National Electrical Code Research Articles

The nuts and bolts of a good installation

Most oil exploration and subsequent refining operations take place outside the continental areas of North America and Europe. There, the National Electrical Code (NEC), Canadian Electrical Code (CEC), and CENELEC standards are not the de facto codes and standards which firms must adhere. There is limited control over where equipment is purchased, with the taut policy to purchase from anyone that can meet the specifications. As a result, specifications become extremely critical since they are the primary means of controlling safety, functionality, maintenance, and reliability of the installation. When designing or specifying IEC standards, there are several major areas consider that contrast from NEC: the use of cabling systems, sealing methods, enclosures, lighting practices, and intrinsically safe circuits.

North American zones: rethinking hazardous location design

Changes to the Canadian Electrical Code (CEC) (1998) and National Electrical Code (NEC) (1996 and 1998), while progressive, are only first steps. The updates allow the use of the International Electrotechnical Commission (IEC) classification system and products. For the purposes of this article, the CEC is used as a starting point. This article examines a combination of the "best practices" from Canada, Europe, and the United States, which relate to petrochemical installations. The optimal design for a facility is not as simple as exchanging products. It is more like rethinking conventional design practices. Area classification, wiring methods, equipment placement, and product design are discussed. The right combination of the two wiring systems is not as simple as applying IEC products to a class-division-type design. While the modular style of IEC products may offer greater flexibility, traditional North American products are readily available and more familiar to most designers. However, since North America, and perhaps to a greater extent Canada, is in the unique position of taking advantage of the best of both systems, the best design is likely to be found in a combination of the two. In Alberta, Canada, regulators granted permission for the use of products approved to standards other than CSA International in selected facilities to accommodate the "combination" design.

NFPA 70E 2000: updating electrical safety requirements for employee workplaces

The authors describe NFPA 70E, which is intended primarily for those who commission, start up, operate and maintain electrical systems and equipment. Safe condition of electrical facilities and equipment is best achieved by adherence to NFPA 70, the National Electrical Code, during the design, procurement, and installation phases of such equipment. Following the policies, principles, practices and procedures advocated by NEPA, 70E provides a reasonable and effective approach to the safe conduct of electrical work by employees in the workplace.

North American and IEC standards for circuit breakers

Which standards are appropriate for molded-case circuit breakers in North America-North American or International Electrotechnical Commission (IEC) standards? Though IEC standards are generally international, they are not adopted worldwide. It is not always recognized that the National Electrical Code (NEC) is also international. The product standards for molded-case circuit breakers in the three North American countries are largely identical to each other, but not equivalent to the IEC standards for circuit breakers. These product standards could also be considered international, at least in content. How does one compare Underwriters Laboratories (UL) and IEC standards for circuit-breaker products? One way is to compare the details of one standard to the corresponding details of the other as would be necessary to convert an existing product designed to one standard to the other. Square D Company did such a comparison in both directions. The process was tedious and the results not practically applicable in specifying a product for a given application. However, the exercise did reveal some very useful points related to the products. This article discusses some of these points to provide an overview of product differences.

Instantaneous arcing-fault models developed for building system analysis

An arcing fault is a dangerous form of short circuit that may have a low current magnitude. In the case of such faults, the magnitude of the current is limited by the resistance of the arc and may also be limited by the impedance of a ground path. This lower level fault current is often insufficient to immediately trip phase overcurrent devices, resulting in the escalation of the arcing fault, increased system damage, tremendous release of energy, and threat to human life. Despite modern advances in system protection and the adoption of National Electrical Code Section 230-95, people continue to be injured or killed from arcing faults, initiated by accidental physical contact or through a glow-to-arc transition. The initial phase of an arcing-fault research project was to review the historical evolution of arc modeling for low-voltage systems. A summary of the electrical aspects and the physics involved in arcing faults appeared in previous work. Today's better analytical tools facilitated the development of new instantaneous arc models with current-dependent arc voltages, which better represent the arcing phenomenon than the assumed arc voltage associated with previous instantaneous arc models. The arc currents in a typical medium-size building system are determined and harmonic analysis is performed.

