In this video, we're going to show you how a circuit is wired
allowing you to turn a light on or off from two different locations.
We are going to refer to this light control circuit as a 2-way switching circuit.
Before we get started, we need to introduce you to some switch terms.
If we are going to turn a light on and off from 2 different locations,
we need 2 “Single Pole Double Throw”, or SPDT, switches.
An SPDT is called a “2-way switch” in the “European Union”,
and “a 3-way switch” in “North America”.
An SPDT switch has 3 terminals.
It will have one terminal in and 2 terminals out.
Each terminal on a SPDT switch has a name.
The input terminal is called “Common”.
The output terminals are called “Normally Open” and “Normally Closed”.
Operating the toggle or lever will cause the “Common” terminal
to connect to the “Normally open”
or “Normally closed” terminal depending on its position.
OK…let’s start wiring!
Back we go to our stairwell lighting circuit.
We have a switch at the bottom of the stairs
and another switch at the top of the stairs.
And, of course, our ceiling light over the middle of the stairs.
For our discussion, let's call the switches “Up” and “Down”.
Either switch can turn the light on or off.
Circuit wiring is very similar in the “European Union” and “North America”
but there are some differences.
Electrical power supply wire insulation colours are different.
In this video, we will be referring to “North America” cables and wire colours.
Another difference is the typical household electrical voltage level.
In “North America”, the voltage is “115 Volts AC”,
while in the “EU” the voltage is “220 volts AC”.
In “North America”, the 2 electrical power supply wires
are called “Line” and “Neutral”
and originate from a “Circuit Breaker” in an “Electrical Panel”.
The “Line” wire has black insulation
and the “Neutral” wire has white insulation.
The cable that leaves the “Electrical Panel” will contain these 2 wires
plus a 3rd wire which is connected to “Earth Ground”.
The “Earth Ground” wire has no insulation.
The cable is referred to as “NMD90 14/2”
because of the size of the conductors and the number of wires inside.
“NMD90 14/2” has 2 wires sized at 14 AWG.
The actual circuit wiring is a bit of a challenge for 2 reasons.
The cables are located behind the walls
and the electrical power cable could enter the circuit at 3 different locations.
The cable could enter at the light or either of the switches.
Just to add more possibilities,
a Cable could run between the switches
and another cable from a switch to the light.
Or, a cable could run from a switch to the light
and another cable to the other switch.
We’re not going to discuss all possibilities in this video.
We will explore a wiring circuit where:
The power enters at the “Down Switch”
There is a cable that runs between the 2 switches
And another cable that runs from the “Up Switch” to the light.
All cables are hidden behind the wall and above the ceiling.
It is easy to identify our wiring circuit by looking at the wires in the ceiling.
There will be 3 wires only.
These wires connect directly to the light.
Before we go any further, this is a good time to remind everyone
that working with electricity is very dangerous!
Leave the electrical work to qualified technicians!
OK…here we go…
Each device will be contained in an electrical box in the wall and ceiling.
As we said earlier,
the electrical power enters through the “Down Switch” electrical box.
For all electrical circuits,
the bare “Earth Ground” wires are connected
and bonded to each electrical box.
We’ve introduced a new cable.
This new cable is called “NMD90 14/3” and has a third red wire.
The electrical power black wire connects to the “Down Switch” common terminal.
The power white wire does not connect to the switch at all
but is connected to the white wire of the “14/3” cable.
The wire connection is completed inside the switch electrical box.
There is another wire connector securing the “14/3” white wire
to the “14/2” white wire of the light cable.
Again, this wire connection is completed inside the “UP Switch” electrical box.
The “14/3” cable connects the 2 switches.
The red wire connects the switches normally open terminals,
and the black wire connects the normally closed terminals.
And finally, the black wire of the light electrical box
connects to the “Up Switch” common terminal.
Let's see how it works!
With the switches in the positions shown,
the electricity will flow from the line wire through the light
and back to the neutral wire.
What happens if we change the “Down Switch” position?
The electrical circuit is broken and the light goes off!
Ok…Let’s see what happens if we change the “Up Switch” position.
If all goes well, the light will come on.
With the switches in the new positions,
the electricity will flow from the line wire
through the light and back to the neutral wire.
Ok…let's review what we’ve covered in this video:
An SPDT is called a “2-way switch” in the “European Union”,
and “a 3-way switch” in “North America”.
An SPDT switch has 3 terminals.
It will have one wire in and 2 wires out.
Each terminal on a SPDT switch has a name.
The input terminal is called “Common”.
The output terminals are called “Normally Open” and “Normally Closed”.
Turning a light on and off from 2 different locations
requires a “2-way switching circuit”.
A 2-way switching circuit requires 2 SPDT switches.
Want to learn PLC programming in an easy to understand format
and take your career to the next level?
Head on over to realpars.com