Please enable JavaScript.
Coggle requires JavaScript to display documents.
Ch. 3 Electrical Theory and Practice - Coggle Diagram
Ch. 3
Electrical Theory and Practice
Electricity- What Is It?
Electricity at Work
A Simple Electrical Circuit
Basic Circuits
Power Calculations
Direct and Alternating Current
More Practical Information
Terms
electricity
A directed flow of electrons used to create kinetic energy.
atom
The smallest particle of a chemical element that retains the structural properties of that element.
proton
A fundamental particle in the structure of the nucleus of an atom; possesses a positive charge.
atomic theory
A generally accepted theory concerning the structure and composition of substances.
electron
A negatively charged fundamental particle that orbits around the nucleus of an atom.
neutron
A fundamental particle in the structure of the nucleus of an atom; possesses a neutral charge.
nucleus
The central part of an atom; composed of protons and neutrons.
valence shell
The outermost shell of orbiting electrons in the structure of an atom.
centrifugal force
Force that moves away from the center; for example, the circular motion of electrons spinning around an atom’s nucleus generates centrifugal force.
law of charges
The law: like charges repel and unlike charges attract.
free electron
An electron that has broken away from its “home” atom to float free.
electrical current
The flow or movement of electrons through a conductor.
ampere
The unit of measurement of electrical current.
conductor
Any material with many free electrons, such as copper, silver, gold, and aluminum.
potential
The difference in electrical charge between two bodies; measured in volts.
volt
The unit of measurement of electrical potential.
source
The origin of electrical potential, such as a battery or 120-volt wall outlet.
load
A device that converts electrical energy into another form of energy; a lamp converts electrical energy to light and heat; an electrical motor converts electricity to mechanical energy.
circuit
A conductive path through which electricity flows.
series circuit
A circuit in which all the electricity flows through every element of the circuit and the voltage is reduced by each load in the circuit.
Series Circuit In a series circuit all of the electricity flows through every element of the circuit
Parallel Circuit
In a parallel circuit only a portion of the electricity flows through each of the branches of the circuit.
Combination Circuit
Any electrical circuit that uses a switch to control a light is a working example of a combination circuit.
Typically, a circuit where the elements are in a parallel configuration and the controls are placed in series with the load.
fuse
A device to protect a circuit from an overload; has a soft metal strip that melts, breaking circuit continuity.
Ohm’s law
The law that states: As voltage increases, current increases; as resistance increases, current decreases.
circuit breaker
A device to protect a circuit from an overload; has a bimetal device that trips open when heated by excess current, breaking circuit continuity.
resistance
The opposition to electron flow within a conductor, measured in ohms; the amount of the resistance is dependent on the chemical makeup of the material through which the electricity is flowing.
The Power Formula
Another formula, which is a derivation of Ohm’s law, is more useful when dealing with the higher voltage encountered in stage lighting systems. It is called the power formula. This formula is used when it is necessary to determine how much power an electrical circuit will consume.
watt
The unit measurement of power required to do work.
resistance
The opposition to electron flow within a conductor, measured in ohms; the amount of the resistance is dependent on the chemical makeup of the material through which the electricity is flowing.
watt
The unit measurement of power required to do work.
Practical Applications of the Power Formula
The following problems illustrate how the power formula can be used to calculate the safe electrical limits of typical stage lighting situations.
insulator
Any material with few free electrons, such as rubber, paper, glass, and certain types of plastics.
Conductors
An electrical conductor is any material with an abundance of free electrons.
Insulators
a material with few free electrons. The lack of free electrons effectively prevents the flow of electricity through an insulator.
short circuit
A short circuit, or short, is created when a very large surge of current causes a portion of a conductor to explosively melt.
Grounding Safety
dictates that all electrical equipment be grounded.
pigtail
A lighting instrument’s electrical cable containing the hot, neutral, and ground wires used to connect the fixture to, typically, a stage circuit.
plug
The male portion of a connecting device.
Double Insulation
While stage lighting fixtures and other devices with metal housings have a grounding plug, some plug-in electrical hand tools—most frequently those with plastic cases—do not have a grounding pin on the plug. The information plate attached to these tools’ casings will probably carry the words “double insulated.” These tools don’t need grounding, because the casing that you hold is actually a second, or outer, casing. These two layers of plastic insulators (the casings) effectively isolate you from any potential short.
system ground
The grounding point—usually a metal rod driven into the earth outside the building or an underground metal water pipe—for an electrical system.
Electrical Power
Service Before beginning this discussion of electric power service, remember: These high-voltage distribution systems can kill; do not work on service panels or disconnect boxes unless you are a qualified electrician.
grounding plug
A plug that contains a ground in addition to its electrical service. The grounding pin is longer than the energized pins to complete the ground before the electrical service is connected.
service panel
Also called fuse box or panel box. Normally contains a primary power switch (called the main disconnect) for the area being served by the panel as well as circuit breakers or fuses for the individual circuits in that area.
disconnect box
Contains a main disconnect, but no circuit breakers for individual circuits. Used as a power source for, normally, 220-VAC equipment.
Overload
An overload occurs when the current flowing through a circuit is greater than the maximum current for which the system was designed.
Shorts
The difference between an overloaded circuit and a short circuit is really just a matter of degree.
Fuses and Circuit Breakers
Fuses and circuit breakers are devices designed to protect circuits from overloads.
amperage
A term denoting current flow within an electrical circuit
Current-Carrying Capacity of Cable
Electrical wires and cables, and the fuses and circuit breakers designed to protect them from overload, are designed to carry specific current loads.
Wiring of Control Devices
Control devices such as switches, dimmers, fuses, and circuit breakers are always placed on the hot leg—the black or red wire—of a circuit.
Input and Output Voltage
Input voltage is the voltage that is fed into a device (dimmer, amplifier, and so forth).