The Basics of Practical Electricity

I attended a vocational high school and majored in electrical work. In my second year, I studied interior house wiring and wired up simple projects. For example, I would wire up a switch and light fixture in a wooden booth. Then the instructor would enter the booth and grade my work. In my third year the instructor took the class out on jobs. My first assignment was to install an outlet in a bedroom. The wall was the common wall between the bedroom and the kitchen. The instructor told me to drill a tiny hole in the bedroom wall and insert a stiff wire in that hole. Then wiggle the wire around to ensure that nothing was blocking the installation of the outlet. He did tell me not to drill through the kitchen wall. So I followed his instructions and stuck a stiff wire in the hole and wiggled it around. I heard a lot of noise. The noise caught the attention of the owner. She opened her wooden cabinet to find one end of a stiff wire flying around hitting all her pots and pans! During my fourth year I studied the National Electrical Code.

This article is a tutorial on the basics of electricity. The first section covers basic electrical theory without the complex math formulas. The second section covers safety issues and the third section covers simple house wiring repairs.

Electricity is energy. The classical analogy used to gain an understanding of electricity is the water pump. The water pump applies pressure to the water which results in the flow of water. Electrical pressure results in the flow of electricity. Electrical pressure is known as electromotive force and it's unit of measurement is the volt. EMF is the abbreviation for electromotive force. The flow of electricity is called current. Current is measured in amperes. Any material that opposes the flow of electricity is said to have resistance. In the sink drain, resistance is provided by food particles and grease stuck in the trap. In electricity, resistance is provided by the components in the circuit, The ohm is the unit of resistance.

In order to understand how electricity flows, we have to understand the atom. The atom consists of protons and neutrons in it's nucleus and electrons circling the nucleus. Each proton has a positive charge and each electron has a negative charge. A little electrical pressure causes some electrons to break away from the atom. That electrons that break free of the atom are called free electrons. The medium of electric current is the free electron. Materials with lots of free electrons are conductors. Materials with a lack of free electrons offer resistance to the flow of electricity. Materials with no free electrons are insulators.

Another words, Any material that does not allow electrical current to flow through it is called an insulator. An insulator has an extremely high resistance. Air is an excellent insulator. Rubber is also an insulator. Any material that allows electrical current flow is called a conductor. Copper and aluminum are good conductors. A conductor does not have an extremely high resistance.

Let's return to the theory of the atom for a moment. It was stated that current is the result of free electrons moving through the conductor. The electron has a negative charge and therefore, would be attracted to the positive terminal of the electrical source. This indicates that current actually flows from negative to positive. However, the conventional assumption was that current flows from positive to negative. If you study electrical analysis, you will learn that it does not matter which way you assume the current is flowing. For this tutorial, we will assume that current flows from positive to negative.

Ohm's law states that one volt of electricity will cause one ampere of current to flow through one ohm of resistance.

EMF = current X resistance

volts = amperes X ohms

The power is the heat dissipated. A watt is a unit of power.
Power = EMF X current

watts = volts X amperes

Equipment and appliance manufacturers provide the power and voltage ratings on a sticker or plate on the side or back of the equipment. 100 W means 100 watts. Likewise, 100 V means 100 volts. Some equipment manufacturers list the amount of current the equipment requires. 10 A means 10 amperes. The abbreviation for the word ampere is amp. Fuses are also rated in amperes. You may want to look at the electrical ratings on a new air conditioner to determine if it has to be connected to a separate fuse or circuit breaker. The rating also indicates alternating current or direct current. A battery delivers direct current. The current is always flowing in the same direction. The abbreviation for direct current is DC. Your electrical outlet delivers alternating current. The direction and magnitude of the current are constantly changing. The abbreviation for alternating current is AC. An outlet delivers 110 volts alternating current or 110 vac.

The current flow through some electrical equipment is very low. The term milliampere means 0.001 amperes. The abbreviation for milliamperes is ma.

The prefix kilo means a thousand. A kilowatt is a thousand watts. If you look at your electric bill, you will find the term kilowatt-hours. The abbreviation for kilowatt-hour is kwh. Kilowatt-hours equal the number of kilowatts multiplied by the number of hours those kilowatts were dissipated. For example, You have nine 100 watt bulbs in nine lamps and all lamps are turned on for two hours. The total wattage is 900 watts.

kilowatts = watts/1000
kilowatt-hours = kilowatts X hours

900 watts/1000 watts per kilowatt = 0.9 kilowatts.

0.9 kilowatts X 2 hours = 1.8 kilowatt-hours.

In general terms, the higher the power rating of an appliance, the higher the electric bill. My old air conditioner was rated at 1400 watts.

kilowatt-hours = kilowatts X hours
Kilowatts = watts/1000 watts per kilowatt.
1400 watts/1000 kilowatts per watt = 1.4 kilowatts.

