(29) Wiring Electrical Circuits.pdf

Study Unit

Wiring Electrical Circuits

All electrical systems have one thing in common—they must be properly connected. Schematic diagramsand wiring plans are needed to properly connect and maintain electrical systems. As an electrician,you should be able to identify and understand the common wiring terms and symbols used in thesediagrams and plans. Although most of the branch circuits discussed in this study unit are based onresidential use, they may also apply to many commercial and industrial applications.

When you complete this study unit, you’ll be able to

� Differentiate between feeder and branch circuits

� Identify the correct type of general or special-purpose circuit when given a list of circuitdescriptions

� Describe how wiring is installed for branch circuits in a residence under particular situations

� Differentiate between portable, fixed, and stationary appliances and describe how eachtype is wired

� Identify the components needed for an electrical circuit

� Calculate the current in a neutral conductor

� Calculate the size of service-entrance conductor needed for a residence

Preview

iii

ELECTRICAL SYSTEM FUNDAMENTALS . . . . . . . . . . . . . . . . . . 1

Parts of an Electrical SystemElectrical CircuitsTypes of Circuits

INSTALLING SERVICE-ENTRANCE COMPONENTS . . . . . . . . . . . . . 16

Sizing and Installing Service-Entrance ConductorsInstalling the Meter BaseSizing and Mounting the Service PanelGrounding and Bonding of Service and EquipmentSubpanels

LOCATING RESIDENTIAL DEVICES . . . . . . . . . . . . . . . . . . . . . 40

Wiring Layout for a Small HouseLocation of ReceptaclesLocation of SwitchesLocation of Lighting OutletsListing of Residential OutletsArea Requirements

GENERAL CIRCUIT WIRING CONSIDERATIONS . . . . . . . . . . . . . . 60

General-Purpose CircuitsSmall-Appliance CircuitsSpecial-Purpose CircuitsCircuit ProtectionCircuit GroundingOther Circuits

SELF-CHECK ANSWERS . . . . . . . . . . . . . . . . . . . . . . . . . . 83

EXAMINATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

Contents

v

ELECTRICAL SYSTEM FUNDAMENTALS

An electrical system may be compared to a tree. As the tree roots supportthe tree trunk and branches, the electrical system, or service, supports theservice-entrance equipment and branch circuits. The type of electricalservice is determined by the public utility supplying the electric power.Most electric utilities produce and distribute alternating current (AC)power to their customers. (The distribution of direct current or DC powerby electric utilities has largely stopped.) While an industrial maintenanceelectrician may still have to work on DC circuits, the vast majority ofresidential circuits are AC powered. Therefore, this study unit will dealmainly with AC power.

The typical residential service is 120/240 V (volts) single-phase ACpower. The slash between 120 and 240 means that both voltages areavailable to the customer. The service-entrance equipment brings theelectric power into the building and then controls it before distributingit to the branch circuits. The branch circuits are the circuits that supplythe loads. The electrical system within a building consists of manycomponents such as wires, fuses, circuit breakers, switches, and lampsor other loads.

Figure 1 shows an electrical system for a residence. Industrial andcommercial systems use similar components in the same way. Forconvenience, the explanations given in this study unit will be for aresidence, although the same rules apply to the complex wiring systemof a large industrial plant.

Parts of an Electrical System

Service equipment and wiring circuits can best be explained by studyingthe wiring layout in Figure 1. Let’s start by looking at the service entrance.It includes the service drop, service-entrance cables, watt-hour meter,service-disconnecting means, and grounding conductor. Let’s look ateach individual part of the service entrance shown in Figure 1A.

� Service Drop. The utility company installs the service drop. Service-drop conductors are shown coming from a utility pole to the firstattachment point on the building. Should the conductors come fromeither a manhole or a pad-mounted transformer to the building,they’re referred to as service lateral conductors. Figure 1B shows atypical underground-service lateral system. The number ofconductors depends on the type of distribution system.

Wiring Electrical Circuits

1

� Service-entrance cable. The service-entrance cable continues from thepoint of attachment to the building through the watt-hourmeter. Underground service might not require that you installservice-entrance conductors or cables. The reason is the servicelateral conductors, which run from the street mains (main electricaldistribution lines) to the building, are terminated by the PowerCompany directly at the meter base.

� Watt-hour meter. The watt-hour meter is the device that measuresthe energy used by the consumer. The utility company generallyspecifies its location. The meter is installed between the servicedrop or service lateral and the service-disconnecting means.

2 Wiring Electrical Circuits

FIGURE 1A—This drawing shows a typical electrical system with the service entrance highlighted.

� Service-disconnecting means. The service-disconnecting means isshown in Figure 1A. In this case, the disconnecting means is acircuit breaker. Switches or fuses may also be used as disconnectingmeans. The service-disconnecting device must be manuallyoperated. It must provide a visual means to tell whether it’s in theopen or closed position. In devices where a circuit breaker handleoperates vertically, the UP position shall be the ON position. Theservice-disconnecting device must be mounted in an accessiblelocation near the service entrance. A service-overcurrent devicemay also be contained within the service-disconnecting device. Eachungrounded service-entrance conductor must have either a fuse orcircuit breaker in series with it. This prevents excessive currentdraw caused by faults, overload of the building’s wiring, or anexcessive supply of electrical power delivered to the service entrance.

Wiring Electrical Circuits 3

FIGURE 1B—This drawing

shows an alternative

(underground) service

lateral configuration.

Remember that a system

also includes loads, like the

range and lamp, as well as

devices such as the

receptacle, light switch,

lamp holder, and circuit

breakers.

� Grounding conductor. The grounding conductor is a low-resistanceconductor connected between the ground and the identified neutralwire of the alternating current service conductors or the housingfor the disconnecting means or both. In a typical installation, theneutral wire is identified by its white or natural gray insulation andthe grounding conductor is either a bare conductor or green in color.

Let’s summarize what’s just been described about the service entrance.It begins at the junction of the service drop and service-entrance cable;it ends where the grounding conductor is grounded. Included in theservice entrance are the insulators and other materials used to supportthe building end of the service drop. Service-entrance installations arecovered in detail in other texts.

To understand how power is fed into the home, let’s look at the rightside of the diagram in Figure 1A.

� Feeder cable. Feeder conductors extend the electrical system. Thefeeder(s) is/are a cable or conductors between the load side of theservice disconnect and the branch circuit panelboard. Generally, noloads are connected between those two points.

� Distribution panel board. The branch circuits are tapped off of thefeeders at the distribution panel board. Such panels contain fuses orcircuit breakers that protect the branch circuits. Although separatedistribution panel boards are shown in Figure 1, such a center maybe enclosed in the same cabinet as the service-disconnecting means.Circuit breakers are shown for protecting the branch circuits. Iffuses were used as service-overcurrent devices, then the branchcircuits would normally also be protected by fuses. However, bothfuses and circuit breakers may be used in the same installation.

� Subpanel feeder cable. The subpanel feeder cable is an extension of themain feeder. The conductors in this cable must be protectedby a circuit breaker or fuses in the main distribution panel. InFigure 1, it’s shown as a cable between the two distribution panelboards.

� Branch circuit cables. Figure 1A shows only four branch circuit ca-bles extending from the distribution panel boards. This means thatonly four of the 15 branch circuits are supplying loads. One of theeight breakers shown in the first panel is protecting the subpanelfeeders. These four branch circuits are 120-V circuits that are sup-plying a duplex receptacle, or convenience outlet, and a lamp that’scontrolled by a switch. Although only single loads are shown foreach circuit, the typical circuit would supply more than one load ordevice of the same type, such as one circuit that supplies current toseveral lamps in an area of the building.


The electric range uses a separate circuit breaker within the equipmentpanel board. In this example, the range circuit is a 240-V circuit that’sprotected by a two-pole circuit breaker. In this study unit, you’ll learnabout the many types of branch circuits found in a modern residence,and how to identify and install the required circuit components.

Electrical Circuits

Definition of a Circuit

According to the NEC, the term electrical equipment means any material,fitting, device, appliance, or apparatus used as part of, or in connectionwith, an electrical installation. The words equipment and component areused interchangeably because each piece of equipment is a componentof the electrical installation. If electrical components are connected togetherproperly, they form an electrical circuit. Simply put, an electrical circuitis the complete path followed by electric current.

A branch circuit consists of the conductors and devices installed betweenthe branch-circuit protection device (breaker or fuse) and the receptacleor connection point of the load. Once an appliance or load is eitherplugged into or connected to the receptacle or connection point, thosecomponents used to plug in or connect to the branch circuit become partof the circuit. These components are sometimes referred to as the “loadcircuit,” although the electrical trade doesn’t recognize this phrase indefining circuits.

Circuit Components

Figure 2 shows the five basic types of components in a simple electricalcircuit. All electrical circuits include, at the very least, the following threecomponents—the power source, load, and conductors that join them.In Figure 2, a transformer is used as a power source and conductors jointhe transformer to a lamp. This is the electrical load or destination.Even without the fuse and switch, a complete circuit would still exist. Thepower source may originate from a panel board, transformer, battery, orgenerator. Most circuits contain at least one or more electrical devicessuch as switches, which are control devices, or fuses, which are protectivedevices. Many circuits also have circuit breakers, devices that both protectand control the circuit. A receptacle is a convenience device, used with amating plug. A plug makes it easy to connect a conductor between thepower source and load.


Types of Circuits

Electric circuits have names such as series circuits, branch circuits, 120-Vcircuits, high-voltage circuits, and remote-control circuits. The differentnames can be very confusing, especially when the same circuit is calledby more than one name. Often, two or more names are combined to givea complete and accurate description of the circuit.

The following list shows how circuits are described in terms of theircharacteristics.


FUSE

CONDUCTORS

SOURCE

LOAD

L2 L1

120V

SWITCH

FIGURE 2—A simple circuit

will always contain at least

three of the five different

components shown

here—the power source,

load, and conductors.

Circuit Characteristics Common Descriptive Terms

Wiring connection Series, parallel, compound, delta, wye

Number of wires Two-wire, three-wire, four-wire

Number of phases Single-phase, polyphase, three-phase

Type of grounding Grounded neutral, ungrounded neutral, with ground

Electrical variables High-voltage, low-voltage, high-ampacity, wattage, 60-Hz (hertz)frequency, low-capacitance, high-impedance

Wiring method Cable, busway, cable bus, conduit, direct burial

Circuits can also be classed in terms of the type of customer, areaserved, section of the total installation, type of load, function, and eventhe method used to control them. The following list shows commondescriptive terms for these classes.

Often there’s no clear-cut category for a circuit. The name of the circuitused at any one time depends on the circuit characteristics beingdiscussed at that time.

Series and Parallel Circuits

When several parts or devices are used in a wiring system, their circuitsmay be interconnected in various ways. The two basic connections ofelectric circuits are series and parallel.

In a series circuit, all parts are connected end-to-end, like the links in achain. This connection forms a closed-path circuit as in Figure 3A. Abasic rule for a series circuit is that the same current flows through eachpart. If 10 A (amperes) flows through the switch, then 10 A will flowthrough the fuse and through each of the heaters. However, the voltagedrop across each part in a series circuit is different and depends on theresistance of that part and the amount of current flowing through it.

In the parallel circuit shown in Figure 3B, two or more parts are connectedacross the same voltage source. The two heaters and fan are connectedin parallel or in shunt with each other and the power source. The basicrule for a parallel circuit is that the same voltage exists across each of theparallel-connected parts. The current branches off and a portion flowsthrough each of the parallel branches. The total of the currents in thebranches if added will be equal to the total current if measured at thesource. This means that the higher the resistance of a branch, the lowerthe current through that branch. If a series circuit is broken (or opened)at one point, the entire circuit’s dead. No current flows in any part of it.If one of the branches in a parallel circuit is disconnected (or opened),the current in the other branches continues to flow. Therefore, an opencircuit in one branch of a parallel circuit doesn’t stop current flow inother branches.


Classes of Circuits Common Descriptive Terms

Customer type Residential, commercial, industrial

Area served Hazardous, outdoor, weatherproof, raintight

Section of installation Service entrance, feeder, branch

Type of load General-purpose, lighting, small appliance

Function Power, communications, alarm, control

Method of control Manual, automatic, remote control

Combination Circuits

Parts of a wiring system may be connected in a combination of seriesand parallel circuits. Figure 4 shows two diagrams of a heater circuit. Inthe schematic view, the heater and switch are connected in series witheach other. The fan motor is connected in parallel with them. The circuithas two parallel branches. One branch has only one part, the fan motor;the other branch contains two parts in series, the heater and the switch.In this heater diagram, the switch controls only the heating element, notthe fan. This is a series-parallel combination, or compound circuit.


FIGURE 3—When a series circuit is opened, no current flows. In a parallel circuit, one branch can

be opened, and current will still flow through the others.

M FAN MOTOR

WHITE

COMMON WIRE

RED SWITCH

BLACK

HEATER

WHITE

SOURCE

TERMINALS

BLACK

SOURCE

TERMINALS

WHITE

WHITEWHITE

RED

FAN

SWITCH

BLACK

BLACK

HEATER

LINE CORD

MOTOR

FIGURE 4—This shows schematic and pictorial diagrams of the same heater/fan circuit.

The pictorial diagram in Figure 4 labels the colors of the wires. Notethat one side of each branch has a white wire. These white wires areconnected to the common white wire, which leads to a source terminal.The red wire from the switch and the red wire from the fan motor areconnected to the black wire. The black wire then leads to the othersource terminal. Remember that in Figure 4, the common wire is whiteand all white wires are connected together.

