Planning Your Electrical Installation

THE PREVIOUS SECTION on standards and codes discussed the importance of following the National Electrical Code (NEC) strictly in order to produce a safe wiring installation. This Section outlines how careful planning will help you make it a convenient, efficient, and practical installation. Here you will find the characteristics of an adequate house wiring installation, the principles of good lighting, and NEC requirements for locating lights, switches, and receptacles.

CONSIDER PRESENT AND FUTURE NEEDS

Plan your electrical installation so you will still be pleased with it in the years ahead. Don’t skimp on the original installation. Adding outlets, receptacles, switches, fixtures, and circuits later usually costs several times more than it would to include them in the original job.

Look ahead to the equipment you are going to be using five or even fifteen years from now. Besides the basics of electric cooking, water heating, and air conditioning, consider items such as computers, entertainment centers, workshop and home business equipment, and even appliances not yet on the market. By installing large wires and extra circuits now you will have adequate wiring in the future. You will be making a good investment.

Install large service entrance: All the power you use comes into the building through the service entrance wires and related equipment. Start your planning with a service entrance that will adequately handle present and future needs. Keep in mind that small service wires won’t carry a large load satisfactorily. Section 8 presents a full discussion of the service entrance installation.

Benefit from larger circuit wires: For house wiring, the minimum circuit wire size permitted by the NEC is 14 AWG, protected by a 15-amp fuse or circuit breaker, except for door chimes and other low-voltage wiring described in Section 18. There is a trend toward using 12 AWG wire, with 20-amp protection, and in a few localities it’s required as a minimum. The larger wire means brighter lights, less power wasted in heating of wires, and less frequent blowing of fuses or tripping of breakers. The use of 12 AWG wire in place of 14 AWG adds very little to the cost of the installation and will prove a good investment. NEC requirements for various types of circuits are discussed later. Special circuits requiring 12 AWG wire are explained under “Special small-appliance circuits”.

Note that the NEC now uses the more technically-correct term “AWG” (as in 12 AWG, standing for “American Wire Gauge”) instead of the old term “No.” (for “Number” as in No. 12), and this guide reflects the new practice. Wire gauge numbers (now expressed as ‘L_ AWG”) apply for wiring up to 4/0 AWG, which covers almost all wiring within the scope of this book. Wires above that size are denominated by their actual cross-sectional area, as in 500,000 circular mils (written 500 kcmil), the usual size for a 400-amp service conductor.

LOCATION OF LIGHTING, SWITCHES, AND OUTLET RECEPTACLES

An adequately wired home is well lighted. The lighting will be from floor and table lamps in some rooms and from permanently installed fixtures in others. Lighting fixtures don’t need to be expensive or elaborate, but you must have outlets for fixtures located to provide sufficient light where needed. In addition, plenty of switches and receptacle outlets are essential for convenience and safety.

Height from floor for switches and receptacles: There is no NEC requirement setting how high switches and receptacles must be from the floor. The typical range is 48 to 52 inches for switches and 12 to 18 inches for general-use receptacles. (People with physical disabilities may require switches to be lower and receptacles higher than usual.) Kitchen receptacles are located in the backsplash above the counters. In the laundry room and the workshop a convenient height for plugging in washer, iron, and tools is 36 to 48 inches above the floor. In new construction make the heights uniform throughout. In a remodel or addition match the existing heights.

NEC requirements for lighting and switches: NEC 2 10.70(A) requires the following areas to have some lighting controlled by a wall switch : every habit able room of a house; bathrooms; hallways; stairways (switches at both ends if comprised of at least six risers); attached garages, and detached garages if wired; attics, underfloor spaces, utility rooms, and basements used for storage or containing air-conditioning, heating, or other equipment requiring servicing. In kitchens and bathrooms the switch must control permanently installed lighting fixtures. In other rooms the switch may control one or more receptacle outlets into which floor or table lamps can be plugged. Each entrance into the house must have an outdoor light controlled by a switch inside the house.

