Posted By Steve Campolo,
Friday, September 01, 2000
Updated: Monday, February 11, 2013
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The National Electrical Code (NEC), sometimes referred to as NFPA 70, is the preeminent code covering electrical installations in the United States and in many other countries. Section 90-1(b) of the 1999 edition says:
(b) Adequacy. This Code contains provisions that are considered necessary for safety. Compliance therewith and proper maintenance will result in an installation that is essentially free from hazard but not necessarily efficient, convenient or adequate for good service or future expansion of electrical use.
It is important to note that 90-1(b) says that proper maintenance is necessary for continued safety. Just how is the maintenance to be performed? Also, how often should it be performed? In many cases, the method and procedure for proper maintenance is described elsewhere.
The National Fire Protection Agency (NFPA) publishes the Standard for Health Care Facilities, NFPA-99, which specifically describes the maintenance and testing of various pieces of electrical equipment. This article will present methods and explanations about receptacle testing in patient care areas.
Section 3-3.3 of NFPA 99 (1999 edition) covers performance criteria and testing. Clause A-3-184.108.40.206 is a 2½- page explanation of grounding system testing and is well worth reading for additional understanding. Essentially, a low impedance ground path will help ensure the rapid breaking of a circuit by the overcurrent protective device when a large ground fault occurs. It also helps reduce the voltage that may appear on the metal housings or frames of grounded appliances. Since the total ground path comprises many elements, there are various methods for testing these elements. One of the elements in the grounding path is the interface between the grounding contact of a receptacle and the ground pin of the plug. This could be a weak link in the grounding chain of cord-connected equipment and should be tested regularly. Impedance measurements are described in detail for some of the ground path elements, however the plug to receptacle interface is checked by measuring retention force.
Clause 3-3.3.3(d) of NFPA 99 says:
The retention force of the grounding blade of each electrical receptacle (except locking-type receptacles) shall not be less than 115 g (4 oz).
If a jurisdiction or health care facility adopts NFPA 99, an accurate and repeatable way to measure receptacle retention force is necessary.
This writer is aware of two hand-held devices that are commercially available to do the job. There are multi-function testers that incorporate retention testing features as well as a variety of force gages that can be adapted for retention testing use. The two testers shown in photo 1 are designed only for outlet retention testing. The smaller tester is a spring scale device containing moving indicators and a printed scale indicating ounces of retention force. The larger tester contains an electronic strain gage and a digital readout indicating ounces and tenths of an ounce. Both testers are small enough to carry in an ordinary toolbox and are intended for hand use. With both testers, the device is inserted into the receptacle and slowly withdrawn. The retention force is read on the scale or digital readout of the tester. Both testers can test the power contacts of a receptacle as well, by using the appropriate tester blade(s).
The digital tester is Listed by Underwriters Laboratories (UL) while the spring scale device is not. It is important to note that Listed testers undergo a rigorous testing regimen by UL to ensure accuracy and long life. The details of the test program are worth summarizing to understand the necessity of using a listed tester or one that meets the requirements of the UL Standard.
UL-1436, the Standard for Outlet Circuit Testers and Similar Indicating Devices contains both construction and performance requirements for Retention Testers. The following summary of some of the tests and requirements will make clear the importance of using a tester that meets the UL requirements.
Paragraph 11.6 of UL-1436 requires that the ground pin shall have a hardness of Rockwell C28 or the equivalent. Since this is much harder than the brass grounding contacts in most receptacles, the pin is not likely to wear out rapidly.
Paragraph 11.8 requires that the scale indicating retention force be calibrated and have 0.5 ounce graduations. This is necessary to ensure an accurate measurement.
Paragraph 11.10 requires that a calibration tool be required with the tester for periodic verification of the device’s indicated values. An example of a calibration tool is an accurate check weight that is supplied with the strain gage tester. The tester is positioned to suspend the weight, thus checking the tester’s accuracy.
Paragraph 16.1 requires that the tester withstand a crushing force of 75 lb. (334N) when compressed between two hard maple blocks of wood. As indicated in paragraph 18.2, the tester must survive a drop test from 5 feet (1.52m). Even the calibration weight must pass a drop test.
Some of the most critical tests and requirements concern the accuracy of the retention tester and are contained in section 23 of the Standard. Basically UL requires that the tester have an accuracy of 2.5%. More importantly, UL further requires that the tester must maintain its accuracy after 100,000 cycles of endurance. That means the mechanism of the tester is exercised 100,000 times and the tester must maintain its 2.5% accuracy. This is very important if accurate measurements are to be made.
The NFPA-99 Handbook (1999 edition) states in the explanatory material for clause 3-3.3.3, that the former Technical Committee on Safe Use of Electricity in patient care areas has considered 4 ounces as a reasonable safety factor in deciding when to change a receptacle. Some may feel that 4 ounces is not much when compared to newer receptacles where ground pin retention can be 30 to 50 ounces. Whatever value you decide upon, be sure to use a tester that is accurate and robust enough to provide meaningful results for a good long time.
About Steve Campolo: Steve Campolo is presently employed by Leviton Manufacturing Company Inc., and is vice president, engineering, personnel protection products. He has been with Leviton over 27 years. He has prior experience at Underwriters Laboratories, Dayton T. Brown Laboratories and others. His education includes a master's degree from Long Island University, a bachelor's degree from New York Institute of Technology and an associate's degree from Suffolk County Community College. Mr. Campolo served on code-making panel 17 for two and one-half cycles and is now serving on panel 18. He also serves on the UL STP for transient voltage surge suppressers, flexible cords, appliance leakage circuit interrupters, electronic controls, arc-fault circuit interrupters, ground-fault circuit interrupters and others. He is also chairman of the NEMA Technical Committee for GFCI's.
Posted By Jim Pauley,
Friday, September 01, 2000
Updated: Monday, February 11, 2013
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The American National Standards Institute (ANSI) — Most in the electrical industry have heard of it, but do you really know what it does? Take the following short quiz:
The American National Standards Institute is:
(a) A standards developing organization (like UL, IEEE, NFPA, etc.)
(b) A facilitator of standards development
(c) A federal government body (like NIST, DoD, etc.)
(d) The US representative to international standards organizations (ISO, IEC)
(e) All of the above
(f) Both "a” and "b”
(g) Both "b” and "d”
Are you ready with your answer? The correct answer is…. (g). Many of you probably picked (a) "A standards developing organization” as your answer. This is a common misconception. ANSI does not develop standards. Rather, it helps to facilitate the development of standards by establishing the guidelines for consensus, due process and openness. Read on to learn more about this critical element of the US Standards System.
Founded in 1918 by five engineering societies and three government agencies, ANSI remains a private, nonprofit membership organization supported by a diverse constituency of private and public sector organizations. ANSI represents nearly 1400 company, organization, government agency, institutional, and international members.
National Standards Activity
Ask most people about ANSI and the odds are good that you will hear something about developing standards. We all talk about "ANSI Standards” which leads us to believe that ANSI actually develops standards. In fact, ANSI actually accredits many different standards developers, including those familiar to the electrical industry like NFPA, UL, and IEEE. By being an accredited developer and following the procedures outlined by ANSI, the developer is allowed to call their finalized standard an American National Standard (ANS).
Developers are not accredited in a haphazard fashion. Each developer desiring to become ANSI accredited must submit a set of standards development procedures for ANSI review.
These procedures must be in compliance with the basic ANSI principles of openness, consensus and due process. In addition, the developer must undergo an audit of their procedures and processes at least once every five years. The purpose of the Audit Program is to confirm adherence to the criteria for accreditation and to confirm that the developers’ procedures and practices continue to be consistent with their approved procedures and current ANSI requirements.
Why is the designation of an American National Standard important?It is the glue that holds together the private sector based standards system. Without a process in place such as that provided by ANSI, we would likely have more governmental control of the standards system and less acceptability of the standards nationwide. Authorities having jurisdiction (inspectors, building officials, etc.), governmental agencies (Federal, State, local) and users recognize and look for standards that are recognized as ANS. By using standards that have been designated as such, they can be assured that the standard has been processed through an open system, where consensus was achieved, and there was ample opportunity for those affected by the standard to participate and comment.
Standards are presently promulgated as ANS, by any one of three methods: Committee, Organization and Canvass.
The Accredited Standards Committee (ASC) Methodis used by developers who chose to form a specific accredited committee to do the standards work. For instance, ASC C2 develops the National Electrical Safety Code. The organization providing the development support is IEEE and they manage the process and the activities of the C2 committee.
The Organization Methodis used by organizations that choose to establish a set of procedures specific to their organizational needs. The procedures must also comply with the ANSI procedures and guidelines, but are typically more extensive in nature. As an example, NFPA develops the National Electrical Code under the organizational method of ANSI.
The Canvass Methodof standards development is used by a wide variety of standards developers. The ANSI procedures outline a specific set of requirements for this method. In this method, a canvass list of interested persons is established and this body provides the review of the standard that is under development. UL, NEMA, ARI, and a host of other developers use this method.
Use of any of the above methods results in a standard that can be designated as an American National Standard. Due process and consensus are the hallmarks of that designation. In all cases, the ANSI process requires a public review period. This allows those who did not directly participate in the development of the standard to still make comments on the technical content of the standard. A single standards developer could have standards produced under one or more of these three methods.