Remember that the same voltage exists across each branch of a parallelcircuit. For that reason, electrical loads are designed to operate at certainstandard voltages. All loads in a typical residence that require alternatingcurrent operate at either 120 or 240 V. Industrial and some commercialequipment are designed to operate at these or higher standard voltages.No matter what the voltage is, all loads will be connected in parallelwith the voltage source.

Electrical devices that protect and control an entire circuit or branch of acircuit will be connected in series with the portion of the circuit wiring orthe load that the devices protect or control. For that reason, electricaldevices such as fuses, circuit breakers, and switches are rated based onthe amount of current they must handle.

Circuit Variables

Most circuits you’ll be dealing with are parallel circuits. These circuitshave the same voltage for all the parallel loads. Suppose you’re goingto connect a new electrical load in a parallel circuit. You’ll need toknow the circuit’s operating voltage and the branch circuit conductor’scurrent-carrying capacity, or ampacity. Suppose the existing circuit israted at 120 V and 20 amperes; the new load will be connected to theexisting circuit to put it in parallel with the circuit. It’s critical that thesum of the currents of all the parallel loads, including the newly addedload, doesn’t exceed 20 amperes.

Two- and Three-Wire Circuits

The circuits discussed so far have been two-wire circuits consisting of anungrounded hot wire and a grounded neutral wire. Figure 5 shows thattwo such circuits running near each other have a total of four wires.Note that lines a and b are hot (ungrounded) conductors. The remaininglines n are the neutrals. These neutrals are connected together at theneutral bus in the panel board. If lines a and b are supplied by oppositesides of the service entrance, the current will flow as shown by the arrows.“Opposite sides of the service entrance” means that if line a is suppliedby the black service-entrance wire, line b will be supplied by the redservice-entrance wire. In this configuration, the voltage between lines aand n (or b and n) is 120 V, while the voltage between lines a and b is 240 V.


Since the neutral conductors are connected together at the panel board,they’re one-wire. Why use two wires when one will do? It’s important tonote that a three-wire 120/240-V circuit will do the work of two, two-wire120-V circuits. However, opposite phase conductors sometimes sharethe same neutral as in the three-wire (multi-wire) circuit shown inFigure 5. If the neutral is disconnected or interrupted, the circuit wouldbecome a series circuit with a nominal voltage of 240 V! The load, if notrated for the higher voltage, would most likely be damaged or destroyedby the higher voltage. For this reason, it’s very important to be cautiousin disconnecting neutral conductors in a panel.

Assume that equal loads of 20 A each are present on the multi-wirecircuit (which in this case is a three-wire circuit) in Figure 5. Then 20 Aflows in lines a and b, but the two arrows on the neutral n are in oppositedirections. Thus, the currents cancel and no current flows in the neutral.The result is no voltage drop in the neutral and less voltage drop in eachcircuit.

When the currents are unequal there’s less current in the neutral than ineither hot conductor. As an example, if line a is carrying 20 A and line bis carrying 15 A, then the neutral n is carrying 5 A (20 – 15 = 5 A).Although the neutral current now is no longer zero, it’s still much lessthan either line current. This example remains there even when the sin-gle loads in Figure 5 are replaced by several smaller loads located whereneeded. However, this is true only if their current is drawn equally fromeach of the two sides of the circuit.


FIGURE 5—This shows

examples of two- and

three-wire circuits.

Grounded Circuits

You’ll remember that the neutral wire in a two-wire system is groundedor connected to the earth. When the neutral wire is connected to the earth,it’s a grounded conductor because it carries current during normal circuitoperation. Don’t confuse the grounded conductor with the groundingconductor. The grounded conductor is part of the current-carrying electricalcircuit whose function is to provide a circuit path and stability to the levelof voltage. A grounding conductor, on the other hand, isn’t a current-carrying conductor. Its function is to provide safety and protection toboth personnel and equipment with a low impedance path to ground incase of a short in the electrical system.

The grounded conductor or neutral wire must be kept continuous. Inresidential wiring, the neutral wire is never interrupted by a fuse, circuitbreaker, switch, or other device. In industrial wiring, the neutral wiremay be interrupted, but only if the ungrounded wires and the neutralwire are interrupted at the same time.

Circuit Description by Load Type

A circuit is often named after or described by the equipment (or load)to which it delivers power. Here’s an example. Some residential circuitsare called small-appliance, general-purpose, electric range, and electricdryer circuits. Each of these circuits has its own basic characteristics.Given the type of load, an experienced electrician could identify manyof the circuit characteristics. The electrician would know such features asvoltage, ampacity, number of phases, and number and size of conductors.

Industrial branch circuits aren’t as standardized as residential circuits.However, given the load (such as a motor or lighting equipment), manyof the circuit characteristics and much of the circuit equipment can oftenbe determined.

Circuit Description by Function

So far, you’ve learned about the standard types of circuits used in electricalwiring systems. There are, however, many special circuits and auxiliarycircuits. These circuits are also described by the function they serve orby the method by which they’re controlled. These circuits may includeemergency power, hazardous-area, alarm, communication, and controlcircuits. The following briefly describes the first four of these circuits.Control circuits will be discussed in a later section.

Emergency power can be distributed in one of two ways. Either theemergency power source, such as a diesel-powered generator or batterysupply, can be switched directly into the main feeder and branch circuits,or the emergency power system may be equipped with its own separatefeeders and branch circuits.


Another type of circuit is the hazardous-area circuit. It’s unique in that thecircuit requires special explosion-proof devices and fittings. Theelectrical loads on these circuits, such as motors and lamps, must be ofspecial construction.

Other unique circuits include alarm circuits, doorbell or chime circuits,fire alarm circuits, and control circuits. Some of these circuits operateon low voltages such as 12 V, 16 V, or 24 V. Figure 6 shows how a doorchime circuit might be connected. The transformer shown in Figure 6could be replaced by a battery in an emergency situation without affectingthe chime’s operation. Control circuits are often found in industrialfacilities and are used to transfer or transmit electrical control signalsfrom one location to another.

Control Circuits

Control circuits are the next most common circuits an electrician has towork on beside branch and feeder circuits. That’s why you, the electrician,must have a thorough understanding of basic electricity and be able toread and understand control drawings. Control circuits are commonlyused to regulate or control the supply of electrical power to a load. Theymay either switch the power on or off or may adjust the power to adesired level. Some control circuits are very simple while others arequite complex.

Many major home appliances and a majority of the electrical equipmentin an industrial setting have control circuits. Figure 7 shows a simplifiedschematic for a home air conditioner. The compressor and fan motor arethe two obvious main loads in the circuit. The other circuit devices—switch,temperature control, and the two capacitors—are control devices. Thesedevices determine when and how long the electrical loads are operated.


TRANSFORMERTWO-DOOR

CHIME

FRONT-

DOOR

SWITCH

BACK-

DOOR

SWITCH

T

L

S-1

S-2

BLOCK DIAGRAM FOR A

TWO-DOOR CHIME CIRCUIT

FRONT BACK

FIGURE 6—The two-door

chime can be wired to

sound a double note for the

front door and a single note

for the back door.

In the control drawing for the air conditioner, the heavy black dots in themode switch indicate which connections are energized for the variousmodes of operation. In the HI FAN position, notice that line terminal L isconnected only to terminal 1, which goes to the fan motor.


FIGURE 7—This shows a control circuit schematic for an air conditioner.

Review

Circuits may be referred to by different names but all circuits are basicallycommon to one another in that each circuit or group of circuits has threecomponents—a source of power, conductors, and an electrical load.Most circuits will also likely contain protective and control devices.

As you gain more experience as an electrician, you should be able todescribe the types of circuits in this study unit and their characteristics.



✔ Self-Check 1At the end of each section of Wiring Electrical Circuits, you’ll be asked to check your under-standing of what you’ve just read by completing a “Self-Check.” Writing the answers to thesequestions will help you review what you’ve learned so far. Please complete Self-Check 1 now.

1. The conductors that run in the air from a utility pole to the first point of attachment on abuilding are called the ________ ________.

2. The two components in Figure 2 that provide the necessary circuit protection and controlare the fuse and the _______.

3. Protective and control devices are connected in _______ with the load.

4. Electricity is distributed by most electric utilities as _______ current.

5. In a three-wire 120/240-V circuit, if the current in line a is 17 A and the current in line b is8 A, the current in the neutral is _______ A.

6. A _______ conductor is connected to the earth and doesn’t carry current during normaloperation.

7. When you call a circuit an electric heater circuit, or a motor circuit, you’re referring to it bythe type of _______ it supplies.

8. Name two types of special or auxiliary circuits.

_______________________________________________________________________________

9. If you’re installing an electrical system in a hazardous area, you must be sure to use_______ devices and fittings.

Check your answers with those on page 83.

INSTALLING SERVICE-ENTRANCE COMPONENTS

Now that you’ve reviewed circuit theory and components let’s considerplacing and sizing the actual components that make up a typical electricalsystem. Keep in mind that the typical residential electrical system includesservice drop or lateral feed, service-entrance conductors, weather head,watt-hour meter, service panel, grounding electrode, groundingconductor, feeders, branch circuits, and various devices. You’ve alsolearned how to route conductors for branch circuits and how to selectthe various electrical devices most commonly installed. Later in this studyunit, you’ll learn to properly design branch circuits and specify thecorrect number of devices for each part of the dwelling. First, however,electricians should understand how the service-entrance componentsare sized and installed. This section provides the information needed toproperly lay out and install a residential electrical system that’s safe,convenient, and code compliant.

Sizing and Installing Service-Entrance Conductors

As learned earlier, the service-entrance conductors provide the path bywhich power moves from the service drop, to the watt-hour meter, andto the service-entrance panel. These conductors are sometimes part of theservice-entrance cable (SE cable). In other installations, they’re individualconductors that run inside conduit. Electricians should follow standardwire-ampacity guidelines to size the service-entrance conductor tomatch the maximum-amperage rating of the service. For instance, if themain disconnecting switch and panel board are sized for 200 A, then 2/0or 3/0 copper wire may be used for the service-entrance conductor. Inthis particular case, while the NEC specifies that a 2/0 copper wire has amaximum ampacity of 200 amps, the electrician may install the nextlargest conductor size for safety and future additions.

However, the local code may dictate that the service load be calculatedusing established methods. One such method is the optional calculationsfor dwelling units described in Article 220-30 of the NEC. The followingsteps show how to compute the estimated load on the hot and neutralservice-entrance conductors using this method. A sample calculation willfollow.

Follow Steps 1 through 6 to calculate the service conductor load.

Step 1: Calculate the volt-ampere (VA) load for the general lightingand receptacles. Find this by multiplying the total square footageof the building by 3 VA as stated in Article 220-30(b)(2) of theNEC. (Note that to convert VA to kVA you divide by 1000.)Save this number for a later calculation.


Step 2: Calculate the volt-ampere loads of the kitchen and laundrybranch circuits by adding together the total number of 2-wire,20-ampere, small-appliance branch circuits in the kitchen andeach laundry branch circuit. Multiply this number by 1500 VAas discussed in Article 220-30(b)(1) of the NEC. Save this resultfor a later calculation.

Step 3: Add together all the volt-ampere load ratings (stamped onnameplates) of appliances that are secured in place (exceptair-conditioning and heating units) as discussed in Article220-30(b)(3) of the NEC.

Step 4: Calculate the total volt-ampere demand load from the last threesteps by applying the demand factors listed in Table 220-30 inthe NEC to the calculated total.

Step 5: Find the larger of the heating or air-conditioning load rating(not both) and apply the demand factors as listed in Article220-30(c). Air-conditioning or heat pumps are calculated at100%, while space heating is calculated at 65% for three or lessunits, and 40% for four or more units. Add this number to thetotal demand load found in Step 4.

Step 6: Divide the total found in Step 5 by the system voltage, usually240 volts. The result is the amperage rating for the serviceconductors as covered in the NEC Article 310-16.

Follow Steps 7 through 8 to calculate the neutral conductorload.

Step 7: Add the general load found in the first step with the kitchenand laundry loads in the second step. Begin the neutral con-ductor calculation by counting the first 3000 VA at 100%, or3000VA. Combine this with 35% of the remaining VA fromsteps 1 and 2. Now add 100% of the dishwasher VA, and 70%of the range and the dryer VA.

Step 8: Divide this total by the system voltage (240 volts) and theanswer is the amperage. According to Article 310-16 of the NEC,you’ll use this number to determine the required neutralconductor type and size for this residence.

Example: Find the total estimated load on the hot and neutralload service-entrance conductors for a dwelling with a total of2500 square feet. The dwelling contains a 3 kVA or 3000 VAwater heater, 1.5 kVA or a 1500 VA dishwasher, and a 5 kVA or5000 VA air conditioner. It also contains four or more combinedspace heaters of 15 kVA or 15000 VA, a 5.5 kVA or 5500 VAdryer, and a 12 kVA or 12000 VA range.

Solution: Follow Steps 1 through 8 above.


Step 1: Calculate the lighting and receptacle load.

2500 sq ft � 3 VA/sq ft = 7500 VA (7.5 kVA)

Step 2: Add together the two NEC-required small-appliance kitchencircuits, and one laundry branch circuit.

3 � 1500 VA = 4500 VA (4.5 kVA)

Step 3: Determine rating total of all secured appliances except heatingand air conditioning.

Range 12000 Vdryer 5500 VAwater heater 3000 VAdishwasher 1500 VATotal 22000 VA

Step 4: Total the figures from Steps 1 through 3.

7500 + 4500 + 22000 = 34000 VA

Apply this to the demand factors based on the optional methodfound in the NEC.

