Final Exam on Alternating Current

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Questions and Answers

What is the most commonly used form of electricity?

Voltage

Direct Current

Static Electricity

Alternating Current (correct)

What device converts mechanical energy into electrical energy?

Generator

What does alternating current refer to?

Constant reversing of polarities

The positions of a sine wave include the , , and __.

Positive Peak, Negative Peak, Neutral Signup and view all the answers

What is the measurement of one cycle per second?

Hertz Signup and view all the answers

What is a single-phase current?

Current produced on one phase or sine wave Signup and view all the answers

In a three-phase system, how must the phases be spaced?

120 degrees out of phase Signup and view all the answers

What converts electrical energy to rotating mechanical energy?

Motor Signup and view all the answers

What is a commutator?

Group of bands providing connections between armature coils and brushes Signup and view all the answers

What are the stationary windings of a motor called?

Stator Signup and view all the answers

Which of the following is a conducting connection to physical earth?

Ground Signup and view all the answers

What provides a fault path for current during a ground fault?

Grounding conductor Signup and view all the answers

What color is a ground wire typically? One way to identify is ______.

Green with yellow stripe or Bare copper wire Signup and view all the answers

List three reasons for having a ground wire:

<ol> <li>Protects devices 2. Ensures all devices requiring a ground have one 3. Grounds must be properly marked and sized.</li> </ol> Signup and view all the answers

What is the purpose of grounding?

Protection of people and equipment Signup and view all the answers

What is identified by 1.Handle, 2.Heel, 3.Lip, 4.Shoe?

Pipebender Signup and view all the answers

What is a raceway?

An enclosed channel designed to hold wires and cables Signup and view all the answers

The LFMC must be secured every and within of a termination point.

4 1/2 feet, 12 inches Signup and view all the answers

Study Notes

Alternating Current

Most prevalent form of electricity used in various settings including homes and industries.
Originates from power plants and is essential for residential, industrial, and commercial applications.

Source of AC

Generators convert mechanical energy to electrical energy, in contrast to motors.
Operating on a rotating mechanism, they produce electrical current stored as electricity.

Characteristics of AC

Alternating current involves the constant reversal of polarities, depicted by a sinusoidal wave (sine wave).

Sine Wave Structure

Consists of three key positions: positive peak, negative peak, and neutral point.

Frequency

Defined as the number of cycles per second, measured in hertz.
One complete cycle corresponds to 360 degrees.

Single Phase

Current generated is concentrated on one phase or sine wave.
Commonly found voltages include 120 volts and 240 volts, typically used for central air conditioning systems.

Three Phase System

Requires three currents spaced exactly 120 degrees apart.
In a 480 volt three-phase system, the voltage reading from a leg to ground is 277 volts.

Motors

Convert electrical energy into rotating mechanical energy.
Function based on the principles of magnetism, with alternating poles causing rotation.

Commutator

Series of bands connecting armature coils to brushes.
Allows for the reversal of electrical current direction.

Stator

The fixed part of a motor, made up of the core, windings, and coils.
Comprised of two main components: stator coils and stator core.

Brushes

Comprise a sliding contact, usually made from carbon and copper, that maintains conductivity with the commutator.
Essential for transferring electricity to a revolving armature.

Motor Types

Series Wound Motor: Current flows through both armature and field windings, adjusting speed based on load conditions and capable of starting under heavy loads.
Parallel Wound Motor (Shunt Motor): Current divides between armature and field windings, maintaining constant speed despite varying loads.

Grounding

Ground provides a conductive connection to the earth for safety.
Grounding conductors offer a fault path for current in the event of a ground fault.

Ground Fault

Occurs when a current-carrying conductor directly contacts the earth.

Importance of Grounding

Protects individuals and equipment from electrical faults.
Requires specific identification methods for ground wires: green with yellow stripe, green, or bare copper.

Ground Wire Specifications

Ground wires must match the size of the largest conductor used, with the possibility of using two sizes smaller.

Raceways

Enclosed channels for holding various electrical conductors, adhering to code specifications.

Installation Rules for EMT

No more than 360 degrees of bends between pull points; all bends must be counted.
Raceways must be fully installed before conductor installation.

Rigid Metal Conduit

Thick-walled conduit, ideal for hazardous areas, requiring secure placement every 10 feet and within 3 feet of termination.

Electrical Metallic Tubing (EMT)

Commonly used tubing, requiring secure installation every 10 feet and within 3 feet of termination points; fittings available, easy to bend, and not threaded.

Flexible Metal Conduit

Also known as "flex," requires securing every 4.5 feet and within 12 inches of termination points.

Liquidtight Flexible Metal Conduit

Known as SEALTITE, suitable for outdoor and humid applications, adhering to a 360-degree bend rule.

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Description

Prepare for your final exam with these flashcards focusing on alternating current (AC). Each card covers essential concepts such as the definition of AC and its sources, along with their applications and functions in various settings. Perfect for reinforcing your knowledge and ensuring success on the test.