LAMPS CONTROLLED FROM A SINGLE POINT: THE SPST SWITCH (PRACTICE)

Welcome to the home’s electrical systems course organized by NPR Online Technologies!

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In this lesson, we will see how to turn on and off lamps by using a single-pole single-throw switch, just as it has been illustrated in the theoretical lesson to which we refer for further information.

Let’s start the lesson by considering again the circuit of the previous practical lesson and insert a switch to allow us to turn on and off a light bulb.

As seen in the theoretical lesson dedicated to the single-pole single-throw switch, it has two terminals.

As illustrated by the connection diagram, we must connect the hot wire to one terminal of the switch. Then we have to connect the other terminal of the switch to one contact of the lamp.

In order to complete the circuit, we have to connect the other contact of the lamp to the neutral wire.

In the following picture, we can see a typical single-pole single-throw switch used in our homes, placed on our work table.

Of course, the shape and size depends on the country considered, but the principle of operation remains the same.

It is noted that the single-pole single-throw switch is equipped with two terminals:

to which it is possible to connect the wires of the electrical system through appropriate screws.

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Well, having made this premise, let’s go back to our switch positioned on the work table. Our objective is to insert this switch in the circuit that we have illustrated in the previous practical session.

To build our circuit, we start from the red and black wires connected to the 9 V battery.

They are then connected to the blue and brown wires.

and finally they reach the screw terminals,

We can consider this specific point as the access point of the neutral and hot wires.

Starting from these terminals, we can see that we have a direct connection of the neutral wire to the light bulb,

while the hot wire is connected to one of the two terminals of the switch.

The other terminal of the switch is instead connected to the other terminal of the light bulb.

In this condition, the light bulb is on, since the switch is closed.

If we flip the switch, the light bulb will turn off, since this operation will open the switch.

Of course, if we flip again the switch, the light bulb will turn on, since the switch will be closed again.

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As explained in the theoretical lessons, the switch is inserted in a box embedded in the wall.

The wires, on the other hand, are passed through electrical conduits and laid in special chases cut in the ceiling, floor and walls.

The goal of this practical session is to simulate on our work table the implementation of a real circuit.

We will make use of components that are actually used in the electrical systems of our homes.

In the following picture we can see that all the elements of a real installation are placed on our work table.

The only difference concerns the power supply voltage: instead of the 230 V alternating current, we will use the direct current of a 9 V battery.

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Let’s analyse in detail the circuit. We observe that the hot and neutral wires coming from the battery

are available inside the junction box.

We can see that the two wires pass through a PVC corrugated tube.

As required by our electrical circuit, the hot wire must be connected to the single-pole single-throw switch.

For this reason, we have used a second tube to bring the hot wire from the junction box to the switch.

Finally, we must use a third tube to bring the hot wire from the switch to the light bulb.

It is obvious that the neutral wire will also be inserted into the second and third tube and will reach the light bulb, starting from the junction box.

We observe that the single-pole single-throw switch is fixed to the electric box by means of a plastic support.

We observe that the pipes and boxes are fastened to the work table with adhesive tape,

but we recall that in real installations they are laid in special chases cut in the ceiling, floor and walls.

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Well, we are now ready to build the circuit through a step-by-step procedure.

Let’s start with the neutral and hot wires that start from the battery and reach the junction box.

The first step is to fix the battery to the work table.

Subsequently it is necessary to insert the hot and neutral wires in a tube of about 30 cm.

This is a work that actually has been already done in the previous practical lesson.

Now we are ready to prepare the junction box.

We can see that it is designed to be able to make holes around its sides. We will see that these holes are used as access points to route the wires of the electric system.

It is sufficient to exert a slight pressure on the sides of the box to make the holes where desired.

In our case, we made three holes on three distinct sides of the junction box.

Then we have positioned the junction box with adhesive tape in such a way as to have a hole oriented to the left, one oriented to the right and the other hole oriented downward.

It is noted that the hole placed downward is not used in this tutorial. It will be used in other exercises, however, for practical reasons, it is better to make it right away.

At this point we must insert in the junction box, the hot and neutral wires coming from the 9 V battery.

Let’s now prepare the switch support. The one we are using in this course can hold up to three switches. However, for this tutorial we will use only one switch.