There are some key groups within ANSI that have responsibility for portions of this national standards system. Each of these groups exists to ensure that the ANSI process is maintained, appeals are heard, and procedural issues are addressed. These are in addition to all of the mechanisms that may exist within the standards developer process.
The Board of Standards Review (BSR)– The Board of Standards Review is responsible for the approval and withdrawal of American National Standards. The functions of the Board of Standards Review include, but are not limited to, the following:
(1) National Standards and adjudicating questions or conflicts that develop in the standards approval procedure; and
(2) Determining whether standards submitted to ANSI for approval or withdrawal as American National Standards meet the requirements of the ANSI and acting on all requests for approval, reaffirmation, revision and withdrawal of American National Standards.
The BSR is not involved in the content of standards and does not hear appeals with regard to technical issues. However, the BSR may hear an appeal with regard to whether a technical issue was given due consideration in accordance with the ANSI accredited standards developer’s procedures.
Executive Standards Council (ExSC)– The Executive Standards Council is responsible for the procedures and criteria for national and international standards development activities of ANSI. The functions of the Executive Standards Council include, but are not limited to, the following:
(1) Developing and promulgating procedures and criteria for the coordination, development, approval and withdrawal of standards as American National Standards;
(2) Developing and promulgating procedures and criteria for the coordination, development and approval of United States positions in the international non-treaty standardization organizations with which the Institute is or may become affiliated;
(3) Establishing and supervising such groups as are needed to plan and coordinate the development of American National Standards and to determine and coordinate United States positions in international standards activities;
(4) Developing and promulgating procedures for auditing the implementation of procedures and operations given in (1), (2) and (3) above;
(5) Hearing and adjudicating appeals pertaining to procedural issues and accreditations; and
(6) Considering and responding to public review comments.
Appeals Board– The Appeals Board considers appeals by directly and materially affected persons (organizations, companies, government agencies, individuals, etc.) who believe they have been, or will be, adversely affected by a decision of ANSI, whether in the form of action or inaction. In recent years, the Appeals Board has primarily considered appeals of appeals decisions issued by the Executive Standards Council (ExSC) or the Board of Standards Review (BSR). However, the Appeals Board may hear appeals with regard to the implementation of additional procedural issues.
The importance of the ANSI process and the auditing program should not be underestimated.
Without this National Standards activity, the US standards system would be open to domination by special interests, have limited acceptance across the country and would negatively impact US competitiveness.
ANSI’s International Role
ANSI is the sole U.S. representative and dues-paying member of the two major non-treaty international standards organizations, the International Organization for Standardization(ISO), and, through the U.S. National Committee (USNC), the International Electrotechnical Commission (IEC).
Through the ANSI umbrella, US positions on issues in IEC and ISO are conveyed to the international community. This role helps the US in maintaining competitiveness in other markets and provides a forum where concepts in US standards can be promoted into IEC and ISO standards.
It should be recognized that by participating in IEC and ISO activities, ANSI is not committing the US to using those standards on a de facto basis. Standards that are developed through IEC or ISO and are being considered for use in the US are (and should continue to be) processed through the ANSI national standards system. This will ensure that all US interests have an opportunity to "weigh-in” on the standard before it becomes accepted as an American National Standard.
The present ANSI membership falls into three categories; Corporate, Government, and Organization.
Corporate membershipis for a corporation, partnership or other entity that is created under the laws of the United States or any State thereof and that is engaged in industrial or commercial enterprise or professional, educational, research, testing or trade activity.
Corporate members include companies such as Square D Company, Caterpillar, AT&T, Microsoft, etc. Corporate member dues to ANSI are determined based on a fee structure related to annual revenue.
Government membersare departments or agencies of the United States government or of any State, interstate or regional authority or agency, or any local or county subdivision of such entities interested in the work of ANSI. Government members include Broward County Florida, City of Jacksonville, National Institute of Standards and Technology, Metro Dade County Florida, US Department of Defense, etc. Government member dues to ANSI are determined based on a fee structure related to their annual budget.
Organizational membersinclude not-for-profit scientific, technical, professional, labor, consumer, trade or other association or organization that is involved in standards, certification or related activities. Organizational members include Underwriters Laboratories, International Association of Electrical Inspectors, National Electrical Manufacturers Association, etc. Organizational member dues to ANSI are based on a basic organizational fee along with a national activity assessment based on the number of standards the member develops and submits to ANSI (if a standards developer) and an international activity assessment based on a level of involvement with ISO and IEC (if they sponsor a technical advisory group or a secretariat).
Membership in ANSI helps not only to support the voice of the US interests internationally, but more importantly it supports the US infrastructure for a voluntary, consensus-based standards system.
In summary, ANSI plays an irreplaceable role in the US standards system. Each participant in the electrical industry (inspector, installer, manufacturer, designer, etc.) must endeavor to understand the role ANSI plays and support that role by actively participating in the standards system and in setting the direction ANSI takes in the future.
One of the key ANSI publications is Standards Action. This document is produced biweekly and indicates what standards are under development and out for public review. Standards Action is available on the ANSI web site. This is required reading for anyone involved in the US codes and standards system.
More information about ANSI and ANSI membership can be found on its web site atwww.ansi.org.
Read more by Jim Pauley
Posted By IAEI,
Friday, September 01, 2000
Updated: Tuesday, February 12, 2013
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The first modern neon sign debuted in 1910 at the Grand Palais in Paris. It was created by a Frenchman named George Claude, who somewhat stumbled upon his discovery by accident. His purpose was actually to employ an inexpensive, high quality method of producing pure oxygen to sell to hospitals and welding shops.
Wanting to find a way to use the large quantities of leftover gases such as argon and neon, Claude decided to fill a "Moore” tube with gases and then bombard those gases with electricity; this process, instead of producing pure oxygen, produced intense red and blue lights. As is the case with many great discoveries George Claude did not think of this process entirely by himself; he merely perfected other inventors’ failed experiments.
Photo 1. Cold cathode lights are easily dimmed with architectural grade dimmers, without resorting to special transformers and ballasts
In 1923, Earle C. Anthony returned home to Los Angeles from a business trip to Paris with two custom signs to be used as advertisements for his Packard dealership at Wilshire and La Brea in Hollywood. But these were no ordinary electric signs: Anthony’s custom order was for the first neon commercial signs in the United States.
Anthony had purchased the blue and orange signs from George Claude, who had perfected the method of filling glass tubes with neon gas and illuminating them. Glass tubes were bent over a flame, electrodes were attached, air was removed by a vacuum and the tube was heated to remove any impurities before Claude pumped in the gas. The process remains the same today. Phosphors make the vast arrays of colors, which when used with different phosphors, can be blended to form a desired or custom color. Neon glows red; argon, blue; and other gases have their own hues, which can be blended to create nearly any desired color.
Photo 2. Cold cathode lights are easily dimmed with architectural grade dimmers, without resorting to special transformers and ballasts
Neon is considered an art or craft. Consequently, the unions invested little into appropriate training programs for the neon industry; as a result there were few neon apprenticeship training programs. When a training program was established, it was because of a sudden increase in needs and activity in the neon industry on the part of one company in particular. The only organized and structured training program was known as the Egani Institute (Egani stood for: Eddie’s Glass and Neon Institute), and was located on 125th Street between Fifth and Madison Avenues in New York City.
The Egani Institue was founded by Edward Seise in 1930, and continued operations until 1971, when he retired. He claimed to have taught approximately 85 percent of all the glass benders in the industry in the United States, and a large percentage of benders in foreign countries. The processes taught by Egani were established by the Claude factories in the 1920s. The philosophy of teaching at the Egani Institute was simple and direct: Neon meant signage, and signage meant glass letters. The glass benders were trained to follow, without deviation, patterns on an asbestos layout. Neon was part of the signmaker’s trade, and the craft belonged to the electric-sign industry. Neon was taught as a craft without an identity of its own. Because of the uniqueness of the Egani Institute and the large number of glass builders trained there, its influence on the neon craft was great.
Photo 3. Neon tubing electrodes, one tubulated for processing, the other for end of tubing
The advent of electricity and light bulbs has done more than merely illuminate the night; it has created an art in the form of neon and other electrical signage. Southern California was, if not the birthplace, certainly the American center of this emerging form many decades ago. It is again at the heart as newly-restored signs once again light up-a fitting homage to the neon pioneers who long ago lit up city streets and skylines at night, making them sparkle for all to see. As an added bonus, the neon restorations help restore economic optimism to the neighborhoods in which they’re located.
Most of the time, electricity is simply the invisible power that provides convenience and comfort to human life; but, when one stops to notice it, electricity can bewitch with its intoxicating, magical glow.
What is Neon?
"Neon” is the term that has come to be used to describe a specific type of lighting, called gas discharge lighting, which is created by passing electricity through a gas. Fluorescent, mercury vapor, sodium vapor and neon lamps are examples of different types of gas discharge lighting.
