The title of this article will seem somewhat presumptuous to many readers. After all, the 1999 National Electrical Code is the result of one of the most significant revisions in the history of the Code. Even the size and printed format have changed-from the familiar size of approximately 5 inches by 8 inches to an 8 1/2 by 11-inch, double-column format that matches other NFPA codes and standards.

The 1999 NEC is packed with expanded rules covering new and emerging technologies or products, such as arc-fault circuit-interrupters (AFCIs), prewired liquidtight flexible nonmetallic conduit, self-protected combination motor controllers, circuit integrity cables for fire-alarm circuits, communications raceway systems, and network powered broadband communication systems. Article 640, which covers audio signal generation, recording, and processing has also been brought up to date.

As usual, the new Code has numerous corrections, technical revisions, and clarifications attempting to clear up erroneous interpretations. For example, the controversy over the placement of receptacles on kitchen islands and peninsulas is visited again, as is the use of ceiling wires for support of wiring methods. Also, the rules for dedicated spaces for panelboards and switchboards are relocated and revised. The three-floor limitation on the use of NM cable has been eliminated for some residential occupancies, and the permitted use of NM cable as a temporary wiring method is more clearly stated. Grounding requirements for separately derived systems and separate buildings are changed and clarified.

In addition, some radical revisions were made for the sake of usability. A large number of exceptions are eliminated and restated in positive code language. Article 250 covering grounding was extensively rewritten and completely reorganized. Articles 210, 215, and 220 are reorganized to relocate rules for branch circuits, feeders, and load calculations to their respective articles. Article 300 covering wiring methods, Article 310 covering conductors, Article 422 covering appliances, Article 695 covering fire pumps, and Article 727 covering instrumentation tray cable have all seen significant rearrangements or complete rewrites. The requirements of deleted Article 710, which covered "high-voltage" installations, are relocated, as appropriate, to Articles 110, 240, 300, and a new Article 490, "Equipment over 600 Volts, Nominal."

Not all users will agree the changes are for the best. Many users may think the 1999 NEC is less usable, especially those who cherish the status quo. Still, few could disagree that there are many important changes. How can 10 changes be identified as the most important? Certainly the manufacturers of steel and nonmetallic products would pick different ones. And, what is important in the residential market may not seem important to industrial users.

The selection of these top-10 NE Code changes was based on three criteria. 1) Changes that represent dramatic departures from previous rules; 2) Changes that are "foot in the door" changes likely to see expansion in future editions; 3) Changes of particular importance to some segment of the industry.

Some "important" changes are not included here. For example, the rewrite of Article 250 is certainly important, but the rewrite does not make major changes in the rules. Rather, it reorganizes the material to improve usability. Many clarifications may seem important to those whose practices or interpretations of previous rules turned out to be different from the intent of the code panel. For example, the method of measuring the length of free conductors in a box was clarified, and the revised rule may affect a lot of users; but the revised rule will not change all interpretations. These issues and many others are covered in a summary of the changes found on page 12.

The 10 changes are not necessarily in order of importance. Instead, they are in the order in which they appear in the Code, by Article or Section number. And, the top 10 1999 NE Code changes are...

1. Section 110-14(c)(1). Temperature Limitations This change is one of many in which exceptions are changed to "positive code language." Exceptions have been significant stumbling blocks for users of the NEC for several reasons. Exceptions often apply to only a part of a rule, and that part is not always easily identified. Some exceptions have the effect of creating a mandatory rule for a specific situation. Many exceptions were not written in complete sentences, which has fostered differing interpretations. Generally, positively stated rules are clearer and more understandable than a general rule and an exception. The code panels have attempted to rewrite exceptions into positive statements, or at least complete sentences.

In the case of Section 110-14(c)(1), the exceptions in the previous rule were reworded into a list of permissible conditions. In addition, text was added to clarify the ratings of motor terminals where the terminals would otherwise have been considered to be 60-deg rated.