For this reason, we will make a central hole. Of course, we can choose the preferred position, but in general, for aesthetic reasons, it is chosen the central position when only one switch must be inserted in the support.

On the contrary, in case of two switches, the lateral positions are used.

Furthermore, it should be considered that decorative wall plates are produced with this logic.

In order to make the desired hole, we have to exert a slight pressure on the central plastic rectangle to remove it and thus create the hole necessary to insert the switch.

In combination with the switch support, we have to use an electric box where the switch support

will be fastened by means of two screws.

The electric box is not only used to fasten the switch support, but it allows the wires to pass through in accordance with the electrical circuit.

For this purpose, as done for the junction box, it is necessary to make lateral holes.

More specifically, we will make a hole on the long side

and one on both short sides of the electric box.

At this point, we must insert the switch in the support.

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The insertion takes place from the back of the support with the metal tab of the switch (the longest one) which is inserted into the appropriate slot in the support.

By exerting a slight pressure, the switch is fastened to the support,

so that in the front part it is possible to maneuver it easily.

We observe that the support is equipped with two screws that are used to fasten it to the electric box. However, this operation will be carried out only when we will have completed the connections involving this part of the electrical circuit.

For the moment, let’s just fasten the electric box to the work table using adhesive tape.

It must be positioned on the right side of the work table and in such a way that the holes are oriented one downward, one upward and the other towards the center of the work table.

We observe from the final circuit that the hole towards the top is used to make the connections towards the junction box,

while the hole towards the center of the work table is used for connections towards the light bulb.

The downward hole will instead be used in a subsequent tutorial.

As required by the electrical circuit, we must bring the hot wire from the junction box to the single-pole single-throw switch.

To do this, we cut a piece of brown wire of sufficient length to cover the distance between the junction box and the switch box. To this length we add another 10 centimeters to ensure that we will be able to make the connections comfortably.

Don’t forget also to strip both ends of the wire.

The first connection is made in the junction box

between the brown wire we have prepared and the hot wire coming from the 9 V battery. The connection is made via the appropriate connector, which in our case is a common screw terminal.

We can now proceed by cutting a PVC flexible tube into which the brown wire is inserted.

The other end of the brown wire must be connected to one of the two contacts of the switch.

We remind you that the connection of the wires to the switch takes place after removing about one cm of insulation from the end of the wire.

The conductors connected to the single-pole single-throw switch must be blocked with the corresponding screws and before testing the system, it is necessary to check that the screws are tightened to prevent the wires from slipping out of their seat.

At this point we can take care of the connection of the neutral wire.

As already mentioned, this wire is available at the junction box,

and it must reach the light bulb passing through the switch box. We must therefore calculate the length necessary to make this connection,

and consequently cut a piece of blue wire of the calculated length. Also in this case, we can ensure a safety length. Afterwards, we will shorten the wire if it turns out to be too long.

The blue wire must be connected to the neutral wire available in the junction box,

then it must be inserted into the flexible tube making it come out in the switch box.

Now let’s make the connection to the light bulb.

We cut a piece of flexible tube to make the connections from the switch box to the light bulb.

A piece of brown wire must also be cut to connect the light bulb to the single-pole single-throw switch.

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The neutral wire and the newly cut brown wire go into the corrugated flexible tube.

At this point, we can make the final connections: the brown wire must be connected to the switch, to the terminal that is still free,

and the blue wire must be connected to the light bulb at the free terminal of it.

At this point we are ready to finalize the assembly of the circuit.

First we fix the bulb to the work surface using adhesive tape.

With the same procedure we place the pipes.

Then we can fasten the switch support to the switch box using the appropriate fixing screws.

We can now close the junction box using the appropriate cover and the four fixing screws.

Well, if you have followed all our instructions precisely, the final circuit will look like the one shown in the following figure. You can then proceed with the test of the circuit.

Well, we have come to the end of this lesson. We have seen how to use and install a single-pole single-throw switch in order to control a lamp or group of lamps from a single point of a room.

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We suggest you immediately consolidate the concepts you have just learned by carefully reviewing this leson and above all by going through all our other lessons on the subject, by also accessing our youtube playlist.

We remind you that in this lesson the concepts have been illustrated on a practical level. Do not forget to deepen the concepts learned, also looking at the theoretical lessons of the course.

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Thanks for your attention and … see you next time!

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