100% of the first 10 kVA 10,000

40% of the remaining 24 kVA (34000 – 10000 = 24000)

24000 � .40 = 9600

Total: 10000 VA + 9600 VA = 19600 VA

Step 5: Add 40% of the larger of the two heating and air conditioningloads to the total from Step 4.

Total from Step 4 19600 VA

40 % of the heating (15000 � .4) +6000 VA

Total 25600 VA

Step 6: Divide the total in Step 5 by the provided voltage.

25600 VA ÷ 240 V = 106.6 A

Keep in mind that conductors should be sized so that the esti-mated amperage load doesn’t exceed 85% of the conductor’srated capacity. For a system with an estimated load of 130 A,the NEC (Table 310-16) requires the service conductors to beequal to or greater than the diameter of #2 AWG wire. Notethat 85% of 130 A is 110.5 A, which is close to 106.6 amperes.However, the service conductors in most situations will besized in accordance to the standard rating of the service equip-ment. In this situation, the service equipment will most likelybe rated at 200 amperes since 130 amperes isn’t a common rating


for service equipment and, therefore, the service conductorsmust be large enough to handle 200 amperes.

Step 7: To determine the service feeder neutral load, apply theappropriate demand factors to all of the loads:

100% of the first 3000 VA 3000

(Step 1 + Step 2 – 3000 = 9000)

35% of the remaining load (.35 � 9000) 3,150

100% of the dishwasher 1,500

70% of the range (12000 � 0.7) 8,400

70% of the dryer ( 5,500 � 0.7) 3,850

Total 19,900

Step 8. Divide 240 V into the total neutral demand found in Step 7.19 900

24082 9

,.

dVA

dVA�

Answer: A minimum of a #4 AWG copper conductor isrequired for the service neutral conductor.

Note that the power company must approve the selected location of themeter base. The electrician will supply the power company with theservice-entrance cable hookup point (covered by a weatherhead or similardevice), then install a meter base and service panel (Figure 8A). Theelectrician will then run the service-entrance cable from the meter baseto the hookup point and from the load side of the meter base to the servicepanel, making sure the grounding electrode and grounding conductorare installed. Only then will the power company hook up their cable,splice their incoming line to the installed service-entrance cable, andinstall and seal the watt-hour meter in the meter base (Figure 8B).

Electricians must follow the NEC and local codes closely when placingthe service-entrance cable. The minimum height of the power line abovepedestrians or vehicle traffic, the size of the conduit required (whenconduit is used), and the space between cable clamps (when service-entrance cable is used) are all closely specified by the NEC (Figure 9).Local codes sometimes expand on the requirements of the NEC but neverreduce the requirements. Always check local codes and ordinances beforeinstallation to assure compliance. When calculating clearance heightsand conductor lengths, remember to account for the amount of conductorthe power company will require for a drip loop and splicing. It’s typicallyacceptable to leave a minimum of two feet of excess cable beyond theweatherhead. The local power company sometimes specifies the lengthof excess cable to be extended beyond the weatherhead.



FIGURE 8—(A) shows a typical service-drop installation while (B) shows how the power company uses splicesto connect the service drop to the service-entrance cable the electrician has installed.

Installing the Meter Base

As you learned earlier, the power company installs the watt-hour meterin a residential application. The power company also supplies the meterbase (or meter socket) but the electrician must install it. Likewise, thepower company must approve the location of the meter base. However,it’s important that the electrician follow local codes and/or utility regu-lations that often govern the meter base’s exact placement. Ordinancesmay include its height off the ground, and how power is run from themeter to the service panel. In addition, the meter base capacity mustmatch the rating of the system and the system configuration (aboveground versus below ground). For example, the meter base for a 200 Aservice won’t suffice if a 400 A service is to be installed.

Sometimes the meter base will be located on the opposite side of thewall from the service panel, as illustrated in Figure 8A. When these twopieces of equipment are located back-to-back, the job of completing theservice-entrance circuit is much easier and less expensive. However, theelectrician usually doesn’t decide on the location of the service.


CLAMPS

WEATHERHEAD

NO MORE

THAN 30"

BETWEEN

CLAMPS

(DEPENDING ON

LOCAL CODES)

NO MORE

THAN 12"

METER BASE


service-entrance cable

support requirements.

If the meter base and service panel aren’t located back-to-back, a longerrun of service-entrance conductor will be needed from the meter base tothe panel. This means that a service disconnecting means will be neededto control the power within that additional run of service cable in case ofa short circuit. If the meter base and service panel are mounted back-to-back, routing the wires from the base to the panel is simple. First, to mountthe meter base on the outside of the house, remove the knockouts fromthe back of the base (designed to allow conductors to run from the baseto the panel box). Hold the meter base level against the building with thecorrect side facing up. Trace the shape of the box opening onto the wall,remove the box, and cut a hole slightly larger than the one traced.Obviously, don’t cut through any wall studs because they’re designedto support the structure.

Now attach any required conduit fittings to the meter base. Conduitfittings attached may be those that accept the service-entrance cable fromthe drip loop or ones that route the cable onto the panel box. Rememberthat for an overhead service the connector on the top of the meter basemust be watertight and matched to the size conduit or service-entrancecable being installed. The service-entrance cable from an undergroundservice will always be installed in conduit and fed into the bottom of themeter base. In this case, the conduit will be joined to the meter base witha standard conduit fitting.

Next, coat the wall around the outside of the hole with a heavy bead ofsealant. Make sure the meter base is level and fasten the meter base tothe wall using screws or appropriate anchors. To provide additionalsealing against moisture, place an additional bead of sealant where thetop and two sides of the meter base meet the wall. Don’t seal where thebottom of the meter base meets the wall because moisture that seeps infrom the top or sides needs to exit the space behind the meter base.

Connecting the Service-Entrance Conductors to theMeter Base

The next step in completing the electrical service is to install the serviceentrance conductors from the weatherhead (for service drops) andterminate them on the line side (top) terminals of the meter base. Ifsheathed cable (SE) is installed inside conduit, be sure to remove onlyenough sheathing so that the sheathing extends through the weatherproofconnector on the top of the meter base. You won’t normally need toinstall the service entrance conductors for lateral feed as the power com-pany will usually do this. Strip enough insulation from the end of theconductors for the connections (normally 3

4 to 1 inch). Connect the incom-ing service-entrance conductors to the meter base. If the service-entrancecable is aluminum, the stripped portion of the conductor must be coatedwith an antioxidant compound before the conductors are connected tothe meter base.

When hooking up the meter base, remember that the incoming powerline is attached to the top (line side) terminals, while the conductors thatexit the meter base and feed the service panel will connect to the bottom


(load side) terminals. This is shown in Figure 10. In higher-amperageservices where two parallel service-entrance cables are used, the hookupprocedure is the same except the two conductors per phase are attachedto a special double terminal inside the meter base. When cables are installedin parallel, it’s very important that service conductors of like phases bekept together. This requires marking the conductors in the meter baseand at the weatherhead (where the power company will hook up) sothat the opposite phase conductors aren’t connected together.


NEUTRALCONDUCTOR

TWO HOTCONDUCTORS

NEUTRALCONDUCTOR

TWO HOTCONDUCTORS

L1 L2


upper and lower terminals

connected to the base.

Wiring from the Meter to the Service Panel

If the meter base and service panel are back-to-back, run a section ofconduit through the wall from the back of the meter base so that it entersthe back of the panel as was shown earlier in Figure 8A. The conduit willoften be a presized galvanized rigid-conduit nipple. The nipple willbe installed with locknuts on both sides of the meter base’s and panelboard’s sheet metal wall. The locknuts ensure that the conduit will pro-vide a good ground path from the base to the panel box. In addition tothe locknuts, the electrician should always install one conduit bushingon the inside of the meter base, and one conduit bushing on the inside ofthe panel. This provides a smooth contact edge for the conductors to en-ter and exit the conduit nipple.

It’s more likely that the service panel won’t be located directly on theother side of the wall from the meter base. If not, the service-entrancecable will exit the bottom of the meter base, and may enter the dwellingas shown in Figure 11.


INSIDE WALL

METER

BASE

SE

CABLE

SERVICE

DISCONNECT

PANEL

BOX

MAIN FLOOR

OF HOUSE

BASEMENT

OUTSIDE

WALL

FIGURE 11—In this example,

a service-entrance cable

exits the bottom of the

meter base, enters the

basement, is routed through

a main disconnect mounted

nearest the point of

basement entrance, and

enters the panel.

Before finishing your final systems design and certainly before purchasingmaterials or submitting a material list or bid, the electrician should layout the complete service entrance on paper. One erroneous dimensioncould result in several improperly placed systems components. BothNEC requirements and local code requirements must be reviewedprior to installing any components to assure compliance. Consider easilyforgotten components such as grounding rods, grounding conductors,clamps, connectors, anchors, fittings, anti-oxidant (for aluminumconductors) and other miscellaneous hardware when preparing amaterial list or bid.

Sizing and Mounting the Service Panel

It’s critical that you install a service panel with enough capacity tohandle a reasonable amount of future expansion in the electrical system.It’s very likely that the homeowner will some day want to modify thedwelling in a way that requires additional branch circuits and/or in-creased load capacity. Although a load calculation may be done prior toinstallation, it’s always best to size the system larger to accommodatelater expansion or additions. If load calculations conclude that thesystem will require 150 amps, it’s good practice to install a 200-amppanel. In fact, electricians should probably install at least a 200 ampere-ratedservice in most modern-day residential systems. The NEC requires theservice to be rated no less than 100 amperes for a one-family residence(Article 230-79[c]).

Of course, some dwellings will need more than a 200-amp service. Ifyour load calculations or other factors indicate a need for a higher am-perage service, 250 amps for instance, install at least a 300-amp service.Based on material and labor cost factors, you or someone else willneed to decide whether it’s more economical to install a single 300-amppanel or 200- and 100-amp panels side-by-side.

Panels are also rated based on the number of breakers they hold. Thelargest-capacity 200-amp panels may hold up to forty-two circuit breakers.In most cases, you should select the panel within the target amperagerange that’s capable of holding the most breakers.

Finally, remember that the electrician is ultimately the person who musthook up the panel. When working with different panel designs, try topre-evaluate them for ease of assembly and growth. The location ofneutral buses, the arrangement of breaker installation, and several otherfeatures contribute to making the panel either easier or more difficult towire.

Sizing and Installing the Main Breaker

In some residential installations, the service disconnecting means willbe the main breaker in the service panel. When this is the case, the mainbreaker controls and protects two of the four conductors entering the


panel, as shown in Figure 12. The switched conductors are always thetwo hot conductors. When the main breaker in the service panel servesas the main disconnecting device, it must be labeled “Service Discon-nect.” The other two conductors entering the panel (neutral and ground)are connected to the neutral bus and grounding bar (not shown) respec-tively. The neutral bar must be bonded to the panel enclosure using abonding screw that’s normally supplied with the panel enclosure. You’lllearn more about bonding in a later section.

If the service disconnecting means is installed indoors but not in theservice panel, it should be located as closely as possible to the pointwhere electrical power enters the building. Sometimes this requires it tobe located in its own separate enclosure, in line with the service-entrancecircuit, and ahead of the service panel.

Installing Circuit Breakers

Later in this study unit, you’ll learn how branch circuits are laid out in atypical dwelling, and why the components in one branch circuit must beseparated electrically from other branch circuit components. For now,however, assume that each branch circuit has been determined and thevarious loads in the dwelling are connected to these branch circuits. Youmay have twelve general lighting circuits (15 A), two small-appliance(20 A) circuits serving the kitchen, one 20 A branch laundry circuit, one20 A branch workshop circuit, and several dedicated branch circuitsserving the dryer, water heater, range, and electric heat pump. As you


FIGURE 12—This shows a

panel enclosure with a

main-breaker switch.

now know, each of these branch circuits requires its own breaker andin many cases, these breakers will be quite different from one another.In this section of the study unit, we’ll discuss the various types of breakersyou’ll encounter and explain how they’re used in a modern residentialservice panel.

You’ve already learned that circuit breakers are installed in a panelenclosure. However, you should be aware that there are severaltypes of breakers, each with its own application. The most commonlyencountered standard breaker (if there is such a thing) is the full-sizebreaker. It’s single-poled, designed to protect a single branch circuit,and is usually rated at either 15 or 20 amps. Electricians refer to this typeof breaker by the number of poles it contains, as well as its amperagerating. In this case, you would refer to the breaker as a single-pole 15-amp(or 20-amp) breaker.

Dual or piggyback breakers can usually be inserted only into panels thatprovide slots for their installation. They’re designed to protect two indi-vidually separate branch circuits. The dual breaker is normally the samewidth as a standard breaker but contains two half-thickness breakers,each with its own handle (Figure 13). A half breaker is simply one-half of adual breaker and can only be connected to one branch circuit. It’s some-times referred to in the trade as a “thin” breaker. As more dual and halfbreakers are used, the number of branch circuits connected in a panelincreases, as does the ambient temperature in the panel enclosure.Therefore, the allowable number of dual and half breakers is limited. Halfand dual breakers can only be installed in slots indicated by the panelbox manufacturer. These panels incorporate a special groove designedto accept a tab that’s formed into the bottom of the breaker. Only panelsthat are equipped with the groove can accept these special breakers.


FIGURE 13—Dual and half

breakers are designed to

fit only grooved slots in a

panel enclosure.

Double-pole breakers connect to both legs of the hot bus. These breakersnormally protect and control branch circuits that supply 240 volts.Double-pole breakers protecting residential branch circuits usually rangefrom 15 to 70 amps, with 30-amp breakers protecting most clothes dryerand water heater circuits. The 40- or 50-amp breakers are normally usedto protect the electric kitchen range and/or oven circuits.

