Introduction to Circuits 201

A

Amperes. A unit of measurement that indicates the amount of current flowing in a circuit. 1 A is equal to 1 V divided by 1 Ω.

Alternating current

AC. Electricity that reverses direction at regularly recurring intervals of time. Alternating current supplied by the U.S. electrical grid switches direction 120 times per second, or at 60 hertz (Hz).

Amperage

A measurement of the amount of current flowing in a circuit. Amperage is measured in amperes (A).

Amperes

A. A unit of measurement that indicates the amount of current flowing in a circuit. Amperes are also called amps.

Amps

A. A unit of measurement that indicates the amount of current flowing in a circuit. Amps are also called amperes.

Batteries

A device that converts 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 in circuit breakers to detect elevated temperatures.

Chassis

The frame or shell of a machine. The chassis of a machine is used for grounding when earth grounding is impractical.

Chassis ground

A grounding system that diverts stray currents to a machine's frame and then back to the source. Chassis grounds are used when grounding a circuit to the earth is not practical.

Chemical energy

The energy created by a reaction between two or more substances. Chemical energy is stored in batteries.

Circuit

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

Circuit breakers

An overcurrent device that automatically trips a switch to open a circuit. Circuit breakers operate using a bimetallic strip or an electromagnet.

Circuit loop

A closed path within a circuit that passes through one or more components and then returns to its starting point. A circuit loop cannot pass through any junction more than once.

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 parallel circuit rules for sections connected in parallel.

Conductor

A material that allows free movement of charged particles and therefore allows easy flow of electricity. Conductors are typically metals.

Contacts

A conductive metal part used in pairs that opens or closes a circuit by separating from or touching a matching part. Contacts close to allow current flow and open to prevent it.

Control

A component in a circuit that stops, starts, or adjusts the flow of electricity. Common controls include switches and resistors.

Copper

A nonferrous metal that is very ductile, thermally and electrically conductive, and corrosion resistant. Copper is often used to make electrical wiring.

Current

I. The flow of electricity. Current strength is measured in amperes (A).

Direct current

DC. Electricity that travels in one direction. Direct current does not reverse the direction of flow.

Earth ground

A grounding system that directs stray currents into the earth's soil. Earth grounding is used for electrical systems in most buildings.

Electric shock

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

Electrical capacity

The maximum amount of electricity that a circuit can supply. Exceeding the electrical capacity of a circuit can damage equipment and cause safety hazards.

Electrical energy

A form of energy created by the movement of charged particles. Electrical energy, also called electricity, can be converted into light, heat, or motion.

Electrical fires

A fire involving energized electrical equipment. Electrical fires are very dangerous because they put employees at risk of electric shock in addition to burns.

Electricity

A form of energy created by the movement of charged particles. Electricity, also called electrical energy, can be converted into light, heat, or motion.

Electromagnet

A magnet that gains an attractive force only when current passes through it. Electromagnets in circuit breakers activate in response to overcurrent.

Electromotive force

E. The electrical pressure or potential that forces current through a conductor. Electromotive force is also called voltage.

Fuses

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

Generators

A device that converts mechanical energy into electrical energy. Generators naturally produce AC but can be modified to output DC.

ground

A source of zero electrical potential, such as the earth or another large conducting body. A ground absorbs electric currents.

Grounding

A means of providing a safe alternate path for electricity in case it strays from its intended path. Grounding directs stray currents to an electrically neutral body.

Grounding conductors

A wire that provides a low-resistance path to ground for stray currents. Grounding conductors often have green with a yellow stripe.

Grounding electrode

A conductor buried in the ground that directs stray electrical currents into the earth. Grounding electrodes are often metal rods or pipes.

Insulator

A material that has little electrical conductivity and high resistance to electrical charges. Common insulators include plastics, rubber, and ceramics.

Junction

A point in a circuit where three or more conductors connect together. Junctions are represented on diagrams by a dot covering the place where conductors meet.

Kirchhoff's Current Law

A rule describing the behavior of current in a circuit. Kirchhoff's Current Law states that the current flowing into a junction is equal to the current flowing out of it.

Kirchhoff's Laws

A set of rules describing the behavior of current and voltage in a circuit. Kirchhoff's Laws are essential for designing, analyzing, and troubleshooting circuits.

Kirchhoff's Voltage Law

A rule describing the behavior of voltage in a circuit. Kirchhoff's Voltage Law states that the voltage drop across a circuit loop is equal to the voltage supplied by the source.

Lathe

A machine tool used to create cylindrical parts. Lathes hold a cylindrical workpiece on one or both ends while moving a single-point cutting tool along the surface of the rotating part.

