Guide to Basic Wiring Techniques: Before You Start / Understanding Electricity
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Guide to Basic Wiring Techniques -- "Table of Contents":
No one would deny that electricity is essential to the modern way of life. It does everything from lighting our homes to performing labor once accomplished only by muscle and sweat. Yet few people know much, if anything, about this current that provides such comfort and convenience; flip a switch or push a button and it works, and that’s all that matters. Beyond that, most people find electricity confusing, if not downright mysterious, and intimidating because of the potential danger. Yes, there is a danger but with reasonable caution and understanding, electrical work can be one of the easiest and most satisfying home-repair and remodeling projects. All that the job requires is a basic knowledge of home wiring. Understanding ElectricityContrary to popular belief electricity isn't difficult to understand. It functions according to mathematical principles and is completely logical. It behaves in a totally predictable way. Understanding that predictability is simply a matter of taking the time to learn the principles behind it, to pick up the jargon, and to master basic wiring techniques. Wiring by the Book Home wiring requires few specialized tools, and most of the procedures and materials used are standardized. Armed with this basic knowledge, which will be provided by this guide, you will be able to do almost any home-wiring project successfully and safely. With electricity, a small amount of knowledge can in deed be a dangerous thing, so this guide covers all the essentials of residential wiring. It begins with the fundamentals of electricity, including a complete review of the typical home electrical system. This is the time to grasp the basic technical aspects of home wiring and the theory behind those basics. This first section also reviews the necessary safety procedures for working with home wiring and provides a glossary of technical terms you will need to understand. The second section presents the step-by-step procedures involved in preparing a wiring project, whether you are wiring an entire house or just adding an electrical outlet. It covers thawing a plan, evaluating whether to use an existing circuit or add a new one, obtaining a permit, and making a materials list. It also discusses tools, safety procedures, and when it might be wise to hire a licensed electrician. The next three sections present practical, step-by-step instructions for basic wiring procedures, from rough wiring techniques to installing a new service entrance to the details of finish wiring. Finally, the last section examines the important issues of energy conservation, energy generation, and the new technologies related to home wiring. Everything in this guide is explained one step at a time using a combination of text and precise technical drawings. Each step builds upon the previous step. Even if you aren’t tackling a project that requires all the steps listed, understanding them all imparts logic to what you are doing. Using this guide as a guide, you should be able to do most simple, common electrical-wiring tasks, from setting a box in a new wall to adding a new receptacle to an existing circuit. If you take the time to acquire a clear understanding of electricity, you may even feel able to do advanced projects such as running a new circuit in your home or yard. From Power Company to Private Home (and Back) Perhaps electricity seems so mysterious because you can’t see it. You can see what it does, and under the wrong circum stances you can feel it, but you can’t see it. This invisibility makes it seem much more complicated than it actually is. Simply stated, electricity is the flow of minute charged particles of energy (electrons) through a conductor, generally a wire. The path this energy follows from its creation or generation until it enters a house is both complicated and incredibly efficient. The path begins at the electric utility company’s power plant where electric energy is produced in huge generators powered by water, coal, oil, or nuclear fuel. Typically, this energy is generated at high volt ages. Then the power plant uses transformers to further in crease its voltage for transmission on high-voltage wires to substations along the line. The actual voltage of each transmission line depends on a combination of factors, including the transmission distance. At the substation the volt age is reduced for distribution to users. The transformers you see hanging on utility poles or mounted on concrete pads along streets and alleys make the final voltage reduction to 120 and 240 volts for use in the home and are the final link in the intricate distribution sys tem. Along the way, a network of safety devices is used to protect and control the power in the system.