Rewriting the exceptions could initially cause some confusion for experienced users. A good example is the lists of uses permitted and not permitted for some wiring methods. An exception to a use that is not permitted actually creates a use that is permitted. Therefore, when an exception was reworded, it may have been moved from one list to another. For example, 340-5 in the 1996 NEC listed four uses of Type TC cable that were not permitted. When the exception to 340-5 was reworded for the 1999 NEC, it became an additional permitted use in 340-4.

Incidentally, a comparison of 340-5 in the 1996 and 1999 Codes will reveal a change in the way lists are formatted in the 1999 NEC. These format changes are editorial rather than substantive, are intended to promote understanding and ease of use, and are not necessarily flagged by lines in the margins, but they do look different.

2. Section 110-26(f). Dedicated Equipment Space

Rules covering the dedicated spaces for panelboards, switchboards, and motor control centers are moved from Section 384-4 to Article 110. The working space and dedicated space requirements are modified, and alternative protection from foreign systems is now recognized in lieu of total exclusion of foreign systems. These rules have been a major source of conflict, especially between electrical installers, designers, and inspectors and the designers and installers of other systems.

The working space requirements previously found in Section 110-16 are moved to Section 110-26 as part of the reorganization of Article 110. The dedicated space requirements for equipment covered by Article 384 is also relocated to Section 110-26, so they are now grouped with the working space requirements for all electrical equipment that may require servicing while energized. This relocation is meant to bring similar requirements together for ease of application.

Section 110-26(a)(3) now allows equipment associated with other electrical equipment to extend up to 6 inches into the workspace for the other electrical equipment. This permits equipment of different depths to be mounted on the same plane instead of having to align the fronts of such equipment.

The dedicated space above panels and the like has been reduced to 6 ft above the equipment. The previous rule required clear space up to 25 ft or the structural ceiling. In addition, foreign systems are now permitted to occupy the dedicated space above equipment if the equipment is protected from those foreign systems. The rule is now worded in such a way that the dedicated space above equipment may be eliminated entirely if the protection, such as a shield to catch leaks, is placed immediately above the equipment. Such a complete elimination of the wiring space was probably not intended, especially considering the battle that has been waged over this rule in recent Codes cycles.

3. Section 210-12. Arc-Fault Circuit-Interrupter Protection

Arc-fault circuit interrupters (AFCIs) are relatively new devices designed to detect the occurrence of an arcing fault and disconnect the faulted circuit from its power source. Ordinary overcurrent devices respond to levels of current that are usually high relative to their ratings. Arcing faults often do not reach the levels of current necessary to operate ordinary overcurrent devices, and yet arcing faults have been found to be a significant cause of fires. Appliance cords and extension cord sets are especially susceptible to damage that may result in arcing faults. Whereas GFCIs respond to current imbalance in a normal circuit, AFCIs look for the distorted waveforms created by arcing in a circuit. Also, although GFCIs will operate to clear some line-to-ground faults, they will not normally operate on line-to-neutral faults. The 1999 NEC requires AFCI protection on circuits supplying receptacles in residential bedrooms. The rule becomes effective January 1, 2002.

Proposals were made to require similar devices under the 1996 NEC. Those proposals were rejected because the Codes panel believed a more thorough analysis of the problems and the devices was needed. Additional information was presented in proposals for the 1999 NEC. Some possible problems were still identified by panel members, including the fact that many appliances produce arcs in normal operation, that AFCIs have been tested primarily in laboratory conditions and actual field experience is limited, and the devices could have a significant impact on residential construction costs. Panel members were also concerned about commercial availability of AFCIs.

Information presented during the public comment period convinced the panel the devices should be required, but the requirements should be phased in gradually. Bedrooms were chosen partly because the occurrence of fires due to faulty or damaged cords was found to be most common in bedrooms and living rooms. Assuming the devices are found to be effective and not subject to excessive nuisance tripping, Code users can reasonably expect the requirements for AFCIs to be expanded to cover other areas and occupancies in the future.