Neon, a chemical element found in the atmosphere, is one of six rare or noble gases. The others are: argon, helium, krypton, xenon and radon. All of these gases, with the exception of radon are used in tubing to make neon signs. When neon is electrically stimulated, it creates a red light. Argon, with a trace of mercury added, creates a blue light. Helium produces a pale yellow light. Krypton generates a white light with a purplish tint, and xenon a white/blue light. Neon and argon/mercury (Hg.) filled tubes are the most common and most economical to produce.
Cold Cathode Lighting in Comparison
Photo 4. Tubing being bent in the crossfire burner
Cold cathode is essentially the same as neon but with larger diameter tubing and higher mA transformers. Cold cathode refers to a special type of custom manufactured fluorescent lamp with the following unique features: As with neon tubing, cold cathode lamps can be bent and shaped to conform to almost any configuration; and with minimal space between lamps, shadowless cove or indirect (shadow effect) lighting can be achieved. Cold cathode tubing used in cathode lighting systems offers several different cathode lighting systems ranging from around 300 lumens per linear foot up to 700 lumens per linear foot for a single row of cold cathode lamps.
Cold Cathode Colors
Over twenty colors and six shades of white are available. Lamp life on a quality constructed cold cathode lighting system is typically 35,000 to 50,000 hours. The term "system” as used here refers to "listed systems or custom built field-installed systems installed as per the requirements of Part Q of Article 410 in the National Electrical Code.”
Cold cathode lights are easily dimmed with architectural grade dimmers, without resorting to special transformers and ballasts (see photo 1 and photo 2).
The main difference between cold cathode, fluorescent lamps, and neon tubes is that the neon and cold cathode tubing electrode is a manufactured, virtually indestructible iron thimble, which allows for instant lamp starting, up to and often exceeding 50,000 hours lamp life, and the ability to dim, without any special dimming ballasts.
In the sign industry, neon filled tubes are referred to as either neon or red. Argon filled tubes, because of the trace of mercury added, are called mercury-filled or blue. These two tubes provide the basic red and blue colors most common in neon signs. This also relates to tube footage charts for sizing transformers. Read either the red for neon or blue chart for argon/mercury; then follow the tube size to find transformer voltage requirements.
Straw or Yellow/White
Typical Neon Colors
Photo 5. Tubing being bent using a ribbon style burner
Several methods are used to create other colors. These include using the other three gases, combining different gases in the same tube, using glass tubing of different colors, and using glass tubing coated on the inside with different phosphorescent materials. Almost any desired color—from soft and subtle shades, to wild and electric psychedelic colors of the clubs and bars—can be created for a neon sign.
Gas discharge lamps have many similarities. They all require gas to be contained in a glass tube or lamp, and all require high voltage to make the gas glow. They all produce light in some visible range of the light spectrum.
The differences are more important. Fluorescent, mercury vapor and sodium vapor lamps, which are used for general-purpose lighting, provide light in the white or yellow range. They are generally used in a fixture designed for the lamp. The transformer or ballast providing the high voltage is a part of the fixture, so there is no high voltage wiring outside of the fixture. These lamps are machine manufactured, which assures consistent operation from lamp to lamp, and are marked to indicate the wattage produced. Generally, one 100-watt mercury vapor lamp can be replaced with another with no noticeable difference in operation or lumen output.
Neon is typically used for sign or decorative lighting. Skeleton tubing neon signs operate at voltages ranging from 2,000 to 15,000 volts. The transformer or ballast providing the high voltage may be remote from the lamp, requiring high voltage wiring to be installed in or on the building where the sign is used. Neon tubes are handmade; therefore, each length of tubing is unique. Consequently, there can be a large variation in operation between two lamps that appear to be identical. Neon tubes are not marked to identify the wattage output expected.
Photo 6. The IAEI Keystone in processed neon tubing
The initial color source is the inert gas, which emits its characteristic color when electricity is applied. The two most common gases are neon, which emits a fiery red, and a mixture of argon and minute particles of mercury, which emits a subdued blue. Clear glass allows you to see the characteristic colors emitted by the gas. Fluorescent powders may be painted and baked to the inside walls of the glass tubing and the source light is then converted into a multitude of shades, such as pink, turquoise, and green. By altering the mixture of phosphors, subtle differences are possible. For example, white is available in a wide array of color temperatures from warm to cool.
Tubing is also produced in colored glass. Deep clear reds, blues, and greens, for example, produce the richly saturated colors referred to as exotic or Euro glass. Colored glass may also have a fluorescent coating, which can change both the quality and color of the light.
Luminous Tube Processing
Neon tubing sections are capped off by two glass electrodes, which have a wire that is connected to an electrode passing from the outside to the inside. One of these electrodes has a tubulation, a small tube that remains as a passage from outside to inside (see photo 3), that is sealed to the pumping system or manifold. The manifold has valves that regulate vacuum while bombarding, in addition to filling the tubing with the correct inert gas. These valves can be selectively opened or closed during the tube pumping process to allow changing from vacuum to filling pressure.
Photo 7. The bombarding stages of neon tube processing
An ultra high vacuum pump pulls the air out of the tube, while a high voltage-high amperage transformer bombards and heats the remaining air to produce glass temperatures in excess of 500°F and electrode temperatures in excess of 1400°F. Much like sterilization, this process allows the tube to achieve a higher degree of purity. When a great vacuum is reached, and the tube has cooled, a small amount of inert gas is introduced from a flask or tank. The tubulation is then heated, and as it is pulled it sucks in to make the tube’s own seal.
Making neon tubing, a simplistic process, is as much an art as it is a science. Glass tubing is produced in sizes ranging from 5 to 25 millimeters. The tubing size used is determined by the size of the letter, both width and length; the brightness desired; and the physical strength required.
In addition to different sizes, glass tubing also is produced in different colors, which can accentuate or modify the color produced by the gas. For example, neon gas in a red glass tube produces a brighter red than neon gas in a clear glass tube.
Glass tubing can also be produced with an internal coating of rare earth phosphors. This material reacts to the ultraviolet light produced by the gas and fluoresces, creating colors different than that produced by the gas itself.
The gas selected, the size of the tubing, the cleanliness or purity of the fill, and the length of the tubing all affect the inherent "resistance” of the finished tube. It is the resistance or impedance of the tubing that determines what size power supply is needed to energize the tube. NEC Section 600-41(a) cautions installers that the "length and design of the tubing shall not cause a continuous overcurrent beyond the design loading of the transformer or electronic power supply.”1
Glass Bending and Cutting
Photo 8. The bombarding stages of neon tube processing
Glass tubing is first cut to size by scoring a mark in the tube with a small file at the desired breaking point, then gently snapping at that line. This process is similar to cutting ceramic tile or glass window panes, which are also cut by scoring or scribing a line with a tile cutter and breaking on the line. The glass is then rotated and rocked (rocked and rolled) in burner flames, which use a gas and air mixture to raise the flame temperature. Generally four burners are used: Crossfire and fishtail burners produce most angled bends and splices. Ribbon burners produce long curves or sweeps. Hand torches are usually used for splices or tapering and tipping off electrodes. Crossfires actually is a specific type of burner, but the term generically applies to the fires that are used for the most common bends (see photo 4). These include single bends such as the right angle, double back, and drop, and combo bends. Here the bender must evenly rotate and rock the glass for even heating and to counter gravity. A ribbon burner is another type of burner commonly used for bending (see photo 5).
The tube making process is really quite simple when done by a skilled bender (see photo 6). A non-tubulated electrode is welded to the end of the straight tube, which is then measured and marked for bending locations. Straight glass tubing is heated in the "”fires”" and formed to the shape and length required for a specific part of a sign. Afterwards, a tubulated electrode is welded to the opposite end. The electrode selection is based on transformer size, typically 30 or 60 milliamperes (mA), and tube diameter used. Each electrode shell has two wires attached and sealed at the ends, which are connected to other tubes, or the secondary-circuit conductor from the transformer or electronic power supply.
To produce a finished tube for a neon sign or border tubing installation, it must be processed. It is first connected to a manifold vacuum system, and a partial vacuum is drawn on the tube. After which, the tube is connected to a bombarding transformer. This device, a step up transformer, is capable of reaching voltages in excess of 20,000 and 1,000 mA. of current. A variac type transformer or a core-and-coil slide-choke regulates the primary input voltage, which also simultaneously regulates the output. As the voltage is applied, the gas heats, pressure is dropped and the current to the electrodes increases, which cause the electrodes to heat turning its color to a cherry red (see photo 7 and photo 8).
How a neon tube produces light
Electrical current bombards the inert gas atoms with electrons, knocking neon’s atoms out of their orbits. The electrons collide with other free electrons, sending them back toward the atoms. As the electrons are absorbed into the atoms, energy is given off as light.
This heating process (out-gassing) will burn off most all impurities and will be withdrawn by the vacuum system. Sensitive gauges carefully monitor and control the electrode and tube temperature, vacuum pressure and gas fill. When the proper temperatures and vacuum have been reached, only then can the gas filling process begin. When the tube has been filled to proper pressure, it is again energized and monitored for leaks or failures. The letter or border tube is set aside and connected to another transformer for aging, which gives the tube a test period before shipping and installation.
