Module 3: Wiring Methods

Open wiring on insulators

• an exposed wiring method using cleats, knobs, stubes, and flexible tubing for the protection and support of single insulated conductors run in or on buildings, and not concealed by the building structure

• shall be permitted on systems of 600 volts, nominal, or less, in wet and dry locations, where subject to corrosive vapors and for services

Concealed Knob-and-Tube

• a wiring method using knobs, tubes, and flexible nonmetallic tubing for the protection and support of single insulated conductors concealed in hollow spaces of walls and ceilings of buildings

• shall be permitted to be installed in the hollow spaces of walls and ceilings or in unfinished attics and roof spaces with additional provisions such as: for extensions of existing installations or elsewhere by special permission

armored cable (type AC)

• aka BX Cable

• is a fabricated assembly of insulated conductors in a flexible metal enclosure

• shall be permitted for branch circuits and feeders in both exposed and concealed work and in bale trays where identified for such use

• shall be permitted also in dry locations and embedded in plaster finish on brick or other masonry, except in damp or wet locations

• shall be permissible to run or fish this cable in the air voids of masonry block or tile walls where such walls where such walls are not exposed or subject to excessive moisture or dampness

• prohibitions:

  (1) In theaters and similar locations

  (2) In motion picture studios

  (3) In any hazardous (classified) locations

  (4) Exposed to corrosive fumes or vapors

  (5) On cranes or hoists

  (6) In storage battery rooms

  (7) In hoistways or elevators

  (8) In commercial garages

Metal-Clad Cable (Type MC)

• a factory assembly of one or more conductors

  • each individually insulated and enclosed in a metallic sheath of interlocking metal tapes, or a smooth or corrugated metallic tube

• shall be permitted in any of the following locations and applications

   Services, feeders, and branch circuits

   Power, lighting, control, and signal circuits

   Indoors and outdoors

   Exposed or concealed

   Direct burial where identified for such use

   In cable tray

   In any raceway

   Open runs of cable

   Aerial cable on a messenger

   In hazardous (classified) locations

   In dry locations embedded in plaster finish on brick or other masonry except in damp or wet locations

   In wet locations where metallic sheathing is impervious to moisture, lead sheath, or moisture-impervious jacket is provided under the metal covering or metallic covering are listed for use in wet location

• shall not be used where exposed to destructive corrosive conditions

  • such as direct burial in the earth, in concrete

  • or where exposed to cinder fills, strong chlorides, caustic alkalis, or vapors of chlorine or of hydrochloric acids

    • unless the metallic sheath is suitable for conditions or is protected by material suitable for the conditions

Mineral-Insulated, Metal-Sheathed Cable (Type MI)

• is a factory assembly of one or more conductors insulated with a highly-compressed refractory mineral and enclosed in liquidtight and gastight continuous copper or alloy steel sheathe

• permitted as follows

   Services, feeders, and branch circuits

   Power, lighting, and signal circuits

   In dry, wet, or continuously moist locations

   Indoors and outdoors

   Exposed or concealed

   Embedded in plaster, concrete fill, or other masonry, whether above or below grade

   In hazardous (classified) locations

   Where exposed to corrosive conditions

   In underground runs where suitably protected against physical damage and corrosive conditions

• shall not be used where exposed to destructive corrosive conditions

  • unless protected by sheath materials suitable for the conditions

Nonmettalic-Sheated Cable (Type NM & NMC)

• a factory assembly of 2 or more insulated conductors having an outer sheath of moisture-resistant, flame-retardant, nonmetallic material

• permitted to use the following:

   One and two-family dwellings

   Multifamily dwellings and other structures

   Cable trays where the cables are identified for their use

   Type NMS cable shall be permitted for both exposed and concealed work in normally dry locations

• shall not be used in

   any multifamily dwelling or other structure exceeding three floors

   as service entrance in commercial garages having hazardous (classified) locations

   places of assembly

   in motion picture studios

   in storage battery rooms

   in hoistways

   embedded concrete, cement, or aggregate

   or any hazardous (classified) locations

Shielded Nonmetallic-Sheathed Cable (Type SNM)

is a factory assembly of two or more insulated conductors in an extruded core of moisture-resistant, flame- resistant nonmetallic material, covered with an overlapping spiral metal tape and wire shield, and jacketed with an extruded nonmetallic material resistant to moisture, flame, oil, corrosion, fungal growth, and sunlight