Regardless of NEC requirements, an adequately wired house will have wall switches located so you can come in through any entrance and move throughout the house from floor to floor without ever being in darkness or leaving lights turned on behind you. A wall switch (shown in FIG. 2—1) costs more than a pull chain, but the wall switch is far more convenient to use, and it provides accident insurance against stumbling while looking for a pull chain in the dark. Installing a pair of three-way switches so a light can be turned on or off from two different places (the bottom and top of a staircase For example, as now often required) costs only a few dollars more than a single switch and is well worth the difference in terms of safety and convenience. Providing convenient switches for lighting also helps to conserve energy since we are less likely to leave lights on if it’s easy to turn them off when they are not needed.

NEC requirements for receptacles : NEC 210.52(A) requires receptacle outlets in each kitchen, family room, dining room, living room, parlor, library, den, sun room, bedroom, recreation room, or similar rooms (or areas, as in the case of an open floor plan) of dwelling units to be installed so that no point along the floor line in any wall space (including spaces behind door swings) is more than 6 feet measured horizontally from an outlet in that space, including any wall space 2 feet or more in width and the wall space occupied by fixed glass panels in exterior walls. The wall space provided by fixed room dividers, such as free-standing counters or railings, is to be included in the 6-foot measurement. Hallways 10 feet or more in length must have at least one receptacle outlet.

FIG. 2-1 : Typical toggle switch. The “plaster ears on the ends of the strap are a great convenience in mounting the switch.

FIG. 2-2 : A duplex receptacle, rated at 20 amps, 125 volts. The more common 15-amp version is identical in configuration except it does not have the horizontal slots extending to the right. The duplex receptacle has two terminal screws on each side, plus one green grounding screw (in this case at the upper right and not visible in this photo).The terminal screws at the left (ungrounded terminals) are finished with a brass or copper color; the screw terminals to the right (not visible) are for the grounded circuit conductor, and have a white or silvery white finish.

Basements are required to have at least one receptacle outlet in addition to any outlets for laundry equipment. Attached garages—and detached garages having electric power—are also required to have at least one receptacle outlet. Every house is required by NEC 210.52(E) to have at least two outdoor receptacles—one on the front of the dwelling and one on the back—for yard tools, appliances, holiday lighting, etc. They must be no more than 6 feet 6 inches above grade level. We will later cover locations where GFCI protection for personnel is required. An adequately wired house has enough receptacles (shown in FIG. 2—2) so that you will never need an extension cord for a lamp, clock, or similar equipment. Extension cords are useful as temporary devices, but they should never be used to permanently carry power from a receptacle to lamps or other equipment. If there are circumstances where you cannot avoid using an extension cord, don’t invite a fire by running the cord under a rug or carpet. Never run one across open floor space—stepping on it could result in damage and fire, and tripping on it could lead to injury. Never tack or staple a cord to a wall. It’s best to reserve extension cords only for temporary use.

Fixtures and receptacles room by room: The following list details both the required and the recommended lighting, switches, and outlets to be installed in each room plus the garage and any accessory buildings.

Living room: Suit yourself about whether to have a fixture in the center of the ceiling or on a wall. Some homes depend entirely on floor and table lamps for living room light. If this is the case, it will be convenient to have one or two wall switches control all the receptacles into which the lamps are plugged so they don’t have to be turned on and off individually. You might choose to have just the bottom or top halves of several duplex receptacles in a room controlled by a switch.

No matter how small the room, there should be a minimum of five receptacle outlets for uses such as TV, stereo, radio, and lamps. Locate one receptacle where it will always be completely accessible for the vacuum cleaner regardless of the furniture arrangement. Many living rooms will be large enough to require more than five receptacles based on the “6 foot” rule. Regardless of room size, consider the probable arrangement of the furniture and place receptacles so they won’t be difficult to reach. This may require an extra receptacle or two, but will be worth it.

Dining room: One ceiling outlet for a fixture should be provided; it must be controlled by a wall switch. Locate this fixture above the center of the dining room table rather than the center of the room. The “6 foot” rule usually will require at least four receptacle outlets. One receptacle should be always accessible from the dining room table for use with items like electric coffee makers, electric woks, and electric knives.

