CHAPTER 4 Wiring Systems Permission granted to reproduce for educational use only.©...

CHAPTER

4 Wiring Systems

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc.

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

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

Armored Cable Connectors

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

Stripping Nonmetallic Sheathed Cable

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

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

Cutting Metal Conduit

• Cutting tools:– Hacksaw– Reciprocating saw– Pipe cutter

• After cutting, use reamer, file, or deburring tool to eliminate sharp edges

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

Back-to-Back Bend

Offset Bend

Offset Bend (cont.)

Preparation1. Measure distance to obstruction2. Measure height of obstruction3. Use offset bend chart to determine

• Angle of offset• Distance between bends• Shrink

Offset Bend (cont.)

Marking conduit1. Add shrink to the distance to the

obstruction, and mark conduit at this distance

2. Measure back the distance between bends

Offset Bend (cont.)

Box Offset

Saddle Bend• Two 22 1/2 bends and one 45 bend• Preparation

1. Measure height of obstruction2. 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)

3. 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.)

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

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

Rigid PVC Conduit (PVC)

• Hard plastic conduit• Lighter than metal conduit• Can be heated and bent• Conduit joined to fittings with glue

PVC Connections

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

CHAPTER 4 Wiring Systems Permission granted to reproduce for educational use only.©...

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