How to make a civil wiring diagram

How to make a civil wiring diagram

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On: 05 Agu, 2020

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Creating an electrical scheme is of primary importance for making an electrical installation. Not only does it allow you to have everything under control (or almost), shedding light on the general situation, but it creates a future vision of the i...

Creating an electrical scheme is of primary importance for making an electrical installation. Not only does it allow you to have everything under control (or almost), shedding light on the general situation, but it creates a future vision of the installation itself. I think it is better to be faced with inconveniences when there is only a few lines on a sheet, rather than being in front of an already installed and wired power line, with this I think you will agree with me. And this is the main reason for the existence of design in any area. If you have not already done so, I recommend reading the article: Electrical design

A technical drawing is used to highlight the construction and functional characteristics of a system, whether mechanical, electronic or electric. In the electrical drawing, therefore, the parts of the system must be schematically represented, such as the connections and electrical equipment and inside there must be all the information useful for the installer and for the future maintenance technician who will therefore be able to perform his / her duties at best.

In this article I will explain something more about the wiring diagrams and finally how to draw them.

First part: The bases for the realization of an electric scheme

The tools to make an electrical diagram

You can make a circuit diagram on a sheet of paper or on the computer. In the first case, the format of the sheets must be of a specific size, which is dictated by the UNI 936 and 737 standards. The orientation of the sheet which can be drawn both vertically and horizontally is not important. This is an advantage because in some cases, to make the whole design fit inside the sheet, it is better to change the orientation.

The following table illustrates the main sheet and squaring formats, expressed in millimeters (mm).

841 X 1’189 820 X 1’169
A1 594 X 841 574 X 820
A2 420 X 594 400 X 574
A3 297 X 420 285 X 400
A4 210 X 297 200 X 285
A5 148 X 210 138 X 200

If, on the other hand, you prefer to create your own scheme on your computer, there are many free programs on the net that will help you make it happen. To name a few:

  • ProfiCAD
  • DesignSpark Electrical
  • SmartDraw
  • Gwcad (Gewiss)
  • Qelectrotech
  • Bticino software
  • PBT-Q (Gewiss)
  • Designspark (Q.el)

The symbols and the cartouche

Whether you make a pencil or computer drawing, you must know that the same graphic signs are used, established by the technical committee 3 (CEI), while at national level by the IEC.

We have already covered this topic in another article, read: electrical symbols

As for the connections (lines), there is no rule dictated by regulations, but methods are adopted to make the technical drawing as comprehensible as possible:

- draw dashed lines in case of mechanical connection
- increase the thickness of the lines when there are higher voltages or currents

The technical drawing also provides for the insertion of a box, in which a presentation is made by entering the title, author, date and number of total pages. This space dedicated to this information is called "Cartiglio".

figure 1

figure 1

The scales of greatness

The UNI standards regarding the size scales of the objects represented on the drawing allow us to choose three different solutions:

natural: the royal scale (natural size), i.e. 1: 1
reductive: are all the scales that reduce its size, that is 1: 5, 1:10 ... and so on
enlarged: are all the scales that enlarge the size, that is, 5: 1, 10: 1 ... and so on

Use a scale suitable for the representation of the objects in the diagram, the goal is to make the interpretation of the design clear. Rely mainly on common sense.

How to create a scaled object

Suppose we draw a wall and that the actual measurements are 2 m, that is 400 cm. To draw it on the sheet you will have to use a ladder. But how do you do it?
As a demonstration, I choose to apply a 1:20 scale, the concept is simple.
1:20 is 1/20 which brings us back to elementary school, do you remember the cake?
If we take a cake we divide it into 20 parts, we get 20 equal slices. For the staircase it is roughly the same reasoning, only that instead of dividing, it imagines to shrink or enlarge an object.
Reduction of an object

If we take a 200 cm wall and reduce it 20 times, we get one that corresponds to the scale of 1:20 compared to the real one. So we will have a 10 cm object representing a 200 cm wall, since (200 x 1): 20 = 10

The object will be drawn on the sheet in scale and alongside, below or above (based on preferences and space) the actual size value may be indicated.
Magnification of an object

To increase the scale the procedure is similar, but the fraction will have a numerator greater than the denominator. Suppose we have to attribute a 4: 1 scale to a 1 cm screw. Imagining to enlarge it four times, we can simply apply the multiplication to the factors, (1 X 4): 1 = 4, since the denominator is 1.

The scale object will be drawn on the sheet, reporting the real value as described in the previous example.

Types of wiring diagrams

The CEI standards classify the types of schemes used in four reading criteria.