Kitchen : Abundant wiring is required in the kitchen. First, it should be well lighted because it’s often the center of activity. A ceiling fixture controlled by a wall switch must be provided for general lighting. (The 2002 NEC has adopted the international term “luminaire” to replace former references to fixtures, but until that term is in more general use this guide will continue the traditional usage.) If there are two entrances to the kitchen, use a pair of three-way switches to control the light from either door. Another light above the sink is necessary so a person does not have to work in his or her own shadow. Consider other kitchen work areas that may need specific lighting.

All fixtures with exposed conductive parts must be grounded. If there is no equipment ground available, you will have to provide one, generally through rewiring the circuit. Otherwise you can use only porcelain- or plastic-bodied fixtures, and this category has very little in the way of variety. These are safety measures:. An ungrounded metal fixture or metal pull chain could become energized through a fault in the fixture and make a serious shock possible.

The NEC requires two special circuits to handle only receptacle outlets for small appliances (including refrigeration equipment) in kitchen, pantry; dining room, and breakfast room (and similar areas). Both of these required small-appliance branch circuits must appear at the kitchen counter outlets (meaning all counter outlets taken collectively, not necessarily both circuits present at each outlet),because that is where the majority of appliances are connected. Install one outlet for the refrigerator, and place the others 6 to 10 inches above the counter in the backsplash. A counter space 12 inches wide requires one receptacle, and others are required so that no point along the counter space is more than 24 inches from a receptacle outlet. Spaces separated by a sink or range top are considered as separate spaces. Because the lack of a backsplash makes receptacle placement at counter peninsulas and islands difficult, the spacing requirement is relaxed to require only one receptacle outlet per counter. Be aware that where receptacles are located in the face of the cabinet within 12 inches below the counter top, cords will be draped over the counter edge providing children a ready means to pull over an appliance that might cause them injury. Locations where GFCI protection is required are discussed later.

Install a range receptacle in the beginning, because installing it later will be much more costly and difficult.

Bedrooms : Some people want a ceiling light in each bedroom; others do not. If you install a ceiling light, have it controlled by a wall switch near the door. If there will be no ceiling light, be sure some of the receptacles are controlled by a wall switch. The “6 foot” rule will probably require at least four receptacles. Plan location carefully; one should be permanently accessible for the vacuum cleaner, and another near the bed for items such as reading lamp, clock radio, and heating pad. If the overhead outlet will be used to support a paddle fan, use the special boxes covered under this topic in Section 9.

Closets: Don’t overlook closet lights. Install the fixture on the ceiling or on the wall above the door so it’s separated from the storage space by 12 inches, defined as at least 12 inches out from the walls, or the actual width of a shelf if greater than 12 inches, all the way to the ceiling. This is a safety measure. Many fires have been traced to clothing touching bare lamps in closets. The temperature of the glass bulb of an incandescent lamp is often higher than 400° F. In no case can a pendant fixture or an incandescent lamp without an enclosure be installed in a closet. If the fixture is a recessed incandescent with a solid lens, or a surface-mounted or recessed fluorescent fixture, the distance from the storage space may be reduced to 6 inches.

Bathrooms: A ceiling light controlled by a wall switch is essential. One additional light above the mirror at the basin is often installed, but that is not good lighting. Two lights—one on each side of the mirror—are needed for applying makeup or for shaving. Fluorescent brackets are ideal for the purpose. Pendant fixtures, ceiling paddle fans, and track lighting are prohibited in the area within 3 feet horizontally and 8 feet vertically of the tub or the shower area. A GFCI-protected receptacle is required within 36 inches of the outside edge of each basin. A dedicated 20-amp circuit is required for all the bathroom receptacles, unless the circuit (which still must serve only bathroom loads) supplies only one bathroom. In this case, the 20-amp circuit may serve the lighting outlets as well as the receptacle within the one bathroom. Thus, you may supply any or all the bathroom receptacles (in however many bathrooms) on a 20-amp circuit, or the entire load, but in only a single bathroom, on a similar circuit.