Service Entrance Cable (Types SE and USE)

is a single conductor or multi-conductor assembly provided with or without an overall covering, primarily used for services and of the following types

Type SE

possesses a flame-retardant moisture-resistant covering

Type USE

• cables used for service laterals shall be permitted to emerge above ground outside at terminations in meter bases or other enclosures where protected

• they can be also be utilized as branch circuit connectors or feeders

Underground Feeder and Branch Circuit Cables (Type UF)

• shall be approved in sizes 2.0 mm2 copper and 3.5 mm2 aluminum or copper-clad aluminum through 100 mm2

• The overall covering shall be flame-retardant, moisture-resistant, fungus-resistant, corrosion-resistant, and suitable for direct burial in the earth.

• shall be permitted for use underground, including direct burial, as feeder or branch circuit cable when provided with overcurrent protection of the rated ampacity

• shall also be permitted for interior wiring in wet, dry, or corrosive locations under the recognized wiring methods.

• if supported by cable trays shall be

  of multi-conductor type

• not used in the following:

   As service entrance cables

   In commercial garages

   In theaters

   In motion picture studios

   In storage battery rooms

   In hoistways

   In hazardous (classified) locations

Power and Control Tray Cable (Type TC)

• a factory assembly of 2 or more insulated conductors, with or without associated bare or covered grounding conductor under a nonmetallic sheath, approved for installation in cable trays, raceways, or where supported by messenger wire

• shall be permitted in:

   Power, lighting, control, and signal circuits

   In cable trays, or in raceways, or where supported in outdoor locations by messenger wire

   Exposed or concealed

   In industrial establishments

• not permitted in the following

   Installed where it will be exposed to physical damage

   Installed as an open cable on brackets or cleats

   Used where exposed to direct rays of sunlight, unless identified as sunlight-resistant

   Directly buried

Flat Cable Assemblies (Type FC)

an assembly of parallel conductors formed integrally with an insulating material web specially designed for field installation in metal surface raceway

Flat Conductor Cable (Type FCC)

• consists of three or more flat copper conductors placed edge-to-edge and separated and enclosed within an insulating assembly

• shall be permitted as

   A branch circuit conductor for general purpose and for appliance branch circuits and for individual branch circuit.

   On continuous floor surfaces made concrete, ceramic, or composition flooring, wood, or similar materials

• shall not be permitted in outdoor and in wet areas or where subject to corrosive vapors and in any hazardous (classified) locations

Nonmetallic Extensions

• are an assembly of two insulated conductors within a nonmetallic jacket or an extruded thermoplastic covering

• classification includes both surface extensions, intended for mounting directly on the surface of walls or ceilings, and aerial cable, containing a supporting messenger cable as an integral part of the cable assembly

• shall be permitted as an extension from an outlet on a 15 or 20 ampere branch circuit or if the extension is run exposed and in a dry location

• restrictions:

   Aerial cable

   Unfinished areas

   Voltage between conductor exceeds 250 volts for nonmetallic surface extensions and 300 volts for aerial cable

   Areas where corrosive vapors may be present

Medium Voltage Cable (Type MV)

• is a single or multi-conductor solid dielectric cable rated at 2001 volts or higher

• shall be permitted for use on power systems rated up to 35,000 volts, nominal in wet or dry locations, in raceways, in cable trays, or directly buried in the earth

• should not be used with risk of exposure to direct sunlight

Messenger -Supported Wiring

• an exposed support system using messenger wire to support insulated conductors by any one of the following

  • A messenger with rings and saddles for conductor support

  • A messenger with a field–installed lashing material for conductor support

  • Factory-assembled aerial cable

  • multiple cable utilizing a bare conductor

  • factory-assembled and twisted with one or more insulated conductors, such as duplex, triplex, or quadruplex construction

• shall not be used in hoistways or where subject to severe physical damage

Integrated Gas Spacer Cable (Type IGS)

