Electrical Circuit Basics for Homeowners

ELECTRICAL CIRCUITS, SHORTS - CONTENTS: How does electricity get to a building? What is an electrical circuit? Definition of electrical short circuit?
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Home electrical wiring basics & definitions: this article answers basic questions about electricity and electrical wiring such as "What is an electrical circuit" and what is a "short circuit".

What is an Electrical Circuit?

Sketches at page top and at left are provided courtesy of Carson Dunlop Associates

[Click to enlarge any image]

At the top of this page we show a very simple electrical circuit. Electrical energy (here very roughly defined as a flow of electrons) moves through a circuit to perform work such as lighting a light or heating a room.

At left we show a common analogy using water flowing in pipes to help understand electrical circuits. Some people explain volts as similar to water pressure in a pipe, and amps as water current or total quantity flow. We discuss volts and amps below and in detail at this website.

A closed path of electron movement is required to put electrical energy into use.

This path is called a circuit. Sketch courtesy of Carson Dunlop Associates.

Every electric circuit has four basic parts:

Electrical Energy Source - a source of electrical energy, AC (alternating current, used in most homes) or DC (direct current)
Electrical conductors - electrical wires to carry electrical energy from its source to the point of use
Electrical Load - an electrical device that uses energy such as a light bulb, computer, or electric heater
Electrical Switches - controls to turn on or off electrical energy being supplied to an electrical load or device. In a home or other building electrical safety devices which protect the building from unsafe conditions such as a fire or electrical shock include circuit breakers or fuses which are really acting as an electrical "switch" to turn off electrical power should an unsafe condition occur.

Where does Electricity in a Building Come From?

Sketch of electrical service to a home (C) Carson Dunlop Associates

The real source electrical power at most buildings is an electric utility company which operates an electrical generator (a power station). The electric utility brings power from its power generators into a neighborhood where power is to be used by means of electrical transmission lines or power lines (big heavy wires).

For efficiency, electrical power is usually delivered into a neighborhood at very high voltage levels. In the neighborhood high voltage is converted by local power transformers (those big boxes or "cans" you see on some electric utility poles) to the lower voltage levels (240V or 120V) used in most buildings.

From the overhead (or in some communities buried) power transmission lines and transformer, a local power distribution wire (also overhead or buried) brings electrical power close to the building being served with power.

A service entry cable (SEC) (which is the responsibility of the building owner) connects the local power distribution wire to an electric meter mounted on or close to the building, and from the electrical meter, the service entry cable continues in to one or more main electrical panels on or inside the building. Sketch courtesy of Carson Dunlop Associates.

The electrical panel provides a place for mounting of fuses or circuit breakers which protect the building wiring from overheating and short circuits as a way to reduce fire risk. Inside of a building electrical power is distributed to various rooms through individual circuits, each of which is fed from the electrical panel(s).

However, for practical purposes, the source of electricity at an individual home or other building may be thought of as the circuit breaker panel or fuse box from which electrical power is distributed throughout a home or other building. Junction boxes and wall outlets may be thought of as secondary sources of electrical power since they convenient points at which a building occupant can connect electrical devices anywhere in a building.

See ELECTRICAL DEFINITIONS for definitions of "Volts", Watts, Amps, etc.

What are Electrical Conductors

Electrical Conductors are the wires that carry the electric energy to the point at which it will be used. Conductors offer little (but not zero) resistance to current flow because atoms in the metals they are made of have lots of free electrons and therefore can transport it efficiently.

What are the Definitions of Electrical Load, Amps, Watts

Sketch explaining electrical AMPS (C) Carson Dunlop Associates

The electrical load is the amount of electrical energy that any device (a light bulb, your toaster or your washing machine, for example) uses to perform some work. The electrical load (unlike the electrical conductors) offers resistance to current flow.

This resistance makes it possible for the device to convert electric energy to another form (heat, light, mechanical movement, etc.).

The load resistance determines how much current will flow in a circuit. Increase the resistance in the load and you automatically decrease the current flowing in the circuit.

If the voltage applied to a circuit is multiplied by the current in amperes, the result is in units called watts. The watt is a unit of power and indicates the rate at which the load is consuming power.

The electrical load on a circuit is measured in Amps, a measure of electrical current. See ELECTRICAL DEFINITIONS for detailed definitions such as "amps", "volts", and "watts". Sketch courtesy of Carson Dunlop Associates.

The Function of Electrical Switches

The fourth element in an electrical circuit is a means of controlling the energy. This is a device that can interrupt and restore current flow as desired by the user. Switches used in home electric systems control current flow by inserting a very high resistance (air gap) in the circuit to stop the current flow and by) removing the resistance (closing the air gap) to start current flowing again.

A basic principle of electrical wiring is that switches should always be wired into the hot (black or red) line leading directly to a device or outlet. When switches in the hot line are turned off, no hot line power is present in the load device. This greatly reduces the possibility of injury or damage resulting from accidental grounding.

What is an Electrical Short Circuit?

An electrical short circuit is a fault that occurs when a low resistance path exists between the hot lead and some grounded points.

When an electrical short circuit occurs, heavy current will flow in the circuit for as long as it takes for the circuit breaker to trip to OFF or for the fuse to blow.