NFPA 70E changes for year 2000

The recognized and generally accepted good engineering practice covering electrical safety in the workplace was adopted in the fall of 1999. The National Fire Protection Association (NFPA) accepted several significant changes to Standard 70E entitled "Electrical Safety Requirements for Employee Workplaces". The changes resulted from public proposals and comments based on new technology and developments, substantiated by testing. Each recommendation was reviewed, discussed and approved by the NFPA 70E Technical Committee during actions on the proposals and comments over the past two years. Text was updated to conform to the 1999 National Electrical Code. All definitions were placed in one section under Introduction. All training requirements and qualifications were placed in one chapter. Additional methods were provided for identifying the level of electrical arc flash hazard, determining safe approach distances, and selecting personal protective equipment appropriate for the degree of hazard available at the work place. Part IV was added to provide guidance for safe work practices around special electrical equipment and systems such as electrolytic cells, batteries, lasers and power electronic equipment.

Grounding medium-voltage mobile or portable equipment

Examples of medium-voltage mobile equipment in pulp and paper mills include rail-mounted portal cranes for log handling, chip and bark stackers, and chip-reclaim screws. No examples of portable medium-voltage equipment can be cited. National Electrical Code (NEC) section 250-188 describes the requirements for system and equipment grounding of portable or mobile equipment rated 1 kV and higher. One of the requirements of NEC section 250-188 is: the grounding electrode to which portable or mobile equipment is connected must be isolated from, and separated in the ground by at least 20 ft. from any other system or equipment grounding electrode. There must be no direct connection between the electrodes such as a buried pipe, fence, etc. This article demonstrates that even if two separate ground systems are installed in the vicinity of each other, with a spacing of 20 ft and no direct metallic bonds between these two systems, a high portion of the system ground potential rate (GPR) will be transferred to the safety ground. A spacing of 20 ft is grossly inadequate to isolate the two grid systems from most faults encountered in utility substations serving industrial distribution systems. We also demonstrate that in an industrial environment, achieving isolation between system and safety grounds may not be practical due to the physical size of the property, existing installations, or geological formations. In addition, it may not be possible to isolate medium-voltage mobile equipment frames from the plant's ground grid.

IEEE Std 515 takes a step toward harmonization

IEEE Recommended Practice 515 for the "Testing, Design, Installation, and Maintenance of Electrical Resistance Heat Tracing for Industrial Applications" was first published in 1983. During the first five-year review cycle, which took place from 1984 to 1990, a major effort was made to harmonize 515 with other North American and European standards. The Project Authorization Request (PAR) for the second five-year review cycle was approved in June 1993. At this time, changes to the United States National Electrical Code (NEC) were proposed that would have a major impact on heat tracing systems. In Article 427, consideration was given to requiring metallic coverings on all heating cables, and ground-fault equipment protection on all heat tracing circuits, regardless of area classification or application. In addition, expanding the 1996 NEC to include IEC Zone methods of hazardous area classification was proposed. Inclusion of area classification Zone methods provides wide harmonization. IEEE 515 is now a standard which will provide the user with a means to achieve a safe and reliable heat tracing system.

"Right sizing" circuit breakers in motor starters

Instantaneous-trip, molded-case circuit breakers (MCCBs) have been applied successfully for low-voltage motor protection for many years. However, the changes in motor-starting characteristics have created more difficult challenges for the application engineer. The major challenge is successfully starting the low-voltage motor without causing the instantaneous-trip breaker to falsely trip without exceeding equipment ratings or violating limitations in the National Electrical Code (NEC). "Right sizing" circuit breakers for use in low-voltage combination motor starters is critical to the successful, reliable operation of plant and process facilities. If not properly applied, false tripping on motor starting and contact welding of contactors may occur. Moreover, changes in the NEC and improved motor efficiencies have impacted equipment selection and protection. The following information is intended to guide application engineers in their selection of the right breaker and its setting for more reliable motor protection: combination motor-starter components, circuit breaker characteristics, circuit breaker and combination. starter testing, motor starting characteristics, and component selection using coordination examples. The examples show how selecting the right breaker and breaker setting can avoid false tripping during starting, mitigate contact welding, and provide backup protection for overload conditions.

