AC Control Equipment

Table of Contents

Chapter 1: Motor Starters

Topics: Motor controllers; Controller enclosures; Starters; Magnetic controls; Interlocks, Reversing and combination starters

Learning Objectives:

• Describe the difference between a manual starter and a magnetic starter.
• Explain the function of a shading coil in a magnetic starter.
• Explain the effects of low voltage on a controller.
• State the reason why holding-circuit interlocks are required on magnetic starters and contactors.

Chapter 2: Switches and Controls

Topics: Pushbuttons; Selector switches; Wall boxes; Contact blocks; Indicating lights; Circuit diagrams; Legend plates

Learning Objectives:

• Discuss the characteristics of industrial switches and controls.
• Identify the five most commonly used NEMA pushbutton stations.
• Demonstrate how to mount an oil-tight control station both vertically and horizontally.
• Explain the difference between standard and press-to-test indicating lights.
• Explain how a three-wire control circuit works.

Chapter 3: Limit Switches

Topics: Precision snapswitches; Limit switches; Mercury-tilt switches; Switch installation and failure

Learning Objectives:

• List the main parts of a precision snap-action limit switch.
• Describe the contact arrangement of a snapswitch.
• Describe the kinds of actuators used in limit switches.
• List the rules for the proper design and application of limit switch cams.
• Explain how a mercury switch works.

Chapter 4: Special Control Switches

Topics: Reversing drum, foot, transfer, plugging, mechanical, magnetic plugging, pressure, temperature, and float switches

Learning Objectives:

• Explain how a drum switch works.
• Select the best switch for stopping a motor quickly.
• List the criteria for selecting a plugging switch.
• Identify different types of pressure switches.
• State the definition of pressure differential.

Chapter 5: Timers and Counters

Topics: Interval and reset timers; Time-delay relays; Repeat-cycle, pulse, and percentage timers;Impulse, electric, and revolution counters; Time totalizers

Learning Objectives:

• Explain how a reset timer works.
• Describe the different types of timers.
• Compare and contrast an electric counter and a time totalizer.
• Select the best control device for use where a machine cannot be controlled by time.
• Demonstrate how to set up a chart for a programed control circuit.

Chapter 6: Control Relays

Topics: Contact operation; Mountings, enclosures, terminals, and definitions; NEMA classes; Causes of failure

Learning Objectives:

• State the definition of a relay
• Explain the function of relay contacts.
• Select the best relay for use where large movement of the contacts or high contact force is required.
• List the advantages of a reed relay.
• Tell why industrial relays usually have double-break contacts.

Chapter 7: Equipment for Hazardous Locations

Topics: Enclosures; Sources of ignition; Switchgear and industrial controls; Lighting; Motors and generators; Plugs and receptacles, Portable equipment; Conduit

Learning Objectives:

• List the requirements an enclosure must meet in order to be called explosionproof.
• List the characteristics of switchgear and industrial controls-in hazardous conditions.
• List three situations in hazardous locations that require the use of seals.
• List the three basic conditions that can cause fire or explosion.
• Demonstrate how to terminate armored cable that enters an explosionproof housing.

Chapter 8: Special Motor Controls

Topics: Synchronous motor control; Sequence-accelerating and decelerating relays; Transformer starters

Learning Objectives:

• Name the two relays required for automatic starting of a synchronous motor.
• Explain how an automatic sequence-accelerating relay works.
• Select the best starter for use where the highest possible starting torque per ampere of line current is required.
• List the characteristics of different types of resistance starters.
• Describe a Y-delta starter.

Chapter 9: Motor Control Centers

Topics: Features and advantages; MCC bus; NEMA standards; Enclosure construction; Wiring; Circuit protection; Installation

Learning Objectives:

• Define the term motor control center.
• Name the main advantages and disadvantages of back-to-back MCC construction.
• Explain how to install an MCC.
• Define a note, a caution, and a warning as each relates to MCC equipment.
• List the checks to conduct prior to releasing an MCC for plant operation.

Chapter 10: Control Panel Wiring

Topics: Enclosures; Terminal blocks; Wire identification; Connections; Connectors; Wire dressing

Learning Objectives:

• State the function of terminal blocks.
• Demonstrate how to make a terminal connection.
• Tell when to use different types of connectors.
• Describe the proper lacing of wires in a control panel.
• Explain when and how to use a wiring duct.

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