Let's assume the air conditioner compressor is constantly on. I would be using 1.4 kilowatt-hours per hour the air conditioner was running.
The electric stove probably has the highest power rating. The refrigerator also has a high power rating.

Wire is available in many sizes. The sizes are denoted by numbers. The smaller the number the thicker the wire and the more current it could handle. The two popular sizes for house wiring is AWG #12 and AWG # 14 copper wire. AWG stands for American Wire Gauge. If a wire cannot handle the current passing through it, the wire will get hot. It is very important to use the correct size wire, especially when adding light fixtures or outlets in your house. Assume that a person uses AWG # 16 wire for a light fixture. When the light fixture is turned on, the wire gets very hot and the insulation starts melting. The fuse is rated for 15 amps and is not heat sensitive. If the light fixture is left on, a fire may start without the fuse blowing. Even if a fire does not start, the strong odor of melting wire insulation is not healthy. Because the wires are not visible, the resident may not realize the danger.
In order for current to flow in a circuit powered by a battery, there must be a conduction path from the plus terminal of the battery to the minus terminal of that battery. The air is not part of that path because the air has an extremely high resistance and will not allow current flow. A conduction path means a path through electrical conductors. Any electrical setup with a source of electricity and electrical components is called a circuit.

Let's examine a battery circuit. One wire is connected from the plus terminal of the battery to one side of a switch. Another wire is connected from the other side of the switch to the light bulb holder. The third wire is connected from the other terminal on the light bulb holder to the minus side of the battery. The light bulb offers resistance to the flow of current and dissipates power. The switch allows the user to make or break the electrical path to the light bulb. When the switch is open, no current flows through the circuit and the light bulb does not illuminate. When the switch is closed, current flows through the circuit and the light bulb illuminates.

You probably have often heard the term short. Ideally, a short means no resistance. Any two wires that have no resistance between them are shorted together. In our battery circuit, a short circuit exists if there is no resistance between the wire connected to the plus terminal of the battery and the wire connected to the minus terminal of the battery. Another words, the resistance of a short circuit is zero ohms. However, the wire does have a very small resistance.

Let's apply Ohm's Law to the definition of a short circuit. Assume that the voltage is ten volts and the resistance is zero ohms. According to Ohms Law,

10 volts = ? amps X total wire resistance.

In this case, when the voltage is divided by the tiny resistance of the wire, the result is an extremely large current.

One handy gadget to have around when you are working on electrical circuits is the multimeter. Most multimeters can read voltage, current or resistance. I recommend the digital multimeter. To read the voltage between a hot wire and ground, plug the multimeter leads into the plus and minus connectors on the multimeter. The red lead should be the plus lead and the black lead should be the minus lead. Set the multimeter range for the range that includes the voltage you expect to read. Connect the other end of the minus lead to ground and the other end of the plus lead to the wire whose voltage you want to measure. If you want to measure the resistance between two terminals, first ensure that power is turned off and no voltage exists between the two terminals. With the leads connected to the plus and minus connectors on the multimeter, set the scale to the appropriate ohms scale. Connect the other end of the leads to the two terminals and read the display.

Before talking about electrical house wiring, let's talk about safety issues. If at all possible, don't work on a live circuit. If you are replacing an electrical outlet or fixture, always pull the fuse for that circuit, You pull the fuse. Don't trust somebody else to pull the fuse. Take the fuse with you to ensure that no one puts the fuse back in while you are working. If you want to work on a light fixture, turn the light on, then pull the fuse. If the light extinguishes, you have the correct fuse. Always use a wooden ladder if you are working on a ceiling fixture. Never use a metal ladder. Remember that a very small current can kill you. Always be aware of where you are standing. Don't stand on a flooded cellar cement floor to work on electrical equipment. A simple experiment will demonstrate my point.

The explanation of this experiment is simple enough so you don't need to build the circuit. You can read the instructions and visualize the circuit. If you want to build the circuit, you will need wire strippers, wire cutters, a screwdriver, long nose pliers, AWG 16 wire, a battery, a battery holder, a glass of water, salt, a bulb and a bulb holder. You will also need small alligator clips and a switch. You could disassemble a flash light to obtain bulb, bulb holder and battery. You could buy a battery holder for your size battery at any store that carries hobbyist supplies.

Connect a wire from the plus terminal of a battery to a glass of water. Make sure that the bare tip of the wire is in the water. Connect a second wire to a light bulb holder. Use the alligator clips to secure the connections to the bulb holder. Ensure that the other end of the wire is in the glass of water but is not touching the wire from the battery. Connect the third wire from the light bulb holder to the minus terminal of the battery. Note that the light bulb is not illuminated. Now pour some salt into the glass of water. Note that the light bulb illuminates. Pure water does not conduct but if you stand in water, your body provides the path to ground in two ways. Your body contributes salt to the water and your body conducts electricity. Cement also conducts electricity.

