Question? Just ask us!
Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair
InspectAPedia ® Home
ELECTRICAL INSPECTION, DIAGNOSIS, REPAIR
ACCURACY vs PRECISION of MEASUREMENTS
AFCIs ARC FAULT CIRCUIT INTERRUPTERS
ALUMINUM SECs & WIRING
ALUMINUM WIRING HAZARDS & REPAIRS
AMPS & VOLTS DETERMINATION
AMPACITY - the LIMITING FACTOR
APPLIANCE EFFICIENCY RATINGS
BACKUP ELECTRICAL GENERATORS
BACK-WIRED ELECTRICAL DEVICES
BOOKSTORE - ELECTRICAL
BUILDING SAFETY HAZARDS GUIDE
Cadet & Encore Heater Recall
CIRCUIT BREAKER FAILURE
CIRCUIT BREAKER SIZE for A/C or HEAT PUMP
Classified CIRCUIT BREAKER WARNING
CORROSION in ELECTRICAL PANELS
CORROSION & MOISTURE SOURCES in PANELS
CUTLER HAMMER PANEL FIRE
DEFINITIONS of ELECTRICAL TERMS
DIRECTORY OF ELECTRICIANS
DMM Digital Multimeter HOW TO USE
ELECTRIC METERS & METER BASES
ELECTRIC MOTOR DIAGNOSTIC GUIDE
ELECTRIC MOTOR OVERLOAD RESET SWITCH
ELECTRIC PANEL AMPACITY
ELECTRIC PANEL INSPECTION
ELECTRIC PANEL MOISTURE
Electric Power Frequency Table
ELECTRICAL DISTRIBUTION PANELS
ELECTRICAL GROUND SYSTEM INSPECTION
ELECTRICAL SERVICE DROP
ELECTRICAL SERVICE ENTRY WIRING
EMF RF FIELD & FREQUENCY DEFINITIONS
FEDERAL PACIFIC FPE HAZARDS
FIRE SAFETY Checklist, CPSC
GFCI PROTECTION,Testing GFCIs AFCIs
HEATING COST FUEL & BTU Cost Table
HEAT TAPE USAGE GUIDE
Hertz - Definitions of KHz MHz GHz THz
KNOB & TUBE WIRING
LIGHTING, EXTERIOR GUIDE
LIGHTING, INTERIOR GUIDE
LIGHTNING PROTECTION SYSTEMS
LOW VOLTAGE BUILDING WIRING
LOW VOLTAGE TRANSFORMER TEST
MAIN ELECTRICAL DISCONNECT
MAIN DISCONNECT AMPACITY
MOISTURE SOURCES in PANELS
MURRAY SIEMENS Recall
PHOTOVOLTAIC POWER SYSTEMS
PUSHMATIC - BULLDOG PANELS
REMOTE ELECTRIC POWER, PHOTOVOLTAIC
RUST in ELECTRICAL PANELS
SAFETY for ELECTRICAL INSPECTORS
SE CABLE SIZES vs AMPS
SIEMENS MURRAY Recall
UNDERGROUND SERVICE LATERALS
VOLTS / AMPS MEASUREMENT EQUIP
VOLTAGE MEASUREMENT METHODS
WIND ENERGY SYSTEMS
WIND TURBINES & LIGHTNING
ZINSCO SYLVANIA ELECTRICAL PANELS
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".
Green links show where you are. © Copyright 2014 InspectApedia.com, All Rights Reserved.
Readers of this article should also see ELECTRICAL DEFINITIONS. 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. Critique and content suggestions are invited. Credit is given to content editors and contributors. Sketch at page top 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:
Where does Electricity in a Building Come From?
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 DEFINITIONSfor definitions of "Volts".
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.
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 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.
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 FAILURE for some examples of problem circuit breakers.
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.
Green link shows where you are in this article series.
Frequently Asked Questions (FAQs)
No FAQs have been posted for this page. Try the search box below or CONTACT US by email if you cannot find the answer you need at InspectApedia.
Questions & answers or comments about electricity & residential electrical circuit basic concepts.
Check the FAQs just above, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
Search the InspectApedia website
HTML Comment Box is loading comments...
Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.