Balancing Circuit Loads

As you’ve already learned, a standard 120/240 service includes two hotwires and a neutral. Each conductor is connected to a specific “bus,”which distributes the function of the conductor. The hot buses distributethe hot lines to the breakers, which in turn distribute the hot lines to theloads. The neutral bus distributes the grounded neutral to the branch-circuit neutral conductors, and the grounding bus distributes the equipmentground to the grounding conductors. The two hot conductors are 180degrees out of phase with each other. This means that when the alternatingcurrent in one hot bus reaches its maximum positive peak, the current inthe other bus reaches its maximum negative peak. Normally, the panel-board is designed so that half of the circuit breaker positions are arrangedto draw current from one of the hot buses while the other half draws fromthe other bus. The panel manufacturers accomplish this by “staggering”the connecting points from top to bottom in the panel. In other words,one breaker will connect to “a” phase while the next breaker will connectto “b” phase. This staggering goes from top to bottom in the panel. Thisisn’t information that you’ll need in your daily functions as an electrician,but it does help you to better understand why certain components aredesigned the way they are.

A balanced circuit load occurs when the current through each hot busis equal. When this happens, the positive peak current cancels out thenegative peak current and no current flows through the neutral conductor.Of course, it’s not likely that the two hot conductor currents will be equal.Hence, when the current levels aren’t equal, the neutral conductorcarries the difference in currents back to the panel. As an example, if branchcircuits attached to one bus draw 65 amps collectively, while those attachedto the other bus draw 75 amps collectively, the neutral conductor willcarry 10 amps (the difference between 65 and 75 amps) back to theneutral bus in the panel.

To better balance a circuit, distribute the loads equally between the twohot buses as much as possible. One method you may use is splitting thetwo small-appliance circuits to the kitchen between the two hot buses.

Installing a Grounding Electrode

As you know, every electrical service panel must include a groundingconductor. If possible, this conductor should be attached to a groundingelectrode. In some localities, it’s allowable to ground the electrical systemto the water main, but this type of grounding must be supplemented byan additional grounding electrode as specified in the NEC Article 250-50and Article 250-52. Grounding electrodes must be at least 8 feet long and


driven into the ground. They should maintain a continuous low-resistanceconductive contact with the soil. Rods made of ferrous (steel or iron)material must be at least 5

8 inch in diameter. Nonferrous rods (copperclad) must be at least 1

2 inch in diameter. The top of the rod to whichyou’ll attach the grounding conductor should be flush with or just belowthe surface. If the presence of rock makes it impossible to fully drive therod into the earth, it may be buried horizontally in a trench that’s at least2 1

2-feet deep, or driven at an angle not exceeding 45 degrees. You maynever shorten the 8-foot length of a grounding rod by cutting portionsfrom the rod. It must always remain 8 feet in length. Depending onlightning hazards, you may need to install more than one grounding rod.

The NEC and local codes specify many of the procedures associatedwith the installation of the grounding system. The NEC also specifiesthat the conductor used to connect the grounding rod to the servicepanel be free from interruptions or splices.

Grounding and Bonding of Service and Equipment

The word bonding is defined as the coming together of all metal parts inthe system so that no potential difference exists between them.

Remember that grounding is the interconnection of all metal componentswith the grounding conductor to provide a low-impedance path forfault-current flow should one of the energized conductors come intocontact with the metal components.

When installing any electrical service, always bond the neutral bar to thepanel enclosure. If any fault current develops on the system it will flowacross the equipment, through the bonding screw and onto the servicegrounded conductor. This will cause the overcurrent device to open,thus eliminating dangerous voltages on the equipment.

The neutral bar may be bonded in any one of the following ways.

� Using a bonding screw. In 100 and 200 ampere panels the bondingscrew is normally a 10/32-type screw that’s generally green incolor.

� Attaching a bonding strap. The thickness of the strap may varydepending on the rated loads of the panel.

� Installing a bonding conductor (or jumper). Consult Table 1 for thesize of bonding conductor needed to bond a neutral bar. Note thatthis table, which is taken from the NEC, is for grounding electrodeconductors. That’s because Article 250-102(c) states that bondingjumpers can’t be smaller than the grounding electrode conductor.


All raceways for the service entrance shall be bonded together. Again,Table 1 indicates the size of the bonding jumper needed. If the conductorswithin the conduit or the conduits themselves are larger than 1100 kcmilcopper or 1750 kcmil aluminum, the bonding jumper shall have an areanot less than 12 1

2 percent of the area of the largest phase conductor. Inthe case of parallel conductors, the largest area of a phase conductor isconsidered to be the sum of the areas of the conductors paralleled in onephase.


Table 1

GROUNDING ELECTRODE CONDUCTOR FOR ALTERNATING-CURRENT SYSTEMS

Size of Largest Service-Entrance Conductor or

Equivalent Area for Parallel Conductors1Size of Grounding Electrode Conductor

CopperAluminum or

Copper-Clad AluminumCopper

Aluminum or

Copper-Clad Aluminum2

2 or smaller 1/0 or smaller 8 6

1 or 1/0 2/0 or 3/0 6 4

2/0 or 3/0 4/0 or 250 kcmil 4 2

Over 3/0 through350 kcmil

Over 250 kcmilthrough 500 kcmil

2 1/0



1/0 3/0



2/0 4/0

Over 1100 kcmil Over 1750 kcmil 3/0 250 kcmil

Notes:

(a) Where multiple sets of service-entrance conductors are used as permitted in Section 230-40, ExceptionNo. 2, the equivalent size of the largest service-entrance conductor shall be determined by the largestsum of the areas of the corresponding conductors of each set.

(b) Where there are no service-entrance conductors, the grounding electrode conductor size shall bedetermined by the equivalent size of the largest service-entrance conductor required for the loadto be served.

1This table also applies to the derived conductors of separately derived AC systems.

2See installation restrictions in Section 250-64(a) of the NEC

(Reprinted with permission from NFPA 70-1999, the National Electrical Code®, Copyright© 1998, National Fire Protection Association, on thereferenced subject which is represented only by the standard in its entirety. National Electrical Code® and NEC® are registered trademarksof the National Fire Protection Association, Inc., Quincy, MA 02269)

Let’s work through several example problems using Table 1.

Problem 1:

What size of copper-bonding jumper is required to bond a metal conduitwith three 500-kcmil THWN Cu conductors and one neutral conductor?

Solution:

Figure 14 shows that we have only one 500 kcmil per phase. Refer toTable 1 under service-entrance conductors in the Copper column. A500 kcmil conductor falls under the “Over 350 kcmil through 600 kcmil”category. Therefore, 1/0-size copper wire is needed to bond the metalconduit properly.



the bonding of a raceway

with three conductors.

Problem 2:

What size copper-bonding jumper is required to bond three racewaysusing one bonding jumper, where each metal conduit contains three600-kcmil Cu conductors that are parallel per phase? Figure 15 illustratesthis example.

Solution:

The first step is to add up the conductors to find the total kcmil perphase (600 � 3 = 1800 kcmil). Now that we know we have an area of1800 kcmil per phase, we can check Table 1 for the size of the bondingjumper needed.

Since Table 1 only goes up to 1100 kcmil Cu, we’re now required to take12 1

2 % of the largest phase conductor. (The largest phase conductor isconsidered to be the total area of the parallel conductors, or 1800 kcmil.)

1800 kcmil � 0.125 = 225 kcmil


FIGURE 15—This shows the

bonding of three raceways

in a series with three

parallel-phase conductors.

Rounding off, we find that 250 kcmil bonding jumper is required tobond all three metal conduits properly.

Let’s take this example one step further. Everything remains the same,except, instead of having all three conduits bonded in a series, eachconduit will be bonded individually. See Figure 16.

Using Table 1, locate the largest phase conductor in the conduit (asexplained in note [a]). This would be 600 kcmil Cu. Then refer to the“Over 350 kcmil through 600 kcmil” column in Table 1. A 1/0-sizeconductor is the minimum size that would be required to bond eachconduit properly.


FIGURE 16—One bonding

jumper to each conduit

requires only a 1/0 Cu

when bonding individually.

This example shows that if the situations permits, it’s more cost-effective(material and labor) to bond each conduit individually in a paralleledsystem.

The interior metal piping through a building must also be bonded. Table 1also sizes the bonding conductor for the metal piping. Refer to Figure 17that shows the proper bonding of the interior metal water pipe. Keep inmind that it serves no purpose to bond non-metallic water piping suchas PVC.

Should you decide or be required to run the bonding conductor in ametal conduit, you then must also bond the conduit itself to thewaterline. See Figures 18 and 19.


FIGURE 17—This shows bonding of interior metal pipes.


FIGURE 18—This shows bonding of a raceway to a water pipe.

The following items should be bonded together to make up the groundingelectrode system if they’re available on the premises: (a) metal under-ground water pipe (10 feet or more of metal pipe in direct contact withthe earth); (b) metal frame of building (where building is intentionallygrounded to the earth); (c) concrete-encased electrode; and (d) groundingring (constructed by burying at least 20 feet of #2 or larger bare copperwire in a trench 2 1

2 feet deep or more, encircling the building or structurerequiring the grounding system). The size of the grounding conductor isfound in Table 1 unless otherwise noted on the plans or drawings.

Should none of these items be available, you would then be requiredto install grounding rods, pipe electrodes (minimum 3

4-inch trade sizeiron or steel, metal coated to prevent corrosion), or electrode plates(minimum 1

4-inch thick iron or steel plate or minimum .06 -inch thicknonferrous plate, with at least 2 square feet of plate surface exposed tothe soil)�

If we installed a 400-A three-phase service and had access to all of theseitems, the installation would look much like the installation in Figure 20.

Bonding and grounding protects against the unpredictable groundfaults and shorts which may develop in any electrical system. Properbonding and grounding of a system won’t only lessen personnel exposureto high voltages and potential damage to conductors and equipment,but should also open affected overcurrent devices.



close-up view of the

bonding jumper area in

Figure 18.


FIGURE 20—This shows a grounding electrode system.

Subpanels

There may be instances in a residential wiring plan that call for a subpanelinstallation. One may be that when a large number of major appliancesand similar heavy loads are located a long distance from the servicepanel, a subpanel may be needed to supply these appliances or loads.Subpanels are also used when an addition is added onto a house.An addition usually requires several branch circuits and is generallylocated quite far from the original service panel. Subpanels are sometimesinstalled when adding equipment such as room air conditioners,dishwashers, etc. because the existing service panel has no more roomfor additional breakers.

In new installations, installing subpanels may reduce the amount ofconductor-routing work by permitting the electrician to install only onelarge feeder cable from the service panel to the subpanel. The subpanelcan then be located much closer to the locations of the loads. A subpanelresembles and functions much like a regular panel, with some exceptions.First, because the subpanel is fed through the main panel, there’s noneed for a main breaker in the subpanel (although you may still installone if you wish). Secondly, the neutral and ground buses in the subpanelmust be completely isolated from one another. This means that theycan’t be directly connected to one another and that the neutral bus mustbe isolated from contacting the subpanel enclosure by mounting it inthe enclosure using some type of insulating material. This is usuallyaccomplished with plastic separators between the neutral bus and theenclosure. As just learned, components such as panels, subpanels, andother enclosures must be connected to equipment ground. Because ofthe required separation between the neutral and ground buses, theequipment-bonding device may only be connected to the ground busand not the neutral bus.

Power is supplied to the subpanel directly from the service panel,normally using a four-conductor service-entrance cable.

Now take a few moments to review what you’ve learned by completingSelf-Check 2.



✔ Self-Check 21. True or False? If possible, it’s best to ground each conductor individually.

2. Bonding screws are used to bond the _______ bar.

3. The main breaker can be used as the service _______.

4. The drip loop of the SEC attached to the building must be at least _______ feet above theground where only pedestrian traffic is a concern.

5. True or False? Residential wiring must always have a subpanel installed.

6. The neutral bus and subpanel are normally isolated by _______.

7. Heating and burning of conductors caused by short circuits can be reduced by bonding and_______.


LOCATING RESIDENTIAL DEVICES

Wiring Layout for a Small House

Quite often, the electrician won’t receive complete and adequate plansfor small residential dwellings. An experienced electrician can use abuilding plan as a basis for designing an electrical layout that complieswith the National Electrical Code and any local codes.

Figure 21 shows a wiring layout plan for a three-bedroom ranch-typehouse with a basement. Assume that the laundry facilities and the servicepanel are in the basement. The basement plan with its wiring layoutisn’t shown in this drawing. The outlets are indicated using the standardelectrical symbols you should be familiar with by now. All duplex receptaclesare grounding-type receptacles.


FIGURE 21—This shows a wiring layout for a small house.

The arrowheads on the circuits indicate the home runs, which are the cableruns to the distribution panel where the branch-circuit protective devicesare located. The number of 2- and 3-wire circuits can be found by countingthe arrowheads. The home runs for each circuit normally begin at theoutlet nearest the panel. The ideal location for the panel is where the loadis concentrated, which is in the kitchen and laundry. The location of thehome runs in Figure 21 isn’t typical of a house because the home runsshown here are scattered without regard to the possible panel location.Branch circuits normally end at lighting outlets or receptacle outlets. Thelight gray lines connecting the outlets in Figure 21 represent runs ofcable. Broken lines are also used sometimes to indicate exposed wiringin the basement, but the basement isn’t shown in this wiring layout.