Aging time for a typical neon tube can vary from manufacturer to manufacturer. The important items that need to be accomplished in the aging process is that the impurities need to be gathered into the electrode shells, and for mercury tubing, the mercury needs to be thoroughly dissipated throughout the tube.
Dangers and Concerns
Are neon tubes dangerous? Neon and argon gases by themselves are not dangerous as they are inert gases and, as such, exhibit great stability and extremely low reaction rates. As with standard fluorescent tubes, the minute droplets of mercury present in some colors are safe as long as the tube is not broken. Improper handling, however, can be a threat to both the environment and health. Many modern neon shops refuse to repair broken argon-mercury tubes for this reason.
Transformers producing voltages in the 2,000 to 15,000 volt range power neon tubing illumination. Even though the current is in the milliamp range, if a neon sign or border tubing installation is not properly mounted, wired, and insulated, the voltage levels required to operate the neon poses both a shock and fire hazard. This is an area where cheapness does not pay off. A well constructed neon system or installation should be problem free for many years. A quality processed and designed neon system can last many years without failures or requiring service repairs. In practical terms the expected life span varies, but it is not uncommon for a quality installation to last up to 20 years before tubes go flat or repairs are needed. Neon tubing can be repaired and recharged as the needs arise.
To summarize, neon and argon are the most common of five gaseous elements used in neon tubing processing today. Neon pumped tubing yields red color, while argon pumped with mercury yields blue. Nearly any color desired can be produced with the proper gas, glass, and phosphor coatings. Most neon tubing is handmade; therefore, each finished piece of tubing is individual and unique. Producing quality neon tubing requires very specific skills, physical coordination and knowledge.
About IAEI: IAEI, as the keystone of the electrical industry, is a membership driven, not-for-profit association promoting electrical safety throughout the industry by providing premier education, certification of inspectors, advocacy, partnership and expert leadership in electrical codes and standards development.
Posted By Philip Cox,
Friday, September 01, 2000
Updated: Tuesday, February 12, 2013
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This is the second part of a summary of proposed changes for the 2002 National Electrical Code® acted on by NEC Code Making Panels in January 2000. Proposals submitted to change the 2002 Code are included in the NEC Report on Proposals. That document is available from the National Fire Protection Association. Those who wish to make comments on actions taken by the code making panels must submit them to NFPA. They must be received by NFPA no later than 5:00 p.m. EDST, Friday, October 27, 2000. Blank forms for those comments are available from NFPA. They are also included in the ROP and can be downloaded from the NFPA web site. The address iswww.nfpa.org. Action will be taken in December 2000 by the 20 NEC Code Making Panels on public comments submitted and the results of panel actions will be published by NFPA in the NEC Report on Comments.
210-52(c)(5). Receptacle Outlet Location.
Proposal No. 2-172:The term "appliance garages” has been added to the last sentence. This change clarifies that a receptacle installed inside an "appliance garage” does not count as the required outlet. An "appliance garage” is understood to be an enclosed area on the countertop where an appliance can be stored and hidden from view when not in use.
Proposal No. 2-175:The second sentence of the Exception has been revised to read, "Receptacles mounted below a countertop that extends more than 6 in. (153 mm) beyond its support base, shall be located so that they are not more than 6 in. (153 mm) from the outside edge of the countertop.”
This change will permit the mounting of receptacles to the underside of extended countertops, provided the receptacles are within 6 inches of the outside edge of the countertop.
210-52(g). Basements and Garages.
Proposal No. 2-196:The last sentence has been changed to read, "Where a portion of the basement is finished into one or more habitable rooms, each separate unfinished portion shall have a receptacle outlet installed in accordance with this section.”
This makes it clear that any unfinished portion of the basement, when separated by a finished portion, will have to have a receptacle outlet installed.
210-70(a)(2). Additional Locations.
Proposal No. 2-226(a):210-70(a)(2) has been restructured for clarity and the last sentence has been revised to become 210-70(a)(2)c and reads, "c. Where one or more lighting outlet(s) are installed for interior stairways, there shall be a wall switch at each floor level, and landing level that includes an entry way, to control the lighting outlet(s) where the stairway between floor levels has six risers or more.”
This change in 210-70(a)(2)c will require a switch at an intermediate landing that has an entry way as well as at each floor level. In addition, the word "step” was changed to "riser” to conform with the accepted terms for the elements of a stairway.
Table 220-36.Optional Method—Permitted Load Calculations for Service and Feeder Conductors for New Restaurants.
Proposals Nos.2-304 and 2-305: Table 220-36 on the optional method for calculation of service and feeder conductors for new restaurants has been changed to reduce the break points from six to four and avoids the problem of adding load and reducing switch sizes, which the existing table would allow in isolated cases.
Article 225 – Outside Branch Circuits and Feeders:
225-26: Vegetation as Support.
Proposal No. 4-16:This section was revised to read: "225.26. Vegetation as Support. Vegetation, such as trees, shall be permitted only for the support of temporary wiring, as covered in Article 305.” The title was expanded by adding the words "as support.” The wording "overhead conductor spans” at the end of the sentence was replaced with "temporary wiring, as covered in Article 305.” The exception was deleted as the concept of temporary wiring is included in the revised section.
225-30: Number of Supplies.
Proposal No. 4-17a:The first sentence of the section was modified by adding the wording "additional” and "that is on the load side of the service disconnecting means.” It will now read: "Where more than one building or other structure is on the same property and under single management, each additional building or other structure served, that is on the load side of the service disconnecting means, shall be supplied by one feeder or branch circuit unless permitted in (a) through (e).” The revised wording adds clarity to the general rule covering the number of supplies permitted for multiple buildings or structures. The additional building or structure covered by this section are those supplied by conductors on the load side of the service disconnecting means.
Proposal No. 4-18a:The word "optional” was deleted from 225-30(a)(4) and will now read: "(4) Standby systems.” This change should eliminate any potential confusion regarding standby systems being permitted under this section.
225-50. Supervised Installations. Proposal No. 4-39:A new section was added to describe conditions under which over 600 volt installations can be considered as supervised installations. The proposal was submitted as a new 225-48, but was renumbered by action on Proposal 4-40b.
225-51. Sizing of Outdoor Circuits.
Proposal No. 4-40b:This new section has been added to include general rules for sizing of outdoor branch circuit and feeder conductors in over 600 volt installations. It also includes provisions for the sizing of conductors rated over 600 volt in supervised installations described in new 225-50. Conductors in supervised installations are permitted to be determined by qualified persons under engineering supervision.
Article 230 – Services
Proposal No. 4-107a:This section was restructured and revised to better describe the required location of a building service disconnecting means and to clarify that a remote control actuator is not recognized as the required disconnecting means.
Article 240 – Overcurrent Protection
240-21(c). Transformer Secondary Conductors.
Proposal No. 10-34:The title of subdivision (3) was revised to read "Industrial Installation” and a new subdivision (6) entitled "Secondary Conductors Not Over 25 ft Long” was added. The change more clearly identified the title of (3) to reflect the restriction to industrial installation and the new (6) provides a general 25 ft tap rule for transformers.
240-33. Vertical Position.
Proposal No. 10-46:The wording "unless that is shown to be impracticable” was added to the end of the first sentence. This change addresses the conditions where circuit breaker enclosures cannot be mounted in the vertical position.
240-83(d). Used as Switches.
Proposal No. 10-63:New wording has been added to this section to require circuit breakers used as switches for high intensity discharge lighting to be marked "HID.”
240-86. Series Ratings.
Proposal No. 10-67:This section has been revised to add a provision for a line-side current-limiting device to be selected under engineering supervision to protect load side circuit breakers that have a lower interrupting rating than the available fault current on the circuit.
Proposal No. 10-77:The main rule covering overcurrent protection for over 600 volt feeders and branch circuits has been revised to provide examples of items to consider when designing the overcurrent protection to be at a location other than at the point where the conductor receives its supply. The design for overcurrent protection to be at an alternate location is required to be done under engineering supervision.
Article 250 – Grounding:
250-2(a). Grounding of Electrical Systems.
Proposal No. 5-60:The wording "required to be” was deleted from 250-2(a). This action should clarify that grounding rules must be followed whether systems are grounded because they are required to be, or if they are grounded by choice.
Proposal No. 5-101:A new paragraph has been added to 250-30(a)(2) to permit a grounding electrode conductor of a separately derived system to be connected to a grounding electrode conductor that extends through a building. This change permits an alternate method of grounding separately derived systems where effectively grounded building steel or grounded metal water pipe is not near the separately derived system.
250-32(f). Grounding Electrode Conductor.
Proposal No. 5-123:The title of 250-32(f) was amended by adding the word "”electrode”" and the reference to the table has been changed from Table 250-122 to read Table 250-66. This modification changes the sizing requirement for the grounding conductor at the second building or structure to that based on Section 250-66. In addition, the term for this conductor is no longer a "”grounding conductor,”" but is a "”grounding electrode conductor.”"
250-36(g). Equipment Bonding Jumper Size.
Proposal No. 5-134:A new 250-36(g) has been added to provide equipment bonding sizing requirements for high-impedance grounded neutral systems.
