Symbols and Diagrams for Motors 311

“Symbols and Diagrams for Motors” introduces different diagrams used to represent motor circuits and symbols that circuit diagrams commonly contain. Pictorial diagrams are the simplest and use illustrated pictures to represent circuit components. Schematic diagrams and line diagrams use symbols to represent components. Wiring diagrams also use symbols, but they are more detailed than the other types of diagrams. Most motor control devices are represented on a schematic diagram.

Being able to interpret motor diagrams is extremely important when working with motor controls because they show how circuits are constructed and how components are connected. Users will also rely on their knowledge of diagrams and symbols when learning about more advanced motor topics and applications.

Class Details

Class Name:
Symbols and Diagrams for Motors 311
Version:
2.0
Difficulty:
Advanced
Number of Lessons:
22
Related 1.0 Class:
Symbols and Diagrams for Motors 210

Class Outline

  • Motor Symbols and Diagrams
  • Types of Motor Diagrams
  • Symbols
  • DC Motor Symbols
  • AC Motor Symbols
  • Motor Symbols Review
  • Contact Symbols
  • Switch Symbols
  • Multiple Contact Switch Symbols
  • Switch and Contact Symbols Review
  • Pushbutton Symbols
  • Momentary and Maintained Contact Pushbuttons
  • Selector Switch Symbols
  • Sensor Switch Symbols
  • Sensor Switch Operation
  • Switch Operation Symbols Review
  • Coil Symbols
  • Timing Relay Symbols
  • Control and Timing Relays
  • Overload Relay Symbols
  • Coil and Relay Symbols Review
  • Final Review

Objectives

  • Describe motor symbols and diagrams.
  • Identify types of motor diagrams.
  • Identify common motor control symbols.
  • Identify DC motor symbols.
  • Identify AC motor symbols.
  • Identify basic contact symbols.
  • Identify basic switch symbols.
  • Identify multiple contact switch symbols.
  • Identify pushbutton symbols.
  • Identify selector switch symbols.
  • Identify sensing device switch symbols.
  • Identify coil symbols.
  • Identify timing relay symbols.
  • Identify overload relay symbols.