In the kitchen, receptacles have been provided for the refrigerator, clock,iron, can opener, toaster, and other small appliances. A special outlet Sis provided for an ironing station. It’s equipped with a switch and pilotlamp so that the homeowner will know whether the iron is on or not. Aspecial receptacle (R) is provided for the range. Several special outletsare represented in the wiring plan, including one for a clock (C),dishwasher (DW), garbage disposal (GD), and range hood (RH). Eachspecial outlet is identified on the drawing to indicate its use. Many rangehoods contain both a fan and a lamp so separate fan and lamp holderoutlets aren’t shown. Note that the kitchen and dining room share twosmall-appliance circuits and these circuits don’t enter other rooms. TheNEC doesn’t permit these circuits to supply power to any other roomsexcept breakfast nooks.

A sufficient number of receptacles are installed in the other rooms. They’respaced approximately equal distances apart. The distance betweenadjacent receptacles in the same room (excluding kitchen and bathroom)should always be less than 12 feet according to the NEC. Each bedroom isequipped with a combination switch and a receptacle outlet as well as aceiling light for general lighting. Each closet has an enclosed lampfixture controlled by a pull-chain switch. The receptacle at the entrancedoor is conveniently located for connecting a vacuum cleaner or othersmall appliances.

The bathroom has a ceiling light for general lighting and special lights atthe mirror. Electric heating is often used in the bathroom to supplementthe regular heating. All receptacles in a bathroom shall be ground-faultprotected. The bathroom circuit may not supply any other room otherthan another bathroom.

A split-wired duplex receptacle is shown near the front door in the cornerof the living room. The top half of the receptacle is wired so that it’s con-trolled by two three-way switches. The bottom half is always energized.This permits a lamp to be plugged into the top half and controlledfrom the front door and the hall, while an appliance such as a clock maybe plugged into the bottom half. The terrace is equipped with twoground-fault-type weatherproof (WP) receptacles for portable lamps,decorative lighting, or tools. Because two receptacles are installed, there’s noneed to pass cords over the doorway, thus reducing the chance of


damaging cord insulation. Switches are often used to control weatherproofoutlets, which allow the outlets to be used more easily.

Three-way switches are used in the hall, kitchen, and living room toreduce the need of retracing steps when a person moves from one partof the house to the other. Another convenient feature is the push-buttondoor-chime switches located at both exterior doors to control the chimelocated in the hall.

Location of Receptacles

There isn’t a required height for mounting receptacles but a convenientrecommended height for duplex receptacles is 16 inches (in.) above thefloor. At that height, the outlet is more accessible and more adaptableto appliance cords. In the kitchen, bathroom, laundry, and garage, arecommended height for receptacles is 48 inches above the floor. Inthe kitchen, that height equates to approximately 12 inches above thecountertops.

Present practice is to provide enough receptacles so that no point in aroom (except kitchen and bathroom) is more than 6 feet from a receptacle.Thus, the distance between receptacles is always less than 12 feet. Anywall space greater than two feet in length shall require a receptacle.Sliding panels, such as sliding glass doors, aren’t counted as wall spaceaccording to the NEC Article 210-52(a)(2)(d). The receptacles should beapproximately equally spaced. However, the spacing may be changedsomewhat to address anticipated placement of furniture. In the kitchen,receptacles installed on a countertop shall be installed so that no pointalong the counter (measured horizontally) is more than 24 inches froma receptacle outlet. A receptacle outlet should also be installed to serveeach counter space 12 inches wide or wider. The receptacle for the refrig-erator should be hidden from view when the refrigerator is in place.

Weatherproof GFCI (ground-fault circuit interrupter) receptacles shouldbe installed at convenient outdoor locations, front and back, for supplyingdecorative lighting and power tools. These receptacles should be kept atleast 18 inches above ground level for protection of the receptacle andease of accessibility. Special receptacles with key locks are available foruse where vandalism is a problem. For extra convenience, wall-mountedswitches may control these outdoor receptacles.

Location of Switches

A convenient height for light switches is approximately 48 inches abovethe finished floor, on the lock side of a door, and within 6 inches of thedoor frame. Switch locations should be carefully planned to accommodatethe residents by following the normal course of passage from room toroom that a resident may normally take. For example, upon entering thehouse a person should be able to turn on a light without taking many


steps. Upon leaving that room, they should also be able to enter the hallor another room, turn on lights conveniently and turn off the precedinglight. This accommodation can be accomplished by installing three- andfour-way switches. A combination switch and pilot may be installed ina situation where a light, such as a basement light, can’t be seen from theswitch location. Of course, the combination switch and pilot lightshould be installed in a convenient place where it can be seen. Whenthe branch-circuit wires are run from the panel to the switch and then tothe light, it’s possible to install a combination switch and receptacle at theswitch location because both the hot wire and the neutral wire are present.With a combination switch and receptacle the receptacle is alwaysenergized regardless of the position of the light switch.

Location of Lighting Outlets

A minimum of at least one lighting outlet controlled by a light switchshould be installed in every habitable room and bathroom. Wall-mountedlighting fixtures are useful at the mirror in the bathroom and should beplaced about 4 1

2 to 5 12 feet above the floor, depending upon their design

and intended use. A fluorescent light on each side of the mirror mayprovide substantial light. Incandescent lamps or a single fluorescentlamp may also be used but don’t always provide sufficient light. Somebathroom cabinets are constructed with lamp fixtures and receptaclesincluded. A wall-mounted light switch should be installed to control thelight on the cabinet regardless of the switching mechanism provided onthe cabinet assembly. Likewise, the receptacle on the cabinet cannot becounted as the necessary receptacle requirement for the bathroom. Wheninstalling lighting in an enclosed shower stall, an approved “ListedFixture,” or “Suitable for Wet Locations” type fixture should be installed.A wall switch outside the shower stall should control the light in theshower. Don’t install the switch in the shower stall.

Hallways, stairways, and attached garages should have at least onelighting outlet controlled by a light switch. Special lighting outlets atbookcases, fireplaces, coves, draperies, cornices, and kitchen workspaces call for special location planning. Consideration should also begiven to outdoor lighting in addition to lighting that may be pluggedinto the weatherproof receptacles. These lighting additions may includeweatherproof spotlights, floodlights, sidewalk lighting, or post lightswith automatic switching. When controlling lights from the exterior ofthe building, always use weatherproof switches.

Listing of Residential Outlets

Table 2 lists suggested outlets for residences. Specialty outlets, whichmay be needed for home businesses and hobbies, aren’t listed andrequire special consideration.


Table 2

SUMMARY OF SUGGESTED OUTLETS FOR RESIDENCES

Space Lighting OutletsType of

CircuitsConvenience Outlets

Type of

CircuitsSpecial-Purpose Outlets

Type of

Circuits

Living room,

library, den,

sunroom,

family room

One ceiling outlet, wall-switchcontrolled. Two outlets whereroom length exceeds twicethe width. Wall, cove, orvalance outlets may besubstituted.

Gen. No point at wall line more thansix ft from an outlet. Wall spacestwo ft or more have outlet,excluding sliding panels. Outletin mantel shelf. One or moreswitch-controlled outlet(s).

Gen. Outlet for room air conditioner if nocentral air conditioner is planned.

Ind.

Dining room,

dinette,

breakfast room

One ceiling outlet, wall-switchcontrolled.

Gen. No point at wall line more thansix ft from an outlet. Wall spacestwo ft or more to have outlet,excluding sliding panels.

App.

Kitchen,

kitchenette

One ceiling outlet, wall-switchcontrolled.

Gen. Two circuit minimum. No pointmeasured horizontally oncountertop shall be more than24 in. from GFCI outlet. OneGFCI outlet at refrigeratorlocation. One GFCI outlet foreach counter one ft or wider.

App. One outlet for range.One outlet for clock.One outlet for vent hood.One outlet for dishwasher.One outlet for garbagedisposal unit.

Ind. (3-wire)GeneralGeneral

Ind.

Ind.

Laundry One ceiling outlet at ironingcenter. Wall-switch control forone ceiling outlet.

One outlet for washer.One outlet for hand iron or ironer.One outlet for clothes dryer.

Ind.Lau.Ind.

Bedrooms One overheadoutlet, wall-switch controlled.

Gen. No point at wall live more thansix ft from outlet. Wall spacestwo ft or more to have outletexcluding sliding panels.

Gen. One outlet for room air conditioneror portable space heater.

Ind.

Reception

room

One outlet, switch-controlled. Gen. One outlet for each 10 ft or morein length.

Gen.

Halls One outlet for each 10 ft,wall-switch controlled.

Gen. Gen.

Stairways One outlet on each floor toilluminate head and foot ofstairway. Each outlet to havemultiple-switch control athead and foot of stairwaywhere difference in floor levelis six or more steps.

Gen. One general-use outlet,especially at intermediatelandings of large area.

Gen.

44W

iring

Electrical

Circu

its

Summary of Suggested Outlets for Residences—Continued

SpaceLighting

Outlets

Type of

CircuitsConvenience Outlets

Type of

Circuits

Special-Purpose

Outlets

Type of

Circuits

Closets,

exterior

entrances

One outlet per closet. One ortwo outlets, wall-switchcontrolled.

Gen. One weatherproof GFCI outletat front and rear entrance 18 in.above grade.

Gen.

Covered

porches

One outlet for 75 sq. ft ofporch floor, wall switch-controlled.

Gen. One weatherproof GFCI outletfor each 15 ft of house borderingporch and located 18 in. abovegrade.

Gen.

Terraces, patios One outlet on post orbuilding, wall-switchcontrolled inside door.

Gen. One outlet for each 15 ft ofhouse wall bordering porchlocated 18 in. above grade.

Gen.

Basement utility

space

One outlet for each enclosedspace, one for workbench,and one for furnace location.Sufficient additional outlets toprovide one for each 150 sq.ft of open space.

Gen. One outlet at workbenchlocation, one at furnacelocation.

Gen. One outlet for electrical equipmentused in connection with furnaceoperation or central electric spaceheater.

Ind.

Accessible

attics

One outlet from foot of stairs.One outlet for each enclosedspace.

Gen. One outlet for general use. Gen. 1 outlet for summer cooling fan,controlled from several switchlocations.

Ind.

Garage One interior wall-switch outletfor one- or two-car garage.One outlet for exteriorlighting, multiple-switchcontrolled if garage isdetached from house.

Gen. One GFCI outlet for one- ortwo-car garages.

Gen. One outlet each for food freezer,GFCI on workbench, etc., ifplanned.

Ind.

1. Gen: outlets supplied by general-purpose circuits2. App: outlets supplied by small-appliance circuits3. Ind: outlets supplied by individual equipment circuits4. Lau: outlets supplied by laundry circuit

Note: A convenience outlet shall be at least of the duplex type (two or more plug-in positions) except as otherwise specified.

All spaces for which wall-switch controls are required, and which have no more than one principal entrance, shall be equipped with multiple-switch control at the lock side of doors or thetraffic side of arches. If this requirement would result in the placing of switches controlling the same light within 10 ft of each other, one of the switch locations may be eliminated.

Wirin

gE

lectricalC

ircuits

45

Not all the outlets listed are likely to be used in any one installation.However, Table 2 is a good checklist to consult when deciding whetherthe planned electrical wiring has enough outlets for safety andconvenience.

Area Requirements

Figure 22 shows a wiring plan for a three-level house. Starting with theliving room, we’ll examine some of the electrical circuits and outlets thatshould be considered when wiring a new home or adding circuits to anolder home.

Living Room Requirements

Wiring requirements for the living room shown in Figure 23 also applyto sun rooms, dens, family rooms, and libraries. Decorative lighting is amajor design feature and often takes precedence over other neededfeatures such as adequate lighting for reading.

In new homes, it’s not an uncommon practice to omit a ceiling lightoutlet in the center of the living room. Lighting is typically installed onwalls, in nooks, or is supplied by portable lamps plugged into general-purpose receptacles. In Figure 23, the two three-way switches in theliving room are used to control a fluorescent lamp that’s installed behinda valance.



FIGURE 22—The GFCI

receptacles are the only

protective devices shown in

this layout. They must be

used in the bathroom,

kitchen countertops,

garages, and on the outside

of the house. It’s important to

note that lighting for closets

is required by the NEC to

have the bulb totally

enclosed.

Because there’s no central ceiling light outlet in the living room, a wallswitch at the living room entrance controls at least one of the convenienceoutlets placed around the room. This arrangement permits a portablelight like an end table lamp to be switched on from the doorway. In somedesigns, the top receptacles of a duplex receptacle are switch controlledwhile the bottom receptacles stay hot at all times.

The switch-controlled outlets are called split receptacles. In such outlets,the common hot metal tab is broken off, making the two receptaclesseparate. The common neutral metal tab remains intact, supplying acommon neutral to both parts of the receptacle.

The location standards for these receptacles are the same as thosementioned earlier in this lesson. The outlets should be installed 12 inchesabove the floor line and installed approximately 12 feet apart around thewall space so that no point along the floor line is more than 6 feet froman outlet.

If there’s a break in the wall, such as a sliding glass door or an archway,locate the outlets near the break.

Some convenience outlets may be flush-mounted on mantel shelves, inbookcases, and in areas for decorative lighting effects.

A special-purpose outlet must be installed if a room-type air conditioningunit is to be installed.


FRONT

DOOR

DINING

ROOMKITCHEN

FLUORESCENT LIGHT

S3 S

3

S3

S

LIVING ROOM WIRING PLAN

TO SECOND

LEVEL

FIGURE 23—Unless there

is a lot of decorative

lighting, the living room

wiring is very simple.

Dining Room Requirements

A dining room normally has a ceiling outlet directly over the proposedlocation of the table, as shown in Figure 24. A wall switch controls theceiling outlet and more often than not, a dimmer switch is used. Break-fast nooks also have ceiling outlets but these outlets aren’t normallydimmer-controlled.