250-50. Grounding Electrode System. Proposal No. 5-134a:This section has been revised to read: "”Grounding Electrode System. If available on the premise at each building or structure served, each item in 250-52(a)(1) through (a)(6) shall be bonded together to form the grounding electrode system. Where none of these electrodes is available, one or more of the electrodes specified in 250-52(a)(4) through (a)(7) shall be used.”"
This revised section includes requirements related to the grounding electrode system and correlates with the revised 250-52 and the new 250-53. The reference to "”made electrodes”" was deleted from this section.
250-52. Grounding Electrodes. Proposal No. 5-162(a):This section was revised by changing the title to "”Grounding Electrodes”" and was restructured to include two subheadings, "”(a) Electrodes Permitted for Grounding”" and "”(b) Electrodes not Permitted for Grounding.”" This section describes electrodes that are permitted for grounding and includes those that were previously described as "”made and other electrodes.”" The reference to made electrodes has been deleted. The change in this section, the amended 250-50, and the new 250-53 should help make it easier to understand the application of those respective rules.
250-53. Grounding Electrode System Installation.
Proposal No. 5-171a:A new section has been added to cover installation requirements for grounding electrode systems. This section includes much of the material in Sections 250-50 and 250-52 of the 1999 NEC. Placing installation requirements for all grounding electrodes in one location will make it much easier for Code users to follow.
Proposal No. 5-212:A new sentence was added to permit an equipment bonding jumper to be longer than 6 feet where used to bond or ground metal raceways and elbows at utility poles.
Proposal Nos. 5-219, 5-220, and 5-221:The word "”interior”" has been deleted and the word "”installed in or attached to a building or structure”" were added in 250-104(e) (1), (2), and (3). This change clarifies the fact that piping installed inside or outside and attached to the building or structure is required to be bonded.
250-104(b). Metal Gas Piping.
Proposal No. 5-229:The text in 250-104(b), which was extracted material from NFPA 54 for bonding metal gas piping systems, was deleted.
250-104(c). Other Metal Piping Systems. Proposal No. 5-238:The term "”interior”" was deleted and the wording "”installed in or attached to a building or structure”" was added. Other piping located inside or on the exterior and attached to the building or structure is now required to be bonded.
250-104(d). Structural Steel.
Proposal No. 5-240:The term "”interior”" in the first sentence was deleted. This change clarifies that structural steel whether interior or exterior that is not intentionally grounded and interconnected to form a building frame must be bonded where it is likely to become energized.
Proposal No. 5-254:The wording "”the smooth or corrugated”" was added before "”Type MC cable to clarify that only the sheaths of smooth or corrugated tube-type MC cable assemblies are suitable for grounding.
250-146(a). Surface Mounted Box.
Proposal No. 5-282:The wording "”or at”" in the first sentence was deleted. This change will permit only surface mounted boxes to be used for direct metal to metal contact between the receptacle yoke and the box as a means of grounding receptacles. This reverses the allowance granted for boxes mounted "”at the surface”" in the 1999 NEC to be acceptable for grounding receptacles.
Proposal No. 5-302:A new 250-184(d) has been added to cover rules on the size and grounding of the neutral and limits the maximum distance permitted between adjacent grounding electrodes on solidly grounded neutral systems to 400 meters.
Article 285 – Transient Voltage Surge Suppressors (TVSS)
Proposal No. 5-316:A new Article 285 was added to requirements for installations of Transient Voltage Surge Suppressors (TVSS). Transient voltage surge suppressors are widely used as part of electrical systems in areas covered by the National Electrical Code but are not directly addressed by the Code.
Chapter 3 Articles
General Changes in Chapter 3:
Considerable work has been done by task groups to continue improving the Code and to make it even more user friendly. Chapter Three of the NEC was included in the task group work and several recommendations were made. The NEC Technical Correlating Committee and Code Making Panels affected by this work took action on task group recommendations and some of those actions are as follows:
Reformatting:Many Chapter 3 articles have been rewritten and reformatted to have similar structure and to comply with the NEC Style Manual. A more uniform method of numbering sections within each article will be used. As an example, the first section in each article is designated for the scope of that article (318-1, 336-1, etc). The second section is for definitions used in that article. "”Uses Permitted”" will have the same extension or section identifier in each applicable article (336-10, 345-10, etc).
Renumbering:Many Chapter 3 articles will be renumbered at the end of the processing of the 2002 NEC. This change includes a grouping of cable and raceway articles in a more logical manner.
Relocation:Some Chapter 3 articles are being relocated to other chapters because the content and scope of those articles are more appropriate for those chapters. As an example of relocation, Article 384, Switchboards and Panelboards, will be moved to Chapter 4 and renumbered.
Article 300 – Wiring Methods and Materials
300-4(d), Exception No. 3.
Proposal No. 3-30:Exception No. 3 which provides that steel plates, sleeves, and similar protection of cables and raceways installed parallel to framing members are not required in mobile homes and recreational vehicles has been deleted. Mobile homes and RVs will be required to comply with the same rules on spacing in this section as applied to other types of buildings.
Proposal No. 3-61:The wording in 300-7(a) requiring a seal for raceways and sleeving for cables against the flow of warm air within the raceway or sleeving to a colder section of the raceway or cable to prevent condensation has been revised. Wording has been added to specifically identify the passing of a raceway or cable from the interior to the exterior of a building and the wording "”and where there is a known condensation problem”" has been added.
300-11(c). Cables Not Used as Means of Support.
Proposal No. 3-73:A new 300-11(c), entitled "”Cables Not Used as Means of Support”" has been added to clarify that cable wiring methods are not to be used as support for other materials and equipment. The present Code covers restrictions on the use of raceways for support of cables, other raceways, or other equipment, but does not specifically prohibit cable from being used in that fashion. It is not uncommon to find one cable installed and supported and others attached to it rather than having individual supports. This new subsection clearly prohibits the use of cable wiring methods as a means of support for other items.
Proposal No. 3-99:The exception that permitted liquidtight flexible metal conduit in lengths not exceeding six feet in spaces used for environmental air has been deleted. The reference to "”single lengths not exceeding 6 ft (1.83 m)”" could have been misinterpreted to permit multiple runs of liquidtight flexible metal conduit in "”other space used for environmental air”" which does not appear to be the intent of the exception.
Article 305 – Temporary Wiring
Article 305. Temporary Wiring.
Proposal No. 3-141:Article 305 has been re-located to Chapter 5 and will be renumbered accordingly. This article is more appropriate for Chapter 5 – Special Occupancies. CMP-3 will retain the responsibility of the relocated article.
Proposal No. 3-124:The provision that allows holiday decorative and similar lighting to be used for a period not longer than 90 days has been amended to provide for such use for more than 90 days where it is provided with arc-fault circuit-interrupter protection. It is extremely difficult to enforce the 90-day rule on this type of installation. Those installations may be de-energized for periods of time and/or redesigned and it is claimed that it constitutes a new 90 day period. The use of AFCIs with those circuits will provide another level of protection for those installations.
305-6(a) Exception No. 2. Proposal No. 3-138a:
The exception that permitted an assured equipment grounding conductor program to be used instead of using ground fault circuit interrupters for personnel in industrial establishments under certain conditions has been deleted. The record of performance of GFCIs in the protection of personnel justifies the use of those devices in the areas exempted by the exception.
Article 310 – Conductors for General Wiring
310-8(d). Locations Exposed to Direct Sunlight. Proposal 6-14a:
The text has been revised to clarify that conductors and cables are required to be "”listed for sunlight resistance”" or "”listed and marked for sunlight resistant”" where they are exposed to the direct rays of the sun.
310-15(b)(2)(a), Exception No. 5. Proposal 6-67:
A new exception has been added that will permit Type AC cable and MC cable without an overall outer jacket to be bundled without having to apply adjustment factors. Certain conditions must be met in order to apply the new exception.
Table 310-22.Ampacities of Two or Three Insulated Conductors, Rated 0 through 2000 Volts, Within an Overall Covering (Multiconductor Cable), in Raceway in Free Air Based on Ambient Air Temperature of 30EC (86EF). Proposal 6-6:
Table B-310-1 in Appendix B to Article 310 has been relocated as Table 310-21. This change locates the table within the requirements of the Code, enabling it to be used without engineering supervision
Article 318 – Cable Trays
318-3. Uses Permitted. Proposal No. 8-15:
A new sentence has been added to read, "”Cable tray installations shall be permitted to be used for feeder circuits, branch circuits, communications circuits, control circuits and signaling circuits.”" This additional wording provides a better description of permitted uses of cable trays.
318-3. Uses Permitted. Proposal No. 8-31:
A new sentence has been added to read, "”Cable trays and their associated fittings shall be identified for the intended use.”" This action provides an important focus on the consideration of cable trays as to their design and intended use so that they are installed and used properly.
318-3(e). Nonmetallic Cable Tray. Proposal No. 8-25a:
The wording in 318-3(e) has been revised by adding "”In addition to the uses permitted elsewhere in Article 318,”" at the beginning of the section. This change is to clarify that nonmetallic cable tray is permitted for purposes other than voltage isolation and corrosive areas.
