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Questions and Answers
What is the purpose of a push-pull operator with normally open and normally closed contacts?
control circuit operation
A skeleton diagram of a control circuit shows L1, L2, L3, and various components like ___, ___, and CR.
C1, C2
Which component is used to regulate voltage in a power supply circuit?
A capacitor is represented by the symbol 'C3' in the circuit diagram.
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What is the principal difference between a contactor and a motor starter?
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What is the function of overload relays in a motor circuit?
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A float switch is used to control the temperature of a liquid in a tank.
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Timing relays can be classified into two general categories: On -delay relay (Delay on energizing, DOE) and **____________ relay (Delay on de-energizing, DODE).
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What is the main purpose of electrical engineering drawing?
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Electrical drawing standards are influenced by manufacturers and contractors.
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What does CAD stand for in the context of drawing?
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_______ are used as auxiliary devices to switch control circuits and large motor starter coils.
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Match the following switch types with their function:
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Study Notes
Electrical Engineering Drawing
- Electrical engineering drawing is essential for effective planning of electrical power and lighting projects.
- It provides a concise picture of project objectives and serves as a record of intent for owners and guidance for contractors.
- It also serves as contract documents that can be used as evidence in court cases involving contractor malfeasance.
Objectives of Electrical Drawings
- Describe electrical projects in sufficient detail to allow contractors to estimate cost of materials, labor, and services.
- Instruct and guide electricians in performing required wiring and equipment installation.
- Warn electricians of potential hazards such as existing wiring, gas pipes, or plumbing systems.
- Provide owners with an "as-built" record of installed electrical wiring and equipment for maintenance and future expansion.
Nature of Electrical Drawings
- Typical electrical drawing consists of solid or dashed lines representing wiring or cables and symbols for luminaires, socket outlets, switches, auxiliary systems, and other electrical devices and their locations on a scaled architectural floor plan.
- Drawings include title blocks to identify the project, designers or engineers, and owners, and change blocks to record any changes made since the drawing was first issued.
- There may be no drawing requirements for simple electrical projects, and all information can be included in a written proposal or other contractual agreement.
Computer-Aided Drawing (CAD)
- Large engineering consulting and architectural firms have transitioned from manual to computer-aided drawing (CAD).
- CAD provides various benefits, including:
- Saving time in preparing electrical drawings
- Eliminating tedious tasks of lettering and drawing uniform lines and symbols
- Permitting rapid changes on completed drawings
- Providing databases of master digitized drawings that can be modified for reuse on other projects
- Allowing multiple persons to work on a specific drawing simultaneously
Motor Control Systems
- Relays are used as auxiliary devices to switch control circuits and large motor starter and contactor coils.
- Relays can be used to control small loads such as small motors, solenoid, electric heaters, pilot lights, and audible signal devices.
- Control relays are available in single or double throw arrangements with various combinations of normally open (NO) and normally closed (NC) contact circuits.
Contactors
- Contactors are electromagnetically operated switches that provide a safe and convenient means for connecting and interrupting branch circuits.
- Contactors are used in combination with pilot control devices to switch lighting and heating loads and to control AC motors.
Overload Relays
- Overload relays are added to the magnetic switch of a motor to form a starter.
- The overload relay acts to open the motor circuit when full load is exceeded.
- Ideal overload protection for motors should have current sensing properties similar to the heating curve of a motor.
Timing Relays
- Timing relays can be divided into two general classifications: on-delay relay (Delay on energizing, DOE) and off-delay relay (Delay on de-energizing, DODE).
- Timing relays are similar to other control relays, but the contacts delay changing their positions when the coil is energized or de-energized.
Limit Switches
- Limit switches are designed to pass an electrical signal only when a predetermined limit is reached.
- Limit switches are used to govern the starting, stopping, and reversal of electric motors.
Float Switches
- Float switches are used to start and stop motor-driven pumps according to changes in water (or other liquid) level in a tank or sump.
Pressure Switches
- Pressure switches are used to control the pressure of liquids and gases within a desired range.
- Pressure switches are used in industrial applications such as air compressors, welding equipment, machine tools, and high-pressure lubricating systems.
Temperature Actuated Switches (Thermostat)
- Thermostats are used to control temperature changes and maintain the desired temperature range of air, gases, liquids, or solids.
Flow Switches
- Flow switches are used to control the flow of liquids or gases and can be inserted in a pipe to activate a switch when liquid or air flows against a part of the device called a paddle.### Electrical Connections and Switches
- Vapour proof electrical connections must be used with vapour proof switches.
- The insulation of the wire leading to the switches must be adequate to withstand the high temperature of the liquid inside the pipe.
Flow Switches
- Flow switches are used in ducts in air conditioning systems to prevent duct heaters from energizing when there is no air movement in the duct.
- Airflow or sail switches are also used in ducts in air conditioning systems.
Push Button Stations
- A push button station is a device that provides control of a motor through a motor starter by pressing a button which opens or closes contacts.
- It is possible to control a motor from as many stations as there are, through the same magnetic controller, by using more than one push button station.
- Push buttons are momentary contacts and they return to their normal position when the pressure on them is released.
- They may be normally closed or open, i.e., the contacts are in a rest position, held there by spring tension and are not subject to either mechanical or electrical external force.
Push-Pull Operator
- A push-pull operator is another type of push button control that contains two sets of contacts in one unit.
- One set of contacts is operated by pulling outward on the button, and the other set is operated by pushing the button.
- They may consist of two normally open momentary contacts, i.e., in its normal position, neither movable contact connects with stationary contacts.
Developing a Wiring Diagram
- A wiring diagram is used to represent the connections between electrical devices and equipment.
Standard Symbols for Electrical Devices and Equipment
- Standard symbols are used to represent electrical devices and equipment on a wiring diagram.
- Examples of standard symbols include those for switches, connectors, fuses, transformers, rectifiers, voltage regulators, capacitors, resistors, and LEDs.
Selecting Elements on a Circuit Diagram from the Eagle Library
- Elements on a circuit diagram can be selected from the Eagle library, which includes a range of components such as connectors, fuses, transformers, rectifiers, voltage regulators, capacitors, resistors, and LEDs.
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Description
Test your knowledge on electrical engineering drawing with a focus on motor control systems. This quiz covers key concepts and fundamentals in electrical engineering.
