Electrical Wiring--Residential

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Electrical Wiring--Residential

• Unit 2Electrical Symbols and Outlets

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FACTSUNIT 2

• By definitions, toggle switches and receptacles
  are devices because they carry current, but do
  not consume power
• When a receptacle is connected to the
  branch-circuit wires, the outlet is called a
  receptacle outlet.
• When a luminaire (light fixture) is attached to
  the branch-circuit wires, the outlet is called a
  lighting outlet.

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FACTSUNIT 2 cont.

• Dashed lines run from an outlet to a switch would
  normally indicate that the switch controls a
  portion of that outlet. The dashed lines are
  curved so that they cannot be mistaken for
  invisible edge lines. Outlets without curved
  dashed lines are independent outlets and have no
  switch control.

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FACTSUnit 2 cont.

• Most modern surface-mounted luminaires (light
  fixtures) can be fastened to a luminaire
  (fixture) stud in the box or an outlet box or
  plaster ring using appropriate No. 8-32 metal
  screws. Special consideration has to be made for
  luminaires that weigh 50 lbs or more and for
  fixtures that weigh only 6lbs or less may be
  mounted with 6/32 screws on a standard outlet box
  (plastic or metal).

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• A box (or fitting) must be installed wherever
  there are splices, outlets, switches, or other
  junction points. The boxes must meet the
  following
• NEC 300.11 and 314.23 Boxes must be securely
  mounted and fastened in place.
• NEC 300.15 Where conduit, electrical metallic
  tubing (EMT), nonmetallic-sheathed cable (Romex),
  Type AC cable or other cables are installed, a
  box or conduit body must be installed at each
  conductor splice connection point, outlet, switch
  point, junction point, or pull point.

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• Boxes cont.--
• NEC 300.15 Where cables enter or exit from a
  conduit or tubing that is used to provide cable
  support or protections against physical damage, a
  fitting shall be provided on the end(s) of the
  conduit or tubing to protect the cable from
  abrasion.
• NEC 314.3 Permits nonmetallic outlet and device
  boxes to be installed where the wiring method is
  nonmetallic sheathed cable or nonmetallic raceway

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• Boxes cont.--
• NEC 314.3 (Exceptions) allows metal raceways and
  metal-jacketed cables (BX) to be used with
  non-metallic boxes provided all metal raceways or
  cables entering the box are bounded together to
  maintain the integrity of the grounding path to
  other equipment.
• NEC 314.16 Boxes must be large enough for all
  of the enclosed conductors and wiring devices.

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• Boxes cont.
• NEC 314.16(C) The exception allows multiple
  cables to be run through a single knockout
  opening in a nonmetallic box (plastic), but not
  for metallic boxes.
• NEC 314.20 Boxes installed in combustible
  material the box must be flush with the outer
  wall surface. If the boxes are installed in a
  noncombustible wall it is acceptable to have the
  front edge of the box set back not more than ¼
  in. (6 mm) for the finished surface.

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• Boxes cont.--
• NEC 314.22 A surface extension from a box of a
  concealed wiring system is made by mounting and
  securing an extension ring over the concealed box
  or by a cover that secures the cover so that it
  will not fall off if it becomes loose. The
  grounding continuity must be independent of the
  connection between the box and cover. You may
  not use the mounting screws of the surface
  extension for the grounding or bonding of the
  extension ring, unless the mounting of the
  extension ring is independent from the cover.

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• Boxes cont.
• NEC 314.23(B)(1) States that when a switch box
  or outlet box is mounted to a stud or ceiling
  joist with nails or screws through the box, the
  nails or screws must be not more than ¼ in. (6mm)
  from the back or ends of the box.Nails or screws
  will not interfere with the wiring devices in the
  box.

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• Boxes cont.--
• NEC 314.25 In completed installations, all
  boxes shall have a cover, faceplate, or luminaire
  (fixture) canopy.DO NOT LEAVE ANY ELECTRICAL
  BOXES UNCOVERED.
• NEC 314.27(A) Boxes used at lighting outlets
  must be designed or installed so that a luminaire
  (lighting fixture) may be attached to it.

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• Boxes cont.--
• NEC 314.27(A) and (B) Listed outlet boxes are
  suitable for hanging luminaires (lighting
  fixtures) that weigh 50 lb. (23 kg) or less.
  Luminaires that weigh more than 50 lbs must be
  supported independently of the outlet box, or the
  outlet box must be listed for the weight to be
  supported.Wall-mounted luminaires of less than 6
  lb may be supported by a box or by a plaster ring
  secured to a box, by not less than two No. 6-32
  or larger screws.