Ensuring that electrical equipment is safe for its intended use

The Occupational Safety and Health Administration (OSHA) regulations, the National Electrical Code (NEC), and several other nationally recognized standards and recommended practices indicate that electrical equipment must be inspected, tested, and evaluated to ensure that it is essentially free of hazards. This article guides the reader toward methods that will ensure that electrical equipment meets the safety intention of present day regulations, codes, and standards. The authors have experienced the situation where an electrical inspector, or a safety inspector, says that a particular piece of electrical equipment cannot be used because it does not have a label stating that it is listed by an nationally recognised testing laboratory (NRTL). The inspector's argument is that without such a label, he or she does not know if the equipment is safe for its intended use. The authors agree that one should try to purchase equipment with an NRTL label. But, if that is not possible, there are other acceptable ways to evaluate the safety of equipment and installations. OSHA allows two alternatives to listing and labeling. One involves the use of another federal agency, state, municipal, or other local authority responsible for enforcing occupational safety requirements. The other involves the use of manufacturer's test data, which the employer must keep.

The outlook for global unity in hazardous-area equipment

Modifications to the National Electrical Code (NEC) and Canadian Electrical Code (CEC) have created changes and complications in the marking and approvals of new explosion-protected products. Instead of making the practice of consolidating approvals for globalized products simpler, Canada and the US have gone in different directions. This, in turn, may confuse many who manufacture, specify, install, and inspect explosion-protected equipment. Europe adopted the ATEX Directive, which creates a new method of approving explosion-protected equipment for Europe. Previously, equipment and materials had to pass equipment and construction standards that limited new ideas and techniques. Now, due to the ATEX Directive, manufacturers have the opportunity to build and test explosion-protected equipment to the new Directive 94-3, which is based on performance testing. This new system may revolutionize the hazardous area industry as well as trade throughout Europe by freeing up manufacturers to use new inventive types of equipment and construction standards.

Industrial facilities gain new area classification guidelines

Both the United States National Electrical Code (NEC) and the Canadian Electrical Code (CEC) provide special rules for installing electrical equipment in hazardous (classified) locations. Hazardous locations are those locations where fire or explosion hazards may exist due to flammable gases or vapors, flammable liquids, combustible dust, or easily ignitible fibers or flyings. Only Class I materials (gases and vapors) are within the scope of American Petroleum Institute (API) RP500 and RP505. These recommended practices offer those in the petroleum industry an opportunity to standardize area classification drawings-both for drawings using the Division method of area classification and for drawings using the Zone method of area classification. Good engineering judgment must be used with RP500 and RP505, but guidelines provided should minimize differences of classifications by qualified individuals classifying the same or similar locations. This article provides an overview of the two recommended practices including outlines of tables of content, but primarily emphasising the substantive changes and additions.

New Technology for Preventing Residential Electrical Fires: Arc-Fault Circuit Interrupters (AFCIs)

A new generation of residential electrical branch circuit breakers that incorporates technology to detect and mitigate the effects of arcing faults is described. Fire loss estimates attributed to electrical wiring and the development of the arc-fault circuit interrupter for the prevention of residential electrical fires are discussed. The industry voluntary standard for arc-fault circuit interrupters as well as the 1999 National Electrical Code requirement are reviewed.

Insulation coordination for power systems

Specifying the insulation strength insulation strength characteristics phase-ground switching overvoltages, transmission lines phase-phase switching overvoltages, transmission lines switching overvoltages, substations the lightning flash shielding of transmission lines shielding of substations review of travelling waves the backflash station insulation co-ordination, the incoming surge the surge arrester station insulation co-ordination, BIL's and clearances line arresters inducedovervoltages contamination national electric safety code overview of line insulation co-ordination.

