old switch.
I know because I installed it myself.
Granted, most people don’t turn the lights
on and off like this.
If you do it like a normal person, then the
contacts are swiftly moved and arcing is minimal.
Still, it annoys me that it’s even possible
to damage the switch at all.
Many switch designs, like these lamp cord
switches, are simply impossible to hold in
a half-on, half-off state.
Sure, they’re not designed to carry the
current of a normal light switch, but I bet
these guys rarely ever fail from bad contacts.
And normal switches can be made impossible
The house I grew up in was quite old, and
a few rooms had toggle light switches that
you could actually move nearly completely
into the opposite position before the internal
mechanism opened or closed the contacts with
a very loud clack.
[a very loud clack]
Those switches were in
service for 50 or 60 years and likely still are.
Granted, they were only controlling a single
light in all but one case (if memory serves)
so they weren’t ever under much electrical
stress, and they required much more force
to use than modern switches, which is probably
why that style went out of favor.
But, this paddle-style dimmer switch has a
mechanism that prevents partial making and
breaking of the contacts without requiring
You can see that even if I use my two thumbs
on both sides of the switch and very, very
slowly move the paddle, the lights only go
on and off with the click of the internal
This design here is what I’d call ideal,
and it proves that easy-to-use switches can
still be made with a fast, clicky, abuse-proof
So if you’re shopping for a light switch
at a hardware store, tactile feel of the switch
does actually matter when it comes to switch
A nice, solid snap makes me more confident
than a smooth, quiet movement.
This cheap toggle switch is what I’d consider
The toggle moves smoothly without much resistance
at all, and the contact is actually broken
when the switch has barely moved out of its
It actually requires conscious effort to ensure
the contacts are quickly moved apart, and
I doubt this switch would last more than a
decade on a circuit with more than a few lights.
In fact, it’s not even fair to say that
this switch actually clicks.
It more or less thuds.
Any switch that’s designed to interrupt
even a modest current flow should, in my opinion,
have a nice audible click.
That plug-in thing-goes-on module?
It got a relay in it.
Relays are electromechanical devices that
control large currents with small currents.
Essentially they’re a switch with some sort
of external control.
In this case, the small computer inside here
will turn on the relay when it’s been asked
to, and click, the light goes on.
The contacts in a relay are closed via an
electromagnet, and are held open with a spring.
And, as luck would have it, this simple arrangement
means the switch opens and closes quickly.
And so, it clicks.
When we need to automatically control very
high current loads, we use what are essentially
large relays, but we call them contactors.
Contactors often just use air to break the
circuit like any other switch, but when we
get into high voltage applications, the contactor
might be contained in a vacuum, and in really
high voltage applications like in power grid
substations, you might find switches and circuit
breakers inside a volume of sulfur hexafluoride,
which is an incredibly good insulator and
this is in fact the primary commercial use
Now, not all switches need to click.
Switches that don’t carry a lot of current,
like the clicky buttons on your mouse, don’t
need to click at all because there’s not
gonna be any arcing going on in there.
They click mainly because that style of switch
is designed to provide a lot of tactile feedback.
And actually, a very clicky switch can be
a disadvantage in digital devices, because
now you might need to implement some sort
of debouncing but that’s beyond the scope
of this video.
Now you know why switches click.
They’re really just prolonging their life.
And if you want to prolong the life of the
switches in your life even more, be sure you
always give them a good flick.
Since many modern designs kinda make you a
part of the contact closing and opening action,
you can and should click to your heart’s
Thanks for watching!
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Thanks for your consideration, and I’ll
see you next time!
♫ illuminatingly smooth jazz ♫
I messed up.
I thought this would go quickly, it’s not
So, if you get them apart quickly …
That was going well, but then it wasn’t.
No no no, that’s the wrong way!
[more struggling sounds]
[also the tripod is creaking, that’s fun]
Now, no I don’t like how I did that eith… eugh.
eugh, well, ugh.
Cra.. that might have been, erm, nevermind.