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Introduction

ARTICLE 90. INTRODUCTION

90.1. Purpose

(A). Practical Safeguarding. The intent of this section is to establish a clearand definite relationship between the National Electrical Code and electricalsystem design as well as field installation. Basically stated, the NE Code isintended only to assure that electrical systems installed in commercial, indus-trial, institutional, and residential occupancies are safe. That is, to provide asystem that is essentially free from hazard. The Code (throughout this man-ual, the words Code, NE Code, and NEC refer to the National ElectricalCode) sets forth requirements, recommendations, and suggestions and consti-tutes a minimum standard for the framework of electrical design. As stated in

its own introduction, the Code is concerned with the practical safeguarding ofpersons and property from hazards arising from the use of electricity for light,heat, power, computers, networks, control, signaling, and other purposes.

The NE Code is recognized as a legal criterion of safe electrical design andinstallation. It is used in court litigation and by insurance companies as a basisfor insuring buildings. The Code is an important instrument for safe electricalsystem design and installations. It must be thoroughly understood by all elec-trical designers and installers. They must be familiar with all sections of theCode and should know the latest accepted interpretations that have been ren-

dered by inspection authorities and how they impact the design and/or instal-lation of electrical systems. They should keep abreast of Formal Interpretations,as well as the issues addressed by Tentative Interim Amendments (TIA) that areissued, periodically, by the NE Code committees. They should know the intentof Code requirements (i.e., the spirit as well as the letter of each provision) and

be familiar with the safety issue at the heart of the matter. And, most important,they should keep a copy of the NEC and this Code handbook close by for readyreference and repeated study.

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(B). Adequacy. Its worth noting that compliance with the provisions of theNational Electrical Code can effectively minimize fire and accident hazards in anyelectrical system. A code-compliant installation will be essentially free from

hazard, but not absolutely so. This provision is essentially unchanged sincethe 1937 edition, and has stood the test of time. Many installations with sub-stantial code violations exist for protracted periods of time without loss experi-ence through good fortune and the fact that protective systems frequentlyoverlap. On the other hand, occasionally a fully compliant installation can fail,usually due to an unforeseen circumstance. Perfect safety is only achievable atinfinite cost. Every three years the National Electrical Code Committee wrestleswith the concept of essentially free as it considers proposed changes to thenext edition.

Although the Code assures minimum safety provisions, actual design workmust constantly consider safety as required by special types or conditions ofelectrical application. For example, effective provision of automatic protectivedevices and selection of control equipment for particular applications involveengineering knowledge above routine adherence to Code requirements. Then,too, designers and installers must know the physical characteristicsapplica-tion advantages and limitationsof the many materials they use for enclosing,supporting, insulating, isolating, and, in general, protecting electrical equip-ment. The task of safe application based on skill and experience is particularly

important in hazardous locations. Safety is not automatically made a charac-teristic of a system by simply observing codes. Safety must be designed into asystem.

In addition to safety considerations, the need for future expansion and othercommon sense aspectssuch as voltage dropmust be considered and fac-tored into the overall system design. The Code in this section makes it clear thatmore than Code compliance will be necessary to ensure a system that is notonly safe but also functional and capable of providing for future needs, withoutcompromising system-operating continuity or integrity. It is up to the designer

and installer, in consultation with the owner, to provide adequate capacity,selectivity, isolation, and protection beyond its minimum requirements inorder to achieve the desired system characteristics. Remember, it is always per-missible to do more than the Code requires, but neverpermissible to do lessthan the Code-prescribed minimum.

Addressing voltage drop illustrates these principles. No definite standardshave been adopted for the maximum allowable voltage drop in mostinstances. There is a good reason for this. In most cases voltage drop is aninefficiency or inconvenience, but it does not rise to the level of a safety hazard.

For example, a motor run at 10 percent voltage drop, but with appropriaterunning overload protection, will have a greatly reduced life span, but notcreate a shock, fire, or electrocution hazard. The National Electrical Code doesnote, however, in a nonmandatory explanatory note, that if the voltage dropfrom the point of service entrance to the final outlet does not exceed 5 percent,there will be reasonable efficiency of operation. The note also explains thatnot more than 3 percent voltage drop should occur in the feeder system aheadof the branch-circuit supply points, which leaves the other 2 percent for the

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branch circuit. In the end, the extent to which voltage drop in an electricalsystem is to be tolerated is the owners decision, because the NEC does notmandate design flexibility.

