WIRING BASICS

Current with 2011-2013 Electrical Codes

Contents
Introduction
BASICS OF WIRING
Working Safely with Wiring
How Electricity Works
Understanding Electrical Circuits
Grounding & Polarization
Home Wiring Tools
Wiring Safety
Wire, Cable & Conduit
Wire & Cable
Introduction
The world of wiring tends to move in cycles, so to speak. The basic
science that causes your blender to whir when you plug the cord into a wall
outlet doesn’t change, but the ways we harness and manage electrical power
are constantly improving—always with an eye toward safety. The Complete
Guide to Wiring changes, too. Now in its 5th edition, this million-selling
book is the most popular do-it-yourself wiring manual in stores today. A big
reason for its success is that we take pains to carefully update the book
every three years, as the national electrical codes are revised.
If you were to place this 5th edition of The Complete Guide to Wiring
next to the 4th edition, you’d notice many similarities off the bat. But when
you look a little more closely, you’ll spot some subtle but key differences
that reflect current practices and product preferences. For example, recent
code changes require the use of tamper-resistant receptacles with a
protective shield that covers each slot so children cannot poke anything into
it except a plug. In this book you won’t find a picture of a receptacle that is
not tamper-resistant unless it is being replaced. We’ve also eliminated
circuit testers that are not of the much safer touch-free variety, and we’ve
included updated grounding strategies on many projects.
Along with these and other updates, we’ve added some new projects that
reflect current interest. Readers demanded more information on backup
power generators, so we have added a complete step-by-step sequence for a
transfer switch installation (the transfer switch redirects key circuit power
demand to a standalone generator during power outages). Because home
power demands are higher now than when many houses were built,
upgrading the capacity of the electrical service panel is a popular project.
But one aspect of upgrading a panel that is often overlooked is the need to
upgrade your grounding and bonding system, too. So we have added a full
sequence for this job: down to driving the 8-ft. grounding rod into the earth.
Are you tired of relying on a couple of pull chains to operate your ceiling
fan and light? We show you how to retrofit a convenient remote control
device so you can turn the light on and off and change fan speed without
leaving your seat.
Alternative energy sources are expanding rapidly in popularity. As
interest grows, manufacturers are finding ways to make the technology DIY
friendly. A perfect case in point is solar energy. It may seem like a simple
technology, but unless you maintain a large RV or boat, working with DC
power sources is a brand new concept to most homeowners. So we have
included a step-by-step demonstration that shows you exactly how to install
a standalone DC power distribution system that is energized by a
photovoltaic panel. You won’t find this project in other DIY wiring books!
Most DIYers who have done it will agree that home wiring is fun and
rewarding. But it is also fraught with danger. That’s why it is critically
important to involve your local electrical inspections department with your
wiring plans from the start. If you are installing new circuits or adding
capacity, you need a permit and most likely a physical inspection of your
work. Do not avoid this step. Local inspectors are generally very helpful
and should be considered valuable resources. Failing to obtain permits or
inspections can result in fines. If the wiring is incorrect or of substandard
workmanship, major disasters can occur. If at any time during a wiring job
you encounter a situation about which you are unsure, stop and get
assistance.
Working Safely with Wiring
The only way you can possibly manage home wiring projects safely is to
understand how electricity works and how it is delivered from the street to
the outlets in your home.
The most essential quality to appreciate about electricity is that the
typical amounts that flow through the wires in your home can be fatal under
certain conditions if you contact it directly. Sources estimate that up to
1,000 people are electrocuted accidentally in the U.S. every year. In
addition, as many as 500 die in fires from electrical causes. Home wiring
can be a very satisfying task for do-it-yourselfers, but if you don’t know
what you’re doing or are in any way uncomfortable with the idea of
working around electricity, do not attempt it.
This chapter is intended to explain the fundamental principles behind the
electrical circuits that run through our homes. It also includes some very
basic tips for working safely with wiring, and it details the essential tools
you’ll need for the job. For the beginner it should be considered mandatory
reading. Even if you have a good idea of electrical principles, take some
time to review the material. A refresher course is always useful.

