WHAT IS ELECTRICITY?

For thousands of years, the nature of electricity puzzled and mystified some of the most brilliant minds. It wasn’t until scientists such as Benjamin Franklin, André-Marie Ampère, Alessandro Volta, and Michael Faraday contributed to our understanding of electricity that we began to unlock its secrets.

Step by step, bit by bit, we built a plausible model of electricity that fits a mathematical model and provides a real-world explanation of this phenomenon. Even after we had a basic understanding of the key relationships and the fundamentals of electricity, early pioneers such as Joseph Swan, Thomas Edison, Nikola Tesla, and George Westinghouse still struggled to harness its power for daily use in a safe and efficient manner.

During that time — the late 1800s and early 1900s — one of the first practical uses of electricity was to illuminate common areas such as city streets and town squares. New York City quickly became entangled — quite literally — in electrical wires and electricity. Horrified bystanders witnessed the accidental electrocution of several workers in the naked light of day, and electricity gained a reputation for being both mysterious and dangerous.

Thomas Edison used the public’s fear to protect his economic interests by promoting DC power distribution over AC power distribution, while George Westinghouse grew his business on the strength of AC and its inherent advantages over DC. The ensuing controversy did nothing to ease the public’s apprehension about electricity, nor did it help to clarify its nature or promote its understanding.

To this day, many people have little understanding of the nature of electricity. Some of us still have difficulty answering the question, “What is electricity?” After all, we can’t see it, hear it, or smell it. And we certainly don’t want to taste it or feel it.

An electrician might understand how to hook up a power distribution system but may not fully understand exactly how electricity behaves. By studying the fundamentals of electricity we can better understand how to use electricity safely, effectively, and legally, and we can excel at our jobs in the entertainment industry.

Electrons in Motion
The short answer to the question “What is electricity?” is the transfer of energy through the motion of charge-carrying electrons. Lightning is an example of electricity and of electrons — lots and lots of them — in motion.

Electricians are generally concerned with a much more controlled situation where electricity flows through a given path in a safe, predictable manner, but the electricity we use in shows is no different than that in a lightning strike, a static discharge, or a flashlight battery. Each is an example of the transfer of energy through the motion of electrons.

But from where do these electrons come? The answer can be found in one of the most basic building blocks of the universe, the atom.

The Atom
The word “atom” comes from the Greek word atomos, meaning indivisible. It is the smallest particle that still retains the properties of the element from which it comes. If you took your side cutters and cut a small strand of copper from a cable, you would have billions of copper atoms. If you then cut that piece in half, and then in half again, and over and over until you got down to the single piece that still looked and acted like copper, then you would have an atom.

But you would have to be pretty good with those cutters. One atom of copper is approximately 10–12 meters in diameter. Put another way, it takes about 254 billion copper atoms placed side by side to make 1 inch. Good luck with that.

Atoms are literally everywhere. They make up the air you breathe, the water you drink, the clothes you wear, and the food you eat. They are the building blocks of the universe.

Subatomic Particles
Despite what the early Greeks thought, atoms can be divided. It turns out that they are made up of even smaller subatomic particles called electrons, neutrons, and protons. These subatomic particles are very important to the understanding of electricity. Electrons carry a negative charge, protons have a positive charge, and neutrons have no charge at all.

It’s the interaction of these charges that causes the phenomenon we call electricity. An atom has a nucleus that is made up of a number of protons and neutrons bound by nuclear forces. The nucleus is surrounded by an electron cloud made up of electrons in orbit about the nucleus. The specific number of neutrons, protons, and electrons depends on the element. For example, copper atoms normally have 29 protons, 35 neutrons, and 29 electrons.

Electrostatic Charges
The vast majority of atoms are electrically neutral because the number of negatively charged electrons is balanced by the number of positively charged protons, creating a net charge of zero. In a copper atom, for example, the number of positively charged protons, 29, matches the number of negatively charged electrons; thus the charges cancel each other, resulting in a net charge of zero.