318-6(c). Supports. Proposal No. 8-56:
A new second paragraph has been added to this section to read, "”Cable trays shall be supported at intervals in accordance with the installation instructions.”" Support requirements have not previously been specified in this section.
318-6(j). Raceway, Cables, and Boxes Supported from Cable Trays. Proposal No. 8-34:
The term "outlet” has been deleted from the title of 318-6(j) and the wording "”and conduit bodies”" added following the word "boxes”. The first sentence has been revised by deleting the word "outlet” and rewording it to read "”boxes and conduit bodies as covered in Section 370-1.”" The word "outlet” was deleted from the last sentence of the section and changed to "”boxes and conduit bodies…”" The reference to Article 370 was changed to Section 370-23. This action will permit other boxes than just outlet boxes to be supported beside or under the cable tray.
318-11(a). Multiconductor Cables. Proposal No. 8-52:
A reference to Section 310-15(a)(2) has been added to this section to provide guidance on the determination of allowable ampacity of multiconductor cables. Where cables are run out of the tray, consideration must be given to the rules for allowable ampacity for conductors in those locations.
318-11(b). Single Conductor Cables. Proposal No. 8-54:
A new first sentence has been added to read, "The allowable ampacity of single conductor cables, shall be as permitted by Section 310-15(a)(2).” This action is intended to address the condition where single conductor cables that leave the cable tray and are run in raceways or locations where the lower ampacity should apply. In those cases, the lower ampacity should be assigned to the cable to better assure that the entire length of the circuit will operate within safe limits.
Article 321 – Messenger Supported Wiring
321-4. Uses Not Permitted. Proposal No. 7-26:
The term "severe damage” was changed to "damage.” The distinction between "damage” and "severe damage” is not clearly defined. It is not desirable that this type of wiring be subject to damage, much less to whatever severe damage might be.
Article 330 – Mineral-Insulated, Metal-Sheathed Cable
330-80. Ampacity. Proposal No. 7-88:
A new Section 330-80 covering rules on the ampacity of Type MI cable has been added.
Article 333 – Armored Cable
333-7(b). Proposal No. 7-101:
This change permits up to 6′ of AC cable supplying lighting fixtures or other equipment in accessible ceilings to be unsupported. In the 1999 Code, this permission was limited to runs directly from an outlet box to the fixture or equipment.
Article 334 – Metal-Clad Cable
334-10(b). Unsupported Cables. Proposal 7-122:
This section was amended by deleting the wording "from an outlet.” The resulting wording is "…or where used in lengths not more than 1.8m (6 ft.) for connections within an accessible ceiling to lighting fixtures or equipment.”
334-22. Metallic Sheath. Proposal 7-126a:
A new second paragraph has been added to read, "A non-magnetic sheath or armor shall be used on single conductor Type MC.” The existing second paragraph is to become paragraph three.
Article 336 – Nonmetallic-Sheathed Cable: Types NM, NMC, and NMS
336-6(f). (To be 336-17). Grommets in Metal Studs. Proposal 7-158:
New text was added to make the language similar to that in 300-4(b)(1) for the protection of nonmetallic sheathed cable run through metal studs and to require that grommets used for cable protection in such studs be listed for that purpose. This text will become a new second paragraph 336-17 in the rewritten Article 336.
336-18, Exception No. 3. Proposal No. 7-169:
This exception was amended by deleting the wording "from an outlet” and the wording "shall be permitted without a support within 300 mm (12 in.) of termination.” This change to Article 336 permits up to 4 1/2′ of NM cable to be unsupported with accessible ceilings in the same manner as AC and MC.
Article 338 – Service-Entrance Cable: Types SE and USE
338-3(b). Grounded Conductor Not Insulated. Proposal No. 7-203:
This provision was revised to prohibit the use of bare grounded conductors, except as permitted by Section 250-140 for existing installations to ranges and clothes dryers. This eliminates the practice of using SE cable with a bare grounded conductor as the feeder to a second building.
338-4(a). Interior Installations. Proposal No. 7-205:
This change clarifies that type SE cable used for interior wiring must comply with the installation requirements of Parts A & B of Article 336, except Section 336-26 which deals with the ampacity of NM cable.
Article 340 – Power and Control Tray Cable: Type TC
340-8. Bends. Proposal No. 7-252a:
The wording in this section has been modified and expanded to read, "340-8. Bending Radius. Bends in Type TC cable shall be made so as not to damage the cable. For Type TC cable without metal shielding, the minimum bending radius shall be:
(1) Cables with an outside diameter of 1.000 inches or less- 4 times the overall diameter
(2) Cables with diameter of 1.001 to 2.000 inch – 5 times the overall diameter
(3) Cables with diameters of 2.001 inch and larger – 6 times the overall diameter
Type TC cables with metallic shielding shall have a minimum bending radius of not less than 12 times the cable overall diameter.”
This change in the minimum bending radius of Type TC cable reflects accepted industry standards.
Article 343 – Nonmetallic Underground Conduit with Conductors
343-1. Description. Proposal No. 8-77:
A provision has been added to this section to require the nonmetallic conduit used in this assembly to be listed. Conductors and cables used in this assembly are required by 343-14 to be listed.
Article 345 – Intermediate Metal Conduit
345-9(a). Threadless. Proposal No. 8-217:
A new sentence has been added to read, "Threadless couplings and connectors shall not be used on threaded conduit ends unless listed for the purpose.” This new provision will aid in the selection and use of threadless couplings on threaded ends of conduit as they will be required to be "listed for the purpose.”
345-12(b)(3). Proposal No. 8-222:
The wording "industrial machinery” has been replaced with "fixed equipment.” This clarifies that IMC can be dropped to fixed equipment where certain conditions are met and that it can be so used in more than just industrial locations.
Article 346 – Rigid Metal Conduit
346-1. Definition. Proposal No. 8-235:
The definition of rigid metal conduit has been revised to read, "Rigid Metal Conduit (RMC) is a threadable raceway of circular cross section designed for the physical protection and routing of conductors and cables and for use as an equipment grounding conductor when installed with its integral or associated coupling and appropriate fittings. RMC is generally made of steel (ferrous) with protective coatings or aluminum (nonferrous). Special use types are silicone bronze and stainless steel.”
346-17. Listing Requirements. Proposal No. 8-253:
A new section under construction specifications has been added to read, "Listing Requirements. Rigid Metal Conduit (RMC), factory elbows and couplings, and associated fittings shall be listed.”
The addition of this new provision is associated with the change made in the definition of RMC. Wording in the former definition in 346-1 that specified that RMC is a "…listed metal raceway…” was deleted. This new section not only specifies that the raceway be listed, but also other components used with it.
346-9(a). Threadless. Proposal No. 8-217:
A new sentence has been added to read, "Threadless couplings and connectors shall not be used on threaded conduit ends unless listed for the purpose.” This new provision will aid in the selection and use of threadless couplings on threaded ends of conduit as they will be required to be "listed for the purpose.”
346-10 and Table 346-10. Minimum Radius of Bends to Centerline of Conduit. Proposal No. 8-245:
The title of the table has been changed from "Radius of Conduit Bends” to "Minimum Radius of Bends to Centerline of Conduit.” The second sentence of the main paragraph has been changed to read, "The radius of the curve of any field bend to the centerline of the conduit shall not be less than indicated in Table 346-10.” This change shifts the focus of the radius from the inner edge of a field bend to the centerline of the conduit. It was pointed out that the measurement for conduit bending equipment for use in the field is based on the conduit centerline and not on the inner edge of the bend.
346-12(b)(3). Proposal No. 8-249:
The wording "stationary equipment or fixtures” has been replaced with "fixed equipment.” This clarifies that rigid metal conduit can be dropped to fixed equipment under certain conditions, but that it is not permitted for that use with stationary equipment or fixtures.
Article 347 – Rigid Nonmetallic Conduit
Table 347-9(A). Expansion Characteristics of PVC Rigid Nonmetallic Conduit Coefficient of Thermal Expansion… Proposal No. 8-267:
A new note has been added to this table to read, "Note: Add 30EF to the estimated temperature range when conduit is installed in direct sunlight to allow for radiant heating.” Rigid nonmetallic conduit exposed to direct sunlight is affected by the heating caused by that exposure and must be considered in the design for the expansion and contraction of this type of conduit.
Table 347-9(B). Proposal No. 8-269:
A new note has been added to this table to read, "Note: Add 30EF to the estimated temperature range when conduit is installed in direct sunlight to allow for radiant heating.” This new wording is the same as that added to Table 347-9(A).
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Posted By Philip Cox,
Friday, September 01, 2000
Updated: Tuesday, February 12, 2013
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Section 90-1(c) is often cited in arguments against submitted Code proposals. In many instances, it is the only defense against proposals, even though the proposals also contain recommended safety rules. One only has to look in previous editions of the NEC Report on Proposals and NEC Report on Comments to see how frequently this reference is used. Since the term "design specification” is not defined in the Code, it appears to take on different meanings, depending upon the situation in which it is used. Because of how it has often been used, it may be best to eliminate 90-1(c) from the Code.