If the classification is based on the extent of the representation, the scheme belongs to you:

Used to represent the electricity distribution and transport system. Some useful information on the power and type of line is highlighted

On together
Shows the primary electrical circuit of the whole system

Shows the primary electrical circuit of a part of the system

If the classification is based on the completeness of the representation, the scheme belongs to it:

Business suit
It is a complete drawing (precisely), very detailed and showing the plant in all its parts

It shows a part of the system in a superficial way as it is not essential to the project, but that it must still be taken into account

In principle
It shows the electrical functioning of the components in a simple and intuitive way
If the classification is based on the representation of the conductors, the following belong to the scheme:

It shows the electrical system focusing on the connection of the cables

As above, but in this case only one line is shown in the drawing which corresponds to the cable bundle

If the classification is based on the way of representation, the scheme belongs to it:

Shows the line and appliances regardless of their location

By Assembly
It shows the connections between the terminals, illustrating the type of equipment using symbols

It shows the arrangement of all the elements taking into consideration the type of installation and the electrical cables used

It is used particularly in an industrial environment to represent the control circuit but also in a civil environment to describe the operation of a specific component or how it interfaces with the electrical system


We have seen a rundown of different wiring diagrams, just to clarify some points, to create the basis. But of all these types of wiring diagrams, only a few are actually useful for the realization of a civil project and are:

Single-line diagram
Multiwire diagram
Functional diagram

We will now go to see in detail how to make these types of wiring diagrams.

Second part: How to make a wiring diagram

A method of drawing a circuit diagram

If you have to create a civil electrical system, first get the site plan, if you can't find one already made, then you will have to draw it. Again you can draw on a sheet of paper or use a computer application. Here is a short list of free applications:

  • Sweethome
  • CadSoft ExpressView
  • Floorplanner (online)
  • Roomarranger
  • Ashampoo software

How to draw the floor plan

First you will have to draw the perimeter wall and then the dividing walls, including doors and windows and stairs. To know their position you will necessarily have to take the measurements with a classic or digital meter, after which you will have to put them on the drawing.

Let's start by making some distinctions between wiring diagrams. Yes, because as you may already know, there are many different types, for different purposes.

figure 2

figure 2

Based on a floor plan, it will be easier to create your single and multi-wire electrical diagrams.

You will have to study where you want to install the electrical equipment and then you will have to draw the respective position of the components. Respect the distances of electrical equipment, to have a system in accordance with the law.

If you have not yet addressed the topic of the heights of electrical equipment, I recommend you read this article: The location of electrical equipment

How to make a single-line diagram

the single-line diagram, as you can guess from its name, is an electrical diagram in which only a trace is drawn that contains multiple electrical cables that are identified with the following symbolism:

figure 3

figure 3

figure 5

figure 5


Usually the single-line diagram is used for the electrical panels, but it is not excluded to find them in other situations where it is needed.

Below, a single-line diagram of an electrical panel:

figure 4

figure 4


While this is a one-line scheme of an apartment:

figure 6

figure 6

As you can see from the second wiring diagram, you can add parameters such as the diameter of the cables and corrugated (example, 3 × 1.5 ø16, that is, three 1.5mmq electric cables and a 16mm diameter conduit) and the type of laying ( 'mom' indicates a pose embedded in the wall. The 'm' represent the brick and the 'o' the conduit).

Making one is quite simple, also with this method it is easier to keep order in the drawing. Based on a floor plan, you will only have to draw traces that connect the electrical components. To make you understand what a single-line scheme is, I could give you a trivial example: imagine looking at a room from above and that the power line on the drawing corresponds to the traces on the wall, on the floor or on the ceiling, made by the masons to pass the corrugated (therefore essentially the path of corrugated). The symbols that indicate the characteristics of the cables will be drawn on the back of the lines that connect the driving force and the lighting. Instead for the symbols dedicated to the electrical components, the usual ones will be used that are used in all the schemes, those dictated by the CEI standards.

How to make a multi-line diagram

In order to have a more detailed and realistic wiring diagram, it will be necessary to create a multi-wire scheme, which also in this case "as you can guess from the name", is made up of several electrical cables. In this type of scheme, it will no longer be necessary to indicate the phases with symbols, but colors can be used to distinguish the type of conductor used.
If you don't know what I'm talking about, I suggest you go deeper into the topic by reading this article: The colors of the electric cables

This type of wiring diagram, highly appreciated in electronics, in some situations may not be the optimal choice when in the presence of many lines it would create a too chaotic design. For civil electrical systems, this type of scheme could be chosen for the construction of an electrical panel or a control panel.

An example of a multi-line diagram:

figure 9

figure 9


How to make a functional scheme

the functional scheme is not represented within a plan. It is used to describe the functioning of an electrical circuit, which can be a plant, a switchboard, an appliance, a component ........ it is also used in electronics. With this type of scheme, the symbols that are used are reduced in number, for example a NO (normally open) switch will not be represented with the usual symbols:

figure 7

figure 7


but instead it will be depicted as an integral part of the wiring diagram:


figure 8

figure 8


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