It’s important to understand the electrostatic attraction between charges: opposite charges attract and like charges repel. For example, two protons will repel each other and two electrons will repel each other, but a proton will attract an electron.

The force of attraction or repulsion depends on two factors: the magnitude of the individual charges and the proximity of the charges. The magnitude of the individual charges, whether they are attracting or repelling, directly affects how strongly the force of attraction or repulsion will be.

Since a single proton carries a fixed positive charge and a single electron carries a fixed negative charge, the magnitude of an individual charge depends on the number of protons or electrons involved.

An atom with two protons, for example, will have twice the force of attraction to an electron as will an atom with a single proton. The force of attraction also varies exponentially as the inverse of the distance between the charges. If the distance between the two charges is doubled, then the force of attraction or repulsion will decrease by a factor of four; if the distance is halved, then the force will increase by a factor of four.

Force = k(q1⋅q2 )÷ d^2,

where force is the magnitude or strength of the force exerted, k is a constant, q1 and q2 are charges on the particles, and d is the distance between them.

This relationship shows how the force of attraction or repulsion depends on the magnitude of the two charges, q1 and q2, and the distance of separation. This law of attraction or repulsion of electrostatic charges is called Coulomb’s law after Charles-Augustin de Coulomb, a French physicist who discovered the relationship.

Since opposite charges attract and like charges repel, the electrons in an electron cloud are held in orbit about the nucleus of an atom by their electrostatic attraction to the protons. However, some of the electrons are orbiting so far away from the nucleus that the bond is relatively weak.

To give you an idea of the relative distances involved, suppose we could scale our copper atom so that the nucleus was the size of a golf ball. Then you would have to go about 2.41 kilometers (a mile and a half) before you would find the outermost electrons.

If another external force, like a voltage, is applied, the electrons in the outer orbit can sometimes be pulled away from their associated atom. When that happens, the atom becomes “ionized.” The free electrons that are pulled away from the nucleus of an atom can either “drift” toward the force of attraction — from the applied voltage — or they can reassociate with another atom by “falling” into its orbit.

An ionized atom that is missing one or more electrons is known as a “hole” in electronics parlance, and it carries a net positive charge. Every electron carries the same quantity of charge. The coulomb (C) is the standard unit of electric charge as defined by the International System of Units (abbreviated SI for the French Système International d’Unitès).

It is derived from the amount of charge carried by 1 ampere of current in 1 second. It turns out that a single electron carries a charge of –1.6022 × 10−19 coulombs (–0.00000000000000000016022 C). Put another way, it takes 6.241506 × 10^18 electrons (6,241,506,000,000,000,000 electrons) to make 1 coulomb of charge.

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ELECTRICITY KILLS, BUT IT DOESN’T HAVE TO – IT IS NOT SUPPOSED TO

Make no mistake about it: electricity can kill. It takes as little as 60 milliamps (a milliamp is one thousandth of an amp) passing through the heart to make it fibrillate and stop, causing death within a few minutes. And that’s not the only way it can kill you.

Even if the current doesn’t pass directly through your heart, it can contract the muscles in your chest and asphyxiate you; it can burn you internally; it can damage your brain so much that you can stop breathing.

Fortunately, our skin, which happens to be the largest human organ, provides a relatively high amount of resistance when it is dry. It helps protect us as long as we use common sense, like wearing rubber soled boots, wearing gloves, and standing on an insulating carpet or rug. On the other hand, risky behavior like standing barefoot on a concrete floor in a puddle of water is asking for trouble.

But the vast majority of fatal accidents involving electricity are not caused by electric shock. They are instead a result of the intense heat and the blast caused by an electrical fault. If you have ever seen video of an arc flash then you understand the potential danger involving high voltage.

When switchgear malfunctions or another problem causes a dead short it can create a huge ball of fire with intense heat that engulfs the immediate surroundings and then dissipates in a fraction of a second. In a closed room like a substation or electrical room it can be a deadly situation.

If you understand how electricity behaves and respect its potential for danger, then you can minimize the dangers and work in relative safety.