Job Roles

Certifications

Glossary

Vocabulary Term Definition
AC Alternating current. Electricity that reverses direction at regularly recurring intervals of time. AC switches direction 60 times per second, or 60 hertz (Hz), in the US.
actuator The part of a limit switch that contacts an object and triggers the switch. Limit switch actuators come in several different styles.
air flow switch An automatic switch that senses the movement of air in a duct. Air flow switch symbols have a flag shape that represents a sail.
alternating current AC. Electricity that reverses direction at regularly recurring intervals of time. Alternating current switches direction 60 times per second, or 60 hertz (Hz), in the US.
armature The part of a motor in which a current is induced to create a magnetic field. The armature usually consists of a series of coils or groups of insulated conductors surrounding a core of iron.
ball float A round floating component used in float switches to detect the level of a liquid. A ball float rests on the surface of the liquid.
battery A device that converts chemical energy into electrical energy. Batteries are a source of direct current.
bimetallic strip A component made of two metals with different expansion temperatures that curls when exposed to heat. Bimetallic strips are often used in temperature switches and circuit breakers to detect temperature.
circuit breakers An overcurrent device with a bimetallic strip that bends and trips a switch to open a circuit. Circuit breakers detect excess current to prevent overheating in a circuit.
circuit logic The reasoning behind the function of an electrical circuit or system. Circuit logic comprises all the principles required to understand electrical circuitry.
coil Multiple loops of conducting wire used to create a magnetic field when current passes through it. Coils are often wrapped continuously around magnetic cores made of iron or steel.
compound motor A DC motor that has both series and shunt field windings. Compound motors combine the advantages of the shunt and series motors.
contacts Connecting points between two conductors that allow electricity to flow when they are closed. Contacts prevent the flow of electricity when open.
control devices A component in a circuit that controls the flow of electricity. Control devices determine when a circuit is energized.
control relay An electrical relay that controls a circuit or other relays. Control relays can open and close many sets of contacts.
control transformers An electromagnetic device that decreases motor voltage to usable levels for the motor control circuit. Control transformers also provide electrical isolation.
current The flow of electricity. Current strength is called amperage and is measured in amperes.
diagram A drawing that illustrates the parts or operation of something. Motor diagrams use pictures and symbols to represent motor components.
diaphragm-operated switch A type of pressure switch that senses small pressure changes at low pressures. Diaphragm-operated switch symbols include a semicircle that represents the diaphragm.
direct current DC. Electricity that flows in one direction. Direct current does not reverse the direction of flow.
double-pole double-throw DPDT. A switch with two moveable contacts that each have two stationary contacts. Double-pole double-throw switches control four circuits, but only two at a time.
double-pole single-throw DPST. A switch with two moveable contacts that each have one stationary contact. Double-pole single-throw switches simultaneously control two different circuits.
electric motor A machine that converts electricity into mechanical energy or motion. Electric motors operate on the principle of magnetic induction.
field The part of a motor that creates a magnetic field around the armature. The field consists of electromagnets and windings.
float switch An automatic switch that senses the level of liquid in a tank. Float switch symbols include a circle that represents a ball float.
flow switch An automatic switch that senses the movement of air or liquid in a duct or pipe. Flow switch symbols include a triangular shape to represent a sail or paddle.
fuses An overcurrent device with a metallic component that melts to open a circuit. Fuses detect excess current to prevent overheating in a circuit.
hydraulic systems A power transmission system that uses the force of flowing liquids to transmit power. Hydraulic systems often use pressure switches.
ladder diagram An electrical print that shows the logic of an electrical circuit or system using standard symbols. Ladder diagrams are also known as line diagrams.
limit switch A mechanical sensor that detects the presence or absence of an object. The limit switch symbol has a wedge that represents an actuator.
line diagram An electrical print that shows the logic of an electrical circuit or system using standard symbols. Line diagrams are also known as ladder diagrams.
liquid flow switch An automatic switch that senses the movement of liquid in a pipe. Liquid flow switch symbols have a flag shape that represents a paddle.
loads A component in a circuit that converts electricity into light, heat, or mechanical motion. Loads include light bulbs, appliances, and machines.
magnetic field The area in and around a magnet in which a magnetic force exists. Magnetic fields exhibit the powers of attraction and repulsion.
magnetic overload relay An overload relay that senses the strength of the magnetic field a motor's current produces. Magnetic overload relays are often used in areas that experience extreme changes in temperature.
maintained contact device A type of device in which the switch or button physically keeps the circuit in the actuated position. Maintained contact devices include emergency stop buttons.
momentary contact device A type of device in which the switch or button closes or opens the circuit only when it is actuated. Momentary contact devices include start and stop pushbuttons.
momentary contact devices A type of device in which the switch or button closes or opens the circuit only when it is actuated. Momentary contact devices include start and stop pushbuttons.
mushroom head A type of pushbutton with a large round head. Mushroom head pushbuttons are easy to operate and often used for emergency stops.
National Electrical Manufacturers Association NEMA. An organization that sets standards for electrical equipment used in the United States. The National Electrical Manufacturers Association provides commonly used electrical symbol standards.
NC Normally closed. An electrical contact that generally allows electricity to flow. An NC contact symbol has parallel lines with a diagonal line crossing them.
NCHO Normally closed held open. A switch with contacts that are generally closed but held open when the circuit is de-energized. NCHO switch symbols show the moveable contact above and away from the stationary contact.
NO Normally open. An electrical contact that generally does not allow electricity to flow. An NO contact symbol has parallel lines with an opening between them.
NOHC Normally open held closed. A switch with contacts that are generally open but held closed when the circuit is de-energized. NOHC switch symbols show the moveable contact touching the bottom of the stationary contact.
normally closed NC. An electrical contact that generally allows electricity to flow. A normally closed contact symbol has parallel lines with a diagonal line crossing them.
normally closed held open NCHO. A switch with contacts that are generally closed but held open when the circuit is de-energized. Normally closed held open switch symbols show the moveable contact above and away from the stationary contact.
normally open NO. An electrical contact that generally does not allow electricity to flow. A normally open contact symbol has parallel lines with an opening between them.
normally open held closed NOHC. A switch with contacts that are generally open but held closed when the circuit is de-energized. Normally open held closed switch symbols show the moveable contact touching the bottom of the stationary contact.
