How to Read and Interpret Electrical Shop Drawings –Part Three


Today, we will explain the Drafting Practices Using Graphical Symbols and abbreviations.
 

 
4- Electrical Symbols
 

 

 
Electrical symbol
 
An Electrical symbol definition:
 
Electrical symbol is a small picture or image called a pictogram used to represent various electrical and electronic devices (such as wires, batteries, resistors, and transistors) in a schematic diagram of an electrical or electronic circuit.
 
Important notes:
  • Electrical drawings use many different graphic symbols, Abbreviations and device function numbers to represent the components being used in the electrical circuits. There are many symbols in use. It is not possible to cover all of them in one article.
  • Additionally, it is not practical for you to try to remember them all; however, you should be aware that the symbols exist, and you should know where a description of their meaning can be found.
  • The important practice in using graphical symbols is not mixing electrical symbols from different standards in one drawing. please see below paragraph for Comparison Of Electrical Circuit Symbols of IEC Vs. ANSI / IEEE.
 
As we indicated in article “How to Read and Interpret Electrical Shop Drawings –Part Two”, that we can find all the graphical symbols for electrical systems in the following resources:  
 
1- American National Standards Institute (ANSI):
 
  • ANSI Y32.2: The American National Standard Graphic Symbols for Electrical and Electronics Diagrams (Including Reference Designation Letters).
  • ANSI Y32.9: American National Standard Graphic Symbols for Electrical Wiring and Layout Diagrams Used in Architecture and Building Construction.
 
2- Institute of Electrical and Electronics Engineers (IEEE):
 
  • IEEE 315: IEEE Standard, Graphic Symbols for Electrical and Electronic Diagrams
  • IEEE C37.2: IEEE Standard Electrical Power System Device Function Numbers and Contact Designations.
 
3- Canadian Standards Association (CSA)
  • CSA Z99: Canadian Standard, Graphic Symbols for Electrical and Electronic Diagrams.
 
4- The International Electrotechnical Commission (IEC)
  • IEC 60617: IEC Standard, Graphic Symbols for Electrical and Electronic Diagrams.
 
5- The British Standards (BS)
  • BS 3939-2: Graphical Symbols for Electrical Power, Telecommunications and Electronics Diagrams.
 

 

 
Again, you can download all the above standards from the following links:
 
 
 

 

 
Comparison Of Electrical Circuit Symbols of IEC Vs. ANSI / IEEE
 
The important practice in using graphical symbols is not mixing electrical symbols from different standards in one drawing. So, for complying with this practice, we list here comparison of electrical circuit symbols which is based on the following international/national specifications:
  • IEC 60617 graphic symbol database (DIN EN 60617-2 to DIN EN 60617-12)
  • NEMA ICS 19-2002 (R 2007), ANSI Y32.2/ IEEE 315/315 A, CSA Z99
 













 

 

 
The common electrical symbols can be downloaded from the following links:
 
 
 
 
 
 
 
 

 

 
5- Electrical Abbreviations
 

 

 
KVA: Kilo Volt Ampere
 
An abbreviation definition:
Abbreviation is a shortened form of a word or phrase. Usually, but not always, it consists of a letter or group of letters taken from the word or phrase.
 
   
Why we need to use these Abbreviations?

Generally, abbreviations are used due to the following reasons:
 
  • Abbreviations can be used to give a different context to the world itself, such as (PIN Number, wherein if the abbreviation were removed the context would be invalid).
  • Abbreviations are used throughout several industries, including automotive, construction, electricity wiring, electronic device repair and manufacturing, and telephony for making short words for long process descriptions.
  • Abbreviations are used for various circuits, conduits, sizes, standardized tools, and more to represent them as short alphabets especially if there are many details need to be represented in small size drawings. 
 
Notes:
 
  • Abbreviations should only be used when absolutely necessary and never be used when the meaning will not be clear.
  • Because electrical work involves significant cost and/or safety risks, understanding these abbreviations and acronyms is important for all involved.
 

 

 
The following list of abbreviations is by no means considered comprehensive, so please download all the files to complete your list of electrical abbreviations:
 
 
 
 
        
 

 

 
6- Device Function Numbers
 

 

 
  • A device function number, with an appropriate prefix and appended suffix is used to identify the function(s) of each device installed in electrical equipment. This includes manual, partial-automatic, and automatic switchgear. These numbers are to be used in drawings, elementary and connection diagrams, instruction books, publications, and specifications. In addition, for automatic switchgear, the device number may be physically placed on, or adjacent to, each device on the assembled equipment. This will enable a device to be readily identified.
  • Device function numbers are used in electrical drawings, diagrams, instruction books, and specifications. Device function numbers save space on a drawing or diagram because they eliminate the necessity of printing descriptions of functions next to diagrammatic symbols.
  • A list of the most commonly used device function numbers from IEEE Standard C37.2 is included in below table.
 
ANSI Device Function Numbers
 
 

 

 
7- Drafting Practices Using Graphical Symbols and abbreviations
 


 
The following Drafting Practices must be taken into consideration when Using Graphical Symbols:
 
  • The orientation of a symbol on a drawing does not alter the meaning of the symbol. This is true even if the symbol is drawn backwards. A symbol is made up of all its various parts.
 
  • The weight (or width) of a line does not affect the meaning of the symbol. In some cases a heavier line may be used for emphasis.
 
  • Symbols are not drawn to scale. They can be drawn to any size compatible with the scale of the drawing.
 
  • Arrowheads can be drawn closed or open, except when showing a "protective gap" (a gap placed between line parts and the ground which limits the maximum over-voltage that may occur.)
 
  • The standard symbol for a terminal (o) can be added to any one of the graphic symbols where connecting lines are attached. This added terminal symbol is not a part of the graphic symbol itself.
 
  • In order to make a drawing simpler, graphic symbols for devices such as relays or contactors may be drawn in parts. However, if this is done the drawing must show how the parts are related.
 
  • Most often, it does not matter at which angle a connecting line is drawn to meet a graphic symbol.
 
  • Broken lines with short dashes: - - - - - - , may be used to show paths or equipment that will be added to the circuit later, or those which are connected to the circuit but are not part of it.
  • If details such as type, impedance, and rating are to be given, they should be drawn next to a symbol. If abbreviations are used, they should be in accordance with the American Standard Abbreviations for Use on Drawings. Letters that are joined together and use parts of graphic symbols are not abbreviations.
 


In the next article, we will explain the Different Types of Electrical Drawings. So, please keep following.


The previous and related articles are listed in the below table:
 


Subject of Previous Article

Article
1- Overview for the articles/courses that give a preliminary explanation for the different Types of Electrical drawings.
2- Electrical Drawings Glossary.
 
 
 
3- Resources used to Read and Interpret Electrical Drawings.
 
 

 



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Electrical Shop Drawings Course
 

 

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