I always wear a pair of gloves and rubber-soled, steel-toe boots when I’m working, not only to protect my hands and feet but also for their insulation value. Most venues do not carpet the areas in which the electrical switchgear is located, so some electricians carry their own rubber matt or carpet to stand on when they are working around live gear or high voltage.

These are just a few steps you can take to protect yourself and keep yourself out of harm’s way. But you first have to understand the dangers before you can take steps to protect yourself and others from them.

There have been far more fatal rigging accidents and pyro accidents in live event production over the past 20 years than there have been fatal electrical accidents. This might be attributed to awareness, education, the constant concern for safety, and perhaps some degree of luck. Never let your guard down.

WHY IS A BIRD NOT ELECTROCUTED WHEN IN A HIGH TENSION LINE/ WIRE? - ZERO VOLT REFERENCE GROUND/ EARTH IN ELECTRICITY BASIC INFORMATION


The earth is the zero-volt reference for power distribution systems. In North America and other countries it’s called ground, and in Europe, Australia, and other countries it is called earth.

Voltage is only meaningful when it is referenced to another point. When a bird lands on a high-voltage wire, it doesn’t get electrocuted because it does not complete a circuit to a zero-voltage reference or to another point in the circuit with a different potential.

If the bird happens to straddle the gap between the high-voltage line and the metal transmission tower or another line, sparks will fly. That’s because the voltage needs a reference.

We typically take zero volts as the absolute reference for voltage measurement. The exception is when we want to know the voltage drop across a particular component such as a resistor or a transistor.

But normally, for example, a 12-volt DC power supply means that the positive terminal is 12 volts higher than a zero-volt reference. When we say a voltage rail is at 5 volts, that implies that is has been referenced against zero volts and it is 5 volts below the reference.

Without some reference point with which to compare, voltage measurements are meaningless. But what is our zero-volt reference based on?

The zero-volt reference is the earth, the largest current sink available to us. The earth is actually a conductor, although various parts of it are better conductors than others. Soil composition, moisture content, mineral content, and other factors influence the impedance of the soil at any given location.

But the earth is a very large current sink, and as long as we can establish good contact with it, we have a good zero-volt reference. Every power distribution system has at least one point that is electrically connected to the earth, usually by means of a copper rod driven into the ground.

We call this zero-volt reference ground in North America, earth in Europe and Australia.

STATIC ELECTRICITY AND AIRPLANE BASIC INFORMATION AND TUTORIALS


As mentioned previously, the effects of static electricity are of considerable importance in the design, operation, and maintenance of aircraft. This is particularly true because modern airplanes are equipped with radio and other electronic equipment.

The pop and crackle of static is familiar to everyone who has listened to a radio receiver when static conditions are prevalent. An airplane in flight picks up static charges because of contact with rain, snow, clouds, dust, and other particles in the air. The charges thus produced in the aircraft structure result in precipitation static (p static).

The charges flow about the metal structure of the airplane as they tend to equalize, and if any part of the airplane is partially insulated from another part, the static electricity causes minute sparks as it jumps across the insulated joints. Every spark causes p-static noise in the radio communication equipment and also causes disturbances in other electronic systems.

For this reason, the parts of an airplane are bonded so that electric charges may move throughout the airplane structure without causing sparks. Bonding the parts of an airplane simply means establishing a good electrical contact between them.

Movable parts, such as ailerons, flaps, and rudders, are connected to the main structure of the airplane with flexible woven-metal leads called bonding braid. The shielding of electronic devices and wiring is also necessary to help eliminate the effects of p static on electrical equipment in the airplane.

Shields consist of metal coverings which intercept undesirable waves and prevent them from affecting sensitive electronic systems. An airplane in flight often accumulates very high electric charges, not only from precipitation, but also from the high-velocity jet-engine exhaust as it flows through the tailpipe.

When the airplane charge becomes sufficiently high, electrons will be discharged into the surrounding air from sharp or pointed sections of the airplane. The level at which this begins is called the corona threshold. Corona discharge is often visible at night, emanating from wing tips, tail sections, and other sharply pointed sections of an airplane.

