Mike Holt - Guide to Low Voltage Systems.pdf - Elektryka(1) - saturn3231

Table of Contents

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

About the Author . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

Unit 1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Unit 2. NEC Introduction [Article 90] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Unit 3. Definitions [Article 100] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Unit 4. General Installation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Unit 5. Understanding Grounding Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Unit 6. Earth Grounding of Communications Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Unit 7. General Wiring Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Table of Contents

Guide to Low-Voltage & Limited Energy Systems

Foreword

The National Electrical Code ® (NFPA stan-

dard 70-1999) contains installation rules for all

kinds of electrical products and systems. It is

adopted into law by more than 42,000 states,

counties, cities, and smaller jurisdictions.

Many electrical professionals, including elec-

tricians, contractors, and even inspectors, think

of the Code primarily as a “power wiring” book.

And so it is. But not just power wiring. The

National Electrical Code also provides detailed

requirements for the installation of many types

of low-voltage wiring systems.

New businesses, home offices, and many

homes today are having low-voltage wiring

installed to meet the need for state-of-the-art

technologies for audio, video, telecorurnunica-

tions, and high speed data transfer. But many

electrical professionals are not familiar with the

important NEC ® safety requirements for the

installation of non-power installations. Too often,

low-voltage systems aren’t installed properly or

inspected for Code compliance and user safety.

Some jurisdictions don’t even require electri-

cal permits for the installation of telephone,

cable TV, access control, nurse call, fiberoptic,

and other low-voltage control and communica-

tions circuits-even though these systems are cov-

ered by the National Electrical Code .

• Telephone - Telephone ringing voltages can

be as high as 90 volts AC.

• Shock hazard - Incorrectly instalied low-

voltage wiring may accidentally become ener-

gized at line voltages, thus endangering both

installers and users.

• Grounding - Proper grounding of communi-

cation circuits, CATV cables, TV and satellite

masts, etc. are essential to prevent fires and elec-

tric shock from dangerous potential differences

between the electrical systems.

• Working space - In general, low-voltage dis-

tribution equipment must meet the same working

clearances as all other equipment rated under

600 volts [Section 110-16].

• Broadband - A new Article 830 on “Net-

work-Powered Broadband Communications Sys-

tems” was added to the 1999 Code , covering

futuristic Information Superhighway wiring sys-

tems for interactive multimedia services.

• Lifeline - Many jurisdictions now require

that free or low-cost “lifeline” telephone service

be made available to all citizens, recognizing that

telephone corurnunication is not an option but a

necessity in today’s world. With new types of

Internet and interactive services beginning to

take over the function of traditional telephones, it

is even more important that these alternative

low-voltage systems be installed safely and reli-

ably- in accordance with the National Electrical

Code .

THE NEED TO INSPECT LOW-VOLTAGE

SYSTEMS

There are important safety reasons to inspect

low-voltage installations for Code compliance.

Here are just a few of them:

• Audio - Audio voltages can be as high as 70

volts AC.

Forword

iii

About the Author

Mike Holt is a former electrician, contractor, and inspector. He is the author of many books and

videos books about the National Electrical Code, and is a regular contributor to Electrical Contractor

magazine. Holt lectures widely and conducts training classes nationwide on such topics as the NEC®,

exam preparation, electrical theory, and estimating and project management. For more information

about Mike’s publications and programs, contact:

Mike Holt Enterprises, Inc.

7310 McNab Road, Suite 201

Tamarac, FL 33321

1-888-NEC-CODE; (954) 720-7955 (fax)

www.mikeholt.com

email: mike@mikeholt.com

Guide to Low-Voltage & Limited Energy Systems

Mike Holt - Guide to Low Voltage Systems.pdf

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