Because a properly-working circuit breaker or fuse cuts off the current flow quickly, the circuit wiring will not have time to overheat to the point where fire may occur.

Sketch courtesy of Carson Dunlop Associates.

Safety Warning: an over-sized or improperly-installed fuse, and also some circuit breakers do not work reliably; a circuit breaker that is damaged by rust, corrosion, modification, or a circuit breaker which was poorly designed in the first place may not trip - resulting in a fire.

See FEDERAL PACIFIC FPE HAZARDS,

ZINSCO / SYLVANIA HAZARDS,

CIRCUIT BREAKER FAILURES for some examples of problem circuit breakers.

What is an Open Circuit?

An open circuit is a fault that cuts off current flow in a circuit. The break that causes the open circuit may be in the hot line, the neutral line, or the load. An open circuit appears to be off. The break that causes an open circuit may be quite small. Vibration or even changes in temperature may suddenly turn the circuit on again. When looking for the cause of an open circuit, be sure power is off at the source.

Watch out: Safety Warning: Do not attempt to work on your electrical wiring, switches, or outlets unless you are properly trained and equipped to do so. Electrical components in a building can easily cause an electrical shock, burn, or even death.

Even when a hot line switch is off, one terminal on the switch is still connected to the power source. Before doing any work on the switch, the power source must be turned off by setting a circuit breaker to OFF or removing a fuse.

See SAFETY for ELECTRICAL INSPECTORS

and ELECTRICAL WIRING BOOKS & GUIDES

What are the definitions of AC and DC Electrical Current?

The electrical energy that flows in circuits and operates loads can be generated in either of two different forms. One form is called alternating current (AC); the other form is called direct current (DC).

Alternating current is almost universally used for home electric power and is, therefore, the kind this article is primarily concerned with. In an AC circuit, the amount of voltage applied to the circuit is constantly changing from zero to a maximum and back to zero in one direction and then from zero to maximum and back to zero in the other direction. The maximum voltage is set by the generating plant.

Direct current is most commonly found in homes in the form of electrical energy stored in batteries. In a DC circuit, the amount of voltage and the direction of application are constant. The amount of voltage is determined by the type and size of battery. The direction of current flow is also constant and, as in AC circuits, the amount of current flow is determined by the load resistance.

DEFINITIONS of ELECTRICAL TERMS defines alternating current and direct current in more detail.

This website provides information about a variety of electrical hazards in buildings, with articles focused on the inspection, detection, and reporting of electrical hazards and on proper electrical repair methods for unsafe electrical conditions.

Continue reading at ELECTRICAL DEFINITIONS or select a topic from the More Reading links shown below.

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Technical Reviewers & References

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Elizabeth Sluder, Montross, VA, the original author of this article [before extensive editing], is a public school teacher who writes basic educational articles about a variety of building, construction, and other topics. Her husband, a licensed electrician, consults for her writing on electrical topics. Her articles appearing at the InspectAPedia ^TM Website have been edited, illustrated, and on occasion content has been added by the website author. These articles are © 2010 InspectAPedia copyright-protected, all rights reserved.
Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
John Cranor is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-747-7747 or by Email: johncranor@verizon.net
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides:
- Commercial Building Inspection Courses - protocol ASTM Standard E 2018-08 for Property Condition Assessments
- Home Inspection Education Courses including home study & live classes at eleven colleges & universities.
- Home Inspection Education Home Study Courses - ASHI@Home Training 10-course program.
  Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference Book, a reference & inspection report product for building owners & inspectors.
  Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
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Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.

Building inspection education & report writing systems from Carson, Dunlop & Associates Ltd

Recommended books on electrical inspection, electrical wiring, electrical problem diagnosis, and electrical repair can be found in the Electrical Books section of the InspectAPedia Bookstore. (courtesy of Amazon.com)
Rust and Corrosion in Electrical Panels, A Study and Report on Frequency and Cause for Electrical and Home Inspectors at Residential Electric Panels
"Electrical System Inspection Basics," Richard C. Wolcott, ASHI 8th Annual Education Conference, Boston 1985.
"Simplified Electrical Wiring," Sears, Roebuck and Co., 15705 (F5428) Rev. 4-77 1977 [Lots of sketches of older-type service panels.]
"How to plan and install electric wiring for homes, farms, garages, shops," Montgomery Ward Co., 83-850.
"Simplified Electrical Wiring," Sears, Roebuck and Co., 15705 (F5428) Rev. 4-77 1977 [Lots of sketches of older-type service panels.]
"Home Wiring Inspection," Roswell W. Ard, Rodale's New Shelter, July/August, 1985 p. 35-40.
"Evaluating Wiring in Older Minnesota Homes," Agricultural Extension Service, University of Minnesota, St. Paul, Minnesota 55108.
"Electrical Systems," A Training Manual for Home Inspectors, Alfred L. Alk, American Society of Home Inspectors (ASHI), 1987, available from ASHI. [DF NOTE: I do NOT recommend this obsolete publication, though it was cited in the original Journal article as it contains unsafe inaccuracies]
"Basic Housing Inspection," US DHEW, S352.75 U48, p.144, out of print, but is available in most state libraries.
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