The visible discharge is often called "St. Elmo's fire." Corona discharge occurs as short pulses at very high frequencies, thus producing energy fields which couple with radio antenna fields to cause severe interference. The solution to the problem is to cause the charge on the airplane to be partially dissipated in a controlled manner so that the energy level of the discharge will be reduced and the effects of the discharge will cause a minimum of interference.

In the past, static-discharge wicks were used to reduce the charge on the airplane.  Because of the high speeds of modern jet aircraft and the fact that they are powered by jet engines which tend to increase static charges, it became necessary to develop static-discharge devices more effective than the wicks formerly used.

A new type of discharger has proved most successful. It is called a Null Field Discharger and is manufactured by Granger Associates. These dischargers are mounted at the trailing edges of outer ailerons, vertical stabilizers, and other points where high discharges tend to occur.

They produce a discharge field which has minimum coupling with radio antennas. Static charges must be taken into consideration when an airplane is being refueled. Gasoline or jet fuel flowing through the hose into the airplane will  usually cause a static charge to develop at the nozzle of the hose unless a means is provided whereby the charge may bleed off.

If the nozzle of the fuel hose should become sufficiently charged, a spark could occur and cause a disastrous fire. To prevent such an occurrence, the nozzle of the fuel hose is connected electrically to the aircraft by means of a grounding cable or other device, and the aircraft is grounded to the earth. In this way, the fuel nozzle and the aircraft are kept neutral with the earth, and no charges can develop sufficient to create a spark.

SENSITIVITY OF COILS USED IN MULTIMETER BASIC INFORMATION


Some meters must be constructed with a high degree of sensitivity. The sensitivity is determined by the amount of current required to produce a full-scale deflection of the indicating needle. Very sensitive movements may require as little as 0.00005 amp to produce a full-scale deflection.

This value is commonly called 20,000 ohms per volt, because it requires 20,000 ohms to limit the current to 0.00005 amp when an emf of 1 volt is applied. Movements having a sensitivity of 1,000 ohms per volt are commonly used by electricians when the power consumed by the instrument is of no consequence.

In electronic work, where very small currents and voltages must be measured, instruments of very high sensitivity are required. Electronic measuring instruments, such as the vacuum-tube voltmeter (vtvm) or the solidstate voltmeter (ssvm), are normally used for the measurement of currents and voltages in electronic circuits.

These instruments are designed to isolate the measuring circuit from the circuit being measured, hence very little loading is applied to the circuit being measured. To understand the importance of sensitivity in an instrument for testing certain values where current flow is very small, it is well to consider a specific example.

A 100-volt battery is connected across two resistors in series. Each resistor has a value of 100,000 ohms, making the total resistance of the circuit 200,000 ohms. Since the two resistors are equal in value, it is obvious that the voltage across each will be 50 volts.

If we wish to test this voltage by means of a voltmeter which has a 1,000-ohms-per-volt sensitivity, we will discover that a large error is introduced into the reading.

Assume that the voltmeter has a range of 100 volts and that it is connected across R, between the points A and B. Since the voltmeter has a sensitivity of 1,000 ohms per volt, its total resistance will be 100,000 ohms. When this is connected in parallel with R,, the resistance of the parallel combination becomes 50,000 ohms, and the total resistance of the circuit is now 150,000 instead of 200,000 ohms.

With the resistants;, between A and B 50,000 ohms and the resistance between B and C 100,000 ohms, the voltage drop will be 33.3 volts between A and B and 66.7 volts between B and C. It is apparent then that the voltmeter used would not be satisfactory for this test.

If we connect a voltmeter with 20,000 ohms-pervolt sensitivity across R,, we will obtain a much more accurate indication of the operating voltage. i The voltmeter has an internal resistance of 2,000.000 I ohms, and this resistance, combined in parallel with R,, will produce a resistance of 95,238 ohms.

This resistance in series with the 100,000 ohms of R, will produce a voltage drop of approximately 48.7 volts across R1 and 51.3 volts across R2. The reading of the voltmeter is then 48.7 volts, which is probably as accurate as necessary for normal purposes.