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Wiring Systems

Wiring Systems. 4. Objectives. Know where to find codes and authorities for an installation. Recognize the marks of the most popular testing agencies. List the different conductor systems used in residential and light commercial wiring. Explain the basics of conduit bending.

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Wiring Systems

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  1. Wiring Systems 4

  2. Objectives • Know where to find codes and authorities for an installation. • Recognize the marks of the most popular testing agencies. • List the different conductor systems used in residential and light commercial wiring. • Explain the basics of conduit bending. • Become familiar with the many different types of raceway systems.

  3. National Electrical Code (NEC) • Rules, regulations, and criteria for installation of electrical equipment • Revised every three years • Compliance typically mandated by state or local building codes • “Authority having jurisdiction”—person responsible for approving electrical installations

  4. Code Alert • Article 90 defines what is and is not covered by the NEC • Article 100 provides definitions of essential terms used throughout the NEC • Article 110 provides general requirements for electrical installations

  5. State and Local Codes • All electrical construction governed by state or local building codes • Be aware of specific codes based on location and type of construction • Codes generally require • Licensing • Permits • Inspection/approval

  6. Additional Organizations • Nationally recognized testing laboratories • Test materials and equipment • Underwriters Laboratories • Occupational Safety and Health Administration (OSHA) • Agency of US federal government • Required safe practices

  7. Wiring Systems • Wiring system—Wiring and related components used in an electrical system • Two primary classifications: • Cables • Raceways

  8. Armored Cable (AC) • Also called “BX” • Components: • Armor (outer covering) • Insulated conductors • Bonding strip (for equipment grounding system)

  9. Armored Cable (AC) (cont.) • Requires anti-short bushings to protect conductors from sharp edges of armor

  10. Armored Cable Connectors

  11. Nonmetallic Sheathed Cable (NM) • Also called “Romex”

  12. Stripping Nonmetallic Sheathed Cable

  13. Service Entrance Cable (SE) • Service Entrance Cable (SE) • Overhead cable • Connects utility company transformer to home’s service panel • Underground service entrance cable (USE) • Below-grade service connections • Underground feeder and branch-circuit cable (UF) • Similar to NM but designed for below-grade use

  14. Code Alert Typical requirements for cable support • Cable must be supported within 12 of a box • Maximum distance between cable supports is 4-6 • Always check support requirements for specific cable type being used

  15. Raceways • Protective tubing installed to house conductors • Conduit—tubing connecting boxes and devices in a wiring system

  16. Common Raceway Systems • Electrical metallic tubing (EMT) • Electrical nonmetallic tubing (ENT) • Rigid metal conduit (RMC) • Rigid PVC conduit (PVC) • Intermediate metal conduit (IMC) • Flexible metal conduit (FMC) • Liquidtight flexible metal conduit (LFMC) • Surface-mount raceways

  17. Electrical Metallic Tubing (EMT) • Also called “thin-wall” conduit • Not threaded • Tubing serves as equipment grounding conductor—proper connections are critical

  18. EMT Connections

  19. Cutting Metal Conduit • Cutting tools: • Hacksaw • Reciprocating saw • Pipe cutter • After cutting, use reamer, file, or deburring tool to eliminate sharp edges

  20. Bending Metal Conduit • Field bend—Conduit bend made on the construction site • Generally, bending is easier and less costly than using fitting • Always use the correct size conduit bender • Always know the minimum bend radius allowed by code

  21. Stub Bend

  22. Back-to-Back Bend

  23. Offset Bend

  24. Offset Bend (cont.) Preparation • Measure distance to obstruction • Measure height of obstruction • Use offset bend chart to determine • Angle of offset • Distance between bends • Shrink

  25. Offset Bend (cont.) Marking conduit • Add shrink to the distance to the obstruction, and mark conduit at this distance • Measure back the distance between bends

  26. Offset Bend (cont.)

  27. Box Offset

  28. Saddle Bend • Two 22 1/2 bends and one 45 bend • Preparation • Measure height of obstruction • Find distance from start of conduit to center of obstruction, then add 3/16 for every inch of obstruction height (for 1/2 conduit). Mark this location (center of bend) • On each side of center mark, measure and mark a distance equal to 2 1/2 times the height of the obstruction

  29. Saddle Bend (cont.)

  30. Electrical Nonmetallic Tubing (ENT) • Often called “smurf tube” or “smurf” • Corrugated, flexible plastic • Easy to install • Cannot be buried or left exposed

  31. Rigid Metal Conduit (RMC) • Galvanized pipe, similar to water pipe • Threaded connectors and fittings • Conduit part of equipment grounding system • RMC has thicker walls than EMT has

  32. RMC Connectors and Fittings

  33. Rigid PVC Conduit (PVC) • Hard plastic conduit • Lighter than metal conduit • Can be heated and bent • Conduit joined to fittings with glue

  34. PVC Connections

  35. Other Raceway Systems • Intermediate metal conduit (IMC) • Walls thicker than EMT and thinner than RMC • Flexible metal conduit (FMC) • Also called “Greenfield” • Similar to armored cable casing • Liquidtight Flexible Metal Conduit (LFMC) • Similar to FMC with a plastic sheath • Surface-mount raceways

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