Equipment ground is another area where caution must be exercised. Consider an electric drill plugged into an outlet that does not have an equipment ground. In this case the electric drill has an internal short causing the metal case of the drill to be at 110 vac. The user of the drill climbs a ladder in the cellar and balances himself by holding on to a water pipe. As soon as the user starts drilling, the user receives an electrical shock. The reason is that the case of the drill is at 110 vac and the water pipe is ground!

Here is another case: A user has a piece of equipment with a metal case. The equipment ground is isolated via a broken prong on the power plug. It is a cold dry day. The user accidentally touches the piece of equipment discharging a static charge into the equipment. The equipment is damaged and no longer works correctly.

In your house, you will find two types of wire: solid and stranded. You can identify stranded wire because when you strip the insulation off the wire, you will find many strands of small wire. If it is solid wire, you will find one solid wire.

The outlet in your wall is mounted in a rectangular utility box. The lighting fixture may be mounted in an octagonal box. Inside the box, you should find information about the maximum wattage bulb to use in the lighting fixture. I was taught that when connecting an electrical cable to a box, always leave a service loop in the cable and make each wire inside the box six inches long. If, during the next service, the wires are not long enough, the electrician could use the service loop to obtain more wire.

The equipment ground wire may be bare or it may be a green wire.

If you want to connect a wire to a screw, use wire stripers to strip some insulation off the wire. Some people use wire cutters or a knife to strip insulation off a wire, but this method often leaves a tiny groove in the wire which makes the wire prone to breaking. Loosen the screw and wrap the wire 270 degrees around the screw in the same direction that you tighten the screw [clockwise]. Make sure the insulated portion of the wire ends at the screw. The bare portion of the wire should be under the screw. No other bare wire should be showing. Cut the end of the bare wire so that no bare wire will extend from the screw and tighten the screw. Repeat this process for each wire you connect.

In electrical wiring, two wires are connected together by making a pigtail splice. To make a pigtail splice with two solid wires, strip about one inch of insulation from each wire. Hold the wires so that they cross each other where the insulated portion ends and the bare portion begins. Grab the wire ends and twist them together. The wire should be twisted together tight enough so that there is no stretch of straight bare wire. Twist a wire cap onto the pigtail splice in the same direction that you twisted the wire. This will insure that the wire does not untwist while you are putting on the wire cap. After the wire cap is on the splice, cover any remaining bare wire with electrical tape.

When I first attempted to make a pigtail splice with one solid wire and one stranded wire, I found that the stranded wire came off too easily. So the first thing I did, after stripping the wire and twisting the strands [of the stranded wire] together, was to tape the insulated portion of the wires together. I put a small bend at the end of the bare solid wire so that the wire cap would have something to catch on. Then I twist the stranded wire around the bare solid wire and screwed the wire cap on. The spring in the wire cap catches the bend in the solid wire. To ensure that the pigtail splice does not unravel, I use electrical tape. I start at the wire cap and wrap the tape tightly around the cap moving slowly towards the insulated wire. I keep wrapping it tightly until it covers a few inches of insulated wire. Never use masking tape on an electrical connection.

Lets consider a sloppy pigtail splice in a ceiling light fixture. When current is flowing the loose splice starts sparking. The fuse is not heat sensitive and does not blow. The sparking splice gets real hot and the insulation near the splice starts melting. The resident is unaware because the splice is not visible. It is hidden in the outlet. Eventually the utility box which holds the light fixture gets hot enough for the surrounding wood to ignite.

In your house wiring, the black wire is the hot wire. The hot wire carries 110 vac. The white wire is the circuit ground and the green wire is the equipment ground. I named the white wire the circuit ground to distinguish it's use from the use of equipment ground. The circuit ground is used for as a return for the equipment. The hot wire connected to the hot terminal of the equipment and the circuit ground is connected to the return terminal of the equipment. The equipment ground is connected to the metal case of the equipment. The long slot in your wall outlet is the circuit ground. The short slot is connected to the hot wire and the small hole is the equipment ground. Current flows through the hot wire to the equipment and back through the circuit ground. The equipment ground ensures that the metal case of the equipment will never be hot.

A lighting fixture has a black wire and a white wire extending from it. The black wire is the hot wire and the white wire is the circuit ground. The fixture's black wire should be connected to the black wire in the utility box via a pig tail splice. Likewise, the fixture's white wire should be connected to the white wire in the box via a pig tail splice.

Your standard outlet has one brass screw on one side and a silver screw and a green screw on the other side. The silver screw is circuit ground. The black wire is connected to the brass screw and the white wire is connected to the silver screw. The green wire is connected to the green screw labeled ground. GND is the abbreviation for ground.

I hope this tutorial has been enlightening.