Load

A component in a circuit that converts electricity into other forms of energy such as thermal or mechanical energy. Common loads include lightbulbs, appliances, and machines.

loop

A complete or closed path that returns to its start point. Closed loops are required for electrical circuits to function.

Magnetic field

The area in and around a magnet in which a magnetic force exists. Magnetic fields exhibit the powers of attraction and repulsion.

Mechanical energy

A form of energy that is produced by force or motion. Mechanical energy can be converted to electrical energy using a generator.

Melting point

The temperature at which a material changes from a solid to a liquid. Melting points vary based on the properties of different materials.

Motor

A machine that converts one form of energy into another. Motors may transform electrical energy into mechanical energy.

Ohms

Ω. A unit of measurement for electrical resistance. One ohm is equal to one amp divided by one volt.

Ohm's law

The equation that describes the relationships between voltage, amperage, and resistance. Ohm's Law states that one volt equals one amp times one ohm.

Overcurrent

Excess current flowing through a circuit. Overcurrent can damage circuit components, potentially causing fires and electric shocks.

Overcurrent device

A component that protects circuits from excess current flow. 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.

Passive resistor

A stationary circuit control device that limits current flow in a circuit. A passive resistor can be combined with a moving contact to create a variable resistor.

Path

A conductor that directs electricity in a circuit. Paths are often made from copper wire.

Pictorial diagram

An electrical print that shows the external appearance of each component in a circuit. A pictorial diagram may use photos or illustrations.

Plastic

A lightweight polymer material that has high corrosion resistance, a high strength-to-weight ratio, and a low melting point. Plastic is often used as insulation around electrical wires.

Polarity

Having a positive or negative charge. Polarity determines the direction in which current flows.

Poles

An input contact in an electrical switch. Poles can move to connect to one or more throws.

Potential difference

The amount of work required to move charged particles between two points. Potential difference decreases after each load in a circuit loop.

Power

P. The rate at which a device converts electrical energy into another form, such as heat or light. Power is measured in watts (W).

Resistance

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

Resistor

A device used in circuits to limit current flow. Resistors can be used to prevent overheating.

Rubber

An elastic polymer made from natural or artificial latex. Some rubbers can be used as insulating materials.

Schematic diagram

An electrical print that represents the components of a circuit with symbols. A schematic diagram shows the electrical relationships in a circuit but not its physical layout.

Selector switch

A control device that moves to open or close multiple circuits. Selector switches can have multiple poles and throws.

Series circuit

An electrical system that has only one route for the flow of electricity. Series circuits are simple to build but will stop functioning if any component breaks.

Silver

A soft, gray-white metal that has the highest electrical conductivity of all metals. Silver is often used as a conductor in electronic devices.

Sine

In a right triangle, the ratio of the side opposite an angle to the longest side of the triangle. When plotted on a graph, sine equations look like a sideways letter 'S.'

Sine waves

A curved waveform that resembles a sideways letter 'S.' Sine waves are the most common type of AC waveform.

Source

A component that provides electrical energy to a circuit. Common sources include batteries and generators.

switch

A control device that opens and closes contacts in a circuit. Switches can operate manually or automatically.

Terminal

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

Throws

An output contact in an electrical switch. Throws each connect to a separate circuit.

Utility companies

An entity recognized by governmental law that installs, operates, and maintains electrical distribution systems. Utility companies supply homes and businesses with AC electricity.

V

Volts. A unit of measurement for the electrical force or pressure that causes current to flow in a circuit. 1 V is equal to 1 A multiplied by 1 Ω.

Variable resistor

A moving circuit control device that can adjust the amount of current or voltage in a circuit. Variable resistors include rheostats and potentiometers.

variables

Factors in electricity that change according to the situation. Variables in electrical work include amperage, voltage, and resistance.

Voltage

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

Voltage drop

A decrease in voltage that occurs as electricity passes through resistance. The total voltage drop in any circuit loop is equal to the total voltage supplied by the source.

Voltage spikes

A sharp, sudden increase in voltage in a circuit that can damage equipment. Voltage spikes are caused by malfunctions or changing load conditions.

Volts

V. A unit of measurement for the electrical force or pressure that causes current to flow in a circuit. One volt is equal to one amp multiplied by one ohm.

W

Watts. A unit of measurement for the power produced or used by a circuit. 1 W is equal to 1 V multiplied by 1 A.

Watts

W. A unit of measurement for the power produced or used by a circuit. One watt is equal to one volt multiplied by one amp.

Watt's Law

The universal principle that describes the relationship between wattage, amperage, and voltage. Watt's Law states that wattage is equal to amperage multiplied by voltage.

Wiring diagram

An electrical print that shows the physical locations of all electrical components in a circuit. A wiring diagram uses the same symbols as a schematic diagram.