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• Boxes cont.--
• NEC 314.27(D) Standard outlet boxes must not be
  used as the sole support for ceiling suspended
  (paddle) fans unless they are specifically listed
  for this purpose.
• NEC 314.29 Conduit bodies, junction, pull, and
  outlet boxes must be installed so the wiring
  contained in them is accessible without removing
  any part of the building.NEVER INSTALL OUTLET
  BOXES WHERE THEY WILL BE INACCESSIBLE BEHIND OR
  ABOVE PERMANENT FINSHED WALLS OR CEILINGS.

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• Boxes cont.
• NEC 314.71 Pull and junction boxes must provide
  adequate space and dimensions for the
  installation of conductors, and devices that are
  to be installed.
• NEC 314.23 (B)(1)stated that when a switch box
  or outlet box is mounted to a stud or ceiling
  joist with nails or screws through the box , the
  nails or screws must be not more than ¼ in. (6mm)
  from the back or ends of the box.THIS ENSURES
  THAT WHEN NAILS OR SCREWS PASS THROUGH THE BOX,
  THEY WILL NOT INTERFERE WITH THE WIRING DEVICES
  IN THE BOX.

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FACTSUNIT 2 cont.

• When two or more switches or receptacles are
  located at the same point , the switches or
  receptacles are referred to as being ganged,
  meaning that they are inside the same box.
• If when installing an outlet box in a combustible
  wall and the box is not flush with the outer
  surface of the wall you may use a box extender,
  sometimes referred to as a goof ring.

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FACTSUNIT 2 cont.

• When raised covers or plaster rings are marked
  with their volume in cubic inches, that volume
  may be added to the box volume to determine
  maximum number of conductors allowed in the
  combined box and raised cover

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FACTSUNIT 2 cont.

• Switch boxes installed between studs using metal
  switch box supports, often referred to as Kruse
  strips. If wood strips are used, they must have
  a cross-sectional dimension of not less than 1
  in. x 2 in. (25mm x 50mm)

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FACTSUNIT 2 cont.

• Four-inch square boxes can be trimmed with
  one-gang or two-gang plaster rings where devices
  will be installed. Luminaires (lighting
  fixtures) will be installed , a plaster ring
  having a round opening should be installed.

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FACTSUNIT 2 cont.

• Remodel work require the use of boxes having
  plaster ears and snap-in brackets that can be
  inserted from the front into the existing walls.
  Another popular method is to use boxes with
  plaster ears, inserting them from the front and
  then using Madison Hold-Its or Madison Hangers

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FactsUnit 2Spread of Fire

• Fire must be contained and not allowed to spread
• Use of 5/8-in gypsum wallboard instead of the
  normal ½-in on the ceiling and on the walls
  between the garage and living areas and requiring
  draft stopping where ducts, cables and piping
  run through bottom (sole) and top plates.This
  requires all holes or openings in these two
  plates to be calked using an approved fire rated
  calk or foam.

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FactsUnit 2Spread of Firecont.

• In walls, partitions, and ceilings that are
  fire-resistance-rated, are defeated if electrical
  boxes are installed back-to-back or in the same
  stud or joist space of common walls or ceilings.
• Rating of fire-resistance materials are rated in
  hours.

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FactsUnit 2Spread of Firecont.Fire rating
of boxes

• The surface area of individual metallic outlet
  or switch boxes shall not exceed 16 square
  inches (i.e., a 4-in. square box is 4 in. x 4
  in. 16 in.2),
• the aggregate surface area of the boxes shall
  not exceed 100 in.2 per 100 ft.2 of wall
  surface,
• boxes located on opposite sides of walls or
  partitions shall be separated by a minimum
  horizontal distance of 24 in. (600mm),

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FactsUnit 2Spread of Firecont.Fire rating
of boxes

• the metallic outlet or switch boxes shall be
  securely fastened to the studs and the opening in
  the wallboard facing shall be cut so that the
  clearance between the box and the wallboard does
  not exceed 1/8 in. (3 mm).
• Using nonmetallic boxes in fire-resistance-rated
  walls, the restrictions are more stringent that
  for metallic boxesi.e. non-metallic boxes may be
  restricted to openings not to exceed between 10
  in.2 to 25 in.2.

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FactsUnit 2Spread of Firecont.Fire rating
of boxes

• Certain molded fiberglass outlet and device boxes
  are listed for use in fire-resistance-rated
  partitions without the use of putty pads, mineral
  wool batts, or fiberglass batts, provided a
  minimum horizontal distance of 3 in. (75 mm) is
  maintained between boxes and the boxes are not
  back-to-back.

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FactsUnit 2Spread of Firecont.Fire rating
of boxes

• Using and intumescent (expands when heated)
  fire resistant material that comes in pads, when
  properly installed may make the 24 in. separation
  between boxes not required. Providing that the
  outlet boxes must not be installed back-to-back.

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