Part of the problem regarding the issue of the Code not being intended as a design specification is the lack of information on the reasons this provision was originally adopted and exactly what was meant by that term "design specification.” The actual wording adopted for the 1937 NEC is "This Code is to be regarded neither as a design specification nor an instruction manual for untrained persons.” It is interesting to note that the same edition of the Code that added this new wording also included a new heading of Chapter 2 that read "Wiring Design and Protection.” That wording remained the title of Chapter 2 from the 1937 edition through the 1987 edition of the Code. A question is obvious. If those who developed the 1937 edition of the National Electrical Code did not intend for it to include design provisions, why did they adopt the title of the chapter with that word in it? By including the word "design” in Chapter 2 of the 1937 Code, it appears that the Code developers clearly understood that design provisions are an integral part of the Code. Most of the rules in Chapter 2 of that edition were clearly design in nature. Chapter 2 rules in the 1999 NEC still contain design requirements as well as many other chapters.
In order to get a better perspective of the original use of the "design specification” statement, it may be a good idea to look at the entire paragraph where that provision was located. That paragraph in the 1937 edition of the NEC stated "The requirements of this Code constitute a minimum standard. Compliance therewith and proper maintenance will result in an installation reasonably free from hazard but not necessarily efficient or convenient. This Code is to be regarded neither as a design specification nor an instruction manual for untrained persons. Good service and satisfactory results will often require larger sizes of wire, more branch circuits, and better types of equipment than the minimum which is here specified.” Did the Code developers mean that designers should not consider the Code as a design specification because it only included rules that were "minimum standards” as contrasted to the need for better performance? It may be that the statement is intended to ensure that designers would not be required to use minimum standards but would be authorized to exceed those minimum standards where better performance was needed. The sentence "Good service and satisfactory results will often require larger sizes of wire, more branch circuits, and better types of equipment than the minimum which is here specified” implies that in many cases the minimum wiring standards required by the Code specifications may not be adequate for how the system will be used. This conclusion may be clearer if the four interrelated key points of the paragraph are viewed together in sequence. They are:
1. Code rules were considered as a minimum standard.
2. The application of that minimum standard would be reasonably safe but not necessarily convenient or efficient.
3. The Code should not be regarded as a design specification.
4. To achieve good service and satisfactorily results, the minimum standards may need to be exceeded.
The way this paragraph is constructed, it appears that the emphasis is on the Code not being regarded as a design specification because it is a minimum standard for safety and that more stringent provisions may need to be applied or different levels of installation may be required that go beyond what the Code requires. The Code should not be used to limit designers’ flexibility of making installations better if they chose to do so.
One of those stated points no longer exists which may change the meaning of that paragraph. The statement in the 1937 NEC that read "The requirements of this Code constitute a minimum standard” was amended over time and finally deleted. The 1968 NEC is the last edition where that provision occurred and it read "This Code contains basic minimum provisions considered necessary for safety.”
It appears that many people interpret 90-1(c) as prohibiting design criteria from being in the Code. This section only states that "This Code is not intended as a design specification.” The purpose of the book is safety. Safety is the result of proper design. The wording in 90-1(a) states "The purpose of this Code is the practical safeguarding of persons and property from hazards arising from the use of electricity.” Rules in the Code should be based on this statement. Another item of importance is the first sentence in 90-1(b), which states "This Code contains provisions that are considered necessary for safety” Combining these two statements should be clear as to intent.
The Code is not a lot of things. Why is it necessary to state what it is not, especially when it identifies only two things it is not intended to be? The provision in 90-1(a) that reads "The purpose of this Code is the practical safeguarding of persons and property from hazards arising from the use of electricity” and the one in 90-1(b) that states "This Code contains provisions that are considered necessary for safety” are sufficient to identify what the Code is.
Take a look at the current NEC Report on Proposals and see how many times proposals have been rejected for this same cause. The deletion of 90-1(c) will make dealing with proposed Code changes more effective because they will have to be evaluated based on how they impact safety. Proposals that contain only design criteria that has nothing to do with safety can clearly and legitimately be rejected based on the purpose of the Code as stated in 90-1(a).
A proposal has been submitted to delete Section 90-1(c) and it was acted on by Code Making Panel No. 1 during the ROP meetings in January 2000. The vote on that proposal (Proposal No. 1-5, page 20 of the 2001 NEC ROP) was 9 to 3. It’s time for 90-1(c) to go.
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Updated: Tuesday, February 12, 2013
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IAEI members and associated organizations rose to the occasion to make possible the completion of a construction project at the IAEI headquarters building in Richardson, Texas.
Finishing the second floor area to create an educational facility has provided a more suitable environment in which to conduct meetings and perform training. In a previous editorial, those individuals and organizations who contributed to make this work possible were identified. I believe it is appropriate to give special recognition to one contributor who has not only risen to the challenge, but has achieved a level of support that could not have been anticipated.
Wisconsin Chapter officers and members have supported the International Office in the IAEI education program by joining with it to conduct seminars within the state of Wisconsin that benefited both the chapter and the IO. Recognizing that developing and producing quality educational material is very expensive for the IAEI International Office, the chapter board of directors chose to work directly with the IO in conducting seminars and to share the proceeds. The chapter had an option of purchasing the material from the IO and conducting those seminars on its own in order to realize a greater return, but chose not to do so. For several years the Wisconsin Chapter has conducted jointly sponsored seminars within the state, and that effort has not only been good for the chapter, but has also significantly helped the International Office. Another result of the seminar activity is the increase in chapter membership to the point that it now has the greatest number of members of any chapter in the IAEI. This model of performance is an example of what can be done when there is the determination to do so.
The Wisconsin Chapter was one of the top two contributors to the IAEI building fund for the education facility at the International Office. However, the chapter did not stop there. After learning that there were not enough funds to install audio-visual equipment in the new education facility, the chapter board of directors authorized funding for the purchase and installation of a high resolution, high lumen output LCD projector, ceiling recessed motorized screen, and supporting current technology rack mounted audio equipment. As a result of this action, quality equipment has been installed in the training room that makes it possible to present information through audio and video mediums from different sources. The system has versatility and can be used as part of the needed equipment when the IAEI is able to develop and implement a remote learning program. Those who have used the equipment and seen it in operation can attest to the value it adds to the education facility. This equipment truly enhances and supports the IAEI in delivering leading edge training information and material with the latest technology at the new training facility.
The IAEI is made stronger by the dedication and support of a multitude of people who never ask, What’s in it for me? but rather, What can I do to make the IAEI better? Every successful organization has this caliber of people who do their job well, and frequently, the extent of that work is unknown by most members.
The Wisconsin Chapter Board of Directors deserves recognition for its decision to support the IAEI education program and the leadership standards it has set. A special thanks goes to Joe Hertel, chapter secretary/treasurer, for his hard work and dedication in making sure all things came together to make the joint seminar program a success. Quality instruction and support for the latest series of seminars was made possible by dedicated IAEI professionals such as Ed Lawry, Tom Garvey, and Joe Hertel, Monte Ewing and others. This commitment and professionalism are two of the key elements of meeting IAEI’s objectives and are commendable. Thank you, officers and members of the Wisconsin chapter.
Posted By Leslie Stoch,
Friday, September 01, 2000
Updated: Tuesday, February 12, 2013
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Computer signals are made up of a combination of zeroes and ones, and they are often below five volts DC. Voltage noise and voltage transients can disrupt the correct flow of electronic data, even when it is as low as two to three volts. A zero may be one to 1-1/2 volts and a one can be 3-1/2 to five volts. Therefore, two or three-volt system noise can change a zero to a one or vice versa, causing inaccurate data and other electronic problems.
The most effective solution is to prevent noise from entering into the system. Electronic equipment must comply with industry shielding standards to keep noise from getting out as well as getting into the equipment. However, when sensitive electronics are connected, transient voltages and electrical noise can enter the equipment through the shielding. Electrical connections and data cabling allow in harmful signals, which may interfere with correct equipment operation.
Usually, good grounding and bonding methods and isolation of data processing equipment from sources of transient voltage interference and electrical noise are the easiest and best ways to correct transient voltages and electrical noise problems, or to prevent them from happening in the first place.
Isolated grounding is also called single point bonding (SPB). Using this method, all data processing equipment is bonded back to a common point. In this way, all equipment is subjected to the same transient voltage surges. When electronics are held to nearly similar voltages, there should be little or no voltage differences. When done correctly, sensitive electronic equipment interconnected with data cabling will have little or no current flow on the interconnecting cabling, reducing data problems. This method usually provides satisfactory results when sensitive electronic equipment is located throughout a facility. Problems may still result with higher frequency current flow on bonding conductors.
The Canadian Electrical Code, Rule 10-906(8) and (9) permits electronic equipment bonding to be separated from bonding for electrical equipment and raceways. Separate bonding conductors may be installed for receptacles and their outlet boxes. It permits insulated bonding conductors to pass through the supplying panelboards without bonding connections with common bonding to an upstream distribution centre. (This rule may be interpreted differently in some provinces). Single point bonding is the result of taking the bonding of all machines back to a common point upstream.
Where data processing equipment is located in a single area such as a computer room, there may be an even more effective method of bonding equipment. Single point bonding usually works very well when sensitive electronic equipment is distributed throughout a facility. However, when equipment is concentrated in one area, transient voltages and high frequency electrical noise can be even better controlled by using a zero signal reference grid (ZSRG). This method may not be practicable when the equipment is widely distributed.
