How to Read and Interpret Electrical Shop Drawings –Part One

1- Introduction
This is the second course for Electrical drawings after our first course “ED-1: Electrical Drawings Course”, Where we explain the following points:  
  1. Reading an electrical drawing,
  2. Basic layout of a drawing,
  3. Types and sizes of drawings,
  4. Numbering system for drawings,
  5. Positioning parts on drawings,
  6. How to create a drawing,
  7. How to check integrity of drawings,
  8. Management of drawings.
Also in the course “EE-2: Basic Electrical Design Course – Level I”, Where we give a preliminary explanation for the different Types of electrical diagrams and we focus on the Single-Line Diagrams.  
And in Course “HVAC-2: Electrical Wiring Diagrams and Calculations for Air-Conditioning Systems” , Where we give a preliminary explanation for the different Types of Electrical Wiring Diagrams for Air Conditioning Systems and we focus on How to read Electrical Wiring Diagrams for Air Conditioning Systems.  
In this course, we will start explaining the theoretical part of the shop drawing course which is “How to Read and Interpret Electrical Shop Drawings”.

In the next course we will explain the practical part of the shop drawing course which isHow to Make The Electrical Shop Drawings.
2- Electrical Drawings Glossary
As-Built Drawing
An Engineering drawing that has been revised to reflect actual field conditions after the completion of construction.
Drawings that show exactly how the facility or equipment was built.
Block Diagram
A block diagram represents the principle parts of a system as annotated geometrical figures that show the functions of the parts and their functional relationships.
Block Diagram
Cable Schedule
A schedule that lists the specifications of cables, the cable’s terminations, and the cable’s routes.
Cable And Conduit Drawings
Drawings that show the approximate location and direction of the cables and conduit run in an area or in a facility.
Cable Schedule

Cable And Conduit Schedule
A chart listing the cable and conduit numbers, identifying the type, size, length and drawing showing the cable or conduit run.
Conduit Schedule
A specific form of a raceway schedule that lists the routes, trade sizes, and lengths of conduits.
Connection Diagram
A connection diagram shows the electrical connections of component devices and contains such detail as is needed to make and trace these connections.
Construction Drawing
A drawing that shows an exact reproduction of the physical arrangements and views of specific electrical equipment to enable assembly of the equipment.
Demolition Drawing
Any existing drawing that shows the extent of the demolition work to be done.
Drawing Number
An arrangement of eight alpha/numeric characters [prefix + size (separated by dash „-„) + number] used to provide the unique identity for individual Engineering Drawings.
Detail Drawing
A drawing of a single item or portion of an electrical system that incorporates all the distinct parts needed to show the worker what type of material is required for the system installation.
Shortened form of “detail drawing”. A detail drawing illustrates all of the distinct parts of an electrical component that are needed for installation.
A drawing that is made for mathematical, scientific, or engineering purposes.
A representation of an object or a plan by means of lines.
Electrical Schedule
A table that contains a list of electrical equipment and technical notes.
Elementary Diagram
An elementary diagram is a special form of a schematic diagram that shows all of the operational elements and all of the circuits of an electrical control system. An elementary diagrams is often used to represent the complete control circuit of a power substation.
A drawing that shows in straight line form the detail wiring of the circuit without regard to physical relationships.
A diagram that shows the complete function and relationship of electrical components in a circuit by means of graphical symbols.
Elementary Diagram

Electrical Area Classification Drawing
A drawing showing classified area where flammable vapors, liquids, gases or combustible dust and fibers may be present.
Electrical Area Classification Drawing
A technical drawing that is constructed from the perspective of a side view.
Emergency Drawing
An Engineering Drawing that has been designated by the Operating Engineering Organization (OEO) as being critical to the plant's operations during a disaster situation. These drawings are given top priority in every case.
Equipment Layout
A drawing that shows electrical equipment in its physical location with respect to other components that are located nearby.
An equipment layout drawing shows how the major electrical equipment is arranged to provide the necessary physical and electrical clearances from all other components that are located in the vicinity.
Electrical Arrangement Diagram
A diagram that shows the placement or location of electrical components or devices.
Electrical Arrangement Diagram with BOQ

External Diagram
An external wiring diagram represents the manufacturer’s recommended arrangement of the circuits that should be connected to the terminals of an electrical device.
Ground Grid
A system of interconnected horizontal conductors that are buried beneath the surface of the earth.
Ground Grid Plan
A ground grid plan drawing shows the locations of the ground conductors, ground electrodes, and ground connectors that are part of a ground grid.
Installation Print
An installation print is a drawing that provides detailed instructions concerning the installation of a component that cannot be included on layout drawing.
Interconnection Diagram
A diagram that shows the connections between the terminals of different control panels or the terminals of other electrical equipment such as motor or auxiliary devices.
Internal Wiring Diagram
An internal wiring diagram shows the internal wiring of an operational element of an electrical control.
Key Drawings
Engineering drawings designated as essential for continued facility operation and maintenance. The Proponent Organization and Project Management jointly determine Key Drawing status.
Layout (Drawing)
A drawing that physically describes the location or assembly of electrical equipment in a room or a prefabricated packaged assembly.
Ladder Diagram
A special form of a schematic diagram that shows a top-down logical line schematic: logical because it moves from power input at the top through sequential operations. Sequential operation means that one function must be complete before the next function can begin.
A ladder diagram is a special form of a schematic diagram that is specifically designed for interpreting control system logic.
Ladder Diagram