Convenience outlets are installed around the dining room walls andmay be supplied by the 20-ampere small-appliance circuits supplyingthe kitchen countertop receptacles. However, it’s highly recommendedthat separate 20-ampere branch circuits supply these receptacles due to ahigh load potential caused by small appliances such as hot plates, toasterovens and the like. When a dining table or breakfast table is placed nextto a wall, an outlet located approximately 4 inches above the proposedtable height is often useful for appliances such as toasters.

Some dining rooms may be equipped with serving counters or servingbars. An extra outlet just above the end of the counter is handy forappliances such as blenders and ice crushers. This outlet is a NECrequirement if the bar is a minimum of two feet by one foot in measure-ment. If the bar is considered a “wet bar” with a water-supplied sink, thereceptacle must be GFCI protected.


FIGURE 24—Dining Room

Layout

Three other noteworthy dining-room circuit features should be pointedout. First, locating the light switch on the other side of the kitchen doormight be convenient. This would make the switch handier for anyoneentering or leaving the back door. Second, notice that a receptacle outletis located on the wall between the kitchen doorway and the back door.Thirdly, in order to comply with the NEC requirement that no pointalong a room’s wall be more than six feet from a convenience outlet,you will need to install a receptacle outlet on the back wall.

Powder Room and Bathroom Requirements

The powder room with only a sink, mirror, and dressing table is becomingmore common, since it relieves the main bathroom traffic. The NECdefines a bathroom as a room that’s equipped with a basin and at leastone of the following: a tub, commode, or shower. If a room doesn’t meetthe criteria found in this definition, it’s not considered a bathroom anddoesn’t have to comply with the electrical requirements for a bath-room. It would then normally require only one receptacle outlet andgood lighting for the mirror.

Rooms like the residential floor plan in Figure 22 and the one shown inFigure 25 are defined as bathrooms and must meet or exceed the electri-cal requirements for bathrooms.


S S

SHOWER

STALL

GFCI

BATHROOM WIRING PLAN

SINK

TOILET

FIGURE 25—Some bathrooms may also have special-purpose outlets for space heaters and exhaust fans. The

switch-controlled fan can be part of a light fixture or an individual fixture. Another option is a light fixture in the

shower stall.

Lighting at the mirror should be carefully planned. Illumination of theentire face and neck without shadows is ideal. Single concentrated lightsources usually don’t accommodate this. Light fixtures ranging from twinfixtures to various kinds of makeup fixtures are much more efficient.

Ceiling lamps installed to provide illumination to the front edge of thewashbasin provide improved personal lighting at the mirror. Whenmore than one mirror is located in the room, extra lighting is requiredfor each mirror.

Shower stalls may have a vapor-proof light fixture installed, with thewall switch installed outside of the stall. Steam bath and whirlpoolappliances are supplied separately or may be plugged into convenienceoutlets if the load isn’t extremely high. Infrared and ultraviolet lightfixtures may be installed as ceiling fixtures. Receptacles should beprovided in proximity to each mirror to accommodate electric razors,hair dryers, and other small, personal appliances. All receptacles in abathroom must be of the GFCI type.

Special-purpose outlets may also be installed in bathrooms to supplyspace heaters and ventilating fans. Usually the vent fan is switch controlled.It may be directly attached to a ceiling light or installed as an individualfixture. Switch-controlled nightlights are also recommended as aconvenience feature in bathrooms.

Kitchen Requirements

The electric requirements of a kitchen are more numerous than otherrooms in a house and call for additional planning (Figure 26).

Wall switches usually control most general lighting in a kitchen. Thekitchen should be illuminated so that light is directed on the countertops,sink, range, dishwasher, work area, and kitchen table. The interiors ofcabinets and other storage areas may have their own fixtures installed tosatisfy special designs.

As a rule, kitchen countertop receptacles should be supplied by atleast two small-appliance circuits. Receptacles on countertops shall beinstalled so that no point along the counter space is more than 24 inches(horizontally) from a receptacle outlet. Countertop receptacles should beinstalled approximately 12 inches from the countertop to the bottom ofthe receptacle. If a kitchen desk or cookbook shelf is planned, one outletshould be installed to supply that specialized area. Tables placed againstwalls should also have one outlet just above table level to accommodatefood preparation and warming appliances.

The refrigerator should have its own circuit and outlet. All otherconvenience outlets may be split-receptacle types connected to two ormore 20-A small-appliance circuits.

Special-purpose circuits and outlets are used for the electric range,ventilating fan, dishwasher, garbage disposal, food freezer, and othermajor appliances located in the kitchen.



FIGURE 26—Note that the

compact kitchen has almost

every major appliance

installed.

Bedroom Requirements

The standard bedroom generally requires ceiling or cornice-type generalillumination. The sample-bedroom layouts shown in Figures 22 and 27indicate ceiling light outlets. Light fixtures over full-length mirrors andvanities are also convenient.


FIGURE 27—Install a sufficient number of receptacles in the bedroom. Usually, the night tables next to a bed will

hold such items as lamps, clocks, and radios.

A bedroom normally requires numerous convenience outlets to powerelectric appliances since furniture arrangements vary extensively. Theseoutlets may accommodate electric blankets, televisions, radios, clocks,bed lamps, electric coffeemakers, and even small refrigerators. The 6-footrule must be followed in locating these receptacles. In many modern,custom-designed homes, remote-control switching consoles may beinstalled to control lighting located both inside and outside the dwelling.The master console unit is usually installed in the master bedroom. Specialoutlets should be provided to supply power to these consoles.

Basement Requirements

The lighting for an unfinished basement, like the one shown in Figure 28,is more functional than decorative. Typical basement wiring can be almostcommercial appearing in nature. General illumination requirements areusually one luminescent light for each 150 square feet of open space.Although there should be no dark areas in a basement, it’s not a require-ment to light individual areas in an unfinished basement.


FIGURE 28—Most modern,

finished basements require

numerous circuits, since

they contain work areas,

laundry areas, and family

rooms.

A wall switch at the head of the stairs should control the light at the footof the stairs. If the number of stairs is six or more, two three-way switchesshould be installed, with one at the top of the stairs and the other at thebottom of the stairs. The switch at the top of the stairs should be equippedwith a pilot light and be located so that no reaching is required to operatethe switch. Fixtures with pull chains may be used in the remainingsections of the basement. If the basement is equipped with a workbench,one 20-ampere circuit and receptacle should be installed to supplypower to the workbench.

Outlets are also required if laundry appliances are located in the basement,but these circuits should follow the same rules that apply to thosepreviously covered for laundry areas. Any other areas set aside in thebasement for special usage should be supplied with the necessary circuitsand receptacles required. Appliances such as emergency water (sump)pumps, dehumidifiers, and space heaters should have special-purposecircuits installed that are rated according to the load demand of theappliance or equipment.

All general-purpose receptacles in an unfinished basement must beGFCI. Receptacles that are of the single type and dedicated to supplypower to equipment such as freezers and pumps aren’t required to beof the GFCI type. Receptacles located in a finished basement aren’trequired to be of the GFCI type.

Outside Area Requirements

When an outdoor roofed area such as a porch has more than 75 sq ft offloor area, a wall switch should control a lighting outlet. Large areasmay need two or more lighting outletsas shown in Figure 29.

Multiple-switch control is especially useful at entrances. This is true whenthe entrance is a passageway such as between the garage and house.When the outdoor area isn’t roofed, such as a terrace or a patio, it shouldbe generally illuminated using wall or post fixtures. A wall switch insidethe house should control that lighting. In the garage or carport, it’scommon to install one ceiling outlet with three-way switching control inthe home and at garage doors.

On the exterior grounds, floodlights are especially useful to illuminatethe area. Colored lights and special effects can add decoration in additionto providing added illumination.

Weatherproof convenience outlets should be installed in convenientoutside locations both front and rear, on walls that border porches,terraces, and patios. The outlets should also have ground-fault protection.


At least one general-purpose convenience outlet should be installedin a one- or two-car garage or carport and it must be GFCI-protected.When the garage is also used to hold a food freezer or is equipped withan electric garage-door opener, special-purpose outlets must be installedto address these additions. These special-purpose outlets aren’t requiredto be GFCI, providing the receptacle is installed as a single-type recepta-cle for special-purpose usage.

Fixtures in Closets

The NEC defines storage space as “a volume bounded by the sides andback closet walls and planes extending from the closet door vertically tothe height of 6 feet, or the highest clothing-hanging rod and parallel tothe walls at a horizontal distance of 24 inches from the sides and back ofthe closet walls respectively, and continuing vertically to the closet ceilingparallel to the walls at a horizontal distance of 12 inches or the width ofthe shelf, whichever is greater.”

In the past, people could install all types of surface-mounted and recessedincandescent fixtures directly over the shelves in closets. When clothes,boxes, etc., were stored on the shelves, some of this material wouldcome in contact with the fixture creating a fire hazard within the closet.


FIGURE 29—Lighting outdoor

areas requires special

considerations.

Because of those potential fire hazards, the NEC now only allows twotypes of lighting fixtures in closets:

1. Surface-mount or recessed incandescent fixtures with the lampcompletely enclosed.

2. Surface-mount or recessed fluorescent fixtures with the lampexposed or enclosed.

A surface-mounted incandescent fixture mounted over a door on thewall or ceiling must be a minimum of 12 inches from the shelf or, ifthere’s no shelf, 24 inches from the wall (Figure 30).

A recessed incandescent fixture must be a minimum of 6 inches fromthe edge of the shelf or 18 inches from the wall to the fixture trim(Figure 31A).

Surface-mount or recessed fluorescent fixtures must be a minimumof 6 inches from the edge of the shelf or 18 inches from the wall(Figure 31B).


FIGURE 30—This shows the

clearance requirements

for surface-mounted

incandescent lightning

fixtures.




the clearance

requirements for

recessed incandescent

and any fluorescent

lighting fixtures.


✔ Self-Check 31. The maximum distance from any point along the floor line to a receptacle in the living

room is ______ feet.

2. True or False? The dining room usually has an outlet for a ceiling-mounted light.

3. Which room in a new house other than the kitchen must have receptacles protected by aGFCI device?

______________________________________________________________________________

4. In which room of a house would you probably find the master control unit for a remotelycontrolled lighting system?

______________________________________________________________________________

5. When should a switch be equipped with a pilot light?

______________________________________________________________________________


GENERAL CIRCUIT WIRING CONSIDERATIONS

When installing general-purpose, small-appliance, and special-purposecircuits, certain considerations must be kept in mind. This section of textexplains these considerations as they apply to each type of circuit. Inaddition, special considerations that apply to larger appliance circuitswill be discussed in greater depth. You’ll learn how the NEC classifiesappliances by groups—fixed, portable, and stationary, that someappliances require their own branch circuit, while others may require agrounded neutral wire.

General-Purpose Circuits

General-purpose circuits are two-conductor circuits that provide 120 V tothe lighting outlets and general-purpose convenience outlets, notincluding the kitchen countertops, laundry room, or bathroom. Tworules of thumb apply for the number of circuits to be installed in aresidence.

� Install one 20-A circuit for no more than 750 square feetof floorspace.

� Install one 15-A circuit for no more than 500 square feetof floorspace.

In residential wiring applications, there aren’t a limited number of recep-tacles that can be installed on a general-purpose circuit. Electriciansusually install six to ten outlets per circuit and divide the circuits as evenlyas possible between the general-purpose receptacles. One considerationin deciding which receptacles should connect to which circuit mightbe economics. A good rule of economics is to connect the outlets in aconfiguration that uses the least amount of wire or cable. Anotheralternative the electrician should consider in the configuration of thecircuitry of the outlets in any one room is connecting the outlets so thatthey’re on more than just one circuit. Wiring in this manner permitssome of the receptacles in the room to remain energized, providinglighting and power when the current serving the rest of the room fails.This is done in case one of the circuits should fail or require turning offfor repair or other reasons. Outlets with split-wired receptacles may beinstalled in the living room, kitchen, family room, dining areas, andlaundry room.

Small-Appliance Circuits

As you know, at least two small-appliance circuits are required in akitchen. These same two circuits can be extended into an adjoiningdining area. However, it’s recommended that you install additionalcircuits for dining areas and other adjoining rooms. Only one appli-ance circuit is required in a separate laundry area.


Special-Purpose Circuits

Certain types of appliances require their own branch circuit. This meansthat each appliance has its own conductors, outlet, and circuit breaker orfuse.

These circuits can have ampacities of 15, 20, 30, 40, 50, 60, or even 70A.These special-purpose or individual equipment circuits are considered to havea relatively high load demand but their ampacities aren’t necessarilyextremely high. One of the reasons an individual circuit may be neededis that the electrical load is heavy enough that no other load can sharethe circuit without overloading it. For example, an electric range may berated at 20 kW (kilowatts). It would require a 240-volt, 50-A, three-wirecircuit. A household electric-clothes dryer may require a 240-volt, 30-A,three-wire circuit. With an insulated neutral conductor should be insu-lated. A standard residential washing machine normally requires a 120-volt, 20-A, two-wire circuit. A combination washer-dryer usually re-quires a 240-volt, 40-A, three-wire circuit. A water heater also requires aspecial-purpose circuit, usually a 240-volt, 30 A, two-wire circuit.