The Basics of Grounding Grounding is electrical contact with the earth; a ground is a conducted path between electrical equipment and the earth. If you are standing on wet earth or a wet concrete floor that adjoins the earth and you contact voltage, you can be come grounded: An electrical current will pass through you, giving you an electrical shock, possibly severe enough to kill you. However, if your home’s electrical system, from the ser vice panel through the branch circuits, is properly grounded, it greatly lessens the chance of shock. One advantage of having a properly grounded neutral conductor in the house is that the voltage to ground will not exceed approximately 120 volts. Typically, voltage to ground in the electrical distribution sys tem ranges from 2,400 to 8,000 volts. The transformer that reduces these high voltages to the 120 volts used in a house has a high-voltage side and a secondary, 120-volt side. Electric power for a home comes from the secondary side. For absolute safety, the distribution system connects the grounded conductor on the high-voltage side of the transformer to the grounded conductor on the 120-volt side. So long as this connection is sound and grounded, an accidental ground on the high volt age feeding the transformer will create a fault that will trip a circuit breaker or open a fuse or otherwise turn off the high voltage and , of course, the 120 volts feeding the house. How ever, if the common connection were still in place but the grounding conductor were eliminated, there could be trouble if an accidental ground occurred in the high voltage supplying the transformer. Although the actual result would depend on the primary voltage involved, theoretically the volt age to ground in your house could exceed 8,000 volts. To further assure proper grounding, all house receptacles, in addition to being connected to a hot wire (most often black or red) and to a neutral wire (white or grayish white), must be connected to a ground wire (always bare copper or green) that joins to a grounded connection in the service panel. This connection is made either through a grounding conductor in the cable feeding the receptacle or through the sheathing of metal-jacketed cable or metallic conduit used in the system. A washing machine serves to demonstrate how this grounding inside the house protects you. When the ma chine is plugged in and turned on, only the hot and neutral wires to which the washer is connected normally carry cur rent. The machine and its drive motor are constructed in such a way that their wiring is insulated or physically isolated from the machine’s metal frame. For further protection, the washer’s frame also is connected to ground through the green wire in its cord and the U-shaped prong in its plug. However, if excess heat or some other cause breaks down the drive motor’s insulation, its frame and the washer’s frame will become energized when the machine is turned on. If the electrical system in the home is properly grounded, the high current flowing through the motor to ground will open the circuit breaker or fuse protecting the circuit supplying power to the washer and no damage will occur. However, if the grounding prong in the plug is missing or the receptacle isn’t properly grounded, and you happen to touch the machine and the properly grounded clothes dryer next to it at the same time, the fault current will flow from the washer through you to ground and a fatality could occur.
Electricity in the Home From the transformer, the power company brings electricity into a home via overhead wires or underground cables. Underground service is aesthetically less intrusive, but there is no difference in the quality or safety of the electrical service you receive. Homes built after 1940, and pre-1940 homes that have had their electrical service modernized, will have three-wire ser vice. This means there are three wires, called service-entrance conductors, connected to the service-entrance equipment of the home. Two of these wires are “hot” (carrying current), the third one is the neutral conductor. The three-wire system pro vides a home with both 120- volt and 240-volt. The neutral wire and either hot wire combine to supply 120 volts for such items as lamps, radios, food processors, and wall receptacles. When 240-volt ser vice is necessary, to operate a major appliance such as a range or clothes dryer, for example, both hot wires combine with the neutral wire to supply the required electricity. However, note that water heaters and large air conditioners also require 240 volts, but they are connected only to hot wires. They don’t have clocks, timers, lights, or other appurtenances that require 120 volts for their operation. Older, unmodernized homes usually have two-wire service and as few as two fuses. This means they have one hot wire and one neutral wire sup plying only 120 volts. This ser vice is wholly inadequate by modern standards, especially if the home is equipped with many large appliances. The Service Entrance The electrical distribution sys tem within the home—an intricate but logical and efficient system—is centered in the home’s service-entrance panel. Three wires bring power from the 120-volt side of the distribution transformer through the electric meter and then into the service-entrance panel. If the house has under ground service, these wires, called the service lateral, rise through the entrance conduit that comes out of the ground alongside the foundation. They then enter the meter, which is mounted on the outside of the house, and continue on to the service-entrance panel inside. If the house has overhead service, the three wires, called the ser vice drop, extend from the secondary side of the distribution transformer to a point near the service-entrance head at the top of the service conduit. Here they are spliced to the service- entrance conductors, which enter this head, drop down through the conduit into the meter, and continue on into the service-entrance panel. The Electric Meter The electric meter is attached to your house but it belongs to the power company. All the electricity entering the house first passes through this meter so the power company can measure the exact amount of electricity you use. This measurement is expressed in kilowatt-hours (the number of kilowatts x the hours of usage). To learn how to read your meter, see below. The Service Panel It would be convenient if all service equipment and every service arrangement were exactly the same, but they’re not. There are many types of panels and many acceptable ways to locate them in relationship to the meter. The common de nominator among panels is that each must be grounded and contain a main disconnecting means and a main overcurrent-protection device. The main disconnect is wired to the load side of the meter and can mechanically turn off all the power in your house. The main overcurrent protection device can automatically turn off all the power to your house. Most contemporary panels combine the main disconnect and the main overcurrent-protection device in the main circuit breaker, usually located at the top of the panel just above the branch- circuit breakers. However, you should be aware that some lo cal electrical codes require the main disconnect to be located outside, away from the service panel. You will have to use the type required by your community’s code. If your home has a fuse box, the main disconnect will consist of a pair of fuses mounted in a pull-out, which is removed to cut the power. With some old split-bus-type panels you may need up to six separate hand movements to disconnect all the incoming power. Be sure you know what type of panel you have and exactly what steps you must take to disconnect the power completely. The service-entrance panel also contains the grounding- electrode conductor, an important wire that grounds the entire house. The neutral wire inside the service panel goes directly to the neutral bus bar. All the neutral wires of the branch circuits connect to terminals on this solid metal bar that's bonded (electrically connected) to the cabinet. The grounding-electrode conductor connects the neutral bus bar to a metal ground rod driven into the ground beyond the foundation of the house. If the water system for the home includes more than 10 feet of under ground metal water pipe (including metal well casing bonded to the pipe), the water system also is connected to the neutral bus bar, as specified by the National Electrical Code (NEC). Working together, the ground rod and the water pipe form the grounding-electrode system that provides a safety path to earth for the electrical system of the home.