In this chapter:
• How Electricity Works
• Understanding Electrical Circuits
• Grounding & Polarization
• Home Wiring Tools
• Wiring Safety
 How Electricity Works
A household electrical system can be compared with a home’s plumbing
system. Electrical current flows in wires in much the same way that water
flows inside pipes. Both electricity and water enter the home, are distributed
throughout the house, do their “work,” and exit.
In plumbing, water first flows through the pressurized water supply
system. In electricity, current first flows along hot wires. Current flowing
along hot wires also is pressurized. The pressure of electrical current is
called voltage.
Large supply pipes can carry a greater volume of water than small pipes.
Likewise, large electrical wires carry more current than small wires. This
current-carrying capacity of wires is called amperage.
Water is made available for use through the faucets, spigots, and
showerheads in a home. Electricity is made available through receptacles,
switches, and fixtures.
Water finally leaves the home through a drain system, which is not
pressurized. Similarly, electrical current flows back through neutral wires.
The current in neutral wires is not pressurized and is said to be at zero
voltage.
Water and electricity both flow. The main difference is that you can see water (and touching water
isn’t likely to kill you). Like electricity, water enters a fixture under high pressure and exits under low
pressure.
 The Delivery System
Electrical power that enters the home is produced by large power plants.
Power plants are located in all parts of the country and generate electricity
with turbines that are turned by water, wind, or steam. From these plants
electricity enters large “step-up” transformers that increase voltage to half a
million volts or more.
Electricity flows easily at these large voltages and travels through high-
voltage transmission lines to communities that can be hundreds of miles
from the power plants. “Step-down” transformers located at substations
then reduce the voltage for distribution along street lines. On utility power
poles, smaller transformers further reduce the voltage to ordinary 120-volt
current for household use.
Lines carrying current to the house either run underground or are strung
overhead and attached to a post called a service mast. Most homes built
after 1950 have three wires running to the service head: two power lines,
each carrying 120 volts of current, and a grounded neutral wire. Power from
the two 120-volt lines may be combined at the service panel to supply
current to large 240-volt appliances like clothes dryers or electric water
heaters.
Incoming power passes through an electric meter that measures power
consumption. Power then enters the service panel, where it is distributed to
circuits that run throughout the house. The service panel also contains fuses
or circuit breakers that shut off power to the individual circuits in the event
of a short circuit or an overload. Certain high-wattage appliances, like
microwave ovens, are usually plugged into their own individual circuits to
prevent overloads.
Voltage ratings determined by power companies and manufacturers have
changed over the years. Current rated at 110 volts changed to 115 volts,
then 120 volts. Current rated at 220 volts changed to 230 volts, then 240
volts. Similarly, ratings for receptacles, tools, light fixtures, and appliances
have changed from 115 volts to 125 volts. These changes do not affect the
performance of new devices connected to older wiring. For making
electrical calculations, use a rating of 120 volts or 240 volts for your
circuits.
Power plants supply electricity to thousands of homes and businesses. Step-up transformers increase
the voltage produced at the plant, making the power flow more easily along high-voltage
transmission lines.
Substations are located near the communities they serve. A typical substation takes current from
high-voltage transmission lines and reduces it for distribution along street lines.
Utility pole transformers reduce the high-voltage current that flows through power lines along
neighborhood streets. A utility pole transformer reduces voltage from 10,000 volts to the normal 120-
volt current used in households.
 Parts of the Electrical System