off-delay timer A timing relay whose contacts change position immediately when the coil is energized, but delay returning to their normal position when the coil is de-energized. Off-delay timers are also known as time-delay opening contacts.
on-delay timer A timing relay whose contacts delay changing position when the coil is energized, but change back to their normal position immediately when the coil is de-energized. On-delay timers are also known as time-delay closing contacts.
output devices A device that performs a mechanical action after receiving the electrical signal to do so. Output devices include machines such as motors.
overload condition A situation in which current exceeds recommended levels. Overload conditions can cause devices to overheat.
overload relay OL. A control relay that protects a motor from overheating due to overload conditions in the machinery. Overload relays can be thermal or magnetic.
paddle A device used to sense changes in liquid flow. Paddles are represented by flag shapes on liquid flow switch symbols.
parallel An electrical system that has multiple routes for the flow of electricity. Parallel windings consist of many turns of thin wires.
pictorial diagram An electrical print that shows the external appearance of each component in a circuit. A pictorial diagram is much like a photograph of the circuit.
pilot lights A type of indicator light found on machines. Pilot lights typically indicate when a device is energized or operating.
pneumatic systems A power transmission system that uses the force of flowing gases to transmit power. Pneumatic systems often use pressure switches.
pole The number of moveable contacts controlled by a switch. The pole includes all of the moveable contacts that belong to a single circuit.
power sources The device that provides electrical energy to a circuit. Power sources include batteries, generators, and other devices.
pressure switch An automatic switch that senses the pressure in a pneumatic or hydraulic system. Pressure switch symbols include a semicircle that represents a diaphragm.
protective devices A circuit component that prevents damage, injury, and/or fire. Protective devices include grounding circuits and overcurrent devices.
pushbutton A manual control device that opens or closes a circuit when pressed. Pushbuttons can be normally open or normally closed, like other switches.
relay An electrically controlled mechanical device that controls one circuit by opening and closing the contacts in another circuit. Relays use electromagnetic coils to open and close contacts.
rotor The rotating part of a motor. The rotor connects to an output shaft that drives the load.
sail A device used to sense changes in air flow. Sails are represented by flag shapes on air flow switch symbols.
schematic diagram An electrical print that uses symbols to represent all electrical components in a circuit. Schematic diagrams show the electrical relationships of all components but not their physical locations.
selector switch A rotating manual switch that makes connections with different contacts when turned to different positions. Selector switches generally have between one and eight positions.
sensor switches A control device that actuates when it detects changes in environmental conditions. Sensor switches include limit, float, flow, pressure, and temperature switches.
series An electrical system that has only one route for the flow of electricity. Series windings consist of a few turns of thick wire.
series field A winding designed to be connected in series with the armature of a DC motor or generator. Series fields consist of a few turns of thick wire.
series motor A DC motor that has field windings connected in series with the armature. Series motors provide very high startup torque but must never be run without a load.
shunt field A winding designed to be connected in parallel with the armature of a DC motor or generator. Shunt fields consist of many turns of thin wire.
shunt motor A DC motor that has field windings connected in parallel with the armature. Shunt motors are commonly used because of their excellent speed regulation.
sine wave The most common type of AC waveform. A sine wave consists of 360 electrical degrees and is produced by rotating machines.
single-phase motor A low-horsepower AC motor that operates on current with only one sine wave. Single-phase motors are often used for simple residential appliances like furnaces, washing machines, and air conditioners.
single-pole double-throw SPDT. A switch with one moveable contact and two stationary contacts. Single-pole double-throw switches alternately control two different circuits.
single-pole single-throw SPST. A switch with one moveable contact and one stationary contact. Single-pole single-throw switches are typical on/off switches.
solenoid An output device that uses a coil to convert electrical energy into linear mechanical motion. Solenoids are often used to control valves in fluid power systems.
squirrel cage motors An AC induction motor with a rotor that consists of metal bars connected at either end. The squirrel cage motor is the most common AC motor.
starting winding An auxiliary stator winding used in single-phase motors that receives current during motor startup. The starting winding is disconnected when the motor reaches 60-80% of the full-load speed.
switch A control device that opens and closes contacts in a circuit. Switches can operate manually, mechanically, or automatically.
symbol A sign or mark that represents something else. Symbols are often used to represent components in diagrams.
temperature switch An automatic switch that senses changes in temperature. Temperature switch symbols use a bent line to represent a bimetallic strip.
thermal overload relay An overload relay that senses how much heat a motor's current produces. Thermal overload relays shut down the motor when they detect excessive heat.
three-phase motor A popular AC motor with a continuous series of three overlapping AC cycles offset by 120 electrical degrees. Three-phase motors are used for all large AC motor applications.
throw The number of stationary contacts that correspond to a switch's moveable contacts. The throw includes all of the stationary contacts for one or many circuits.
time-delay closing TC. A timing relay whose contacts delay changing position when the coil is energized, but change back to their normal position immediately when the coil is de-energized. Time-delay closing contacts are also known as on-delay timers.
time-delay opening TO. A timing relay whose contacts change position immediately when the coil is energized, but delay returning to their normal position when the coil is de-energized. Time-delay opening contacts are also known as off-delay timers.
timing relay A control relay that delays changing the position of its contacts instead of opening or closing them immediately. Timing relays may delay before opening contacts or before closing contacts.
torque A force that produces rotation. Torque is measured in pound-feet in the English system and Newton-meters in the metric system.
volts A unit used to measure electromotive force or pressure, which is called voltage. One volt of force is needed to cause one coulomb to do one unit of work.
winding Wire wrapped around a core or into a coil that is used to conduct current. Windings form electromagnets and magnetic fields in motors and other devices.
windings Wire wrapped around a core or into a coil that is used to conduct current. Windings form electromagnets and magnetic fields in motors and other devices.
wiring diagram An electrical print that shows the physical locations and electrical relationships of all electrical components in a circuit. Wiring diagrams use symbols, like schematic diagrams, but they are much less common.
wound rotor motor An AC induction motor with a rotor that contains windings. Wound rotor motors produce high startup torque.