On completion of this module, you will be able to:
- Recognize the importance of interpreting electrical drawings accurately.
- List the plans and drawings that are included in electrical drawings.
- Describe the various terms associated with electrical drawings.
- Discuss the drawing layout, the common drafting lines, and the electrical symbols used in the trade.
- Explain what is meant by scale drawings, power plans, lighting floor plans, electrical details and diagrams.
Introduction to Basic Electrical Drawings
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Electricians follow the drawings and specifications before conduits are installed, wires are pulled, or equipment is mounted.Electrical drawings are customer requirements, and provide specific instruction. Although styles vary, standard symbols are used in the industry to represent types of material, raceways, conduits, equipment, and circuit connections. Therefore, it is the electrician’s job to interpret the drawings accurately.
Electrical drawings include the following plans and drawings:
A site plan indicating the location of the building on the property.
Floor plans showing the walls and partitions for each floor or level.
Elevations of all exterior faces of the building.
Several vertical cross sections to indicate clearly the various floor levels and details of the footings, foundations, wall floors, ceilings, and roof construction.
Large-scale detail drawings showing such construction details as may be required
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Architectural DrawingsWorking drawings consisting of plans, elevations, details, and other information necessary for the construction of a building
Block Diagram
A single-line diagram used to show electrical equipment and related connections.
Blueprint
Blueprint
An exact copy or reproduction of an original drawing.
Detail Drawings
Detail Drawings
An enlarged, detailed view taken from an area of a drawing and shown in a separate view.
Dimensions
Dimensions
Sizes or measurements printed on a drawing.
Electrical Drawing
Electrical Drawing
A means of conveying a large amount of exact, detailed information in an abbreviated language.
Consists of lines, symbols, and notations to accurately convey an engineer’s design to electricians who install the electrical system on a job.
Elevation Drawing
An architectural drawing showing height, but not depth -- usually the front, rear, and sides of a building or object.
Floor Plan
A drawing of building as if a horizontal cut were made through a building at about window level, and the top portion removed.
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Ammeter
An ammeter is a measuring instrument used to measure the electric current in a circuit.
Electric currents are measured in amperes (A), hence the name.
Instruments used to measure smaller currents, in the milliampere or microampere range, are designated as milliammeters or microammeters.
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Early ammeters were laboratory instruments which relied on the earth's magnetic field for operation.
By the late 19th century, improved instruments were designed which could be mounted in any position and allowed accurate measurements in electric power systems.
Galvanometer
A galvanometer is a type of ammeter, which is an instrument for detecting and measuring electric current.
It is an analog electromechanical transducer that produces a rotary deflection of some type of pointer in response to electric current flowing through its coil in a magnetic field.
The commonly used sensing-mechanism in DC ammeters, voltmeters, and ohmmeters is a current-sensing device called a D’Arsonval meter movement.
The D’Arsonval movement is a DC moving coil-type movement in which an electromagnetic core is suspended between the poles of a permanent magnet.
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Portable instruments, usually equipped to also measure current and resistance in the form of a multimeter, are standard test instruments used in electrical and electronics work.
Any measurement that can be converted to a voltage can be displayed on a meter that is suitably calibrated; for example, pressure, temperature, flow or level in a chemical process plant.
Voltmeter Accuracy
General purpose analog voltmeters may have an accuracy of a few percent of full scale, and are used with voltages from a fraction of a volt to several thousand volts.
Digital meters can be made with high accuracy, typically better than 1%. Specially calibrated test instruments have higher accuracies, with laboratory instruments capable of measuring to accuracies of a few parts per million.
Meters using amplifiers can measure tiny voltages of microvolts or less.
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Ohmmeter
An ohmmeter is an electrical instrument that measures electrical resistance -- the opposition to an electric current.
Micro-ohmmeters (or microhmmeter) make low resistance measurements.
Megohmmeters (or in the case of a trademarked device Megger) measure large values of resistance.
The unit of measurement for resistance is ohms (Ω).
The original design of an ohmmeter provided the following:
A small battery to apply a voltage to a resistance.
A galvanometer to measure the electric current through the resistance. The scale of the galvanometer was marked in ohms, because the fixed voltage from the battery assured that as resistance decreased, the current through the meter would increase.
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Floor Plan
A drawing of building as if a horizontal cut were made through a building at about window level, and the top portion removed.
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One-line Diagram
A drawing that shows, by means of lines and symbols, the path of an electrical circuit or system of circuit along with the various components.
It is also called a single-line diagram.
Power-Riser DiagramA single-line block diagram used to indicate the electric service conductors and feeders, and subpanels.
ScaleOn a drawing, the size relationship between an object’s actual size and the size it is drawn. Scale also refers to the measuring tools used to determine this relationship.