Special-purpose circuits are also used for appliances that are eitherautomatically controlled or will be running for long periods withoutsupervision. For example, the circuit that supplies power to fuel-firedheating equipment such as a furnace is normally controlled by a thermo-stat. An individual circuit is required so that if a fault develops in theequipment, the circuit’s protective device will open, removing powerfrom only the one outlet. This avoids the likelihood of other nonrelatedcircuits being opened as a result of the equipment problem. Should agroup of outlets share the same circuit as other major appliances andone of the connected loads causes the breaker to trip, power could beinterrupted to equipment such as food freezers, refrigerators and thelike, resulting in expensive food spoilage.

Dishwashers and garbage disposals are sometimes connected to the samecircuit since they’re seldom in operation at the same time. The preferredway, however, is to have each one on its own circuit. Table 3 lists theelectrical and wiring requirements for several special-purpose circuits.Always check the nameplate on the equipment to verify the equipment’sload demand, as it may differ from those listed in Table 3.


Appliance Circuit Connections

Let’s look at how some special-purpose circuits are wired. Smallerappliances can be connected to the standard receptacles, which are ratedat 15 or 20 A. A small appliance is one that can be easily moved fromone location to another by simply unplugging it, picking it up andmoving it. This type of appliance may include a blender, toaster, foodprocessor, etc. Heavier-load demanding appliances often need their owncircuit and require special connection configurations. Figure 32 showstwo types of special receptacles generally used for some of theseheavier-load demanding appliances such as clothes dryers and electricranges.

Clothes Dryers

The receptacle shown in Figure 32A is a 30-ampere-rated, 4-wire receptaclegenerally used to connect clothes dryers. Prior to the 1996 revision ofthe NEC, the 30-A receptacle was only required to have three slots forconnection. All new clothes dryers now come equipped with the standard4-prong pigtail and will require a 4-slot receptacle.

Freestanding (Self-Contained) Electric Ranges

The receptacle shown in Figure 32B is a 50-ampere-rated, 4-wire receptaclegenerally used to connect freestanding electric ranges. Previously ittoo, like the 30-ampere receptacle, had only three slots for connection.These changes were made in the NEC for the protection of people. Byadding and requiring the fourth slot, a separate equipment-groundingconductor must be installed and connected from the grounding terminalin the panel to the frame of the equipment. Prior to the NEC change,it wasn’t uncommon to use the grounded conductor (neutral) as theequipment-grounding conductor in these special circuits. Keep in mindthat these two receptacles aren’t restricted to use on only dryers and


Table 3

SPECIAL-PURPOSE BRANCH CIRCUITS

Appliance Circuit Voltage AWG

Range 50 A, three-wire 120/240 No. 6

Washer/dryer 40 A, three-wire 120/240 No. 8

Clothes dryer 30 A, three-wire 120/240 No. 10

Washer 20 A, two-wire 120 No. 12

Fuel-fired heater 15 A, two-wire 120 No. 14

Workbench 20 A, two-wire 120 No. 12

Central air conditioning 40 A, two-wire 240 No. 8

Water pump 20 A, two-wire 240 No. 12

ranges. Any appliance or equipment that has the voltage and amperagerequirements to match may be connected using these receptacles. Youmay find welding machines and other equipment connected in thismanner. However, never use the 30-ampere receptacle in a 50-ampererequirement. In addition, freestanding electric ranges may be connecteddirectly into the junction box provided on the range. The basic rule theelectrician generally follows is that if the equipment comes equippedwith a 50-ampere rated pigtail, use the 50-ampere receptacle. If therange comes equipped with a junction box and no pigtail, either use the50-ampere receptacle by adding a 50-ampere pigtail, or connect the rangedirectly into a wall-mounted junction box with proper connectors. Alwaysmake sure that any conductor used in the connection of these appliancesis in accordance with Table 310-16 in the NEC and never use the pigtailas the disconnecting means for the circuit.

Sectional Electric Ranges

In sectional ranges, the oven is a separate unit installed in the wall orbetween kitchen cabinets. The cooktop is usually installed on the kitchencounter at a convenient location.


30-AMPERE

4-WIRE RECEPTACLE(A)

50-AMPERE

4-WIRE RECEPTACLE(B)

FIGURE 32—30-ampere

and 50-ampere 4-wire

receptacles

There are two basic methods of wiring sectional ranges.

1. Supply each section with its own individual branch circuit.

2. Supply both sections from one 50-A circuit.

Sectional ranges may be connected by installing two separate branchcircuits, one for the cooktop, and one for the oven. Factors that maydictate using this method are (1) customer preference, (2) electrical plansindicating separate circuits, or (3) nameplate load ratings indicating aseparate branch circuit. Should this be the case, run individual branchcircuits to each piece of equipment following the steps outlined abovefor free standing units. Make sure you mark the panel indicating whichcircuit breaker or fuse protects the cooktop and which circuit breaker orfuse protects the oven.

If none of the factors are present that require two individual branchcircuits for the sectional range, one branch circuit may be installed and“tapped” in a junction box to provide power to each piece of sectionalrange. Figure 33 shows such a configuration. Before installing any branchconductors or devices, always check the nameplate load rating on thespecific equipment to make sure that all circuit components meet orexceed the requirements of the NEC. When connecting a sectional rangeusing the single-branch circuit method, the electrician will normally runa 50-ampere-rated conductor from a double-pole circuit breaker in thepanel, to a centrally located junction box, convenient to both the cooktopand the oven. An example of this is shown in Figure 33. The electricianwill then tap or connect from this junction box with two separate load-ratedcables to both the cooktop and the oven. Always check the nameplate oneach piece of equipment. This determines what size conductor you shouldinstall to each piece of equipment from the main branch-circuit junctionbox. Normally the conductors to each separate cooking unit will besmaller in size than the conductor used to feed the main circuit, since thismain circuit is based on the total of the loads of both pieces of equipment.Connecting the equipment to the tapped circuits may be accomplishedby using the proper receptacle and pigtail or by direct connection intothe manufacturer-supplied junction box. Labeling the cables in thejunction box with what appliance they supply is also a good practice.

Water Heaters

In connecting residential water heaters, it’s common practice in the elec-trical trade to use a two-wire, No. 12 cable, with a grounding conductor.Be certain the nameplate load rating on the water heater doesn’t exceedthe ampacity of the No. 12 cable. However, when wiring in this man-ner remember that the conductor colors in a No. 12 cable are usuallyblack and white, which requires the electrician to re-mark the whiteconductor with black tape or paint it at any point where the white con-ductor is accessible or visible. This is to prevent someone from mistakingit for a grounded conductor. The grounding conductor, usually a barecopper conductor, must be connected to the frame of the water heater.The equipment manufacturer usually provides a green terminal screw


located inside the junction box for this purpose. Figure 34 shows a dia-gram for a standard two-element water heater. Notice that the waterheater doesn’t require a grounded conductor, or neutral, to operate prop-erly. Also noted is that the disconnect isn’t required as long as the circuitbreaker that supplies the branch circuit to the water heater is “readilyaccessible”. The water heater normally is connected by using a pigtailfrom the water heater to either a wall-mounted junction box or a single240-volt, 30-ampere rated receptacle. As is the case with any larger ap-pliance, never use the plug/receptacle as a disconnecting means for theappliance. The reason for not using the plug/receptacle for a disconnect-ing means on any large-load appliance is that larger appliances (ranges,dryers, dishwashers, and water heaters) have working amperage levelsthat are relatively high compared to smaller appliances, such as blendersand radios. Should someone use the plug as a disconnecting means andunplug a larger appliance while the load is applied, electrical arcing andserious injury due to burn or shock can result. The electrical currenthas a natural tendency to try and “stay connected” and will arc to itself.This effort causes the arcing to be exposed to the person holding thepigtail and most likely damaging the plug and/or receptacle.

Electric Space Heater Connections

Fixed electric space heaters are supplied from individual branch circuitsrated at 15, 20, or 30 A. Because the heaters are considered to be continuousloads, the circuit current can’t be over 80% of the wire ampacity. Forexample, a 20-A branch circuit shouldn’t carry over 16 A (0.80 � 20 = 16).When a long cable supplies the heater, a larger-size cable may be neededto reduce the voltage drop and maintain the heater output.


FIGURE 33—This shows the connections for a sectional range using one branch circuit.

Figure 35A shows a baseboard-type heater controlled by a two-poleline-voltage thermostat. A 240-V two-wire circuit with an ampacityof 20 amps supplies the heater. The typical two-pole line-voltage thermo-stat is rated at 5000 W, but the load should be limited to 80% of therating (0.80 � 5000 = 4000 W.) Use a No. 12 copper wire rated at 20 Aat a reduced ampacity of 16 A. The two-pole line-voltage thermostatwon’t normally control more than 3840 W (16 A � 240 V = 3840 W).The same calculation made with a 230-V supply line would be16 A � 230 V = 3680 W.

Thermostats are normally mounted on 2-inch � 3-inch device boxes.In Figure 35A, a two-wire cable from the panelboard runs to the two-pole line-voltage thermostat. Another two-wire cable runs from thetwo-pole line-voltage thermostat to the overheat switch on the heater. Theoverheat switch is a thermostat that runs the full length of the heater.One ungrounded conductor is connected in series with the overheatswitch. The switch shuts the heater off if the temperature in the heatergets too high. This could happen, for example, if the heater were



the connections to a

standard two-element

water heater.

completely blocked off by draperies. The overheat switch is constructedas part of the heater to make the installation more safe. From the over-heat switch, a wire runs to one connection of the heating element. Theother wire from the two-pole line-voltage thermostat connects to theother terminal wire of the heating element within the heater. When thetwo-wire cable contains a grounding wire, the grounding wire is fas-tened to the heater frame.

The low-voltage control system in Figure 35B uses a thermal relay to controlthe power to the heater. The thermal relay includes a transformer T, whichsteps 240 volts down to 24 volts. The low-voltage thermostat controls theflow of current through a resistance heater R. When the thermostat closes,it calls for heat and current flows through the resistance heater R. Theheater is wound on the bimetallic strip constructed of two different met-als. The resistance heater heats a bimetallic strip and causes it to bendand close the switch contacts of the thermal relay. When the room tem-perature rises, the thermostat opens. This action stops the flow of current


FIGURE 35—Space heaters are considered to be fixed appliances.

through the resistance heater, which allows the bimetallic strip to cool.After the bimetallic strip cools, the switch contacts of the thermal relayopen. Thus, the thermal relay silently controls the current flowing to theheater.

As shown in the low-voltage control diagram in Figure 35B, the cablefrom the panelboard runs to the thermal relay. This is the point wherethe branch circuit connects to the transformer’s primary terminals. Afterthe splice, one wire runs directly to the heating element while the otherone is connected to a terminal on the switch of the thermal relay. Fromthe thermal relay terminal a wire is connected to the overheat switch ofthe heater and then to the heating element.

In this system, the thermal relay directly controls the power to the heater.The thermal relay could also be used to control a remotely locatedswitch such as a relay or contactor. This flexibility permits placing thelow-voltage thermostat and thermal relay in the most convenient places.It also permits the installation of short cables to the heater.

Circuit Protection

The NEC devotes two parts of Article 422 to the electrical installationand protection of appliances. Basically, the nameplate load ratingdetermines the branch circuit rating. If the nameplate rating isn’t available,then Article 422 dictates how the branch circuit should be sized. Forsmall appliances whose rating is 13.3 amperes or less, the branch circuitrating may not exceed 20 amperes. If an appliance is rated over 13.3 andthe branch-circuit maximum rating isn’t marked on the appliance, thebranch circuit rating may not exceed 150 percent of the estimated demandload. For household-type appliances with surface heating elementshaving a maximum demand of more than 60 amperes, the branch circuitmust be split into two circuits, with overcurrent protection rated lessthan 50 amperes on either circuit. Electric heating appliances that useresistance-type heating elements that have a demand of more than48 amperes must have the heating elements subdivided so that no oneload is more than 48 amperes. The overcurrent protection device can’texceed 60 amperes on either circuit. An individual branch circuit mustsupply central heating equipment. Branch circuits that supply waterheaters less than 120 gallons (household water heaters) must be rated atno less than 125 percent of the nameplate load demand on the waterheater.

A means of disconnecting appliances from all ungrounded conductorsmust be provided. For those permanently connected appliances(appliances that are fastened in place in one location) whose loaddoesn’t exceed 300 volt-amperes (watts) or 1

8 horsepower, the overcur-rent protection device may be used as the disconnecting means. Forthose permanently connected appliances, whose load does exceed 300volt-amperes (watts) or 1

8 horsepower, the overcurrent protection devicemay be used as the disconnecting means as long as the overcurrent


protection device is within sight of the appliance and can be locked inthe open position. In the case of cord-and-plug-connected appliances,the cord-and-connector is an acceptable means of disconnect. However,the branch-circuit protection device should always be placed in the openposition before disconnecting any appliance other than small portableappliances using the cord-and-plug method. Severe arcing, shock, orburns could result, in addition to component damage should a person“unplug” a large appliance while the load is applied.

Circuit Grounding

Let’s review the two types of conductors used in a grounded circuit.First is the grounded conductor. This current-carrying circuit conductoris grounded at the service entrance and is called the neutral wire. Sinceit’s grounded, there’s no voltage between the neutral wire and groundunless the wire is disconnected from the ground connection. Then anyconducting material, including the human body, that completes thepath from the grounded conductor or neutral to earth ground while thecircuit’s energized will become part of the current-carrying conductor!

The other conductor associated with grounding is the equipment-groundingconductor, usually called the ground or grounding wires. These conductorsconnect the non-circuit metal parts of electrical equipment to ground.These conductors don’t conduct any electrical current unless a fault(short circuit) occurs in the circuit. This type of fault is called a ground fault.When a ground fault occurs, current flows from one of the non-groundedcircuit conductors through the grounding wire to ground. The groundingwires place the metal parts of equipment at ground potential (thesame as ground itself), thus making it reasonably safe to touch electricalequipment even when a ground fault exists.

