Fundamentals of electricity

Electricity Defined
Electricity is nothing more than an organized flow of electrons and protons behaving in response to the attraction of oppositely charged particles and the repulsion of like-charged particles. If you can get enough electrons to break free of their orbits and start flowing in one direction or another, you have a flow of current. This current, or power, is defined as electricity. The device that frees the electrons form their orbit is called a power generator. To create vast amounts of electrical power, large generators must be turned on a massive scale.

Terminology of Electricity
As with most subjects, electricity has its own vocabulary. It is important to know the meaning of only four key terms: ampere (amperage), volt (voltage), watt (wattage), and ohms (resistance). By mastering these terms, you will better understand electricity.

Ampere:
An ampere, or amp, measures the rate, or quantity, of electrical flow. A typical contemporary home, for example, might have an electrical system of 150 to 200 amps. Amperage, in contrast, is the actual measure of current flowing in a circuit to an appliance. Although this can be measured only when the circuit is turned on, the rating of an electric appliance, in volts and amperes, or volts and watts, is required by the National Electrical Code to be marked on the identifying nameplate of the appliance. Amperes are designated by the letter A.

Ampacity is the amount of current in amperes a wire can safely conduct. Determining the correct ampacity of a wire is important because using an incorrect-size wire can create a fire hazard. Each wire carries a limited amount of current before it will heat to the point of damaging its insulation. For example, a 14-gauge wire can take a maximum current of 15 amps, a 12-gauge wire 20 amps, and so on. If a wire is too small for a job, generated heat can destroy its insulation, causing a fire. Amperage ratings are also important when you but fuses or circuit breakers. Amperage of fuses or breakers, circuit-breaker amperage will cause these protection devices to blow or trip. Too much will permit a dangerous amount of over-current, or flow, which occurs when too many appliances are used on the same circuit or during power surge. The result is overheating of the circuit, which will create a potential for fire.

Volt:
A volt measures the pressure exerted by electrical power. Voltage is the moving (electromotive) force that causes current to flow in an electrical circuit. A generator creates the pressure that keeps the electrical current flowing through conductors, known as wires.

Voltage, designed by the letter V, pushes a current that alternates between positive and negative values. This is known as an alternating current (AC). It periodically reverses, or alternates, direction in cycles, called Hertz. One cycle takes 1/60 second to complete. This is usually expressed as a rate of 60 cycles per second. The average voltage on this cycle is measured at 120 volts on the return, or neutral, wire and 240 volts across both of the two hot utility wires entering a home.

Contemporary three-wire residential wiring carries both 120- and 240-volt power. Large appliances like air conditioners, electric ranges, and clothes dryers typically use 240-volt wiring. Electrical devices must be labeled with their operating voltage level. This means that the product has been designed to operate at the listed voltage only. Do not, for example, hook up an electrical device rated at 125 volts to a circuit that supplies 220 to 240 volts. You’ll burn it out.

Watt, Wattage:
In practical terms, wattage is the amount of energy used to run a particular appliance. The wattage rating of a circuit is the amount of power the circuit can deliver safely, which is determined by the current-carrying capacity of the wires or cables. Wattage also indicates the amount of power a fixture or appliance needs to work properly.

To calculate the wattage, or power, available in a circuit, first determine its amperage (amp rating). It will be marked on the circuit breaker or fuse for that circuit in the service-entrance, or main, panel-15 or 20 amps for most room circuits, 30 to 50 amps for most heavy-duty circuits. Then, Watts=Volts x Amps. A 15-amp circuit with 120 volts carries 1,800 watts (15 x 120); a 20-amp circuit carries 2,400 watts (but not under continuous load).

Resistance:
Electrical resistance, measured in ohms, restricts the flow of current. The higher the resistance, the lower the current. The higher the resistance, the lower the current. This resistance causes a change of electrical energy into some other form of energy, usually heat. It is this heat, for example, that is used to warm the water in your water heater.

Calculating Current
A quick way of calculating 240-volt current is to figure 4 amps per 1,000 watts of power (8 amps for 120-volts). In the water-heater example given below, you would divide 4,500 watts by 1,000, getting 4.5. Multiplying this by 4 amps yields 18 amps; which are close to the formula answer.

To Find Current:Divide VOLTS by OHMS

To Find RESITANCE:  Divide VOLTS by AMPS

Divide AMPS by OHMS

Ohm’s Law formally states that the current in an electrical circuit is directly proportional to the voltage and inversely proportional to the resistance. From this we can derive equations to solve for all three; current, voltage, and resistance.

Calculating Capacity of an Electric Water Heater If you want to install a new electric water heater in your home, you must first determine its capacity. Let’s assume that you have a family of four in a home with two tubs/showers, one dishwasher, and one clothes washer. Referring to the table below, “Usage Points,” this gives you a total of 8 points. An adequately sized water heater for your home would have a 65-gallon capacity. A standard 65-gallon water heater has heating elements rated at 4,500 watts and 240-volt AC wiring. From this information, you can calculate how much current the water heater will use when you install the heater. Because power (wattage) equals voltage (volts) multiplied by current (amps), and you know power and voltage, you can calculate the current:

4,5000 watts divided by 240 volts Equals 18.75 amps

Usage Points
If your usage points equal            Then you need a
4 or less…………………….40-gal. Water heater
5 or 6…………………….....50-gal. Water heater
7 or 8……………………….65-gal. Water heater
9 or more……………..……..80-gal. Water heater

HOW TO: Install Cabling Outlets
Difficulty Level:

Tools and Materials

• Drywall saw
• Screwdrivers
• Punch-down tool
• Crimping tool
• Hollow-back boxes
• UTP cable
• Coaxial cable
• Wall plates
• Terminal jacks & caps as needed

Structured Cabling Outlets
You will need to run cable, either Category 5 or coaxial or both, from the structured media center to the different rooms in your house.

Assess Your Needs. Plan your installation carefully. It may pay to simply run Category 5 cable and coaxial cable from the media panel to every room in the house. Structured cabling can accommodate phone lines for voice, fax, and computer networking. The structured cabling outlets connect your equipment with the structured media panel. An outlet can contain multiple connections. For example, a single outlet may have connections for phone service, a computer network, and video.

Install the Box. Hollow back boxes have open spaces at the rear of the box, so it is easy to pull a number of cables into the same box. If you’re working on a finished wall, use a drywall saw to cut an opening for the box.

Make Connections. When installing UTP cable, remove the cable casing and fan out the wires. The current technology recommends installing Category 5 or Category 5e UTP, but in some cases Category 3 cables are acceptable. Attach the cable wires to the terminal with a punch-down tool. The terminal is color coded, so you will know where each wire should be placed. The punch-down tool makes the connection between the wire and the lead on the terminal.

Attach the Terminal Jack to the Wall Plate. The products available to you may be different. This connected terminal jack simply snaps into the wall plate.

If you’re making a coaxial cable connection, attach the metal color to the end of the cable using a cable crimper. Then attach the F-connector to a wall jack connector designed for the purpose.

Attach the Wall Plate. Secure the plate to the box with screws. Wall plate designs vary. This plate can accommodate two connections. For illustration purposes, we made one connection. The bottom space is filled with a plug, which you can remove to make an addition connection later.

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