4 Wiring Systems

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.

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

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

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

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

Wiring Systems Wiring system—Wiring and related components used in an electrical system Two primary classifications: Cables Raceways (Goodheart-Willcox Publisher)

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

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

Armored Cable Connectors (Goodheart-Willcox Publisher)

Nonmetallic Sheathed Cable (NM) Also called “Romex” (Goodheart-Willcox Publisher)

Stripping Nonmetallic Sheathed Cable (Goodheart-Willcox Publisher)

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

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

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

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

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

EMT Connections (Goodheart-Willcox Publisher)

Cutting Metal Conduit Cutting tools: Hacksaw Reciprocating saw Pipe cutter After cutting, use reamer, file, or deburring tool to eliminate sharp edges (Goodheart-Willcox Publisher)

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

Stub Bend (Goodheart-Willcox Publisher)

Back-to-Back Bend (Goodheart-Willcox Publisher)

Offset Bend (Goodheart-Willcox Publisher)

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

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

Offset Bend (cont.) (Goodheart-Willcox Publisher)

Box Offset (Goodheart-Willcox Publisher)

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

Saddle Bend (cont.) (Goodheart-Willcox Publisher)

Electrical Nonmetallic Tubing (ENT) Often called “smurf tube” or “smurf” Corrugated, flexible plastic Easy to install Cannot be buried or left exposed (Goodheart-Willcox Publisher)

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

RMC Connectors and Fittings (Goodheart-Willcox Publisher)

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

PVC Connections (Goodheart-Willcox Publisher)

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