Table of Contents - summittechs.com

1 Table of ContentsiForeword .. iiiAbout the Author .. ivUnit 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 ContentsiiGuide to Low- voltage & Limited Energy SystemsThe national electrical code (NFPA stan-dard 70-1999) contains installation rules for allkinds of electrical products and systems. It isadopted into law by more than 42,000 states,counties, cities, and smaller electrical professionals, including elec-tricians, contractors, and even inspectors, thinkof the Codeprimarily as a power wiring so it is.

2 But not just power wiring. TheNational electrical Codealso provides detailedrequirements for the installation of many typesof low- voltage wiring businesses, home offices, and manyhomes today are having low- voltage wiringinstalled to meet the need for state-of-the-arttechnologies for audio, video, telecorurnunica-tions, and high speed data transfer. But manyelectrical professionals are not familiar with theimportant NEC safety requirements for theinstallation of non-power installations. Too often,low- voltage systems aren t installed properly orinspected for Codecompliance and user 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 NEED TO INSPECT LOW-VOLTAGESYSTEMST here are important safety reasons to inspectlow- voltage installations for are just a few of them: Audio - Audio voltages can be as high as 70volts AC.

3 Telephone - Telephone ringing voltages canbe as high as 90 volts AC. Shock hazard - Incorrectly instalied low- voltage wiring may accidentally become ener-gized at line voltages, thus endangering bothinstallers and users. Grounding - Proper grounding of communi-cation circuits, CATV cables, TV and satellitemasts, etc. are essential to prevent fires and elec-tric shock from dangerous potential differencesbetween the electrical systems. Working space - In general, low- voltage dis-tribution equipment must meet the same workingclearances as all other equipment rated under600 volts [Section 110-16]. Broadband - A new Article 830 on Net-work-Powered Broadband Communications Sys-tems was added to the 1999 code , coveringfuturistic Information Superhighway wiring sys-tems for interactive multimedia services.

4 Lifeline - Many jurisdictions now requirethat free or low-cost lifeline telephone servicebe made available to all citizens, recognizing thattelephone corurnunication is not an option but anecessity in today s world. With new types ofInternet and interactive services beginning totake over the function of traditional telephones, itis even more important that these alternativelow- voltage systems be installed safely and reli-ably- in accordance with the national to Low- voltage & Limited Energy SystemsMike Holt is a former electrician, contractor, and inspector. He is the author of many books andvideos books about the national electrical code , and is a regular contributor to electrical Contractormagazine. Holt lectures widely and conducts training classes nationwide on such topics as the NEC ,exam preparation, electrical theory, and estimating and project management.

5 For more informationabout 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) : the AuthorUnit 1. Introduction1 Low- voltage and Limited-energy are terms notdefined by the national electrical code . Andstrictly speaking optical fiber cable systems,which transmit information using high-speedbursts of light generated by tiny lasers, are no-energy and no- voltage . In developing this bookwe considered various alternative terms fordescribing all the different technologies. But inthe end, we decided to stick with low-voltageand limited-energy to describe these diversesystems because they are familiar terms widelyunderstood in the electrical covering Low- voltage and limited-energy devices, wiring, and systems are general-ly contained in Chapter 7 and 8 of the NationalElectrical code .

6 Even the code itself seems mconsider them to be an after-thought, since itgroups most of them in the back of the NEC. Inaddition to the requirements of Chapter 7 and 8,we must be aware of the rules that apply to low- voltage lighting (Article 411), Intrinsically SafeSystems (Article 504), and Sound (Audio)Systems (Article 640). The following is a briefdescription of each system and its requiredwiring CHAPTER 4- EQUIPMENT FORGENERAL USEA rticle 411 - Low- voltage LightingArticle 411 covers listed low- voltage lightingsystems consisting of an isolating power show window and landscape light-ing are examples of lighting systems required tocomply with Article 411. At the time of publica-tion, there was no listed low- voltage lightingsystem that complies with Article 411, butUnderwriters Laboratories Inc.

7 (UL) is currentlydeveloping a standard (UL 2108) for these sys-tems,Fig. - Listed low- voltage lighting sys-tems must operate at no more than 30volts on the secondary, with each circuitlimited to 25 amperes [411-2].Wiring Method - Low- voltage lightingmust be installed in accordance with thelisted system instructions [110-3(b)]using listed systems power supply, fix-tures, and cables [411-2].NEC CHAPTER S - SPECIAL OCCUPANCIESA rticle 504 - Intrinsically Safe SystemsArticle 504 covers the installation of listedintrinsically safe systems, apparatus, and wiringin Class I, TI, and III hazardous (classified) loca-tions. Intrinsically safe systems and devices suchas switches, thermocouples, light-emittingdiodes, connectors, and resistance temperaturedevices limit spark or thermal temperatures to alevel that prevents ignition of flammable orcombustible 1.

8 IntroductionFIGURE1-1 Wiring Method Intrinsically safe apparatusand wiring can be installed exposed using any ofthe wiring methods suitable for unclassified loca-tions, including Chapter 7 and Chapter 8 cablessuch as CL2 (Class 2), CL3 (Class 3), MP(multi-purpose coaxial), or PLTC (power-limitedtray cable) [ CHAPTER 6- SPECIAL EQUIPMENTA rticle 640 - Sound SystemsArticle 640 covers equipment and wiring foraudio signal generation, recording, processing,amplification and reproduction; distribution ofsound, public address and speech-input systems;temporary audio system installations; and elec-tronic organs or other electronic musical of permanently-installed distributedaudio system locations include but are not limit-ed to restaurants, hotels, business offices, com-mercial and retail sales environments, churchesand schools.]

9 Both portable and permanentlyinstalled equipment locations include but are notlimited to residences, auditoriums, theaters, sta-diums, movie and television studios. Temporaryinstallations include auditoriums, theaters, stadi-ums, and outdoor events such as fairs, festivals,circuses, public events and concerts,Fig. :Fire and burglary alarm signalingdevices are not covered by Article Limited by the listing of Method The wiring method forsound systems are dependent on the volt-age and power output limitation of thesound system equipment. It can be Class1, Class 2 or Class 3 wiring according tothe amplifier listing and marking, butgenerally the following applies [640- Class 2 Wiring Methods- Sound sys-tems of 25 volts and not over 100 watts(typically residential systems) must bewired with Class 2 wiring methods.]

10 Class 3 Wiring Methods- Sound sys-tems of volts, and not over 100 watts(typically commercial systems) must bewired with Class 3 wiring methods. Class 1 Wiring Methods- All othersound CHAPTER 7-SPECIAL CONDITIONSA rticle 720 - Circuits Operating At Less than 50 VoltsArticle 720 was originally developed for low- voltage installations known as farm lightingplants which operate at about 32 volts (six 6-volt batteries connected in series, allowing forvoltage drop),Fig. in rural areas whodidn t have access to electric utility powerinstalled this low- voltage system. Today, thisarticle applies to any low- voltage systems wiringthat is not covered by Articles 411-Low-voltageLighting, or 725-Control, Signaling and PowerLimited to Low- voltage & Limited Energy SystemsFIGURE1-2 FIGURE1-3 Power Wiring complying with Article720 cannot operate at more than 50 volts,but there is no power or current limitationfor these Method Section 90-3 specifiesthat all wiring must be installed in accor-dance with the general requirements ofChapters 1 through 4 unless modified byChapters 5 through 7.