Stairs: Where there are stairs, locate a fixture where it will light every step. Use three-way switches so the light can be turned on and off from both the top and bottom of the stairs. This is inexpensive insurance against accidents, and it’s an NEC requirement if the stairs have six risers or more. If there is an intermediate landing with an entryway, as in many split-level houses, an additional switch must be placed at the intermediate landing.

Hallways, entrances, and basement: Every hallway deserves a light. For a long hallway, install three-way switches to control the light from either end. Install a receptacle for a vacuum cleaner. At each entrance to the house, outdoor lights controlled by switches indoors are essential. A motion-sensitive light is an option for your outdoor lighting. When people approach the door from outside at night, the light will turn itself on automatically. This is especially useful if the house does not have an attached garage. In the basement, install numerous receptacles for washer and dryer, workshop motors, and similar uses. If the basement has a finished room, the receptacles in that room follow the normal rules for habitable rooms, and at least one additional receptacle must be located in the unfinished portion. If the finished portion divides the basement into two or more unfinished areas, receptacles need to be provided for each unfinished area.

GFCI protection is required for receptacle outlets in unfinished basements. There are some important exceptions, including receptacles that aren’t readily accessible. In addition, receptacles supplying appliances that aren’t easily moved (including laundry equipment) and receptacles supplying alarm systems are exempted as well, but only a single contact point for each such load. For example, a receptacle for a piped-in-place sump pump would be exempt, but you would need a single receptacle (accommodating only a single plug and typically round, unlike the duplex receptacle in FIG. 2—2 that accommodates two plugs). In the case of an alarm system transformer, you will often find a mounting bracket designed to be secured to the cover mounting screw in the middle of a duplex receptacle. In this case, ask the inspector whether he or she would accept a conventional duplex receptacle with only the bottom receptacle connected.

Garage and accessory buildings : If the garage is attached to the house, treat it as another room as far as lighting is concerned. Three-way switches are preferred for convenience, one at the garage door and the other at the door between garage and house. There are several considerations for a detached garage. Most of these considerations apply to other accessory buildings as well. The minimum wiring in a garage is a receptacle plus a light controlled only by a switch in the garage, fed by a pair of wires from the house. Most people will want a light that can be controlled from both the garage and the house, requiring a three-way switch at each end.

NEC 210.52(G) requires every garage (if wired) to have at least one GFCI-protected receptacle outlet. More than one may be desirable for a battery charger, tools, etc. In garages and accessory buildings, receptacle outlets that are not required to be GFCI-protected include outlets that are not accessible, such as a ceiling outlet for a garage door opener, and outlets for appliances in dedicated space, such as a freezer. Here too, only a single receptacle can be available without GFCI protection, in this case the one for the appliance. All others must be GFCI-protected. In a garage, it’s very convenient to have receptacle outlets that are always live rather than receptacles that are turned off with the garage light. With receptacles permanently on, you can plug in a battery charger and have it work all night without having the garage light on. See out section on procedures and wiring diagrams for detached buildings.

CHOOSING LIGHTING FIXTURES

Good lighting requires not only sufficient light but also proper distribution of light throughout the room. It’s easier to read in the shade of a tree than in direct sunlight even if there is less light in the shade. Indirect sunlight, the light all comes from one point—the sun. In the shade of a tree, it comes from all directions. Similarly, fixtures with exposed lamps produce light from one point, causing sharp shadows and glare that make reading or sewing or other close work difficult. Provide well-diffused “shade of the tree” light by using fixtures that don’t have exposed lamps.

For best lighting, ceilings should be a light color. A white ceiling reflects most of the light thrown against it. Ivory is not quite as good for the purpose. A flat finish is better than a glossy finish.

Some fixtures provide good illumination and others are primarily decorative. If you have good floor and table lamps to provide plenty of lighting where people sit, there is no reason why fixtures in the same room cannot be the decorative kind that provide some general lighting but not enough for exacting work. When ceiling fixtures are to be the primary source of light in a room, take care to locate them where they will provide lighting for critical seeing tasks. Buy the styles of fixtures that suit your taste and budget. Make sure the fixtures you select are electrically good and safe—look for the listing label on each fixture. Good lighting is not necessarily expensive. Lighting fixtures are available in a wide range of prices, and in many places a 100-watt lamp can be burned for a penny an hour.

