Electrical Systems

Introduction to Circuits 201

Introduction to Circuits provides a foundational overview of electrical circuitry. Whether wired in series, parallel, or a combination of the two, all circuits consist of a source, path, control, and load. Each of these components serves a purpose, and many circuits have extra components to prevent safety hazards and damage. Visual representations of circuits, such as schematic diagrams, use symbols of these components to illustrate the circuit’s layout. This method makes it easier to understand circuits and the rules that describe how they function, such as Kirchhoff’s Laws.

Understanding how circuits work is essential when working with electricity. This includes being familiar with circuit components, circuit diagrams, and the rules that govern circuits, which serves as the basis for understanding advanced electrical topics. Without the foundational information presented in this class, users would not be prepared to study more complex aspects of electrical systems.

  • Difficulty Intermediate

  • Format Online

  • Number of Lessons 19

  • Language English


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Course Outline
  • Circuits
  • Components of a Circuit
  • Diagrams and Abbreviations
  • Circuit Basics Review
  • Source
  • Path
  • Resistance
  • Control
  • Load
  • Circuit Components Review
  • Protective Devices
  • Grounding
  • Overcurrent Devices
  • Protective Devices Review
  • Kirchhoff’s Laws
  • Series Circuits
  • Parallel Circuits
  • Combination Circuits
  • Final Review
  • Define circuit.
  • Identify the components of a circuit.
  • Describe the purpose of symbols and abbreviations in schematic diagrams.
  • Describe the source in a circuit.
  • Describe the path in a circuit.
  • Describe resistance in a circuit.
  • Describe the control in a circuit.
  • Describe the load in a circuit.
  • Describe the purpose of common protective devices.
  • Describe grounding. Describe a chassis ground.
  • Describe overcurrent devices.
  • Describe Kirchhoff’s Laws.
  • Describe series circuits.
  • Describe parallel circuits.
  • Describe combination circuits.
Vocabulary Term

alternating current

AC. Electricity that reverses direction at regularly recurring intervals of time. Alternating current switches direction 60 times per second, or 60 hertz, in the U.S.


I. The strength or intensity of an electrical current. Amperage is measured in amperes (A).


A tiny particle that makes up all materials. Atoms are the smallest distinguishable units of an element that retain the element's characteristics.


A device that uses metals to convert 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 up when exposed to heat. Bimetallic strips are often used to detect elevated temperatures in circuit breakers.

bus bar

A grounded metal bar in an electrical box to which all neutral and grounding wires are connected. Bus bars often connect to long metal poles embedded in the earth.


A nonmetallic material made from clay and hardened by firing at a high temperature. Ceramic materials are insulators.


The frame or shell of a machine. The chassis of a machine often serves as the neutral source for grounding when earth grounding is impractical.

chassis ground

A wire that runs from a machine's motor to its frame to divert stray currents. Chassis grounds are used when grounding a circuit to the earth is not practical.


A controlled path for electricity. A circuit includes a source, path, load, and control.

circuit breaker

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.

combination circuit

An electrical system that has elements of both series and parallel circuits. Combination circuits follow series circuit rules for sections connected in series and follow parallel circuit rules for sections connected in parallel.


A material or element that allows free movement of electrons and therefore allows easy flow of electricity. Conductors are typically metals.


Connecting points between two conductors that allow electricity to flow when they are closed. Contacts prevent the flow of electricity when open.


A component in a circuit that controls the flow of electricity. The control determines when a circuit is energized.

electric shock

The flow of electricity through the body. Electric shock can be fatal.

electrical box

The system that serves as the source for household or building electricity. The electrical box is where the main electrical power comes in and is distributed throughout the building.


A form of energy created by the movement of electrons. Electricity can be converted into light, heat, or motion.

electromotive force

EMF. The electrical pressure or potential that pushes electrons through a conductor. Electromotive force is measured in volts (V) and is also called voltage.


A negatively charged particle that orbits the nucleus of an atom. Electrons flowing between atoms causes electricity.


A thin wire that becomes hot and bright when electricity passes through it. Filaments are used in most light bulbs.


An overcurrent device with a metallic component that melts to open a circuit. Fuses detect excess current to prevent overheating in a circuit.


A device that converts mechanical energy into electrical energy. Generators operate on the principle of magnetic induction.


Safely connected to a neutral body, like the earth, that can absorb stray electrical charges. Grounded equipment diverts current to prevent electric shock.

grounded conductor

The wire that returns electricity to the source and completes the circuit. The grounded conductor is usually covered with white insulation and is also called the neutral wire.

grounding circuit

An electrical system that diverts stray current to a neutral object if it strays from its intended path. Grounding circuits have extra wires that send stray currents to a neutral body.

grounding conductor

The wire that provides a low-resistance path to ground for stray currents. The grounding conductor is usually bare copper or covered with green insulation.

hot wire

The electrically charged conductor that provides electricity to the load. The hot wire is usually covered with black insulation.

hydroelectric plants

An electricity-generating facility that uses water to create power. Hydroelectric plants use magnetic induction to produce electricity from the mechanical motion of water.


A material that has little electrical conductivity and high resistance to electrical charges. Insulators include plastics and ceramics.

Kirchhoff’s Laws

Two laws that describe the flow of current in an electrical circuit. Kirchhoff's Laws imply that what goes into a circuit must come out.


A component in a circuit that converts electricity into light, heat, or mechanical motion. Loads include light bulbs, appliances, and machines.


The reasoning behind the functioning of something. Circuit logic comprises all the principles required to understand electrical circuitry.

neutral wire

The conductor that returns electricity to the source and completes the circuit. The neutral wire is usually covered with white insulation and is also called the grounded conductor.

overcurrent device

A component that protects circuits from excess current flow to prevent fires. Overcurrent devices include fuses and circuit breakers.

parallel circuit

An electrical system that has multiple routes for the flow of electricity. Parallel circuits allow loads to operate independently of one another.


A conductor that directs electricity in a circuit. The path is often copper wire.

protective devices

A circuit component that prevents damage, injury, and fire. Protective devices include grounding circuits and overcurrent devices.


R. The opposition to current flow. Resistance is measured in ohms (Ω).

schematic diagram

An electrical print that represents the components of a circuit with symbols. Schematic diagrams show the general layout of a circuit.

series circuit

An electrical system that has only one route for the flow of electricity. Series circuits are limited because, for any load to work, every load in the circuit must be switched on.


A component that provides electrical power to a circuit. The source is the origin of electricity, such as a battery or a power plant.


A connecting point in a circuit where a wire can be attached to connect a component. Terminals are either negative or positive.

valence electrons

An electron in the valence, or outermost, shell of an atom. Valence electrons influence resistance.

valence shells

The outermost orbit of electrons in an atom. Valence shells can have only eight electrons.


E. The electrical pressure or potential that pushes electrons through a conductor. Voltage is measured in volts (V) and is also called electromotive force.

voltage drop

A decrease in voltage along a conductor through which electricity flows. Voltage drop occurs when electricity passes through resistance.


P. The amount of electrical power required by a device to work properly. Wattage is measured in watts (W).


The result of electricity flowing through some type of resistance. Work appears in the form of heat, light, or motion.


The flow of electricity. Current strength is called amperage and is measured in amperes (A).