## 2 Electric Diagrams  
According to UNE-EN ISO 10209:2012 [14], a diagram (in process industry) is a drawing using graphical symbols that shows the functions of the objects composing a system and their interrelations. A graphical symbol is also defined by the International Organization for Standardization, ISO, as a visually perceptible figure used to transmit information independently of language [15]. Therefore, electric diagrams depict the interaction and physical connections of components composing electrical circuits by means of symbolic representations. The symbols are defined by ISO 14617 standard [16]. In this work, we focus on two different types of electric diagrams: _wiring_ and _ladder_. The former gives information about real relative physical position and locations of the elements composing devices or installations. It is used for building electrical systems and it helps for troubleshooting. The latter, explains the functioning of the circuit as it gives information about the interaction and dependencies between elements. It represents the flow of each branch of electricity from one line to the other. Engineers are required to master both types of diagrams when designing an electrical system. Thus, one of the main goals of the Industrial Design subject is to teach engineering students the abilities required to convert a wiring diagram into a ladder one. The process is highly mechanical, with some basic rules like: (i) conductors are represented using horizontal or vertical lines; (ii) there are exactly the same number of elements in both diagrams; (iii) conductors cannot be crossed in ladder diagrams, or (iv) in ladder diagrams, elements of the same component can be placed separately (e.g., switches and coil in a relay) however, in wiring ones they must be placed together, etc.. Figure 1a,b shows an example of each type of diagram of a simple circuit. Figure 1a shows the wiring diagram of an electrical circuit. The operation of the system is hardly understandable until every connection is thoroughly checked, even though it is a very simple system. However, the relative physical location is noticed at first glance. Figure 1b represents the ladder diagram of the wiring one explained above. This diagram graphically explains the dependencies between components of the circuit and its operation. There is one horizontal line for each set of dependent elements. In this specific diagram, there is no clue about the physical location of components nor their relative distances. However, we can easily check the functionality of the circuit, and the dependencies between components. In the displayed circuit, there are two different ways for turning on the three lamps. On the one hand, changing the position of Commut Q1, directly activates all the lamps. They turn off changing Q1 to its original state. On the other hand, we can observe that when any of the three push buttons S2, S3, or S4 are pressed, the relay K1 is excited and its two associated switches change their state. One of them turns on the three lamps H1, H2, and H3, and the other switch serves as feedback mechanism that keeps the relay excited, so that the lamps keep on until S1 is pressed. Additionally, there are also three bells Z1, Z2, and Z3 each of them with an associated push button S5, S6, and S7, respectively. The transformation of the wiring diagram into a ladder one is direct if specific rules are applied. However, most of the engineering students, in their early years at university, are not very familiar with the basics of electricity and find difficulties in understanding the process. Existing commercial software tools are either graphical tools for creating good-looking diagrams but with no functionality, or very complex software for designing real installations, able to integrate different aspects in the same  
Figure 1: Example of a simple wiring diagram (**a**) and its corresponding ladder diagram (**b**). model. Next, we present some of the most relevant software tools available in the literature for creating and designing electrical systems.