ScheduleA systematic drawing method of presenting equipment lists on a drawing in tabular form
Schematic DiagramA detailed diagram showing complicated circuits, such as control circuits.
Sectional ViewA cutaway drawing that shows the inside of an object or building.
Shop DrawingA drawing that is usually developed by manufacturers, fabricators, or contractors to show specific dimensions and other pertinent information concerning a particular piece of equipment and its installation methods.
Site
A drawing showing the location of a building or buildings on the building site.
Such drawings frequently show graphical lines, electrical and communication lines, water and sewer lines sidewalks, driveways, and similar information. Plan
Written Specifications
A written description of what is required by the owner, architect, and engineer in the way of materials and workmanship.
Together with working drawings, the specifications form the basis of the contract requirements for construction.
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The drawings or blueprints used for building construction projects are drawn on sheets in various sizes. The drawings sheet has border lines framing the overall drawing and one or more title blocks. The types and sizes of title blocks vary.
Besides the title block, these drawing sheets will also contain the following blocks
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Drafting Lines
There are many types of drafting lines. Varying the width of the lines or breaking the lines in some similar way gives a distinct and specific meaning to each type of line, thereby contrasting it with other types of lines.
Some of the common drafting lines are as follows:
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The electrical power plan shows the complete floor plan of the building with all interior partitions drawn to scale. Sometimes, the physical locations of all the wiring and outlets -- outlets for lighting, power, signal and communications, special electrical systems, and related equipment -- are shown on the same plan.
A power plan includes the following:
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Architectural Drawings:
Working drawings consist of plans, elevations, details, and other information necessary for the construction of a building.
An architectural drawing usually includes:
A site (plot) plan indicating the location of the building on the property.
Floor plans showing the walls and partitions for each floor or level.
Elevations of all the exterior faces of the building.
Several vertical cross sections indicating clearly the various floor levels and details of the footings, foundations, walls, floors, ceilings, and roof construction.
Large-scale detail drawings showing such construction details as may be required.
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The key points from this module are:
Electrical drawings are prepared by architects and engineers. These drawings provide specific instructions to electricians working on a particular job.
It is important that an electrician interprets the drawings accurately before commencing work, i.e., before installing conduits, pulling wires, or mounting electrical equipment.
Electrical drawings include a site plan, floor plans, details drawings, schedules.
Detailed information consisting of lines, symbols, and notations is used to convey an engineer's design to electricians.
A one-line diagram shows the path of an electrical circuit or system of circuit along with the various components.
Electrical symbols -- a combination of abbreviations and pictographs -- are used to represent a component used in electrical systems.
Electrical drawings are drawn to scale due to the large size of the components. These drawings are called scale drawings.
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On completion of this module, you will be able to:
State the uses of electrical test instruments and meters.
Explain the terms associated with electrical test equipment.
Describe electrical current testing instruments such as an ammeter and a galvanometer.
Summarize how a moving-coil meter operates.
Identify the purpose of testing equipment such as voltmeter, ohmmeter, multimeter.
List the difference between an analog and a digital voltmeter.
Use the general points mentioned in order to select a meter.
Integrate the precautions listed in the module for working safely with test equipment.
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Electrical Test Equipment
Electrical systems must be tested for proper operation when they are installed and also periodically for maintenance purposes. The use of electronic test instruments and meters generally involves:
Troubleshooting electrical / electronic circuits and equipment
Verifying proper operation of instruments and associated equipment
A written description of what is required by the owner, architect, and engineer in the way of materials and workmanship.
Together with working drawings, the specifications form the basis of the contract requirements for construction.
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Drawing Layout, Drafting Lines, Electrical Symbols
The drawings or blueprints used for building construction projects are drawn on sheets in various sizes. The drawings sheet has border lines framing the overall drawing and one or more title blocks. The types and sizes of title blocks vary.
Besides the title block, these drawing sheets will also contain the following blocks
- Revision block
- Approval block
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Drafting Lines
There are many types of drafting lines. Varying the width of the lines or breaking the lines in some similar way gives a distinct and specific meaning to each type of line, thereby contrasting it with other types of lines.
- Medium full line
- Heavy full line
- Extra-heavy full line
- Hidden line
- Dimension line
- Short break line
- Match line
- Secondary line
- Light full line
Additional lines are used to represent circuits and their related components.
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Scale Drawings:
Electrical drawing components are so large that it would be impossible to draw them actual size. For this reason, drawings are made to some reduced scale; i.e., all the distances are drawn smaller than the actual dimensions of the object itself, with all dimensions being reduced in the same proportion.
The following is an example of a scale drawing:
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A power plan includes the following:
- Key plan
- Symbol
- Floor plan
- Branch circuit layout for power
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Lighting Floor Plans:
A lighting floor plan shows the outlet symbols found on the drawing for the building, representing both incandescent and fluorescent types. A circle on most electrical drawings represents an incandescent fixture, and a rectangle represents a fluorescent one.
