Unit 4 Symbols

Objectives After studying this unit, you should be able to: Identify common electrical symbols used in motor control diagrams Use electrical symbols in drawing schematic and wiring diagrams Draw and define supplementary contact symbols

Introduction Pictorial shorthand Shows how pieces of electrical equipment are connected in a circuit No actual standard Vary from one manufacturer to another, or one country to another Most standard set used in U.S. is NEMA symbols

Symbols Push buttons

Symbols (cont’d.) Switch symbols Represent common control-sensing devices

Symbols (cont’d.) Switch symbols (cont’d.)

Symbols (cont’d.) Basic schematics Show components in electrical sequence Without regard for physical location Show components in de-energized or off state Any contact that has the same label or number as a coil is controlled by that coil When a coil energizes, all contacts controlled by it change position

Symbols (cont’d.)

Sensing Devices Control systems depend on devices to know circuit conditions Limit switches Float, pressure, flow, and temperature switches Coils Timed contacts Contact symbols Other

Sensing Devices (cont’d.)

Sensing Devices (cont’d.)

Sensing Devices (cont’d.)

Explanation of Common Symbols

Explanation of Common Symbols (cont’d.)