The Role of the NEC The electrical practices and procedures presented in this guide are based on the National Electrical Code, hereafter referred to as the NEC or the Code. Sponsored by the National Fire Protection Association, the NEC establishes national minimum safety standards for the installation of electrical wiring and equipment. The Code has one purpose: to safeguard people and property from hazards arising from the use of electricity. It is designed for mandatory application by any authority having legal jurisdiction over electrical installations. By con forming to the NEC, a book such as this is able to provide accurate instructions to a nationwide audience of readers, even though they are governed by local electrical codes that can vary from community to community. Most of these local electrical codes, whether city, county, or uniform state codes, are based on the NEC, but they may vary in significant ways; they may be more stringent or they may not be as up-to-date. The NEC revises the Code every three years. Since all electrical work in the home must be done according to code, you must check out your local electrical code be fore you even begin planning your project. To do this, con tact the building-inspection department for your community, usually located in city hall, and ask for a list of electrical-code requirements. Also ask if the code follows the NEC. If there are significant deviations, what are they? Some local codes may regard the NEC as an acceptable alter native. Whatever the situation, all your electrical work must be done according to the code used by the authority that has jurisdiction over your residence. Even though you have a copy of your local electrical code, you should still familiarize yourself with the NEC. The best way to do this is to obtain a current guide to the NEC, because the Code itself is quite complex.
Individual Appliance Circuits:
You are charged for the electricity you use in kilowatt-hours (kwh). Kilo means thousand, so a kilowatt is a thousand watts. These kilo watts are measured by the electric meter attached to the house, which runs continuously and registers your use on the four or five dials on its face. Some meters have a counter similar to the mileage indicator on a speedometer, but most have dials that resemble clocks, with numbers running from zero to nine. Look closely at these dials and you’ll see their numbers alternate between running clock wise and counterclockwise. To read your meter, start with the left-hand dial and work to the right, jotting down the numbers as you go. If the hand lies between two numbers, always use the lower number even if the hand is almost on the higher number. However, if the hand is directly on a number, check the dial immediately to the right. If the hand on that dial has reached or just passed zero, use the number indicated on the previous dial; however, if the hand of the dial on the right has not reached zero, use the next lowest number on the previous dial. Some homeowners like to take their own meter readings every once in a while in order to check the accuracy of the power company’s readings. To do this, write down the meter reading at the same time the company reads the meter. Do this again the following month, and subtract the first reading from this second reading. Then compare your consumption with that stated on your electric bill for that month. If there is a significant discrepancy, contact the power company. The Brunch Circuits Branch circuits within the home are formed by the wiring that connects electrical outlets (receptacles) and permanently connected appliances to the service-entrance panel. Each individual circuit has its own hot wire and neutral wire as well as an overcurrent-protection device capable of turning off power to the individual branch circuit. In the panel, two hot wires from the main circuit breaker energize two bus bars constructed of heavy metal, usually copper or aluminum. Each branch circuit is connected to one or both of these hot bus bars via individual overcurrent protection devices, either circuit breakers or fuses. A 120- volt circuit has one hot wire coming from a single-pole circuit breaker, that's , a circuit breaker connected to one hot bus bar, and a neutral wire or conductor that's connected to the neutral bus. A 240-volt circuit has two hot wires connected to a double-pole (or two- pole) circuit breaker, that's , a circuit breaker that's connected to both hot bus bars. However, this 240-volt branch circuit may or may not have a neutral wire connected to the neutral bus; that’s because 240- volt circuits for water heaters and large air conditioners do not require neutral wires (see page 9 for explanation). It is important to remember that all neutral conductors terminate at the neutral bus. Most homes are equipped with a variety of branch circuits. The NEC recognizes three types. General-purpose Branch Circuits These 120-volt circuits supply a number of receptacles used for lighting and small appliances. Some designers and installers prefer to assign a circuit only to lighting or only to receptacles. While this practice isn't an NEC requirement it may be a local code requirement in some communities. It may also be common practice even where it isn't an actual code requirement. This approach is advisable for houses that include many permanently installed light fixtures. Small-Appliance Branch Circuits These 120-volt circuits supply power to receptacles to which small appliances such as toasters and food processors are to be connected. Typically, these circuits are restricted to kitchens and eating areas. A minimum of two such 20-amp circuits are routinely installed in kitchens built within the last 30 years. Individual Branch Circuits These circuits supply only one appliance. There are two types: 120-volt circuits and 240-volt circuits. The 120-volt circuits service appliances such as dish washers, food disposers, trash compactors, and washing machines. The 240-volt circuits are for appliances and equipment with greater power requirements, such as clothes dryers, ranges, water heaters, and air conditioners. |
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