Electrical Details and Diagrams:
Electrical diagrams are drawings that are intended to show electrical components and their related connections.
They show the electrical association of the different components, but are rarely drawn to scale.
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Written Specifications:
The written specifications for a building or project are the written descriptions of work and duties required of the owner, the architect, and the consulting engineer.
Along with the working drawings, these specifications form the basis of the contract requirements for the construction of the building.
The written specifications for a building or project are the written descriptions of work and duties required of the owner, the architect, and the consulting engineer.
Along with the working drawings, these specifications form the basis of the contract requirements for the construction of the building.
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Architectural Drawings:
Working drawings consist of plans, elevations, details, and other information necessary for the construction of a building.
An architectural drawing usually includes:
A site (plot) plan indicating the location of the building on the property.
Floor plans showing the walls and partitions for each floor or level.
Elevations of all the exterior faces of the building.
Several vertical cross sections indicating clearly the various floor levels and details of the footings, foundations, walls, floors, ceilings, and roof construction.
Large-scale detail drawings showing such construction details as may be required.
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The key points from this module are:
Electrical drawings are prepared by architects and engineers. These drawings provide specific instructions to electricians working on a particular job.
It is important that an electrician interprets the drawings accurately before commencing work, i.e., before installing conduits, pulling wires, or mounting electrical equipment.
Electrical drawings include a site plan, floor plans, details drawings, schedules.
Detailed information consisting of lines, symbols, and notations is used to convey an engineer's design to electricians.
A one-line diagram shows the path of an electrical circuit or system of circuit along with the various components.
Electrical symbols -- a combination of abbreviations and pictographs -- are used to represent a component used in electrical systems.
Electrical drawings are drawn to scale due to the large size of the components. These drawings are called scale drawings.
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Electrical Test Equipment: Learning Outcomes
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On completion of this module, you will be able to:
State the uses of electrical test instruments and meters.
Explain the terms associated with electrical test equipment.
Describe electrical current testing instruments such as an ammeter and a galvanometer.
Summarize how a moving-coil meter operates.
Identify the purpose of testing equipment such as voltmeter, ohmmeter, multimeter.
List the difference between an analog and a digital voltmeter.
Use the general points mentioned in order to select a meter.
Integrate the precautions listed in the module for working safely with test equipment.
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Electrical Test Equipment
Electrical systems must be tested for proper operation when they are installed and also periodically for maintenance purposes. The use of electronic test instruments and meters generally involves:
Troubleshooting electrical / electronic circuits and equipment
Verifying proper operation of instruments and associated equipment
Coil
A number of turns for wire, especially in spiral form, used for electromagnetic effects or for providing electrical resistance.
Continuity
An electrical term used to describe a complete (unbroken) circuit that is capable of conducting current. Such a circuit is also said to be closed.
D'Arsonval
A meter movement that uses a permanent magnet to move a pointer across a scale.
Movement
The number of cycles completed each second by given AC voltage, usually expressed in hertz. One hertz equals one cycle per second.
Frequency
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Ammeter
An ammeter is a measuring instrument used to measure the electric current in a circuit.
Electric currents are measured in amperes (A), hence the name.
Instruments used to measure smaller currents, in the milliampere or microampere range, are designated as milliammeters or microammeters.
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Early ammeters were laboratory instruments which relied on the earth's magnetic field for operation.
By the late 19th century, improved instruments were designed which could be mounted in any position and allowed accurate measurements in electric power systems.
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Galvanometer
A galvanometer is a type of ammeter, which is an instrument for detecting and measuring electric current.
It is an analog electromechanical transducer that produces a rotary deflection of some type of pointer in response to electric current flowing through its coil in a magnetic field.
The commonly used sensing-mechanism in DC ammeters, voltmeters, and ohmmeters is a current-sensing device called a D’Arsonval meter movement.
The D’Arsonval movement is a DC moving coil-type movement in which an electromagnetic core is suspended between the poles of a permanent magnet.
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The process for a moving-coil meter movement is listed below:
A coil of very fine wire is wound on a light aluminum frame.
A permanent magnet surrounds the coil.
The aluminum frame is mounted on pivots to allow it and the coil to rotate freely between the poles of the permanent magnet.
When current flows through the coil, it becomes magnetized, and the polarity of the coils is repelled by the field of the permanent magnet.
This causes the coil frame to rotate on its pivots, and the distance it rotates is determined by the amount of current that flows through the coil.
By attaching a pointer to the coil frame and adding a calibrated scale, the amount of current flowing through the meter can be measured.
Multiplier resistors are used to extend the range of the meter movement for voltage measurements, while shunt resistors are used to extend the range of the meter movement for current measurements.