The service mast is the metal pole and weatherhead that create the entry point for electricity into
your home. The mast is supplied with three wires carrying 240 volts and originating from the nearest
transformer.
The electric meter measures the amount of electrical power consumed. It is usually attached to the
side of the house, and connects to the service mast. A thin metal disc inside the meter rotates when
power is used. The electric meter belongs to your local power utility company. If you suspect the
meter is not functioning properly, contact the power company.
The main service panel, in the form of a fuse box or breaker box, distributes power to individual
circuits. Fuses or circuit breakers protect each circuit from short circuits and overloads. Fuses and
circuit breakers also are used to shut off power to individual circuits while repairs are made.
Electrical boxes enclose wire connections. According to the National Electrical Code, all wire
splices or connections must be contained entirely in a covered plastic or metal electrical box.
Receptacles, sometimes called outlets, provide plug-in access to electrical power. A 120-volt, 15-
amp receptacle with a grounding hole is the most typical receptacle in wiring systems installed after
1965. Most receptacles have two plug-in locations and are called duplex receptacles.
Switches control electrical current passing through hot circuit wires. Switches can be wired to
control light fixtures, ceiling fans, appliances, and receptacles.
Light fixtures attach directly to a household electrical system. They are usually controlled with
wall switches. The two common types of light fixtures are incandescent and fluorescent.
A grounding wire connects the electrical system to the earth through a metal grounding rod driven
next to the house, eliminating shock hazards from equipment and metallic objects.
 Glossary of Electrical Terms
Ampere (or amp): Refers to the rate at which electrical power flows to
a light, tool, or appliance.
Armored cable: Two or more wires that are grouped together and
protected by a flexible metal covering.
Box: A device used to contain wiring connections.
BX: See armored cable (Bx is the older term).
Cable: Two or more wires that are grouped together and protected by a
covering or sheath.
Circuit: A continuous loop of electrical current flowing along wires or
cables.
Circuit breaker: A safety device that interrupts an electrical circuit in
the event of an overload or short circuit.
Conductor: Any material that allows electrical current to flow through
it. Copper wire is an especially good conductor.
Conduit: A metal or plastic pipe used to protect wires.
Continuity: An uninterrupted electrical pathway through a circuit or
electrical fixture.
Current: The movement of electrons along a conductor.
Duplex receptacle: A receptacle that provides connections for two
plugs.
Feed wire: A conductor that carries 120-volt current uninterrupted from
the service panel.
Fuse: A safety device, usually found in older homes, that interrupts
electrical circuits during an overload or short circuit.
Greenfield: Materials used in flexible metal conduit. See armored
cable.
Grounded wire: See neutral wire.
Grounding wire: A wire used in an electrical circuit to conduct current
to the earth in the event of a short circuit. The grounding wire often is a
bare copper wire.
Hot wire: Any wire that carries voltage. In an electrical circuit, the hot
wire usually is covered with black or red insulation.
Insulator: Any material, such as plastic or rubber, that resists the flow
of electrical current. Insulating materials protect wires and cables.
Junction box: See box.
Meter: A device used to measure the amount of electrical power being
used.
Neutral wire: A wire that returns current at zero voltage to the source
of electrical power. Usually covered with white or light gray insulation.
Also called the grounded wire.
Non-metallic sheathed cable: NM cable consists of two or more
insulated conductors and, in most cases, a bare ground wire housed in a
durable PVC casing.
Outlet: See receptacle.
Overload: A demand for more current than the circuit wires or
electrical device was designed to carry. Usually causes a fuse to blow or
a circuit breaker to trip.
Pigtail: A short wire used to connect two or more circuit wires to a
single screw terminal.
Polarized receptacle: A receptacle designed to keep hot current
flowing along black or red wires, and neutral current flowing along
white or gray wires.
Power: The result of hot current flowing for a period of time. Use of
power makes heat, motion, or light.
Receptacle: A device that provides plug-in access to electrical power.
Romex: A brand name of plastic-sheathed electrical cable that is
commonly used for indoor wiring. Commonly known as NM cable.
Screw terminal: A place where a wire connects to a receptacle, switch,
or fixture.
Service panel: A metal box usually near the site where electrical power
enters the house. In the service panel, electrical current is split into
individual circuits. The service panel has circuit breakers or fuses to
protect each circuit.
Short circuit: An accidental and improper contact between two current-
carrying wires, or between a current-carrying wire and a grounding
conductor.
Switch: A device that controls electrical current passing through hot
circuit wires. Used to turn lights and appliances on and off.
UL: An abbreviation for Underwriters Laboratories, an organization
that tests electrical devices and manufactured products for safety.
Voltage (or volts): A measurement of electricity in terms of pressure.
Wattage (or watt): A measurement of electrical power in terms of total
energy consumed. Watts can be calculated by multiplying the voltage
times the amps.
Wire connector: A device used to connect two or more wires together.
Also called a wire nut.
 Understanding Electrical Circuits
An electrical circuit is a continuous loop. Household circuits carry power
from the main service panel, throughout the house, and back to the main
service panel. Several switches, receptacles, light fixtures, or appliances
may be connected to a single circuit.
Current enters a circuit loop on hot wires and returns along neutral wires.
These wires are color coded for easy identification. Hot wires are black or
red, and neutral wires are white or light gray. For safety, most circuits
include a bare copper or green insulated grounding wire. The grounding
wire conducts current in the event of a ground fault, and helps reduce the
chance of severe electrical shock. The service panel also has a grounding
wire connected to a metal water pipe and metal grounding rod buried
underground.
If a circuit carries too much power, it can overload. A fuse or a circuit
breaker protects each circuit in case of overloads.
Current returns to the service panel along a neutral circuit wire. Current
then becomes part of a main circuit and leaves the house on a large neutral
service wire that returns it to the utility pole transformer.
 Grounding & Polarization
Electricity always seeks to return to its source and complete a continuous
circuit. In a household wiring system, this return path is provided by white
neutral wires that return current to the main service panel. From the service
panel, current returns along a neutral service wire to a power pole
transformer.
A grounding wire provides an additional return path for electrical
current. The grounding wire is a safety feature. It is designed to conduct
electricity if current seeks to return to the service panel along a path other
than the neutral wire, a condition known as a ground fault.
A ground fault is a potentially dangerous situation. If an electrical box,
tool, or appliance becomes short-circuited and is touched by a person, the
electrical current may attempt to return to its source by passing through that
person’s body.
However, electrical current prefers the path of least resistance. A
grounding wire provides a safe, easy path for current to follow back to its
utility transformer. If a person touches an electrical box, tool, or appliance
that has a properly installed grounding wire, any chance of receiving a
severe electrical shock is greatly reduced.
In addition, household wiring systems are required to be connected
directly to the earth. This helps to ensure that all equipment and metallic
objects are held at Earth’s potential (zero volts) to eliminate shock hazards.
Note: A short circuit is also can occur when a hot and a neutral conductor
come in contact. When your electrical system is functioning properly, the
fuses or circuit breaker will de-energize the circuit to clear the fault.
Grounding of the home electrical system is accomplished by wiring the
household electrical system to a metal cold water pipe and metal grounding
rods that are buried in the earth.
After 1920, most American homes included receptacles that accepted
polarized plugs. The two-slot polarized plug and receptacle was designed to
keep hot current flowing along black or red wires, and neutral current
flowing along white or gray wires.
Normal current flow: Current enters the electrical box along a black hot wire, then returns to the
service panel along a white neutral wire. Any excess current passes into the earth via a grounding
wire attached to grounding rods or a metal water pipe.
Short circuit: Current is detoured by a loose wire in contact with the metal box. The grounding wire
picks it up and channels it safely back to the main service panel. There, it returns to its source along a
neutral service cable or enters the earth via the grounding system.