There are some instances, however, where voltage drop does directly bear onsafety and the NEC contains mandatory rules accordingly. For example, if theconductors to a fire pump are not sized to prevent the voltage drop while start-ing (i.e., while under locked-rotor conditions) from exceeding 15 percent, mea-sured at the controller terminals, the control contactor for the motor maychatter and not reliably hold in, resulting in a failure to start with disastrousconsequences.

(C). This single sentence is also crucial. The NEC is not written for norintended to be used by untrained individuals. Qualified electricians and engi-

neers spend many years reviewing and thinking about its provisions.(D). Relation to Other International Standards. This section simply states that

the National Electrical Code addresses the same safety issues addressed by theInternational Electrotechnical Commission (IEC) Standard for ElectricalInstallations of Buildings. Because the NEC covers the same consideration forsafety as related to protection against electrical shock, protection against ther-mal effects, protection against overcurrent, protection against fault current,protection against overvoltage, faults between circuits, and so forth that arecovered by the IEC Standard, it was considered necessary to establish that fact.

This statement in this section facilitates the adoption of the Code by foreigncountries and is consistent with the ongoing process of harmonizing the NECand other accepted standards from around the world.90.2. Scope

(A). Simply stated, the Code applies to all electrical workindoors andoutdoorsother than that work excluded by the rules of part (B) in this section.Installation of conductors and equipment, anywhere on the load-side of thepoint of connection to the serving utility, must comply with the provisionsgiven in the NEC.

The scope of the NEC includes the installation of optical fiber cable, part (A).As part of the high-technology revolution in industrial and commercial build-ing operations, the use of light pulses transmitted along optical fiber cables has

become an alternative method to electric pulses on metal conductors for data,voice, and video networks, as well as for control and signaling. Although thetechnology of fiber optics has grown dramatically over recent years, it is stillprimarily used as a trunk line or backbone for high-speed networks, whilehorizontal distribution is generally accomplished via a twisted-pair or coaxialcopper medium. Although coaxial cable can handle high rates of data trans-

mission involved in data processing and computer control of machines andprocesses, optical fiber cables far outperform metallic conductorseven coaxialcablewhen it comes to bandwidth as well as cost of materials. (See Fig. 90-1.)NEC Art. 770, Optical Fiber Cables, covers the installation and use of fiber-optic cables.

Part (A)(1) provides a laundry-list of specific indoor installations thatmust be in compliance with the applicable requirements given in the Code.Note that this section makes clear that the NE Code also applies to floating

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buildings because the safety of Code compliance is required for all placeswhere people are present. Coverage of floating buildings is contained in NECArt. 553.

Part (A)(2) identifies specific outdoor installations, including carnivals andindustrial substations, while part (A)(3) mandates that supply equipment andconductorswhether supplied from a utility as a service or from on-site gener-ators as a separately derived systemas well as all other outside equipmentand conductors must satisfy the rules and regulations of the NEC. Use of theword equipment in parts (A)(2) and (A)(3) makes clear that the NE Code

applies to electrical circuits, systems, and components in their manner ofinstallation as well as use.

The following discussion and the discussion in 90.2(B)(5) are very closelyrelated and often hotly debated. Information has been provided from both sidesof the discussions as well as the commentary from the Code-making panels(CMPs) where available. The purpose is to allow each designer and installer tomake their own judgment with regard to how these matters will be resolved

based on a full understanding of both sides of the arguments.

4 INTRODUCTION 90.2

Fig. 90-1. The NEC covers the technology of fiber optics for communication and data transmission.

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Although generally exempt from compliance with the NEC, according to90.2(A)(4) certain utility-owned or -operated occupancies must be wired perthe NEC. The wording in this section along with the companion rule of

90.2(B)(5) is intended to identify those utility electrical installations that aresubject to the rules of the NEC and those that are not. Basically stated, anyutility occupancy that is not an integral part of a generating plant, substa-tion, or control center must comply with the NEC in all respects. Clearly, anyoffice space, storage area, garage, warehouse, or other nonpower-generatingarea of a building or structure is not an integral part of the generation,transmission, or distribution of electrical energy and therefore is covered bythe NEC.