Lamps (light bulbs) : Bulbs? Lamps? Different people call them by different names. Lamps are commonly bought and sold as “light bulbs” but technically only the outer glass globe is a bulb, while the entire unit is a lamp. In this book, they are called lamps in accordance with the terminology used in the NEC. See FIG. 6—1 for the symbol used to indicate a lamp in diagrams used in this book.

Types and efficiency : There are many types of lamps : incandescent, fluorescent, metal halide, mercury vapor, sodium vapor, etc. Three 60-watt lamps (total 180 watts) give 10 percent more light than five 40-watt lamps (total 200 watts). One 150-watt lamp gives twice as much light as five 25-watt lamps (125 watts). One

100-watt lamp gives 15 percent more light than three 40-watt lamps (120 watts). In other words, a fixture that uses one large lamp will in general provide more light than one using several small lamps of equivalent total wattage.

Labeling : Federal regulations require most of the commonly used incandescent and fluorescent lamps to be labeled with the light output measured in lumens, energy used measured in watts, and the life in hours. To save energy, choose a lamp based on the light output and then select the lowest wattage lamp that will deliver that light.

Incandescent lighting : Ordinary lamps have an average life of 750 to 1,000 hours if used on circuits of the voltage stamped on the lamps, which is the voltage for which they were designed. There are also several newer types on the market.

“Long life” incandescent lamps : It’s a simple matter to increase the life of a lamp by burning it at a voltage lower than it was designed for, as is done in “long life” lamps. For example, a lamp designed for 135 volts but burned at 120 volts will last about four times longer; a 140-volt lamp burned at 120 volts will last about eight times longer. But there is a catch—the light per watt is reduced by 20 to 30 percent and the cost is increased by 25 to 35 percent. In addition, such “long life” lamps sometimes consume more watts than the number stamped on them. If such a lamp is marked “60 watts” but actually consumes 70 watts, it will seem to produce just as much light as a standard 60-watt lamp with a 1,000-hour life. Such “extended service” lamps can be useful if located where replacement is difficult. Some lamps have reduced wattages. For example, replacing a 75-watt lamp with a 67-watt lamp will certainly save energy—but it will also give less light.

Energy-efficient incandescent lamps : There have been some real advances in incandescent lamp efficiency. Bulbs filled with krypton gas instead of nitrogen reduce energy consumption by 10 to 20 percent with no noticeable decrease in lamp life or light output. The lamp-within-a-lamp has a tungsten-halogen lamp inside a compact quartz tube within a conventional lamp bulb. The halogen gas re-deposits tungsten particles back onto the filament, reducing blacking and providing up to three times the life of a conventional incandescent lamp.

Although the initial cost is higher, these energy-efficient lamps provide a return on investment of up to five times over their life. They last longer and use less electricity, saving you money and conserving energy at the same time. They come in 42-watt, 52-watt, and 72-watt sizes to replace standard 60-watt, 75-watt, and 100-watt incandescents. Their average life is 3,500 hours.

Fluorescent lighting : Fluorescent lighting has many advantages over incandescent. It produces far more light per watt of power used, and fluorescent lamps last much longer than ordinary lamps. The life of fluorescent lamps depends mostly on the number of burning hours per start. If turned on and left burning continuously, they will last at least eight to fifteen times as long as ordinary lamps. Even if turned on and off frequently, the fluorescent will last three to five times as long as an ordinary lamp. Fluorescent lamps used in homes come in lengths from 18 to 60 inches, consuming from 15 to 60 watts. The 48-inch/40-watt is the most common.

Brightness and whiteness : A further advantage of fluorescent lamps is that their surface brightness is much lower than that of filament lamps, providing light that is more diffused and thus more comfortable. Standard fluorescent lamps come in an assortment of different kinds of “white:’ including deluxe warm white, warm white, white, cool white, and deluxe cool white. The cool white is most commonly used. It produces light most like natural light and emphasizes the blue and green colors in objects lighted. The warm white produces light more like that of ordinary filament lamps and emphasizes red and brown. The deluxe varieties emphasize these qualities still more but are a bit less efficient, producing a little less light per watt consumed.

