Renovation 4th Edition

by Michael Litchfield

  Service conductors are attached to a meter

  base and then to the service panel. Straddling the

  two sets of terminals on its base, the meter mea-

  sures the wattage of electricity as it is consumed.

  The service panel also routes power to various

  You never know what you’ll find inside a

  circuits throughout the house.

  service panel, so stay out. This panel is so

  The utility company will install the drop

  crowded that it will be tough to replace

  wires to the building and will install the meter.

  the cover.

  a service entrance and Panel

  Weatherhead

  zzzzzz

  Service drop

  A typical three­wire service assembly

  has two insulated hot conductors

  wrapped around a bare messenger

  Mast

  cable, which also serves as the

  neutral.

  Meter base

  Conduit

  90° LB condulet

  The service panel distributes power to circuits throughout

  the house. Breakers interrupt power if the circuits become

  overloaded.

  Service panel

  (entrance panel)

  262 Chapter 11

  Wires,

  inside the service Panel

  Cables,

  and ConduCtors

  zzzzzz

  the terms wires, cables, and conductors are often

  Hot feeder lines

  (incoming power)

  used interchangeably, but they are not exactly the

  same. a conductor is anything that carries or con-

  Incoming neutral

  ducts electricity. a wire is an individual conduc-

  Main breaker

  tor, and cable is usually an assembly of two or

  Main bonding jumper

  more wires, protected by plastic or metal sheath-

  Neutral buses

  Incoming ground

  ing (also called a jacket). a cable derives its name

  Single-pole breaker

  from the size of the wires within and the type of

  Hot buses

  Hot wire

  sheathing it is assembled with. For example,

  12-gauge cable contains 12aWg (american Wire

  Ground buses

  Circuit cable

  gauge) wire. more specifically, 12/2 with ground

  Neutral wire

  denotes cable with two 12aWg wires plus a

  Ground wire

  ground wire. nm designates nonmetallic sheath-

  Grounding

  ing, mC for metal-clad sheathing and so on.

  electrode

  Knockouts for

  conductor

  circuit cables

  on all sides

  of panel

  The homeowner is responsible for everything

  beyond that, including the meter base and break-

  er panel, which a licensed electrician should

  install.

  serviCe Panels

  At the main service panel, the two hot cables

  from the meter base attach to lugs or terminals

  on the main breaker. The incoming neutral cable

  Incoming ground

  attaches to the main lug of the neutral/ground

  bus. In the main panel, neutral/ground buses

  hot feeder lines (incoming power)

  must be connected together, usually by a wire or

  Incoming neutral

  metal bar called the main bonding jumper. In

  subpanels and all other locations downstream

  main breaker

  from the main service panel, ground and neutral

  hot bus bar (behind breakers)

  components must be electrically isolated from

  each other.

  neutral bus bar

  In a main fuse box, the hot conductors from

  the meter attach to the main power lugs, and the

  ground bus bar

  neutral cable to the main neutral lug. Whether

  the panel has breakers or fuses, metal buses run

  from the main breaker/main fuse. Running down

  the middle of the panel, hot buses distribute

  power to the various branch circuits either

  through fuses or through breakers. The neutral/

  ground buses are long aluminum bars containing

  many terminal screws, to which ground and neu-

  tral wires are attached.

  grounding electrode conductor

  Each fuse or breaker is rated at a specific

  number of amps (15- and 20-amp breakers or

  fuses take care of most household circuits).

  When a circuit becomes overloaded or a short

  The main panel (service panel) houses incoming cables from

  circuit occurs, the breaker trips or a fuse strip

  the meter as well as the breakers and wires that distribute

  electricity to individual circuits. At the service panel,

  melts, thereby cutting voltage to the hot wire. All

  neutral conductors (white wires), equipment­grounding

  current produces some heat, and as current

  conductors (bare copper or green insulated wires), the metal

  increases, the heat generated increases. If there

  service panel, and the grounding electrode system

  were no breakers or fuses, and if too much cur-

  (grounding rods) must be bonded together.

  electrical Wiring

  263

  Stay away from the area around the main breaker. The terminals above the

  A service entrance panel being used as a meter­main.

  breaker remain hot even when the main is off, presenting a serious hazard if

  Placed outside the house, it provides easy access for

  the cover is off.

  service or emergencies.

