Fy7w04 Electrical Module 1 Lesson 15

NNPC FSTP Technicians

Fundamentals of Electricity Course Code: FY7W 04 Lesson 15

Contents

Electrical Drawings & Diagrams

Performance Objectives Upon completion of this Course, students will be able to: • Explain the purpose of electrical drawings & diagrams • State the four main ways of representing an electrical circuit & explain/describe their differences • Draw the symbols for an alternating current; a conductor; a fuse; a single phase transformer; a 3 phase transformer; a generator & a motor • Describe the 3 main types of Architects Drawings • Given a drawing or diagram, extract information from it as required

Introduction to Drawings, Diagrams, & Symbols

Electrical Drawings There are many different ways of showing in drawing form how an electrical circuit works; these are all termed ‘diagrams’. Diagrams use simple symbols to represent complete equipment or elements that make up an electrical circuit.

Types of Diagrams There are 4 main ways of representing an electrical circuit, whether it is for generation, distribution or control circuitry. These are: • Block Diagrams • Single Line Diagrams • Wiring Diagrams • Schematic Diagrams or Drawings

Block Diagrams A simple form of diagram, when it is not required to go into detailed circuits is the ‘Block Diagram’. Here complete units of equipment, or separate stages of a piece of equipment, are shown by single blocks. The blocks are connected together with single lines indicating the logical path of the circuit. These blocks either have their electrical symbol or their title written in them. The left to right or top to bottom progress should be followed.

A Typical Block Diagram

Single Line Diagrams Another simple type of diagram used to represent an electrical layout similar to the block diagram is the ‘One Line Diagram’. It is basically a schematic diagram but only uses one line to denote all the cables or wires.

A Typical Single Line Diagram

Wiring Diagrams The wiring diagram shows the actual wiring between every terminal in an electrical equipment or group of equipments. In some cases details of the type of wire used, or its colour is shown. AN ACTUAL EXAMPLE FOLLOWS

An Actual Example of Wiring Diagram

Wiring Diagrams It can be seen that by using a wiring diagram it can be difficult to see how a system works, especially with a more complicated circuit. Another form of diagram or drawing is used in conjunction with the wiring diagram called a ‘schematic diagram’

Schematic Diagrams or Drawings The schematic diagram shown in the next slide is exactly the same motor control system as shown in the wiring diagram, and the simplification is very obvious. Whereas the wiring diagram shows the physical location of the equipment and the actual physical wiring, the schematic diagram shows the electrical circuit and how it works. When trouble shooting or fault finding on a piece of electrical apparatus very often the wiring diagram and the schematic are used together.

Schematic Diagrams or Drawings

Diagrams showing a circuit & a wiring diagram of the same electrical circuit

Schematic Diagrams or Drawings

Piping Drawing for a Refrigerator

Electrical Schematic for the same refrigerator

Symbols or Legend Care has to be taken when reading/interpreting electrical drawings. The symbols designating individual pieces of electrical equipment can vary depending on the country of manufacture. THEREFORE THE ‘DRAWING LEGEND’ SHOULD ALWAYS BE OBTAINED REFERRED TO.

Symbols or Legend There are several national and international standards for graphical symbols in circuit diagrams, in particular: • IEC 60617 (also known as British Standard BS 3939) • ANSI standard Y32 (also known as IEEE Std 315) • IEC 60617 originally consisted of 13 parts, from resistors and capacitors to logic symbols and even a generalised drawing standard of connections and bus line widths. It is now published as a subscription online database IEC 60617-DB • Different symbols may be used depending on the discipline using the drawing; for example, lighting and power symbols used as part of architectural drawings may be different from symbols for devices used in electronics.

Symbols or Legend

Some Common Symbols Used for Drawing Circuits

Other Types of Drawings

Pictorial drawings show a picture of the plant or equipment

Pictorial drawings show a picture of the plant or equipment

A modern electric motor fitted with a ‘mist’ system to lubricate the front & rear shaft bearings

Exploded Views EXPLODED VIEWS are often used to give extra detail for assembly of a component

Cut-Away Views and Sectional Views CUT-AWAY VIEWS and SECTIONAL VIEWS are used to give extra internal detail of a component. The diagram below shows an example of both the cut-away and sectional view.

The Sectional View can be used to show how the device operates

Assembly Drawings Assembly drawings are used to show how things are put together (assembled). They show how the different parts of a piece of equipment are put together to make the complete unit. The diagram shows an assembly drawing of a cable gland. The diagram shows how the gland should be assembled on the cable.

Drawings Supplied by Architects

Architects Drawings There are different types of architects’ drawings for different purposes. Architects’ drawings show the physical locations of electrical wiring, fittings and equipment. They also show the layout of the site or building. The most common types of architects drawings are: • Plans • Plot Plans • As-Fitted

Plans Plans are also called floor plans or layout diagrams. The term plan is generally used to describe the layout drawing of the site or building. A plan is a drawing of the details of a site or building seen from above.

Importance of a Plan The plan is an important way of giving information. First it shows the outline of the site or building. Secondly, it gives information about structural details, such as the position of doorways, windows, stairs, etc

As-Fitted (As Built) Drawings Plans can be changed to show progress of work, material requirements etc. These modified plans are called as-fitted drawings. The as-fitted drawing is a plan which shows the exact location of cables, method of installation and the final position of all equipment. The as-fitted drawing is constantly kept up to date as the work continues. It shows any changes that have been made from the original drawings. On completion of the work copies of the as-fitted drawing are given to the customer.

Plot Plans Plot plans show a top view of the site or plot. They show existing buildings, equipment, roadways, etc. Plot plans are used to: • plan where new buildings and equipment can be located. • plan the best use of services and utilities (e.g. water, electricity, roads, etc.) • show the location of existing buildings, equipment and services / utilities, etc. • give information about equipment / buildings.

distances

between

Plot Plans Plot plans can be used to show the electrical distribution system on a site or plot. The diagram here shows the plot-plan of an industrial site. It shows the route of the overhead high-voltage system as well as the underground duct system. The plot-plan shows where the electrical cables are actually installed. Plot plans use symbols to give information. Sometimes the symbols used are not the usual ones, so you must read the legend on the drawing.

Practice in Reading Drawings & Diagrams

Your Instructor will ask you questions

Practice in Reading Drawings & Diagrams

Practice in Reading Drawings & Diagrams

Practice in Reading Drawings & Diagrams