Armored cable and metal conduit, widely installed in homes during the
1940s, provided a true grounding path. When connected to metal junction
boxes, it provided a metal pathway back to the service panel.
Modern cable includes a green insulated or bare copper wire that serves
as the grounding path. This grounding wire is connected to all three-slot
receptacles and metal boxes to provide a continuous pathway for any
ground faulted current. By plugging a three-prong plug into a grounded
three-slot receptacle, people are protected from ground faults that occur in
appliances, tools or other electric devices.
Use a receptacle adapter to plug three-prong plugs into two-slot
receptacles, but use it only if the receptacle connects to a grounding wire or
grounded electrical box. Adapters have short grounding wires or wire loops
that attach to the receptacle’s coverplate mounting screw. The mounting
screw connects the adapter to the grounded metal electrical box.

Modern NM (nonmetallic) cable, found in most wiring systems installed after 1965, contains a bare
copper wire that provides grounding for receptacle and switch boxes.

Armored cable is sold pre-installed in a flexible metal housing. BX, Greenfield, and MC are three
common types. Metal-clad cable Type MC is shown here. It contains a green insulated ground wire
along with black and white conductors.
Polarized receptacles have a long slot and a short slot. Used with a polarized plug, the polarized
receptacle keeps electrical current directed for safety.

Three-slot receptacles are required by code for new homes. They are usually connected to a
standard two-wire cable with ground.
Receptacle adapter allows three-prong plugs to be inserted into two-slot receptacles. The adapter
can be used only with grounded receptacles, and the grounding loop or wire of the adapter must be
attached to the coverplate mounting screw of the receptacle.

Double-insulated tools have non-conductive plastic bodies to prevent shocks caused by short
circuits. Because of these features, double-insulated tools can be used safely with ungrounded
receptacles.
 Home Wiring Tools
To complete the wiring projects shown in this book, you need a few
specialty electrical tools as well as a collection of basic hand tools. As with
any tool purchase, invest in good-quality products when you buy tools for
electrical work. Keep your tools clean, and sharpen or replace any cutting
tools that have dull edges.
The materials used for electrical wiring have changed dramatically in the
last 20 years, making it much easier for homeowners to do their own
electrical work. The following pages show how to work with the following
components for your projects.