Ground Faults

When a short circuit occurs in a circuit, it will usually cause a very highcircuit current to flow. This high current normally causes the circuitprotection device, whether a fuse or circuit breaker, to open. Whathappens if the current isn’t high enough to blow a fuse or open thecircuit breaker?

For example, suppose the insulation between a hot wire and groundwire doesn’t break down fully and develops only a leakage of currentwith a resistance of 240�.

Thus,120

240

V

�

I = 0.5 A

Should this happen, 0.5 A of current flows from the ungrounded con-ductor through the parallel circuit created by the short circuit, to earth


ground. The 15- or 20-A circuit breaker or fuse won’t open because ithasn’t been exposed to an excess of 15 or 20 amperes of current flow.It allows the 0.5 A to flow. It doesn’t recognize that it’s a ground-faultcurrent. If a person like the one in Figure 36 should touch the hot wirewhile also touching ground, that person’s body would provide the sametype of leakage path to ground. The leakage current wouldn’t be highenough to trip the breaker, but it could be high enough to injure or killthe person. For that reason, a ground fault circuit interrupter (GFCI) isrequired in some areas for protection against ground faults. A GFCI isdesigned to trip when it senses a ground-fault current of only 0.005 A.This amount of current isn’t enough to kill or even injure a person.

GFCI-Protected Circuits

As you know, the NEC requires that GFCIs be used in locations where afault current would most likely occur. For a residence, GFCIs are re-quired to protect the receptacles in the bathroom, kitchen countertops,wet bars, garages, and on the outside of the house, including swimmingpool areas. To protect workers on construction jobs, GFCIs are requiredin most of the general-purpose circuits, especially in those circuits usedto furnish power to hand-held power tools. The worker in Figure 36would most likely be protected from electrical shock if the circuit thatthe electric saw connects to was protected by a GFCI device.

There are three basic types of GFCI protection devices—GFCI receptacles,GFCI circuit breakers, and portable GFCIs. Figure 37 shows three stylesof GFCI receptacles. The flush-mounted and surface-mounted styles areavailable in terminated or feed-through models. Terminated models aredesigned only to protect the one receptacle load from ground fault.


FIGURE 36—The ground-fault

circuit interrupter responds

to the leakage current

returning to a voltage source

by a route other than the

normal return wire. In this

illustration, that route is

through the worker’s body.

Feed-through models are designed to protect the one receptacle load andall other receptacles that are installed downstream from that receptacle.However, the other receptacles must be connected to load side of theGFCI unit. The plug-in unit shown in Figure 38 is available only in aterminated model.

The second type of GFCI is the GFCI circuit breaker. In this type, a circuitbreaker and a GFCI are combined, providing both overcurrent andfault-current protection. The circuit-breaker switch may also be used asan on/off switch for the circuit.


FIGURE 37—The

flush-mounted and

surface-mounted models

of circuit interrupters fit into

the outlet boxes normally

used to support and protect

power receptacles. The

receptacle into which it’s

plugged supports the

small plug-in model.(Bottom photo courtesy of LevitonManufacturing Co., Inc.)

Circuit breakers with GFCI capability are available in models that can beinstalled to replace most standard circuit breakers now in use. Examplesof circuit breakers with GFCI protection are shown in Figure 38. Notethat the devices shown also contain test buttons.

The third type of GFCI device is the portable unit. These devices incorpo-rate both receptacles and circuit breakers. You’ll most likely find thesedevices in use on construction sites, where the NEC requires their use.The ground-fault circuit in a device of this type may or may not be partof the circuit-breaker assembly.

Other Circuits

Signal Circuits

A chime controlled by push-button switches is one of the most commonsignal circuits that’s installed in residential wiring. Figure 39 shows acircuit that’s supplied by a small step-down control transformer. Thistransformer steps the 120 V down to between 12 and 20 V. Because thetransformer power demand is very limited, the normal door chimetransformer primary wires can be connected directly to a 15-A or 20-Alighting or general-purpose circuit without a special circuit protection.Small wiring referred to as bell wire, having very thin insulation, isgenerally used as conductors in these circuits. This wiring should bekept at least 2 inches from other wires to prevent currents from beinginduced into the bell wire by electromagnetic force, which may cause


FIGURE 38—GFCI Circuit Breakers

unwanted control voltages. Many chimes are designed to sound twonotes, one for the front door and one for the back door. Special push-button switches are used to activate the chimes.

Buzzers and doorbells were commonly installed before chimes becamepopular. They’re similar to chimes in operation and require between 6and 10 V to operate.


FIGURE 39—The transformer secondary connections for a door chime circuit are shown in both block diagram

and schematic form. The transformer, shown as the low-voltage AC power source, could be replaced with DC

battery packs for emergency systems.

Communication Wiring

Computer/Internet connections, cable television, telephone, and audiospeakers are all examples of communications systems now installed inmodern homes. Communications circuits are often installed in a newlyconstructed residence in the same way as electrical branch circuits.Modern residential as well as commercial wiring jobs often demandthat electricians install data cable for computers, cable for television,telephone wires, and speaker wire throughout a building.

Wiring for communication systems is often specified on the wiringdiagram to be installed and hooked up by the electrician. When facedwith the job of installing communications wiring, it’s important to selectthe correct wire for each communication application and to have theskills necessary for installing and terminating the cables and connectors.As the world adapts to the interface of communications systems, thedemand for residential installations is increasing rapidly. The electricianmust now know how to identify cables and devices used to connect datacommunications such as computers, DVD, and satellite systems, alongwith coax cables for television, telephone cables, and all associated equip-ment and devices.

Telephone Wiring

Modern residences are often wired with built-in telephone connectionsthroughout the dwelling. Computer Internet access, fax machines, andthe demand for more than one voice line have all contributed to theincreasing complexity of the typical residential telephone system.

When a telephone company installs a telephone line at a residence, it’sconnected to an enclosure called a demarcation box, shown in Figure 40.This box may be placed either inside or outside the building. Terminalblocks are usually located in the demarcation box. Terminal blocks(Figure 41) are devices that allow multiple lines to be connected from thedemarcation box to multiple locations within the house or building. Thinkof the demarcation box/terminal block combination as a distributionpoint not unlike the service panel or branch-circuit distribution panelof the electrical system.

Telephone cable is installed from the terminal block to the wall-mountedlocations in the residence, at which point the residents may connecttheir individual telephone equipment. The wall-mounted locations arecommonly referred to as telephone jacks. Special care must be taken inconnecting the telephone cables to the telephone wall jacks, since thecable is much more fragile than the electrical cable that electricians areaccustomed to installing. Carefully strip the insulation from the pairedtelephone cable, preferably using the proper stripping tool, or a strippingknife. Loosen the terminal screw marked Red and insert the red wirethrough the opening in the back of the jack. Wrap it around the terminaland carefully tighten the screw. The wire should be wrapped in a clock-wise direction to avoid unwrapping it while tightening the screw terminal.



CUSTOMER ACCESS COVER OPEN

CUSTOMER ACCESS COVER CLOSED


demarcation box with the

access panel open and

with the access panel

replaced.

Do the same with the green wire. If only one line is being installed,you’ll need only to install the red and green conductors. The black andyellow conductors are for a second line if one is to be installed. Anexample is shown in Figure 42. After the telephone company hasconnected the demarcation box to the telephone service line, test thetelephones for proper operation, and then install the cover on eachtelephone jack.

As mentioned previously, a new residential wiring diagram may includewiring instructions for the communication system conductors as well asthe conventional electrical wiring.


FIGURE 41—A terminal block allows multiple jacks to be installed. This style of block is mounted

separately from the demarcation box.

Telephone cables may also be routed through walls by drilling holes inthe wall studs, or installed over ceiling joists. However, telephone wireis much more delicate and must be handled, protected and supportedaccordingly. The NEC covers the installation of communications wires inArticle 800. It states that all communications wires should be installedseparately from light and power circuits unless they’re contained withinor permanently separated by a cable or raceway. If they’re not contained,at least 2 inches of space must be maintained between the electrical andcommunications conductors.

Telephone cables are constructed with color-coded conductor pairs.Cables range in sizes including 2-, 3-, 4-, 6-, 12-, 25-, and 50-conductorpairs. The numbered sizes correspond to the number of pairs within acable. For example, a two-pair conductor has four individual wires; athree-pair conductor has six wires, and so on. Telephone conductors arealso categorized by the speed of the equipment they’re designed toserve. When speeds such as those associated with computers and otherdata equipment are involved, the requirement to reduce interferenceand cross talk is much higher. Cross talk is noise crossing over from oneline to another when the lines are installed in the same direction next to


BK=BLACK

RD=RED

YL=YELLOW

GR=GREEN

FIGURE 42—Conductors are simply attached with the screws according to the color code.

one another and don’t have enough space separating them. To avoid crosstalk, modern telephone cables contain only twisted pairs of conductors.“Twisted pair” means that the wires in each conductor-pair are evenlytwisted around each other.

Communications wires can carry AC and DC volts and should bedisconnected from the circuit before working with the lines. The currentflows when the telephone rings, so taking the telephone off the hook isalso an option. Another way to avoid electrical shock is to connect theinside lines prior to the telephone company connecting the outside orfinal circuit in the demarcation box.

Wiring for Cable Television

Cable television is another type of communications equipment thatrequires special communications wiring. Old-style cable televisionwiring is normally 75-ohm coaxial cable. Coaxial cable consists of outerinsulation, a braided section, an inner insulation, and a center copperconductor. Normally the coaxial cable is installed throughout the residence,then terminated on its own terminals at a wall plate. Terminating thecable, which may or may not be part of the electrician’s job, involvesinstalling a connector. When stripping the cable to install a connector,use the proper coax-stripping tool. The prepared cable should resemblethe one shown in Figure 43A. After the end is prepared, install theconnector by twisting it onto the prepared coax cable end. The connectorcontains internal threads that allow it to be threaded onto the coax cable.An installed coax connector will resemble the one shown in Figure 43B.NEC requirements for installing coaxial cable are covered in Article 820and are basically the same as those used to correctly install telephonecables. New technology in residential television reception, computeraccess, and data communication calls for continuous training on the partof the electrician. Digital and DVD signals are now common in resi-dences. The cables and connectors used to connect to this new technologyrequire special stripping and installation tools, as well as specializedtraining. It’s recommended that as you encounter these types of installa-tion, you locate the proper training and tools to properly complete theassigned task.


Smoke, Heat, and Carbon Monoxide Detectors

Smoke, heat, and carbon monoxide detectors are installed in residencesto warn the occupants of the presence of fire or toxic fumes. Heat detectorsare now being installed in residences in addition to smoke detectors.They’re not designed to replace smoke detectors. Carbon monoxidedetectors are new on the detector scene but are becoming quite commonin the design and installation of systems in residential dwellings becauseof the increasing usage of natural gas as an energy source in homes. TheNational Fire Protection Association Standard No. 72 covers the minimumrequirements and installation of heat and smoke detectors in homes aswell as any fire warning equipment. Standard No. 720 covers carbonmonoxide detection and protection. The two types of common smokedetectors are the photoelectronic type and the ionization type. Mostdetectors have an indicator light that shows that the detector is receivingpower. Likewise, the detectors are commonly equipped with a testbutton that allows the homeowner to periodically test the unit forproper operation. Contrary to some belief, smoke detectors won’t sense


FIGURE 43—Use the correct

dimensions (A) when

stripping coaxial cable.

The connector should look

like (B) when finished.

heat. Because of this, it’s recommended that homeowners also incorpo-rate heat detectors into their fire safety protection system. When installingsmoke detectors, the following guidelines provide a minimum ofprotection:

1. Always install smoke detectors on every level of a residence.

2. Always install at least one smoke detector in every sleeping roomof the house.

3. If installing detectors in new construction, always interconnectsmoke detectors so that when one operates, all will operate.

4. Make sure that the detectors are UL listed.

Keep in mind that these are only minimum requirements. The ideal pro-tection system in a home will include an array of intruder alarms,smoke detectors, heat detectors, and if natural gas is present, carbonmonoxide detectors.



BLACK

120V WHITE

RED

(INTERCONNECT WIRE)

FIGURE 44—When smoke detectors are wired in this manner, it causes all of them to sound if smoke is detected

in an area.


✔ Self-Check 41. General-purpose circuits are usually _______ -conductor circuits that distribute 120 V.

2. An electric dryer, 4-wire receptacle is normally rated at _______ amperes.

3. The minimum number of small-appliance circuits required in a kitchen is _______.

4. List the three groups into which the NEC classifies appliances.

5. True or False? Pigtail cords can be used as a disconnecting means for fixed appliances.

6. The neutral wire is a _______ conductor.

7. A standard circuit breaker will trip when a _______ _______ occurs.

8. _______ _______ is used to deliver traditional cable television service.


1

1. service drop

2. switch

3. series

4. alternating

5. 9 (17 – 8 = 9)

6. grounding

7. load or equipment

8. Any two of the following are correct:Emergency power, Hazardous area,Alarm, Communication, Control

9. explosion-proof

2

1. True

2. neutral

3. disconnect

4. 10

5. False

6. plastic separators

7. grounding

3

1. 6

2. True

3. The bathroom

4. The master bedroom

5. A switch should be equipped with apilot light when the switch is out ofsight of the light it controls.

4

1. two

2. 30

3. two

4. Fixed, Portable, Stationary

5. False

6. grounded

7. short circuit

8. Coaxial cable

Self-Check Answers

83

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(29) Wiring Electrical Circuits.pdf