Code requirements and standards for installations of photovoltaic systems in the US

Electrical code requirements and a broad base of standards for PV installations in the US have been written. The National Electrical Code® (NEC®) focuses primarily on electrical system installation requirements in the US. The NEC addresses both fire and personnel safety. This paper describes recent efforts of the PV industry in the US and the resulting requirements in the 1999 National Electrical Code—Article 690—Solar Photovoltaic Systems. It provides an overview of the most significant changes that appear in Article 690 of the 1999 edition of the NEC. A summary of the Institute of Electrical and Electronic Engineers (IEEE) PV standards and current standards development efforts is also provided. Related and coordinated efforts of the other standards-making groups are also briefly reviewed. Published in 1999 by John Wiley & Sons, Ltd. This article is a US government work and is in the public domain in the United States

Dust explosions in process plants

Dust explosions have caused extensive property damage and fatalities in process plants. Because of their familiarity, dusts do not get the respect that flammable vapors and gases receive. Dust explosion safety rules are entirely different from the safety rules for gases and vapors; dust is an entirely different phenomenon. Dust area classification standards and the electrical installation practices are found in the National Electrical Code. This paper provides assistance in applying these dust standards and practices and provides recommendations concerning their application.

Thermally Induced Failure of Low-Voltage Electrical Nonmetallic-Sheathed Cable Insulation

Nonmetallic sheathed cable assemblies are commonplace throughout the electrical construction industry. The maximum current and ambient temperatures to which these cables can be exposed are listed in NFPA 70, National Electrical Code® (NEC)®. Laboratory test data presented here show the effects of exceeding these limits. Properties of the insulation materials in a standard cable assembly are evaluated using simultaneous thermal analysis (thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC)) coupled with Fourier transform infrared spectroscopy (STA/FTIR). Cable temperature under actual-use conditions is presented as a function of load current. Insulation resistance measurements of heated cable are included.

Implementing electrical safety regulations and standards

Since the creation of OSHA in 1912, there have been continuing changes in regulations, codes and standards impacting work practices and exposure to hazardous electrical energy. These include, but are not limited to, various OSHA regulations, NFPA 70E (1988 & 1995), National Electrical Code and National Electrical Safety Code. These consensus documents are written with the intention to establish lower injury performance expectations, or to offer guidance in developing work practices that lower the risk of personnel injury. In order to have an impact in the workplace, people in the workplace must transform often general or generic expectations or guidance into changes in specific practices that may be unique for their industry, plant or work environment. A successful and effective transformation process typically requires participation and support from management, technology experts, safety professionals, and the work force (whom the changes are intended to protect). This article provides insight in the transformation process used successfully in several companies. While the details may vary from company to company, as well as from different plants within each company, the elements for success are viewed as common.

Simplifying motor coordination studies

Low-voltage motor protection is normally the starting place for coordination studies of new industrial facilities. Also, improper low-voltage motor coordination is the source of many existing facility problems. Some engineers may frequently do coordination studies, but many engineers only occasionally do coordination studies. Trying to recall the applicable codes, standards, and references is difficult. Funds may not be available to hire experts for this type of study. The flow chart developed is to guide the occasional coordination engineer and to assist coordination experts by providing a reliable method for performing low-voltage three-phase motor coordination studies. The flow chart methodology is suggested for simplifying low-voltage overcurrent device coordination studies for new and existing three-phase motor installations. The flow chart provides references to codes and standards, highlights benchmarks for coordination, provides guides to device selection, and notes the overcurrent values of interest. The text elaborates the use of the National Electrical Code (NEC) for complying with legal requirements, and notes some significant changes in the 1999 NEC. The text also discusses some device selection criteria and expands on the decision points of the flow charts. Other flow charts for upstream devices and medium voltage equipment are being developed for future publication.

Less-flammable liquids used in transformers

Two main types of replacement liquid have been developed, high molecular-weight hydrocarbons and polydimethylsiloxane (silicone). These liquids are formulated to withstand fairly large amounts of electrical arcing, and are less flammable than mineral oils. These properties qualify the liquids for use in installations where less-flammable liquids are required and where the use restrictions associated with the products are followed. The requirements of the National Electrical Code are described and the advantages of using less-flammable liquids are also described. The fault mechanisms of transformers are discussed. The UL investigation of transformer liquids and the limitations of use are also discussed.