Energy-efficient fluorescent lamps : There are energy-efficient lamps and ballasts, including solid-state ballasts, that have ratings other than “standard,” and these are truly more efficient than the lamps and ballasts they replace. Compact fluorescent lamps as small as 7 watts can replace incandescent lamps in many applications at great savings in energy. These compact lamps are made with a self-contained ballast and an Edison screw-shell base so they can very simply replace an incandescent lamp. A compact fluorescent rated around 25 watts replacing a 100-watt incandescent ranges in price from $10 to more than $20. A 15-watt compact fluorescent lamp replaces a 60-watt incandescent, a 20-watt fluorescent replaces a 75-watt incandescent, and a 25-watt fluorescent has light output equivalent to a 100-watt incandescent. These fluorescent lamps have an average life of 10,000 hours. Another type is the two-piece circular compact fluorescent lamp that has a reusable electronic ballast. It comes in 22-watt and 30-watt sizes to replace 100-watt and 150-watt incandescent lamps.

Compact fluorescent lamps come in many different styles and shapes. Newer types are labeled “electronic” because of the type of ballast used. Some have large bases that may not fit within the harps of your table and floor lamps, so measure the harp width before your trip to the hardware or home center store where the compact fluorescents are available. (Some electric power suppliers also sell them.) Generally a square style will fit in a smaller space than a circular shape. The lamps cannot be used with dimmers, electronic timers, or photocell devices. Read the package before purchase to make sure you can use the lamp for your intended purpose.

Operation: In fluorescent lamps, the electric current does not flow through a filament as in ordinary incandescent lamps, but rather jumps as an arc from a contact in one end of the lamp, through a gas in the glass tube, to another contact at the other end of the lamp. If you had such a fluorescent lamp made of clear glass in a dark room, you would see only a slight blue glow when the lamp was turned on. The arc in the lamp provides mostly ultraviolet light which is invisible. The inside of the lamp is coated with a special powder that fluoresces (glows) when struck by ultraviolet light, producing the visible light we see.

The electrical operation of a fluorescent lamp is a bit complicated. The easiest way to learn is to look at older styles having visible separate components. The complete circuit includes the lamp, a ballast, and a starter. The most common fluorescent lamp has a filament (“cathode”) at each end, but these are lighted only for a second or so when the light is first turned on. The ballast—an electrical winding on a steel core—does two things : it limits the total power that can flow through it, and it has the peculiarity that when power flowing through it’s disconnected, it momentarily delivers a voltage much higher than the original voltage flowing through it—for a brief moment it becomes a step-up transformer. The starter is a switch that opens itself after power has flowed through it for a moment, and then remains open. (The magnetic ballast described is gradually being replaced by the electronic ballast, which accomplishes the same ends by different and quieter means.)

Figure 2-3 shows the circuit for the first second or so after the light is turned on. The current flows first through the ballast, then through the filament at one end of the lamp, then back to SOURCE. The starter opens itself, and after that there is no circuit other than the lamp that the current can flow through. As the switch in the starter opens, the ballast delivers a momentary high-voltage kick that is enough to jump the gap inside the lamp; the current then flows through the lamp from end to end. See FIG. 2-4 showing the circuit after the switch in the starter has opened and the lamp is in normal operation. A bit of mercury in the tube vaporizes when the lamp goes into operation, helping the current flow through the lamp. The ballast limits the current through the lamp, keeping it at a proper value. Some fluorescent lamps, such as the rapid-start and instant-start types, start somewhat differently. The diagrams of Figs. 2—3 and 2—4 are for a fixture with only one lamp. Diagrams for fixtures with two or more lamps are more complicated. Modern fluorescent fixtures rarely use the external starter shown in the drawing, however, the basic principle of producing a larger voltage to start a flow of current through the lamp, followed by a controlled lower voltage to operate the lamp remains valid.

FIG. 2-3 The current has just been turned on. The starter is still closed.

« Standards, Codes, and Safety   •  Measuring Electricity  »

Home •  • 

Top of page