There has been discussion and disagreement over the meaning of the phrase,

not an integral part ofa generating plant . . . etc. Some feel that the phrasenot an integral part of applies to the process of generation, and so forth.Others believe that it applies to the building. That is, if an occupancy identifiedin 90.2(B)(4) is part of a generating plant, it is exempt from compliance with theNEC. Although that doesnt seem to make sense, past comments made by theCMP indicate that it is the intent of this rule to exempt, say, office spaces withina generating plant. However this is not completely clear from the wording used.To prevent any problem with this section, one could choose to interpret thisrule to require NEC compliance for any occupancy that is not an integral part

of the process and wire such spaces in accordance with the NEC. Such inter-pretation cannot be disputed. That is, satisfying the more rigorous NEC require-ments cannot be construed as a violation. But, if one does not comply, thepotential for legal liability exists.

Some may feel that the term integral part should be interpreted to meanintegral part of the process (i.e., generation, transformation, or distribution ofelectric energy), according to commentary in the NEC Committee Reports for the1987 NEC. Others feel that it should be taken to mean an integral part of the

building or structure. Be aware that the first contention seems more reasonable.

That is, just because an office is in a generating plant, it shouldnt be exemptfrom the NEC, especially since these areas will be occupied by the general pub-lic. And it seems logical that the same should apply to the cafeteria, bathrooms,and other areas within the plant that are not directly related to the task of gen-erating and delivering electrical energy and will be occupied by other thanqualified plant electrical personnel.

With that said, it should be noted that the wording here could be read bothways and it will be up to the local AHJ to interpret what is and what is notrequired to comply with the NEC.

It should be noted that equipment installed by the utility to perform associ-ated functions, such as outdoor lighting at an outdoor substation, is intended to

be considered as an integral part to the process and is therefore exempt fromcompliance with the NEC (Figs. 90-2 and 90-3).

(B). Not Covered. The rules of the Code do not apply to the electrical workdescribed in (1) through (5). The most common controversy that arises con-cerns exclusion of electrical work done by electric utilities (power companies),especially outdoor lighting.

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6 INTRODUCTION 90.2

Fig. 90-2.Circuits and equipmentof any utility company are exempt from the rule of the

NEC

whenthe particular installation is part of the utilitys system for transmitting and distributing power to theutilitys customersprovidedthat such an installation is accessible only to the utilitys personnel andaccess is denied to others. Outdoor, fenced-in utility-controlled substations, transformer mat installa-tions, utility pad-mount enclosures, and equipment isolated by elevation are typical utility areas towhich the NEC does not apply. The same is also true of indoor, locked transformer vaults, or electricrooms (Sec. 90.2). But electrical equipment, circuits, and systems that are involved in supplying light-ing, heating, motors, signals, communications, and other load devices that serve the needs of person-nel in buildings or on premises owned (or leased) and operated by a utility are subject to NE Coderules, just like any other commercial or industrial building, provided that the buildings or areas arenot integral parts of a generating plant or substation.

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This rule emphatically explains that not all electrical systems and equipmentbelonging to utilities are exempt from Code compliance. Electrical circuits andequipment in buildings or on premises that are used exclusively for the gener-ation, control, transformation, transmission, and distribution of electric

energy are considered as being safe because of the competence of the utilityengineers and electricians who design and install such work. Code rules do notapply to such circuits and equipmentnor to any communication or meter-ing installations of an electric utility. But, any conventional electrical systemsfor power, lighting, heating, and other applications within buildings or onstructures belonging to utilities must comply with Code rules where suchplaces are not used exclusively by utilities for the supply of electric power tothe utilities customers.

An example of the kind of utility-owned electrical circuits and equipment

coveredby Code rules would be the electrical installations in, say, an officebuilding of the utility. But, in the Technical Committee Report for the 1987 NEC,the Code panel for Art. 90 stated that it is not the intent of this rule to have NECregulations apply to office buildings, warehouses, and so forth that are an inte-gralpart of a utility-generating plant, substation, or control center. Accordingto comments from the CMP, NEC rules would not apply to any wiring or equip-ment in a utility-generating plant, substation, or control center and would notapply to conventional lighting and power circuits in office areas, warehouses,

90.2 INTRODUCTION 7

Fig. 90-3. Those buildings and structures that are directly related to the generation, transmission, or

distribution of energy are intended to be excluded from compliance with the NEC. However, the rulescovering this matter also indicate that functionally associated electrical equipmentsuch as the out-door lighting for the utility-owned and -operated outdoor substationare also exempt from the NEC.

