Hey there guys, Paul here from TheEngineeringMindset.com. In this video we're going to be looking at how to control a light
fitting with two switches. This is very useful, for example, when placing a light switch
at the top and bottom of a set of stairs, or at
different doors in a room. We're going to look at two
common ways to do this, as well as some different
variations on the second version. Now, the colour of the cables
varies around the world, according to different standards. I'm going to be using
the European colour code for this video, but you should
check your local regulations. I just want to remind you that working with
electricity is dangerous. We're covering just the
theory in this video, so please do not undertake
any electrical work unless you are qualified and competent. So, to control a light with two switches, we of course need two switches, which have three terminals on the back. I'll leave some links in the
video description down below, for where to buy these
switches online very cheaply. The name for these type
of switches is different depending on where in the world you are. The US/North America call
these three-way switches. But the EU calls these two-way switches. The switch can only be
flipped one of two ways, either up or down. But if we look at the back of the switch, then we'll see there are three terminals, and that means there's four ways for electricity to flow
through the switch. These will all depend on
how the switch is wired. One terminal is called the common, and then we have a
terminal called line one, and another terminal called line two. Let's say we want to
control this light fitting using two switches. I'll flip them over so you
can see how this would work. I'll also just rotate
these to make the drawing a little easier to understand. So we have the electricity coming in from the consumer unit and
feeding the light fitting. We therefore take the live wire and divert this into the
common terminal of switch one. We run another wire from the
common terminal of switch two, and connect this to the lamp. We now need to connect the two switches. So we connect terminal L1 of switch one with terminal L2 of switch two. We need to place a brown
sleeve at each end of this wire to warn that it is intermittently live. We then run another wire from
terminal L2 of switch one, and connect this to
terminal L1 of switch two. Again, placing a brown sleeve to indicate that this can be live. At the moment, the electricity can make it through switch
one and into switch two, but the circuit is broken at switch two. If we then flip the switch,
the circuit is complete so electricity runs
through the entire circuit, and the lamp lights up. If we then flip switch one,
the circuit is broken again, so the lamp turns off. But electricity still flows to switch two where the circuit is broken. We could flip switch one
again to complete the circuit or we can flip switch two, and
the circuit is also complete. So we can therefore flip
either switch one or switch two to make or break the circuit, and thus control the light
fitting with two switches. The second common way to control
a light with two switches, is to convert a one-way
switch into a two-way. Again, we need two switches,
and you need to check the back to ensure that they have
three terminals on each. If your one-way switch
only has two terminals, then you need to replace this. So we cut the live wire feeding the lamp, and run this into
terminal L1 of switch one. We then run a grey wire from
terminal L1 of switch one to terminal L2 of switch two. We need to place a brown
sleeve at either end, to warn that this is intermittently live. We run a brown wire between
the two common terminals of both switches. Then we run a black wire from
terminal L2 of switch one to terminal L1 of switch two. Again, we need to place a
brown sleeve at each end to warn that this is intermittently live. Lastly, to complete the
circuit, we connect terminal L2 back to the supply of the light fitting. Again, using a brown sleeve to warn that it's intermittently live. The electricity can now flow, and it will pass through switch one and into switch two where
the circuit is broken. If we flip switch two,
we complete the circuit so the electricity can
flow through the common and out into the lamp. If we flip switch one, we break the circuit to the light fitting so the lamp turns off. If we then flip switch two,
we make the circuit again, and electricity will flow
to the light fitting. So the alternative ways
work almost identically to the conversion we just saw. But in this method, we run
the live to L2 of switch one. Then we run a brown cable
from L2 of switch one over to L1 of switch two. Then we run the grey wire
from L2 of switch two over to L1 of switch one. We need to place a
brown sleeve at each end to warn that this is intermittently live. Then we run a black wire
between both commons of both switches. Again, we need to place a
brown sleeve at each end. Finally, we connect the blue
wire from L1 of switch one back to the light fitting. Again, placing a brown sleeve at each end. So to start with, the circuit is broken, so electricity passes through switch one and into switch two, but
it reaches a dead end. If we then flip switch one,
we complete the circuit, and electricity can
flow through switch one and into switch two,
then back to switch one, and up into the lamp. If we flip switch two,
we break the circuit, electricity just flows
between the two switches, and doesn't reach the light. If we flip switch one, the
electricity will flow to switch one and over into switch two, across the switch, and
back over to switch one where it can flow to the light fitting. On the third variation,
I won't animate the lines being connected for this
one, as you get the idea, but we connect the live
to L1 of switch one. Then we run a brown wire
between L1 of switch one to L1 of switch two. And we run a grey wire
between L2 of switch two, and L2 of switch one. Then we run the black wire
between the two commons. And finally, we connect the blue wire between L2 of switch
one, and then the lamp. Remember to add a brown
sleeve at all the cables to warn that they are intermittently live. The fourth variation is very
similar to the last one, except that the black wire is connected between the two L1's of both switches, and the brown wire is connected
across the two commons. Again, remembering to place
a brown sleeve on the wires to indicate that they intermittently live. Okay guys, that's it for this video. But to continue your learning, just click on one of the
videos on the screen now, and I'll catch you there
for the next lesson. Don't forget to follow us on Facebook, Twitter, Instagram, and of course, check out TheEngineeringMindset.com