4. Article 240, Part H. Supervised Industrial Installations

A new Part H of Article 240 defines Supervised Industrial Installations and provides special rules for overcurrent protection in such occupancies. Part H includes Sections 240-90, 240-91, and 240-92. Section 240-90 includes the permission to use the new rules and the conditions under which the rules may be used. Section 240-91 defines Supervised Industrial Installations. The new rules are contained in Section 240-92. The primary effect of the revision is to provide special tap rules for large transformers and outside feeders in certain industrial locations.

The new rules of Part H are significantly different from previous rules in at least five ways. 1) Rather than providing overcurrent protection in some specifically prescribed manner, overcurrent protection may be provided by engineering design and calculation. 2) Devices other than circuit breakers and fuses are recognized as overcurrent protective devices. 3) The overcurrent devices may be broken up into separate devices with short-circuit and ground-fault protection provided by one device and overload protection provided by another device. 4) Overcurrent protection at the load end of conductors other than service conductors may be provided by up to six separate devices. 5) The limits on conductor lengths are generally longer than provided in other installations.

5. Section 250-30. Grounding Separately Derived Alternating Current Systems

Rules for grounding separately derived systems are relocated from 250-26 to 250-30 as part of the reorganization of Article 250. At least four significant revisions were made to the requirements for grounding separately derived systems. 1) Section 250-30(b) was added to cover ungrounded separately derived systems. 2) Sections 250-30(a)(1) and (2) now require the bonding jumper and grounding electrode conductor connections to a grounded system conductor to be in the same location. 3) Section 250-30(a)(3)(b) now considers a suitable water pipe electrode to be within 5 ft of the water pipe entrance to the building. 4) Section 250-30(a)(3) Exception allows a grounding electrode connection for a separately derived system to be made to the equipment grounding bus of service equipment under specified conditions.

Probably the most dramatic of these changes is the revision to Section 250-30(a)(3)(b). The new rule has the effect of either eliminating the water pipe as an electrode for many separately derived systems or requiring long grounding electrode conductors. In steel structures, especially high-rise structures, the separately derived system will almost always be closer to building steel than to the water pipe entrance. On the other hand, in a high-rise building constructed of concrete, the water pipe entrance will be nearer than the nonexistent building steel, even for a separately derived system on a high floor. Thus, a long grounding electrode conductor will be required.

Although Section 250-104(a)(4) will still require the local water pipe to be bonded to the separately derived system, the revised rule seems to ignore the definitions of "Ground" and "Grounded" in Article 100, which recognize bodies that may serve in place of earth. Certainly, on some high floor of a building a reference to the surrounding metal systems to which a person may come in contact is more important than a reference to the earth, which is far below. Proper bonding will provide the local reference, but some of the intent of grounding systems seems to be lost in this revision.

6. Section 250-32. Two or More Buildings or Structures Supplied from a Common Service

The requirements for grounding at separate buildings were extensively rewritten and clarified. The revised wording clearly states electrodes must be established at separate buildings unless the separate building is supplied by a single branch circuit that includes an equipment grounding conductor. The revision also clarifies that an equipment grounding conductor is not always required to be run from one building to another. However, a significant revision requires an equipment grounding conductor if a path parallel to a grounded conductor is created by metallic systems common to both buildings. Also, an equipment grounding conductor must be run if the upstream building has ground fault protection for equipment installed on the common service.

The new rule is found in Section 250-32(b), which requires compliance with 250-32(b)(1) or (2). Compliance with these rules will require examination of the installation for metallic pathways such as water pipes, sprinkler systems, ground grids, or other structures or systems common to two buildings even though they may not be electrical systems. The new requirement is directed at eliminating parallel pathways for neutral or other grounded conductor currents.

7. Section 336-4. Uses Permitted (NM Cable)

The height restriction on NM cable in one- and two-family dwellings was removed. However, the selected wording may not be completely clear. The intent was to allow NM cable in one- and two-family dwellings of any height, but for other types of buildings, the use of NM cable is still restricted to structures of not more than three floors above grade. As revised, 336-4 allows NM cable in one- and two-family dwellings, and permits the use of NM cable in multifamily dwellings and other structures except as restricted in 336-5. Section 336-5 prohibits NM cable in multifamily dwellings and other structures of more than three floors above grade. If "other structures" is taken very literally, the three-floor restriction can still be applied to one- and two-family dwellings.