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maintenance shops, or any other areas of utility facilities used for the genera-tion, transmission, or distribution of electric energy for the utilitys customers.But NEC rules would apply to all electrical work in otherbuildings occupied by

utilitiesoffice buildings, warehouses, truck garages, repair shops, etc., thatare in separate buildings or structures on the generating facilitys premises.And that opinion was reinforced by the statements of the CMP that sat for the1996 NEC. With that said, it should be noted that the actual wording used herein the Code could be read both ways and it will be up to the local AHJ to inter-pret what areas are and what areas are not required to comply with the NEC.

The wording used in 90.2(B)(5)(c) recognizes non-NEC-complying utilityinstallations in legally established easements or rights-of-way. This clearlyexempts utility activities on public streets, alleys, and similar areas, even for

street and area lighting for adjacent parking lots. However, the 2008 NEC deletedthe phrase or by other agreements from this list. The concern was that thisprovision opened the door to utility noncompliance throughout a facility, pro-vided an agreement could be struck with the owner and ratified by the govern-mental authority having jurisdiction over utility practice. Since utilities aregoverned by the National Electrical Safety Code (NESC) whose provisions areentirely inappropriate for premises wiring, this concern is not inconsequential.

In the 2011 version an elaborate compromise was struck that addressed numer-ous areas where formal easements are impractical, including federal lands and

military bases, Indian reservations, railroad property, and state agencies, depart-ments, and port authorities. This successfully covered many instances where theremoval of the other agreements permission caused problems. Its list of gov-ernmental entities that are unique to the United States may, unfortunately, createadoption issues in foreign jurisdictions in which the NEC is or may in the future

be adopted.However, the change remains extremely controversial because it has the

potential to unravel over a century of established precedent regarding sitelighting by utilities, where all of the work is on the line side of any service

point, or where there is no service point whatsoever, as illustrated in Fig. 90-4.Virtually every electric utility has permission to supply outdoor lightingaccording to rates established by the governing authority, and that lightingneed not be in a public way or in an easement, provided it is not premiseswiring. The key to understanding the problem is the concept of a servicepoint, defined in Art. 100. The NESC applies on the supply side of servicepoints, where they exist. The NEC applies on the load side of service points,where they exist. It is instructive to review the premises underlying the 2005NEC language.

The entire premise behind allowing the NESC, substantially different fromthe NEC, to apply to utility work is a simple one: The organizational perma-nence, engineering supervision, and workforce training in the utility environ-ment are fundamentally different than for premises wiring. Therefore, differentstandards can be applied to installations under their exclusive control.Whether this also applies to an Energy Service Company (ESCo) doing mainte-nance under contract with the utility is a regulatory matter that will depend onthe degree of command and control exercised by the regulated utility.

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Area lighting wired to the NESC will lack local disconnects, specific over-current protection, and separate equipment grounding conductors, for just afew examples. Is this a safety issue if a utility line crew does the maintenance?Apparently not, given the ubiquitous presence of street lighting wired this way.

Would it be a safety issue if it were premises wiring, maintained by others? Cer-tainly, given that the NEC has never allowed such practices over its long history.The fact that these two statements are self-evidently both true leads to this con-clusion: You cannot write and apply installation rules without taking the oper-ational context into account. The NEC does exactly the same thing over and overagain when it creates special exceptions and allowances for work that will beperformed under qualified maintenance and supervision.

Part (C) gives the AHJ the discretion to permit other than utilities theoption to install conductors between the utility supply and the service conduc-

tors for individual buildings without complying with the NEC. Any such waiveris limited to outdoor portions of the electrical installation, or to conductorsinside a building but only to the extent necessary to terminate at the nearestpoint to where the conductors enter the building. And as discussed at 230.6(5),as soon as wiring penetrates the outer membrane of a building, whether or notit has fully entered occupied space, it is inside the building for code enforce-ment purposes. Essentially it allows the inspector to permit the use of anotherstandard such as in the utilities code, the NESC. Such permission is typically

90.2 INTRODUCTION 9

Fig. 90-4. This drawing shows an actual example of a practice that is widespread throughout theUnited States and many other countries. There is no service point, the parking lot luminaire is notpremises wiring, and the maintenance will be performed by a utility line crew in the same bucket

truck as services the street lighting, at the same time. The drug store is, in effect, buying the 27,500-lmoutput from each of the two 250-W high-pressure sodium (HPS) lamps. The 2011 NEC purports toclaim jurisdiction over this portion of the parking lot lighting.