Hand tools you’ll need for home wiring projects include: Stud finder/laser level (A) for locating
framing members and aligning electrical boxes; Tape measure (B); Cable ripper (C) for scoring NM
sheathing; Standard (D) and Phillips (E) screwdrivers; Utility knife (F); Side cutters (G) for cutting
wires; Channel-type pliers (H) for general gripping and crimping; Linesman pliers (I) combine side
cutter and gripping jaws; Needlenose pliers (J); Wire strippers (K) for removing insulation from
conductors.
Use a tool belt to keep frequently used tools within easy reach. Electrical tapes in a variety of colors
are used for marking wires and for attaching cables to a fish tape.
A fish tape is useful for installing cables in finished wall cavities and for pulling wires through
conduit. Products designed for lubrication reduce friction and make it easier to pull cables and wires.
Diagnostic tools for home wiring use include: Touchless circuit tester (A) to safely check wires for
current and confirm that circuits are dead; Plug-in tester (B) to check receptacles for correct polarity,
grounding and circuit protection; Multimeter (C) to measure AC/DC voltage, AC/DC current,
resistance, capacitance, frequency and duty cycle (model shown is an auto-ranging digital multimeter
with clamp-on jaws that measure through sheathing and wire insulation).
 Wiring Safety
Safety should be the primary concern of anyone working with electricity.
Although most household electrical repairs are simple and straightforward,
always use caution and good judgment when working with electrical wiring
or devices. Common sense can prevent accidents.
The basic rule of electrical safety is: Always turn off power to the area or
device you are working on. At the main service panel, remove the fuse or
shut off the circuit breaker that controls the circuit you are servicing. Then
check to make sure the power is off by testing for power with a voltage
tester. Tip: Test a live circuit with the voltage tester to verify that it is
working before you rely on it. Restore power only when the repair or
replacement project is complete.
Follow the safety tips shown on these pages. Never attempt an electrical
project beyond your skill or confidence level. Never attempt to repair or
replace your main service panel or service entrance head. These are jobs for
a qualified electrician and require that the power company shut off power to
your house.
Shut power OFF at the main service panel or the main fuse box before beginning any work.

Create a circuit index and affix it to the inside of the door to your main service panel. Update it as
needed.
Confirm power is OFF by testing at the outlet, switch, or fixture with a voltage tester.

Use only UL-approved electrical parts or devices. These devices have been tested for safety by
Underwriters Laboratories.
Wear rubber-soled shoes while working on electrical projects. On damp floors, stand on a rubber
mat or dry wooden boards.

Use fiberglass or wood ladders when making routine household repairs near the service mast.
Extension cords are for temporary use only. Cords must be rated for the intended usage.

Breakers and fuses must be compatible with the panel manufacturer and match the circuit capacity.
Never alter the prongs of a plug to fit a receptacle. If possible, install a new grounded receptacle.

Do not penetrate walls or ceilings without first shutting off electrical power to the circuits that may
be hidden.
Wire, Cable & Conduit
Wire and cable comprise the electrical infrastructure in your home.
Selecting the appropriate size and type and handling it correctly is
absolutely necessary to a successful wiring project that will pass inspection.
Copper wire is the primary conductor of electricity in any home. The
electricity itself travels on the outer surfaces of the wire, so insulation is
normally added to the wires to protect against shock and fires. The insulated
wires are frequently grouped together and bound up in rugged plastic
sheathing according to gauge and function. Multiple wires housed in shared
sheathing form a cable. In some cases, the conductors are further isolated
and grouped in metal or plastic tubes known as conduit. Conduit (also
known as raceway) is used primarily in situations where the cables or wires
are exposed, such as open garage walls.
This chapter introduces all of the many varieties of wire, cable, and
conduit used in home construction, and explains which types to use where.
It also will demonstrate the essential skills used to run new cable, install
conduit, strip sheathing, make wire connections, and more.

In this chapter:
• Wire & Cable
 Wire & Cable
Wires are made of copper, aluminum, or aluminum covered with a thin
layer of copper. Solid copper wires are the best conductors of electricity and
are the most widely used. Aluminum and copper-covered aluminum wires
require special installation techniques.
A group of two or more wires enclosed in a metal, rubber, or plastic
sheath is called a cable (photo, opposite page). The sheath protects the
wires from damage. Metal conduit also protects wires, but it is not
considered a cable.
Individual wires are covered with rubber or plastic vinyl insulation. An
exception is a bare copper grounding wire, which does not need an
insulation cover. The insulation is color coded (chart, left) to identify the
wire as a hot wire, a neutral wire, or a grounding wire.
In most wiring systems installed after 1965, the wires and cables are
insulated with plastic vinyl. This type of insulation is very durable and can
last as long as the house itself.
Before 1965, wires and cables were insulated with rubber. Rubber
insulation has a life expectancy of about 25 years. Old insulation that is
cracked or damaged can be reinforced temporarily by wrapping the wire
with plastic electrical tape. However, old wiring with cracked or damaged
insulation should be inspected by a qualified electrician to make sure it is
safe.
Wires must be large enough for the amperage rating of the circuit (chart,
right). A wire that is too small can become dangerously hot. Wire sizes are
categorized according to the American Wire Gauge (AWG) system. To
check the size of a wire, use the wire stripper openings of a combination
tool (page 30) as a guide.
 Wire Color Chart
WIRE COLOR FUNCTION

White Neutral wire carrying current at zero

voltage.