  rent continued to flow, the wires would overheat

  Edison-style fuses are more common. They have

  and could start a fire. Amperage ratings of break-

  little windows that let you see a filament. When

  ers and fuses are matched to the size (cross-

  the circuit has been overloaded and the fuse is

  sectional area, measured as “gauge”) of the

  blown, the filament will be separated. A black-

  circuit wires.

  ened (from heat) interior could mean a short cir-

  cuit—a potentially dangerous situation calling

  the main breaker. All electricity entering a

  for the intervention of a licensed electrician. The

  house goes through the main breaker, which is

  less common cartridge fuses are used to control

  usually located at the top of a main panel. In an

  240v circuits and are usually part of the main dis-

  emergency, throw the main breaker to “off” to

  connect switch, or serve heavy-duty circuits for

  turn off all power to the house. The main breaker an electric range or a clothes dryer.

  is also the primary overcurrent protection for the

  electrical system and is rated accordingly. (The

  grounding basiCs

  rating is stamped on the breaker handle.) If the

  main breaker for a 200-amp panel senses current Because electricity moves in a circuit, it will

  that exceeds its load rating, the breaker will auto-

  return to its source unless the path is interrupted.

  matically trip and shut off all power.

  The return path is through the white neutral

  wires that bring current back to the main panel.

  Meter–mains. Increasingly common are meter–

  Ground w
ires provide the current with an alter-

  mains, which house a meter base and a main

  native low-resistance path.

  breaker service in a single box. Meter–mains

  Why is having a grounding path important?

  allow a homeowner to put the main breaker out-

  Before equipment-grounding conductors (popu-

  side the house, where it can be accessed in an

  larly called ground wires) were widespread,

  emergency—if firefighters need to cut the power

  people could be electrocuted when they came in

  to the house before they go inside, for example.

  contact with voltage that, due to a fault like a

  When meter–mains are used, electricians often

  loose wire, unintentionally energized the metal

  locate a panel with the branch circuit breakers

  casing of a tool or an electrical appliance.

  (called a subpanel) in the garage or another cen-

  Ground wires bond all electrical devices and

  tralized location inside that is easy to access,

  potentially current-carrying metal surfaces. This

  such as a laundry room.

  bonding creates a path with such low impedance

  A fuse box subpanel.

  Fuse boxes. Many older homes still have fuse

  (resistance) that fault currents flow along it,

  boxes. Fuses are the earliest overcurrent protec-

  quickly tripping breakers or fuses and interrupt-

  tion devices, and they come as either Edison-type ing power. Contrary to popular misconceptions,

  (screw-in) fuses or cartridge (slide-in) fuses.

  the human body usually has a relatively high

  264 Chapter 11

  impedance (compared with copper wire); if elec-

  tricity is offered a path with very low resistance—

  Making sense of grounding

  the equipment grounding conductor—it will take

  the low resistance path back to the panel, trip the

  grounding confuses a lot of people, including some electricians. Part of the

  breaker, and cut off the power.

  problem is that the word ground has been used imprecisely for more than a century

  Ground wires (equipment grounding conduc-

  to describe electrical activity or components. The term ground wire, for example,

  tors) connect to every part of the electrical sys-

  may refer to one of three different things:

  tem that could possibly become energized—

   The large, usually bare-copper wire clamped to a ground rod driven into the

  metal boxes, receptacles, switches, fixtures—and,

  earth, or to rebar in a concrete footing. because the rod or the rebar is technically a

  through three-pronged plugs, the metallic covers

  grounding electrode, this “ground wire” is correctly called a grounding electrode

  and frames of tools and appliances. The conduc-

  tors, usually bare copper or green insulated wire,

  conductor.

  create an effective path back to the main service

   short conductors that connect one piece of electrical equipment to another to

  panel in case the equipment becomes energized.

  eliminate the possibility of a voltage difference between the two. These wires

  That allows fault current to flow, tripping the

  should be called bonding conductors.

  breaker.

   The bare copper or green insulated wires in all modern circuits, which ultimately

  the neutral/ground bus. In the service panel,

  connect electrical equipment, such as receptacles and fixtures, to the service panel

  the ground wires attach to a neutral/ground bus

  neutral/ground bar. These connections create a low-impedance fault path back to the

  bar, which is bonded to the metal panel housing

  service panel. Why? in case the equipment becomes energized by a hot wire touching

  via a main bonding jumper. If there’s a ground

  a metal cover or other part, this conductor allows current to flow safely and trip the

  fault in the house, the main bonding jumper

  breaker. in this book, the term ground wire or grounding conductor refers to this con-

  ensures the current can be safely directed to the

  ductor. These wires are properly called equipment-grounding conductors.

  ground—away from the house and the people

  inside. It is probably the single most important

  connection in the entire electrical system.