2011

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limited to campus-type environments where the utility supply to the premisesis medium-voltage and distribution to, and between, buildings is installed andmaintained by on-site personnel. Its worth noting that any such permission

granted by the AHJ must be written permission to satisfy the definition of spe-cial permission, as given in Art. 100. Today, however, such occupancies fre-quently take service at an elevated voltage at a central point, and all themedium voltage feeders to serve the buildings are just that, feeders. As soon asthe service point becomes a central medium voltage switch, this provision canno longer be applied to the individual buildings.

There are far more mundane uses for this permission. Many CATV (seeArticle 820) companies rely on powered amplifiers mounted near the top of util-ity poles to keep their signal strength where it needs to be. Those amplifiers will

have a small disconnect and overcurrent protective device located adjacent tothe amplifiers. There are no provisions within the body of the NEC that allow fora service disconnect to be located at such a location, which is certainly not read-ily accessible. However, the entire installation is confined to the pole top, andspecial permission under 90.2(C) is routinely granted in such cases.90.3. Code Arrangement. This section provides guidance on which rule takesprecedence where two rules covering a particular installation are at odds. Basi-cally, the rules in Chaps. 1 through 4 apply at alltimes, except for installationscovered by Chap. 8, which stands alone. Installations covered by Chaps. 5, 6,

and 7 must always comply with the requirements given in Chaps. 1 through 4,unless a specific rule in Chaps. 5 through 7 requires or permits an alternatemethod. One implication of this principle is that exceptions in Chaps. 1through 4 that allow for different procedures in Chaps. 5 through 7 are unnec-essary. The NEC Style Manual has been rewritten to take this into account, andsuch exceptions are disappearing from the NEC for this reason. Provisions inChaps. 1 through 7 of the NEC only apply in Chap. 8 when a Chap. 8 articlespecifically cites them, and the numbers of such citations in Chap. 8 articles aresteadily increasing for this reason. Chapter 9 consists of tables that are manda-

tory, but only applicable as referenced in earlier articles. The graphic providedin this section facilitates understanding of the relationship between variousCode chapters.90.4. Enforcement. This is one of the most basic and most important of Coderules because it establishes the necessary conditions for use of the Code.

The NE Code stipulates that when questions arise about the meaning orintent of any Code rule as it applies to a particular electrical installation,including signaling and communication systems covered by Chap. 8, the elec-trical inspector having jurisdiction over the installation is the only one autho-

rized by the NE Code to make interpretations of the rules. The wording ofSec. 90.4 reserves that power for the local inspection authority along with theauthority to approve equipment and material and to grant the special permis-sion for methods and techniques that might be considered alternatives to thoseCode rules that specifically mention such special permission.

It should be noted that any deviation from standard Code enforcementmust be done in accordance with the provisions given in Art. 100 by the def-inition of Special Permission. The most salient requirement is the need for

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documentation. That is, in order to comply with the definition of specialpermission, such permission must be in writing. This will serve to providea written record of the circumstances surrounding the granting of a waiver.

The NE Code permits the electrical inspector to waive specific require-ments or permit alternate methods in any type of electrical installation. Inresidential, commercial, and institutional electrical systemsas well as inindustrialinspectors may accept design and/or installation methods that donot conform to a specific Code rule, provided they are satisfied that the safetyobjectives of the Code rule are achieved. In other words, there must be a find-ing of equivalent safety before the permission is granted, and the permission todeviate from them must be provided in writing as required by the first sentenceof the second paragraph in this section and stated by the definition of special

permission given in Art. 100 (Fig. 90-5).

90.5 INTRODUCTION 11

Fig. 90-5. Inspectors authority maybe exercised either by enforcement ofthat individuals interpretation of aCode rule or by waiver of the Coderule when the inspector is satisfiedthat a specific non-Code-conformingmethod or technique satisfies the

safety intent of the Code (Sec. 90.4).

This recognition of practices at variance with the Code is provided only forspecial conditions and must not be interpreted as a general permission toengage in non-Code methods, techniques, or design procedures. In fact, it islikely that inspectors will exercise this authority only with reluctance and thenwith great care, because of the great responsibility this places on the inspector.This is especially true because such permission may only be granted in writing.

Clearly, this requirement for documentation will give many inspectors pausefor reflection and reconsideration. It seems almost certain for the exercise ofthis prerogative.