Logic Diagram
A logic diagram shows the logic for a complex circuit, process, or device. A logic diagram utilizes block-type symbols to represent highly complex functions that are performed either by integrated processing modules or by individual devices.
A logic diagram represents the logic elements of a control system or a control device and their interconnections without necessarily representing physical construction or engineering details.
Logic Diagram Margin References
Margin references are numerical addresses on ladder diagrams that allow a relay’s output contact symbols to be located quickly and accurately.
One-Line Diagram
A one-line diagram uses single lines, standard graphical symbols, and standard nomenclature to show the power paths of an electrical circuit or a system of circuits. A one-line diagram also shows the component devices or parts of a power system. In a one-line diagram, the multiple conductors of power circuits and control circuits are shown as single lines.
A drawing that indicates by means of single lines and symbols the interconnection and component parts of an electrical circuit or system of circuits.
A one-line diagram shows, by means of single lines and graphical symbols, the course of an electric circuit or system of circuits and the component devices or parts used therein.
Operational Elements
Elements that perform an operation in a control circuit, such as relays, meters, switches, pilot lights, diodes, heaters, arresters, transformers, and circuit breakers.
A technical drawing that is constructed from the perspective of an overhead view.
Polarity Marks
The marks that exist on instrument transformers and the diagrammatic symbols of instrument transformers to identify the winding terminals that reach positive peaks in voltages at the same time.
A print is a copy of a reproducible drawing. Note: In this training course the words “print” and “drawing” are used interchangeably.
Any channel designed specifically for and used exclusively for holding electrical conductors.
Raceway Schedule
A schedule that lists the routes, trade sizes, and lengths of raceways.
Riser Diagram
A layout diagram that shows all panels, feeder circuits, switches, switchboards, and other major components in relationship to a vertical section taken through a building.
A drawing that indicates by means of single lines and simplified symbols, the distribution of electrical systems in a multistoried structure.
Schedule (Electrical)
A graphical or tabular chart of electrical data or equipment; for example, a circuit breaker schedule or a conduit and wiring schedule.
Schematic Diagram
A diagram that shows, by means of graphical symbols, the connections and functions of an electrical circuit without necessarily representing the physical size, shape, or location of the circuit components. A schematic diagram facilitates tracing the circuit and understanding its functions
A drawing that shows the physical terminal arrangement and internal connections for an electrical piece of equipment.
An elementary diagram showing the functions and relations of electrical components in a circuit by means of graphical symbols.
Single-Line Diagram
A diagram in which single lines are used to show component interconnections even though two or more conductors are required in the actual circuit.
Single-Line Diagram

Sectional Views
Supplementary views or details that show additional information that is required to communicate the intention of the designer.
Switch Development Table
A switch development tables lists all possible positions of the operating handle of a switch and indicates the expected open close states of all output contacts for each handle position.
Terminal Blocks
An insulating base (block) that has terminals for connecting control wiring.
Three-Line (Diagram)
A diagram that provides detailed information pertaining to three-phase circuitry that is not shown on a one-line diagram.
Title Block
The reserved portion of a drawing containing information about the drawing, project and plant.
Title Block

Vendor Drawing
Any document developed by a manufacturer that supports the technical requirements of material or equipment and received as part of a purchase order.
Wiring Diagram Or Connection Diagram 
A wiring diagram uses standardized symbols to show the physical devices of an electrical control panel and lines to show the wires that connect these devices to each other.
A diagram that shows electrical equipment or components together with all interconnecting wiring.
Wiring Diagram
Under-Floor Raceways
Metal ducts of various forms and shapes that are laid onto a rough concrete slab and then covered with finished concrete.
Underground Duct Bank
A conduit that consists of two or more ducts that is installed under the surface of the earth and is encased in concrete.
Utility Site Plan Drawing
A utility site plan drawing shows the property lines and the nearest locations of the electrical, water, gas, sewer and communication system utilities.
Winding Polarity Diagram
A small diagram that accompanies a standard diagrammatic symbol for a transformer and indicates the delta or wye connection of the transformer’s windings.
Wireless Connection Diagram
A wireless connection diagram is a list of wire numbers, originations, and destinations of conductors. Rather than being represented by lines, wires and connections are represented by the information on the list.
A wireway is a sheet metal trough with a hinged or removable cover for housing and protecting wires and cables. The conductors are laid in place after the wireway is installed as a complete system.
In the next article, we will explain the standards used for shop drawings drafting. So, please keep following.


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