Black Hot wire carrying current at full voltage.

Red Hot wire carrying current at full voltage.

White, black Hot wire carrying current at full voltage.

markings

Green Serves as a grounding pathway.

Bare copper Serves as a grounding pathway.

Individual wires are color-coded to identify their function. In some circuit installations, the white
wire serves as a hot wire that carries voltage. If so, this white wire may be labeled with black tape or
paint to identify it as a hot wire.
 Wire Size Chart
WIRE GAUGE WIRE CAPACITY & USE

#6 60 amps, 240 volts; central air conditioner, electric

furnace.

#8 40 amps, 240 volts; electric range, central air conditioner.

#10 30 amps, 240 volts; window air conditioner, clothes dryer.

#12 20 amps, 120 volts; light fixtures, receptacles, microwave

oven.

#14 15 amps, 120 volts; light fixtures, receptacles.

#16 Light-duty extension cords.

#18 to Thermostats, doorbells, security systems.

22

Wire sizes (shown actual size) are categorized by the American Wire Gauge system. The larger the
wire size, the smaller the AWG number.
A. NM (nonmetallic) sheathed cable should be used for most indoor wiring projects in dry
locations. NM cable is available in a wide range of wire sizes, and in either “2-wire with
ground” or “3-wire with ground” types. NM cable is sold in boxed rolls that contain from 25 to
250 ft. of cable.
B.Coaxial cable is used to connect cable television jacks. Coaxial cable is available in lengths up
to 25 ft. with preattached F-connectors (A). Or you can buy bulk cable (B) in any length.
C. Large-appliance cable, also called SER cable, is used for kitchen ranges and other 50-amp or
60-amp appliances that require 8-gauge or larger wire. It is similar to NM cable, but each
individual conducting wire is made from fine-stranded copper wires. Large-appliance cable is
available in both 2-wire and 3-wire types.
D. THHN/THWN wire can be used in all conduit applications. Each wire, purchased individually,
is covered with a color-coded thermoplastic insulating jacket. Make sure the wire you buy has
the thhn/thwn rating. Other wire types are less resistant to heat and moisture than thhn/thwn
wire.
E. UF (underground feeder) cable is used for wiring in damp locations, such as in an outdoor
circuit. It has a white or gray solid-core vinyl sheathing that protects the wires inside. It also can
be used indoors wherever NM cable is allowed.
F.Telephone cable is used to connect telephone outlets. Your phone company may recommend
four-wire cable (shown below) or eight-wire cable, sometimes called four-pair. Eight-wire cable
has extra wires that are left unattached. These extra wires allow for future expansion of the
system.
 Tips for Working With Wire
WIRE GAUGE AMPACITY MAXIMUM WATTAGE LOAD

14-gauge 15 amps 1440 watts (120 volts)

12-gauge 20 amps 1920 watts (120 volts)

3840 watts (240 volts)

10-gauge 30 amps 2880 watts (120 volts)

5760 watts (240 volts)

8-gauge 40 amps 7680 watts (240 volts)

6-gauge 50 amps 9600 watts (240 volts)

Wire “ampacity” is a measurement of how much current a wire can carry safely. Ampacity
varies according to the size of the wires, as shown at left. When installing a new circuit, choose
wire with an ampacity rating matching the circuit size. For dedicated appliance circuits, check
the wattage rating of the appliance and make sure it does not exceed the maximum wattage load
of the circuit.
 Reading NM (Nonmetallic) Cable

NM (nonmetallic) cable is labeled with the number of insulated wires it contains. The bare
grounding wire is not counted. For example, a cable marked 14/2 G (or 14/2 WITH GROUND)
contains two insulated 14-gauge wires, plus a bare copper grounding wire. Cable marked 14/3 WITH
GROUND has three 14-gauge wires plus a grounding wire. NM cable also is stamped with a
maximum voltage rating, as determined by Underwriters Laboratories (UL).
 Reading Unsheathed, Individual Wire