This section also covers instances when the the NEC has changed and newproducts are not yet available in the local market to comply with the revisedterms. The AHJ may, but is not required to, permit the use of previously com-pliant products.90.5. Mandatory Rules and Explanatory Material. This section provides guidanceregarding proper application of the NEC. Although the NE Code consists essen-

tially of specific regulations on details of electrical design and installation,there is much explanatory material in the form of notes to rules.

Part (A) of this section addresses mandatory rules, which typicallyemploy the phrases shall or shall not. Compliance with the Code consistsin satisfying all requirements and conditions that are stated by use of the wordshall or shall not where used in the body of a Code rule or Exception.Those words, anywhere in any rule or exception, designate a mandatory rule.Failure to comply with any mandatory Code rule constitutes a Code violation.

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Part (B) of this section indicates the wording that is used in permissiverules. These rules are typified by the use of phrases such as shall be permittedor shall not be required. Such rules typically provide or accept alternate mea-

sures or suspend requirements under certain conditions. It is not necessary todo what these rules permit; it is essentially an optional approach.

Note that under the provisions of the NEC Style Manual, the word may isnot to be used to set forth a permissive rule. When may is being used to indi-cate permission, it can only be used in the context of a discretionary action ofthe authority having jurisdiction. For example, NEC 430.26 authorizes, but doesnot require, an AHJ to permit the application of a demand factor to the loads ona motor feeder being sized under 430.24. This is an excellent example of theappropriate use of the word, as in . . . the authority having jurisdiction may

grant permission for feeder conductors . . . .Part (C) explains that informational notes [formerly called fine-print notes

(FPN)s, a change that has been applied throughout the NEC in this edition] areincluded, following certain Code rules, to provide additional informationregarding related rules or standards. This information is strictly advisory orexplanatory in nature and presents no rule or additional requirement. Thesame is true for bracketed information that references other NFPA standards.The inclusion of the referenced standard is to inform the reader of the origin ofextracted text, where that text is taken from an NFPAstandard. However, the

reference to another NFPA standard in no way makes the referenced standardpart of the Code; nor does such reference oblige compliance with other rules inthe referenced standard. Informational notes explain NEC rules, they do notchange NEC rules. If, in reading an informational note, it appears to allow orrequire something different from the rule that precedes it, then you are mis-reading the rule and you should read the rule again.

Part (D), new for the 2011 edition covers the annexes at the end of the NEC,changing their titles to include the word Informative. This paragraph, in con-cert with the terminology change regarding informational notes, attempts to

clarify a distinction between actual rules and merely informative text providingbackground or interpretive assistance.90.6. Formal Interpretations. Official interpretations of the National Electrical Codeare based on specific sections of specific editions of the Code. In most cases,such official interpretations apply to the stated conditions on given installa-tions. Accordingly, they would not necessarily apply to other situations thatvary slightly from the statement on which the official interpretation was issued.

As official interpretations of each edition of the Code are issued, they arepublished in the NFPA News, and press releases are sent to interested trade

papers.All official interpretations issued on a specific Code edition are reviewed by

the appropriate CMP. In reviewing a request for a formal interpretation, a Codepanel may agree or disagree. They will render a simple yes or no to thequestion, which places the burden on the questioner to provide a question thatcan be answered in the affirmative or negative. At some point in future Codes,the CMP might clarify the Code text to avoid further misunderstanding ofintent. On the other hand, the Code panel may not recommend any change in

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the Code text because of the special conditions described in the request for anofficial interpretation. For these reasons, the NFPAdoes not catalog official inter-pretations issued on previous editions of the Code within the Code itself. Such

Formal Interpretations can be obtained through the National Fire ProtectionAssociation.

Under NFPArules, Formal Interpretations require a four-fifths vote, which caneasily result in sufficient dissent to preclude their issuance. They are issued ona specific edition of a standard, and are retained until the wording to whichthey applied changes. In addition, when a formal interpretation is issued, thetechnical committee (in this case a CMP) is encouraged (but not required) toreview the disputed text that provoked the request for interpretation when theyprocess the next edition. A classic example of a Formal Interpretation, on the

text of the 1978 NEC, asked whether reinforcing steel in a concrete foundationwas available for connection after the concrete had hardened. It was commonfor inspection authorities in Florida at the time to insist that footings be jack-hammered and connections be made so as to bring these concrete-encased elec-trodes into the grounding electrode system. The panels answer was No andthat interpretation retained its validity until the 2005 NEC changed the wordavailable to present in what is now 250.50.