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Various Meters
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Voltmeter
A voltmeter is an instrument used for measuring electrical potential difference between two points in an electric circuit.
Analog voltmeter - Analog voltmeters move a pointer across a scale in proportion to the voltage of the circuit.
Digital voltmeter - Digital voltmeters give a numerical display of voltage by use of an analog to digital converter.
Voltmeters are made in a wide range of styles.
Instruments permanently mounted in a panel are used to monitor generators or other fixed apparatus.
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Portable instruments, usually equipped to also measure current and resistance in the form of a multimeter, are standard test instruments used in electrical and electronics work.
Any measurement that can be converted to a voltage can be displayed on a meter that is suitably calibrated; for example, pressure, temperature, flow or level in a chemical process plant.
Voltmeter Accuracy
General purpose analog voltmeters may have an accuracy of a few percent of full scale, and are used with voltages from a fraction of a volt to several thousand volts.
Digital meters can be made with high accuracy, typically better than 1%. Specially calibrated test instruments have higher accuracies, with laboratory instruments capable of measuring to accuracies of a few parts per million.
Meters using amplifiers can measure tiny voltages of microvolts or less.
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Ohmmeter
An ohmmeter is an electrical instrument that measures electrical resistance -- the opposition to an electric current.
Micro-ohmmeters (or microhmmeter) make low resistance measurements.
Megohmmeters (or in the case of a trademarked device Megger) measure large values of resistance.
The unit of measurement for resistance is ohms (Ω).
The original design of an ohmmeter provided the following:
A small battery to apply a voltage to a resistance.
A galvanometer to measure the electric current through the resistance. The scale of the galvanometer was marked in ohms, because the fixed voltage from the battery assured that as resistance decreased, the current through the meter would increase.
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Ohmmeters form circuits by themselves; therefore, they cannot be used within an assembled circuit.
A more accurate type of ohmmeter has an electronic circuit that passes a constant current (I) through the resistance, and another circuit that measures the voltage (V) across the resistance.
A more accurate type of ohmmeter has an electronic circuit that passes a constant current (I) through the resistance, and another circuit that measures the voltage (V) across the resistance.
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Megohmmeter
A megohmmeter is a special type of ohmmeter used to measure, or rather test, the insulation resistance of insulators.
For this purpose, special ohmmeters called megohmmeters which can provide high voltages (typically in ranges from 500V to 2 kV) at specified current capacity are used.
The minimum insulation tolerated is in the range of 1 to 10 mega-ohms, depending on the standards referred to.
A megohmmeter is a special type of ohmmeter used to measure, or rather test, the insulation resistance of insulators.
- Insulators have electrical resistance in the range of millions of ohms compared to conductors which are measured in ohms.
- Insulators need testing for their insulation strength at the time of commissioning. Testing is also a part of the maintenance process for electrical equipment and installations.
For this purpose, special ohmmeters called megohmmeters which can provide high voltages (typically in ranges from 500V to 2 kV) at specified current capacity are used.
The minimum insulation tolerated is in the range of 1 to 10 mega-ohms, depending on the standards referred to.
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Multimeter
A multimeter or a multitester, also known as a VOM (Volt-Ohm meter), is an electronic measuring instrument that combines several measurement functions in one unit.
A typical multimeter may include features such as the ability to measure voltage, current, and resistance.
Multimeters may use analog or digital circuits. Analog multimeters are abbreviated as AMM and digital multimeters as DMM or DVOM.
A multimeter or a multitester, also known as a VOM (Volt-Ohm meter), is an electronic measuring instrument that combines several measurement functions in one unit.
A typical multimeter may include features such as the ability to measure voltage, current, and resistance.
Multimeters may use analog or digital circuits. Analog multimeters are abbreviated as AMM and digital multimeters as DMM or DVOM.
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- Analog instruments are usually based on a microammeter whose pointer moves over a scale calibrated for all the different measurements that can be made.
- Digital instruments usually display digits, but may display a bar of a length proportional to the quantity being measured.
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A multimeter can be a hand-held device useful for basic fault-finding and field service work, or a bench instrument which can measure to a very high degree of accuracy.
It can be used to troubleshoot electrical problems in a wide array of industrial and household devices such as electronic equipment, motor controls, domestic appliances, power supplies, and wiring systems.
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Other Tools of the Trade
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- The following is a list of some other basic tools used by electricians.
Click on each name to see what the given tool looks like:
Cable Cutters
Claw Hammer
Cordless Drill
Drill Bits
Ear Plugs
Flash Light
Hacksaw
Hard Hat
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Pliers
Power Strips
Safety Goggles
Screw Drivers
Tool Pouch
Utility Knife
25" Tape Measure
50" Extension Cord
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