Unsheathed, individual wires are used for conduit and raceway installations. Wire insulation is
coded with letters to indicate resistance to moisture, heat, and gas or oil. Code requires certain letter
combinations for certain applications. T indicates thermoplastic insulation. H stands for heat
resistance and two Hs indicate high resistance (up to 194° F). W denotes wire suitable for wet
locations. Wire coded with an N is impervious to damage from oil or gas.
Use wire connectors rated for the wires you are connecting. Wire connectors are color-coded by
size, but the coding scheme varies according to manufacturer. The wire connectors shown above
come from one major manufacturer. To ensure safe connections, each connector is rated for both
minimum and maximum wire capacity. These connectors can be used to connect both conducting
wires and grounding wires. Green wire connectors are used only for grounding wires.
Use plastic cable staples to fasten cables. Choose staples sized to match the cables. Stack-It®
staples (A) hold up to four 2-wire cables; 3/4" staples (B) for 12/2, 12/3, and all 10-gauge cables;
1/2" staples (C) for 14/2, 14/3, or 12/2 cables; coaxial staples (D) for anchoring television cables; bell
wire staples (E) for attaching telephone cables.

Push-in connectors are a relatively new product for joining wires. Instead of twisting the bare wire
ends together, you strip off about 3/4" of insulation and insert them into a hole in the connector. The
connectors come with two to four holes sized for various gauge wires. These connectors are perfect
for inexperienced DIYers because they do not pull apart like a sloppy twisted connection can.
 How to Strip NM Sheathing & Insulation

Measure and mark the cable 8 to 10" from end. Slide the cable ripper onto the cable, and squeeze
tool firmly to force cutting point through plastic sheathing.
Grip the cable tightly with one hand, and pull the cable ripper toward the end of the cable to cut
open the plastic sheathing.
Peel back the plastic sheathing and the paper wrapping from the individual wires.
Cut away the excess plastic sheathing and paper wrapping, using the cutting jaws of a combination
tool.
Cut individual wires as needed using the cutting jaws of the combination tool. Leave a minimum of
6" of wire running past the edge of the box.
Strip insulation for each wire, using the stripper openings. Choose the opening that matches the
gauge of the wire, and take care not to nick or scratch the ends of the wires.
 How to Connect Wires to Screw Terminals

Strip about 3/4" of insulation from each wire using a combination tool. Choose the stripper
opening that matches the gauge of the wire, then clamp the wire in the tool. Pull the wire firmly to
remove plastic insulation.
Form a C-shaped loop in the end of each wire using a needlenose pliers or the hole of the correct
gauge in a pair of wire strippers. The wire should have no scratches or nicks.
Hook each wire around the screw terminal so it forms a clockwise loop. Tighten screw firmly.
Insulation should just touch head of screw. Never place the ends of two wires under a single screw
terminal. Instead, use a pigtail wire (page 35).
 How to Connect Wires with Push-ins

Mark the amount of insulation to be stripped from each wire using the strip gauge on the back of
the switch or receptacle. Strip the wires using a combination tool (step 1, above). Never use push-in
fittings with aluminum wiring.
Insert the bare copper wires firmly into the push-in fittings on the back of the switch or receptacle.
When inserted, wires should have no bare copper exposed. Note: Although push-in fittings are
convenient, most experts believe screw terminal connections (above) are more dependable.
Remove a wire from a push-in fitting by inserting a small nail or screwdriver in the release opening
next to the wire. Wire will pull out easily.
 How to Join Wires with a Wire Connector

Ensure power is off and test for power. Grasp the wires to be joined in the jaws of a pair of
linesman’s pliers. The ends of the wires should be flush and they should be parallel and touching.
Rotate the pliers clockwise two or three turns to twist the wire ends together.
Twist a wire connector over the ends of the wires. Make sure the connector is the right size (see
page 29). Hand-twist the connector as far onto the wires as you can. There should be no bare wire
exposed beneath the collar of the connector.
Option: Reinforce the joint by wrapping it with electrician’s tape. By code, you cannot bind the wire
joint with tape only, but it can be used as insurance. Few professional electricians use tape for
purposes other than tagging wires for identification.
Option: Strip 3/4" of insulation off the ends of the wires to be joined, and insert each wire into a
push-in connector. Gently tug on each wire to make sure it is secure.
 How to Pigtail Wires

Cut a 6" length from a piece of insulated wire the same gauge and color as the wires it will be
joining. Strip 3/4" of insulation from each end of the insulated wire. Note: Pigtailing is done mainly
to avoid connecting multiple wires to one terminal, which is a code violation.
Join one end of the pigtail to the wires that will share the connection using a wire nut (see previous
page).
Alternative: If you are pigtailing to a grounding screw or grounding clip in a metal box, you may
find it easier to attach one end of the wire to the grounding screw before you attach the other end to
the other wires.
Connect the pigtail to the appropriate terminal on the receptacle or switch. Fold the wires neatly and
press the fitting into the box.
 Conversions
Metric Equivalent
Converting Measurements
TO CONVERT: TO: MULTIPLY BY:

Inches Millimeters 25.4

Inches Centimeters 25.4

Feet Meters 0.305

Yards Meters 0.914

Miles Kilometers 1.609

Square inches Square centimeters 6.45

Square feet Square meters 0.093

Square yards Square meters 0.836

Cubic inches Cubic centimeters 16.4

Cubic feet Cubic meters 0.0283

Cubic yards Cubic meters 0.765

Pints (U.S.) Liters 0.473 (lmp. 0.568)

Quarts (U.S.) Liters 0.946 (lmp. 1.136)

Gallons (U.S.) Liters 3.785 (lmp. 4.546)

Ounces Grams 28.4

Pounds Kilograms 0.454

Tons Metric tons 0.907

Millimeters Inches 0.039

Centimeters Inches 0.394

Meters Feet 3.28

Meters Yards 1.09

Kilometers Miles 0.621

Square centimeters Square inches 0.155

Square meters Square feet 10.8

Square meters Square yards 1.2

Cubic centimeters Cubic inches 0.061

Cubic meters Cubic feet 35.3

Cubic meters Cubic yards 1.31

Liters Pints (U.S.) 2.114 (lmp. 1.76)

Liters Quarts (U.S.) 1.057 (lmp. 0.88)

Liters Gallons (U.S.) 0.264 (lmp. 0.22)

Grams Ounces 0.035

Kilograms Pounds 2.2

Metric tons Tons 1.1

Converting Temperatures
Convert degrees Fahrenheit (F) to degrees Celsius (C) by following this
simple formula: Subtract 32 from the Fahrenheit temperature reading. Then
mulitply that number by 5/9. For example, 77°F - 32 = 45. 45 × 5/9 = 25°C.
To convert degrees Celsius to degrees Fahrenheit, multiply the Celsius
temperature reading by 9/5, then add 32. For example, 25°C × 9/5 = 45. 45
+ 32 = 77°F.
Copyright © 2012
Creative Publishing international, Inc.
400 First Avenue North, Suite 300
Minneapolis, Minnesota 55401
1-800-328-0590
www.creativepub.com
All rights reserved

10 9 8 7 6 5 4 3 2 1

President/CEO: Ken Fund

Digital edition: 978-1-61060-192-4

Softcover edition: 978-1-58923-601-1

Library of Congress Cataloging-in-Publication Data

The complete guide to wiring. -- 5th ed.

p. cm.
“Current with 2011-2013 Electrical codes.”
“Black & Decker.”
Includes index.
Summary: “New 5th edition is fully compliant with the 2013
National Electrical Code.”-- Provided by publisher.
ISBN-13: 978-1-58923-601-1 (soft cover)
ISBN-10: 1-58923-601-7 (soft cover)
1. Electric wiring, Interior--Amateurs’ manuals. 2. Dwellings--
Maintenance and repair--Amateurs’ manuals. 3. Dwellings--Electric
equipment--Amateurs’ manuals. I. Black & Decker Corporation
(Towson, Md.) II. Creative Publishing International. III. Title: Black
&
Decker, the complete guide to wiring.
TK3284.C65 2011
621.319’24--dc22

2011000820

Home Improvement Group

Publisher: Bryan Trandem

Managing Editor: Tracy Stanley
Senior Editor: Mark Johanson

Creative Director: Michele Lanci-Altomare

Art Direction/Design: Brad Springer, James Kegley, Kim Winscher

Lead Photographer: Corean Komarec

Set Builder: James Parmeter
Production Managers: Laura Hokkanen, Linda Halls

Edition Editor: Chris Sibell

Page Layout Artist: Danielle Smith
Technical Consultant and Shop Help: John Keane
Proofreader: Ingrid Sundstrom Lundegaard

The Complete Guide to Wiring 5th Edition

Created by: The Editors of Creative Publishing international, Inc., in
cooperation with Black & Decker.
Black & Decker® is a trademark of The Black & Decker
Corporation and is used under license.
NOTICE TO READERS
For safety, use caution, care, and good judgment when following the
procedures described in this book. The publisher and Black & Decker
cannot assume responsibility for any damage to property or injury to
persons as a result of misuse of the information provided.
The techniques shown in this book are general techniques for various
applications. In some instances, additional techniques not shown in this
book may be required. Always follow manufacturers’ instructions
included with products, since deviating from the directions may void
warranties. The projects in this book vary widely as to skill levels
required: some may not be appropriate for all do-it-yourselfers, and
some may require professional help.
Consult your local building department for information on building
permits, codes, and other laws as they apply to your project.