Proponents of the removal of the height restriction wanted it removed, or at least modified, for all building types. They claimed a reason was never given for imposing the restriction in the first place. This claim is not entirely accurate; the original intent appears to have been to restrict NM cable to buildings of combustible construction. Nevertheless, the action of the Codes panel has been appealed, and the final outcome of those appeals may not be known until after the 1999 NEC is published.

8. Sections 760-2, 760-31(g), and 760-61(g). Circuit Integrity Cable Circuit Integrity Cable is intended to withstand fire conditions well enough to allow a fire-alarm circuit to continue functioning for a certain period of time. Ordinary conductors and cables will lose their functionality rather quickly when exposed to flame or high temperatures because the insulation will melt or be consumed in the fire. When the insulation is destroyed the conductors are likely to short together or to ground and lose their "integrity" or ability to function.

One method of providing circuit integrity for conductors and cables involves using both special fire-resistive primary insulation and a fire barrier. The fire barrier is placed directly on the conductor material between the conductor and the primary insulation. When exposed to flame or high temperature, if the fire-resistive primary insulation fails, the components of the fire barrier melt together to form a ceramic-like insulating covering that allows the conductors to continue to function. One type of cable currently in use in many countries other than the United States has a three-hour fire rating.

Currently the only wiring method recognized for general use by the NEC with a significant inherent fire rating is Type MI cable. Manufacturers of what the 1999 NEC refers to as Circuit Integrity Cable would also like to gain approval of their product for some of the uses currently dominated by MI cable, such as for power cables that need to continue to function for a period of time under fire conditions. Such applications may include wiring for fire pumps, wiring on oil platforms, wiring in tunnels, and wiring in nuclear power plants. Although inclusion of circuit integrity cables for fire alarm systems is intended only as an alternative way of meeting the survivability requirements for some fire alarm circuits, expanded uses of this type of product are likely, and are already under consideration by some jurisdictions in the United States.

9. Section 800-48. Raceways for Communications Wires and Cables This new section requires raceway systems used for communications wires and cables to be selected from Chapter 3 wiring methods and installed in accordance with Chapter 3. According to Section 90-3, Chapter 8 is independent of the rest of the Codes and the provisions of Chapters 1 through 7 apply to Chapter 8 installations only where such provisions are specifically referenced in Chapter 8. Prior to the 1999 NEC, there were few such references, but this new reference is very broad. For example, many communications installers have long maintained they did not have to comply with the conduit fill requirements of Chapters 3 and 9 because there was no reference to such requirements in Chapter 8. This new reference incorporates the conduit fill requirements of the Chapter 3 raceway wiring methods and all other requirements of the respective raceway articles as well. There is an exception to this new requirement for "listed nonmetallic communications raceways" requiring such raceways to comply with certain rules for electrical nonmetallic tubing. Section 331-6 covering conduit fill is not included in those requirements, but wiring methods such as EMT (Article 348) or PVC (Article 347) are not covered by the exception.

10. Article 830. Network-Powered Broadband Communications Systems The new Article 830 recognizes a type of communications system that can deliver more than one type of communications service through a single cable. For example, a single line may carry voice, data, audio, video, and interactive services. The power for this type of system is provided from the network rather than from the normal premises wiring system. Significantly, a network-powered system introduces a power source to a building without the usual requirements of a service. For example, no main disconnecting means is required. For that matter, a disconnect may not be desired where the system is used for communications such as for alarm systems or other emergencies.

Network power sources must be limited. The power sources are classified as Low and Medium. Low power networks are limited to 100 V and 250 VA. Medium power networks are allowed up to 150 V, but the power limitation is still 250 VA. A high power classification of up to 150 V with no power limitation was proposed but rejected and held for more study.