  Ground Faults Can kill

  Current flowing unintentionally

  to ground (“earth”) is called a

  avoiding electrical shocks

  ground fault. the ground wire is

  One hand

  intended to be a low-impedance

  zzzzzz

  touches defective

  appliance with

  path to ground, to safely carry

  fault.

  the current of a ground fault

  until the circuit breaker trips.

  You, however, can also be a path

  to ground should you come in

  contact with an energized con-

  Current flows

  through body.

  STAY OUT

  ductor. In this case, you would

  OF THIS

  become part of the circuit, with

  LOOP!

  current flowing through you. so

  Other hand touches

  grounded water pipe

  be careful: only a little current

  (faucet).

  flowing through your heart can

  kill you.

  electrical Wiring

  265

  Major grounding elements

  The equipment-grounding system acts as an expressway for stray current. by

  bonding conductors or potential conductors, the system provides a low-impedance

  path for fault currents. in a ground fault, the abnormally high amperage (current

  flow) that results trips a breaker or blows a fuse, disconnecting power to the circuit.

  it’s required by the neC to ground metal water piping and metal gas piping in

  case it becomes energized. an underground metal water pipe can’t serve as the only

  grounding electrode. otherwise, someone could disconnect the pipe or install a sec-

  tion of nonconductive pipe such as PvC, thus interrupting the grounding continuity

  and jeopardizing your safety. in new installations, code requires that underground

  metal water piping be connected to the electrode system and supplemented with

  another electrode.

  At the service panel, the smaller

  copper wire at the top runs to a

  Major grounding elements

  ground rod; the thicker copper wire

  below and the neutral wire feed a

  Metal water

  zzzzzz

  subpanel within the house.

  pipes

  Bonding

  Clamp

  Neutral/ground

  jumper

  bus

  Service

  panel

  Bonding

  Main bonding

  conductor

  jumper

  Water

  heater

  Grounding

  electrode conductor

  The main ground wire from the

  service panel clamps to an 8­ft.

  grounding electrode (or ground rod)

  Grounding

  electrode

  driven into the earth. It diverts

  (ground rod)

  outside voltage, such as lightning

  str
ikes.

  Bonding

  Clamp

  jumper

  Service

  panel

  Main bonding

  jumper

  Grounding

  electrode

  conductor

  Water

  heater

  Connections to cold­water pipes and

  gas pipes prevent shocks should the

  pipes become inadvertently

  energized.

  Grounding

  electrode

  Cold-water

  (ground rod)

  jumper

  266 Chapter 11

  Also attached to the neutral/ground bus in the hot tubs, and the like. Wiring a GFCI receptacle

  service panel is a large, usually bare, copper

  is covered on pp. 302–303.

  ground wire—the grounding electrode conductor

  (GEC)—that clamps to a grounding electrode

  CuTTing PoWer aT The Panel

  usually either a ground rod driven into the earth,

  always shut off the power to an outlet before

  or a “Ufer grounding electrode”, a 20-ft. length of working on it—and then test with an electri-

  steel rebar or heavy copper wire in the footing of

  cal tester to be sure there’s no voltage present.

  the foundation. The grounding electrode’s prima-

  In rare instances, a circuit may be mistakenly fed

  ry function is to divert lightning and other out-

  by more than one breaker! Because individual

  side high voltages to the earth before they can

  devices such as receptacles, switches, and fix-

  damage the building’s electrical system. Although tures can give false readings if they are defective

  the grounding electrode system (GES) is con-

  or incorrectly wired, the only safe way to shut off

  nected to the equipment grounding system at the the electricity is by flipping a breaker in the ser-

  service panel, the GES has virtually nothing to do vice panel or subpanel.

  with reducing hazards from the problems in the

  Turning off the power at a breaker panel is

  wiring inside the house. That’s the role of the

  usually straightforward. After identifying the

  equipment grounding conductors.

  breaker controlling the circuit, push the breaker’s

  The National Electrical Code (NEC) requires

  handle to the off position. The breaker handle

  grounding electrode conductor size to be based

  should click into position; if it doesn’t, flip it

  on the sizes and types of conductors in the ser-

  again until you hear a click. (A breaker that won’t

  vice. Typically, residential GECs are size 6

  GfCI receptacles detect miniscule

  snap into position may be worn out or defective