Final Exam on Alternating Current

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.