• is a factory assembly of one or more conductors, each individually insulated and enclosed in a loose-fit nonmetallic flexible conduit as an integrated gas spacer cable rated at 0-600 volts

• shall be permitted for use underground, including direct burial in the earth, as service entrance conductors, or as feeder or branch circuit conductors

• shall not be used as interior wiring nor be exposed in contact with buildings

Raceway

an enclosed channel designed expressly for holding wires, cables, or busbars with additional functions

Intermediate Metal Conduit (IMC)

• a metal raceway of circular cross-section with integral or associated couplings, connectors, and fittings approved for the installation of electrical conductors

Rigid Metal Conduit (RMC)

• specially constructed for the purposed of pulling in or the withdrawing or cables after the conduit is in place and made of metal pipe of standard weight and thickness permitting the cutting of standard threads

• shall be permitted

  (1) Protected by enamel

  Ferrous raceways and fittings protected from corrosion solely by enamel shall be permitted only indoors and in occupancies not subject to severe corrosive influences

  (2) Dissimilar metals

  Where practicable, dissimilar metals in contact anywhere in the system shall be avoided in order to prevent the possibility of galvanic corrosion

  (3) Corrosion protection

  Ferrous or non-ferrous metal conduits, elbows, couplings, or fittings shall be permitted to be installed in concrete, in direct contact with the earth, or in areas subject to corrosive influences where protected from corrosion and judged suitable for the condition

Rigid Nonmetallic Conduit

• a type of conduit and fittings of suitable nonmetallic material that is resistant to moisture and chemical atmosphere

• for use underground, it shall also be flame-retardant, resistant to impact and crushing, resistant to distortion from heat under conditions liely to be encountered in service, and resistant to the effects of low temperature and sunlight

Liquidtight Flexible Metal Conduit

a raceway of circular cross-section having an outer liguidtight, nonmetallic, sunlight-resistant jacket over an inner flexible metal core with associated couplings, connectors, and fittings, all approved for the installation of electric conductors

Flexible Metallic Tubing (FMT)

• non-rigid metal conduit into which conductors may be drawn

• may be used on the following locations

  • dry locations

  • in accessible locations protected from physical damage or concealed above ceiling

  • for 1000 volts or more

  • in branch circuits

Electrical Metallic Tubing (EMT)

• metal pipe into which electrical conductors may be drawn

• has a thinner wall thickness than a rigid metal conduit

• shall be permitted for both exposed and concealed work

• shall not be used:

  • where, during and after the work, it will be subject to severe physical damage

  • where protected from corrosion solely by enamel

  • in hazardous locations

Surface Metal Raceway (SMR)

• a raceway consisting of an assembly of metal backing and capping

• shall be permitted in dry locations

• shall not be used in

  • where subject to severe physical damage unless otherwise approved

  • where the voltage is 300 volts or more or more between conductors unless the metal has thickness of not less than 1 mm

  • where subject to corrosive vapors

  • where concealed

Surface Nonmettalic Raceway

• a type of nonmetallic raceway

• shall not be used on the following

  • concealed areas

  • areas where it will be subject to severe physical damage

  • 300 volts or more between conductors

  • in hazardous (classified) areas

Underfloor raceway

• raceway type suitable for use under floor

• installation shall be permitted beneath the surface of concrete or other flooring material or in office occupancies, where laid flush with concrete floor and covered with linoleum or equivalent floor covering

cellular floor raceway

• the hollow spaces of cellular metal floors together with suitable fittings which may be approved enclosure for electrical conductors

• shall be defined as a single, enclosed tubular space in a cellular metal floor member

Multi-outlet assembly

• a type of surface flush raceway designed to receive conductors and receptacles assembled in the field or in the factory

• a steel or metal troughing (usually with removable cover) and fitting, so formed and constructed that insulated conductors may be readily drawn in and withdrawn, or laid in and removed with injury either conductor or covering

Busway

an approved, completely assembled metal troughing and fitting containing bare conductors intended for use as feeders, the conductors being suitably supported on insulators

cable tray

a unit of assembly of units or sections and associated fittings forming a rigid structural system used to support cables

cable bus

an approved assembly of insulated conductors with fittings and conductors terminating in a completely enclosed ventilated metal housing