Mechanical Drawings Mechanical drawings include all drawings and notes that have something to do with the water supply, sewage, drainage, heating and ventilating, refrigeration, air conditioning, and gas supply systems. It may also include other drawings that are necessary to present the system properly in relation to the other portions of the project.

Shop Drawings Shop drawings are drawings and related data used to show some portion of the work prepared by the construction contractor, manufacturer, distributor, or supplier. Product data, such as brochures, illustrations, standard schedules, performance charts, and other information, are furnished by the contractor or the manufacturer to show a material, product, or system for some portion of the work. Engineering Aids are sometimes required to draft shop drawings for minor shop and field projects. These drawings may include shop items, such as doors, cabinets, and small portable buildings (prefabricated berthing quarters and modifications of existing structures), or they may come from portions of design drawings, specifications, or freehand sketches given by the design engineer. Working from a shop drawing is much like working from other working drawings. You convert the ideas you get from your interpretation of the lines and symbols into the product represented by the drawing.

ELECTRICAL DIAGRAMS In addition to the construction drawings discussed above, you will be working with other types of electrical drawings or diagrams. These drawings show the arrangement and relationship of parts. Electrical diagrams are usually used to show how the parts of one or more pieces of equipment are wired together. There are several types of these diagrams. They are similar, yet different in some way. The short description of each that follows should enable you to recognize their differences.

Isometric Diagram The isometric diagram is not often seen in electrical work. It may be used to show the electrical wiring system in multilevel buildings. Appliances sometimes have an isometric diagram glued to an access panel so that it may be referred to for a quick look at an entire wiring system. (See fig. 2-13.) 

Block Diagram A block diagram is a simple drawing showing the relationships of major parts of a wiring circuit or system. Figure 2-14 shows a block diagram of a motor control system You can easily see how it gets its name. Sometimes the blocks are connected with only one line that may represent one or more conductors or cables. Either major or minor components or parts may be represented by blocks. This type of diagram is often used to show something of the relationship of components in a power distribution system. The block diagram provides little help in troubleshooting.

Figure 2-13.- Isometric wiring diagram.Wiring Diagram

Figure 2-14.- Block diagram.

Figure 2-15.- Wiring diagram.

The wiring diagram is almost a picture drawing. It shows the wiring between components and the relative position of the components. Figure 2-15 shows a wiring diagram of the same motor control system represented by the block diagram in figure 2-14. In the wiring diagram, components are shown much as they would appear in a picture. The lines representing wires are marked with numbers or letter-number combinations. Lines L1, L2, and L3 are incoming power leads. The diagram shows which terminals these power leads are connected to in the motor starter. Leads connected to terminals T1, T2, and T3 are the motor leads.

The numbers without letters mark the control terminals of the starter. Wiring diagrams are often used along with a list of repair parts. Wiring diagrams may be of some help in troubleshooting circuit problems.

Connection Diagram Figure 2-16 is a connection diagram. By comparing the symbols from this diagram to those in figure 2-6, you can see that graphic symbols are used to represent parts or components in the connection diagram. The connection diagram in figure 2-16 is a combination of basic symbols (like the open- contact symbol). You can see how the controller pictured in figure 2-15 works internally.

Figure 2-16.- Connection diagram.

Figure 2-17.- Schematic diagram. The connection diagram shows all the internal and external connections. The circuitry can be traced more easily than on the wiring diagram. The components are still shown in their relative positions. This diagram can be used to help you connect all the wiring and trace any part of the circuit. The connection diagram is a valuable troubleshooting tool. This type of diagram is often found inside the access cover of a piece of equipment.