CHAPTER

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.

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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 Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website.

Code Alert

• • •

Article 90

defines what

is NEC

and

is not

covered by the

Article 100

provides definitions of essential terms used throughout the

NEC Article 110

provides general requirements for electrical installations Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website.

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 Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website.

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 Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website.

Wiring Systems

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

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Armored Cable (AC)

• • Also called “BX” Components: – Armor (outer covering) – Insulated conductors – Bonding strip (for equipment grounding system) Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website.

Armored Cable (AC) (cont.)

• Requires anti-short bushings to protect conductors from sharp edges of armor

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Armored Cable Connectors

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Nonmetallic Sheathed Cable (NM)

• Also called “Romex”

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Stripping Nonmetallic Sheathed Cable

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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 Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website.

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 Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website.

Raceways

• • Protective tubing installed to house conductors Conduit —tubing connecting boxes and devices in a wiring system Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website.

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 Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website.

Electrical Metallic Tubing (EMT)

• • • Also called “thin-wall” conduit Not threaded Tubing serves as equipment grounding conductor —proper connections are critical Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website.

EMT Connections

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Cutting Metal Conduit

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

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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 Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website.

Stub Bend

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Back-to-Back Bend

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Offset Bend

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Offset Bend (cont.)

Preparation 1. Measure distance to obstruction 2. Measure height of obstruction 3. Use offset bend chart to determine • • Angle of offset Distance between bends • Shrink Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website.

Offset Bend (cont.)

Marking conduit 1. Add shrink to the distance to the obstruction, and mark conduit at this distance 2. Measure back the distance between bends Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website.

Offset Bend (cont.)

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Box Offset

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Saddle Bend

• • Two 22 1/2 bends and one 45 bend Preparation 1. Measure height of obstruction 2. 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 Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website.

Saddle Bend (cont.)

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Electrical Nonmetallic Tubing (ENT)

• • • • Often called “smurf tube” or “smurf” Corrugated, flexible plastic Easy to install Cannot be buried or left exposed

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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 Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website.

RMC Connectors and Fittings

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Rigid PVC Conduit (PVC)

• • • • Hard plastic conduit Lighter than metal conduit Can be heated and bent Conduit joined to fittings with glue Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website.

PVC Connections

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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 Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website.