It should be remembered that, according to 90.4, the authority having juris-diction has the prime responsibility of interpreting Code rules in its area and

disagreements on the intent of particular Code rules in its area; and disagree-ments on the intent of particular Code rules should be resolved at the locallevel if at all possible. A Formal Interpretation is not really a viable avenue fora couple of reasons. One is the amount of time it will take for the CMP to ren-der its decision, which is generally months. The other is that even if yourequest a Formal Interpretation and the CMP agrees with your application,there is no guarantee that the authority having jurisdiction will accept the find-ings of an official interpretation, nor are they required to do so.

Although this section deals with Formal Interpretations, it should be noted

that changes in the Code are promulgated in a very similar manner. That is,changes to Code rules are generally precipitated by a request for change fromthe field. Guidance for submittal of a Code change is provided closely follow-ing the Index in the back of the Code.90.7. Examination of Equipment for Safety. It is not the intent of the National Elec-trical Code to include the detailed requirements for internal wiring of electricalequipment. Such information is usually contained in individual standards forthe equipment concerned. Note that Annex A at the end of the Code bookincludes the recognized product standards that the testing laboratories use to

evaluate the products for which NEC rules require listings.The last sentence does not intend to take away the authority of the local

inspector to examine and approve equipment, but rather to indicate that therequirements of the National Electrical Code do not generally apply to the internalconstruction of devices which have been listed by a nationally recognized elec-trical testing laboratory.

Although the specifics of Code rules on examination of equipment for safetyare presented in 110.2 and 110.3, the general Code statement on this matter is

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made here in 90.7. Although the Code does place emphasis on the need forthird-party certification of equipment by independent testing laboratories, itdoes not make a flat rule to that effect. However, the rules of the U.S. Occupa-

tional Safety and Health Administration (OSHA) are very rigid in insisting onproduct certification.

Codes and standards must be carefully interrelated and followed with careand precision. Modern work that fulfills these demands should be the objectiveof all electrical construction people.90.8. Wiring Planning. These two sections address concepts that are essentiallydesign-oriented. Part (A) alerts the reader to the fact that simply designing toCode-mandated minimums will not provide for any future expansion. Addi-tional capacity in raceways, boxes, enclosures, and so forth, should be consid-

ered, but spare capacity is not required. Part (B) points out the fact thatminimizing the number of conductors within a given raceway will minimizethe number of circuits affected during a fault. Additionally, extra room in yourraceways (i.e., fewer conductors than the maximum permitted) will also facili-tate pulling of the conductors into the raceway. Again, providing extra room inraceways or limiting the number of circuits is only required as indicated else-where in the Code (e.g., 314.16 on box fill).90.9. Metric Units of Measurement. Part (A) identifies metric measurements asthe preferred measurement, although English units (i.e., inch-pounds-feet) are

also provided as indicated by part (B).In part (C), the Code discusses when one is required to use a soft conver-

sion and where a hard conversion is permitted. A soft conversion is directmathematical conversion, for example, 1 m = 39.3 in.; a hard conversion ismore practical, e.g., 1 m = 3 ft. It may seem counterintuitive to have a hardconversion as the inexact conversion. Another way to express the concept isthat a hard conversion is the conversion a hard-core metric user would do, thatis, use a round number for his or her metric measurement. The various expla-nations that follow in the NEC at this point regarding hard and soft con-

version are primarily aimed at CMPs. They must make the decisions aroundwhich metric unit would unacceptably degrade safety, or cause wholesalechanges in industry specifications. For example, CMP 9 used soft conversionsin Table 314.16 because hard conversions would result in every steel box

being at variance from NEC provisions, not by much, but enough to force exten-sive redesign of manufacturing facilities with no real safety benefit. CMP 1made the decision that reducing the minimum workspace width in front of apanel from 762 mm (the soft conversion from 30 in.) to 750 mm (the hard con-version) would unacceptably degrade safety, and so that dimension has been

retained as a soft conversion.The rule of part (D), Compliance, addresses the coexistence of the two sys-

tems of measurement. There the Code states that use of either the SI or theEnglish units shall constitute compliance with this Code. Clearly, designersand installers may use either of the designated values. However, it should benoted that only one, or the other units of measure should be used throughout agiven project. Inspectors have raised objection to mixing and matching units ofmeasure.

14 INTRODUCTION 90.8