A commercially available copper mesh grid or the computer room’s raised floor can be used as a zero signal reference grid for equipment bonding. Differences in potential among equipment are eliminated by bonding metallic equipment enclosures to the grid. A zero signal reference grid creates low impedance to high frequency signals and noise of all types, controlling or eliminating high frequency current flow on data cabling between the equipment.
A zero signal reference grid is most effective when data processing equipment is located in one area. Building steel and all adjacent metallic objects such as metal piping, raceways, located within two metres should be bonded to the grid. Sensitive electronic equipment should be bonded to the center of the grid by connections as short as possible with no sharp turns or bends. Heating, ventilating and air conditioning can be connected to the outermost grid conductors. Bonding conductors for sensitive equipment should be at least two metres from building steel or other potential lightning paths. All power supplies should be bonded to the grid. Keep all data and power cables close to the grid.
Transient voltage interference also comes from other systems connected to the same power supply, including transformers and lighting panelboards. Computer rooms usually have their own air conditioning systems. Separate power supplies to data processing and air conditioning systems or other electrical equipment helps prevent electrical interference from cycling equipment.
No matter the circumstances, one should always comply with all Canadian Electrical Code requirements for safe grounding and bonding. There should be no conflict between electrical safety and the methods applied to sensitive electronic equipment.
However,Rule 10-200 Current Over Grounding and Bonding Conductorsdoes give some alternatives when there is unwanted current flow in grounding and bonding. The rule says that: (1) Grounding and bonding should be arranged to avoid objectionable current flow; (2) This does not include temporary situations such as ground faults, etc.; (3) Objectionable current flow may be eliminated by (a) abandoning one or more grounds; (b) relocating grounds; (c) interrupting continuity between grounding conductors; (d) other effective action.
As in past articles, a local electrical inspection authority should be consulted for a more exact interpretation of any of the above.
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Posted By David Young,
Friday, September 01, 2000
Updated: Tuesday, February 12, 2013
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With the incentive of Internet access business, some telephone and cable TV companies are scrambling to add more communication cables to some already overcrowded utility poles. Each additional cable, whether installed as a separate attachment or installed by overlashing on an existing cable, adds mechanical load to the poles.
The National Electrical Safety Code® (NESC®) in Rule 252 requires the pole and foundation strength to be adequate to support the equipment and conductors attached to the pole under windy conditions. To insure that the proposed addition is not the "straw that breaks the camels back,” someone must calculate the transverse wind loading on the pole and all the attachments. If the calculated load multiplied by the appropriate safety factor exceeds the rated strength of the pole and foundation, the pole must be replaced with a larger pole set deeper in the ground. In my part of the country, the first indication we usually get that a pole/foundation is overloaded is leaning.
Because of the sandy soil, the foundation strength is usually less than the pole strength. From a safety standpoint, a leaning pole is better than a broken pole. However, a leaning pole can also be dangerous. When poles lean, the sag of some conductors increases. As the sag increases, conductors get closer to the ground. I’ve heard some people say, "So what if the communications cable get too low to the ground, the voltage isn’t high enough to hurt anyone.” That is true, but I have seen lots of accidents where poles broke off at the ground line and all conductors, including the high voltage ones, came crashing down to the ground because a tractor trailer truck was snagged by a low communications cable. For additional information on pole loading, please see my January / February 1998 article, "Strong Enough to be Safe.” Each additional cable must also comply with the clearance requirements of the NESC®.
In general, the NESC® minimum clearance requirements between communications conductors and electric supply conductors are set to protect the communications workers and equipment from dangers of the electric supply conductors. Prior to the 1987 edition of the NESC®, the electric supply conductors were always installed at the top or on the upper section of poles in the "supply space.” The communications conductors were installed below the electric supply conductors in the "communications space.”
There was a safety zone separating the two spaces in that the electric supply and communications conductors had to be separated by 40 inches at the pole and 30 inches at mid span. Depending on the sags of the two conductors, a clearance greater than 40 inches often had to be maintained at the pole in order to meet the 30-inch mid span requirement. The 30 inch minimum at mid span must be met with the upper conductor at its maximum sag conditions and the lower conductor at its final sag under the same ambient conditions as the upper conductor. The safety zone kept the communications workers more than an arm’s length from the electric supply conductors.
In 1987, it was recognized that an effectively grounded neutral (a 230 E1 conductor) was not as dangerous as triplex energized at 120/240 (a 230C3 conductor). For that reason, an exception was added to Rule 235 C2b(1)(a) to allow communications conductors to be as close as 30 inches at the pole and 12 inches at mid span to effectively grounded neutral conductors as long as they are electrically bonded together. As a result of numerous changes incorporated into the 1990, 1993 and 1997 editions of the NESC®, some communications conductors can now be installed outside the "communications space” as long as the appropriate clearances are met and the conductors are installed and maintained by personnel qualified to work in that area of the pole.
Fiber-optic type communications cables may be installed in the supply space. If the cable is entirely dielectric, or is entirely dielectric and supported on a messenger that is entirely dielectric or effectively grounded, the cable shall have the same clearance from communications facilities located in the communications space as required for an effectively grounded neutral (Rule 230F1a&b), i.e., 30 inches at the pole and 12 inches at mid span. The minimum clearance between the above "fiber-optic supply cable” and the electric supply conductors is specified by Rule 235C (Table 235-5) row 1b for communications cables located in supply space. The NESC® does not specify a minimum clearance between entirely dielectric "fiber-optic supply cables” or entirely dielectric "fiber-optic supply cables” supported on a messenger that is entirely dielectric and electric supply conductors (Table 235-5 Footnote 11).
The personnel who install and maintain communications conductors in the supply space must be qualified to work in proximity to the electric supply lines. This is both a NESC® and an OSHA requirement. As I discussed in my March/April 2000 article on "Working in Dangerous Proximity to Overhead High Voltage Lines,” workers who are not qualified to work on high voltage lines are not qualified to work in close proximity to high voltage lines and therefore must stay at least ten feet away from high voltage lines to comply with OSHA regulations. If the voltage is greater than 50,000 volts, the minimum distance is even greater.
If you have general questions about the NESC®, please call me at 302-454-4910 or e-mail me email@example.com.
National Electrical Safety Code® and NESC® are registered trademarks of the Institute of Electrical and Electronics Engineers.
Read more by David Young
Posted By Underwriters Laboratories,
Friday, September 01, 2000
Updated: Tuesday, February 12, 2013
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Question: Outlet box
How do I know if an outlet box can be used in a fire-rated assembly?
Metallic Outlet Boxes are Listed under the category Metallic Outlet Boxes (QCIT), in the UL Electrical Construction Equipment Directory. The Guide Information for QCIT specifies the installation requirements for use in fire-rated assemblies. Information about UL-Listed metallic outlet boxes, including the Guide Information, can also be found by accessing UL’s online product certification database atwww.ul.com.
Metallic outlet boxes for use in firerated wall assemblies include single and double gang metallic outlet and switch boxes equipped with Listed metallic or nonmetallic cover plates. These outlet boxes are intended for installation in bearing and non-load bearing wood or steel stud gypsum wallboard walls with fire resistance ratings of 2 hours or less. The metallic outlet or switch boxes must be securely fastened to the studs. Openings in the wallboard facing are to be cut so that the clearance between the box and wallboard does not exceed 1/8 inch. The surface area of individual metallic outlet or switch boxes must not exceed 16 square inches. In addition, the entire surface area of the boxes must not exceed 100 square inches per 100 square feet of wall surface.
A minimum horizontal distance of 24 inches must separate metallic boxes located on opposite sides of walls or partitions. This minimum horizontal spacing may be reduced through the use of UL Classified Wall Opening Protective Materials (QCSN), commonly known as "putty pads” or "insert pads.” Further, metallic boxes cannot be installed on opposite sides of walls or partitions in staggered stud constructions unless putty pads or insert pads are installed with the metallic boxes in accordance with the Classification requirements for the protective materials.
Wall Opening Protective Materials are found under the category QCSN in the UL Electrical Construction Equipment Directory, and also under the category CLIV in Volume 1 of the UL Fire Resistance Directory, or online at UL’s product certification database.
Listed metallic outlet boxes with metallic or nonmetallic cover plates may be used in fire-rated floor/ ceiling and roof/ceiling assemblies with ratings not exceeding two hours. Such assemblies must be equipped with gypsum wallboard ceilings.
The metallic outlet boxes shall be securely fastened to the joists and the opening of the wallboard facing must be cut so that the clearance between the box and the gypsum wallboard does not exceed 1/8 inch. The entire surface area of the boxes must not exceed 100 square inches per 100 square feet of ceiling surface.
Information regarding the use of outlet boxes in fire-rated floor/ceiling and roof/ceiling assemblies can be found on page 4 in Volume 1 of the 2000 edition of the UL Fire Resistance Directory. This information was recently published to be consistent with those requirements specified by the International Conference of Building Officials (ICBO), the Southern Building Code Conference International (SBCCI), and the Building Officials and Code Administrators (BOCA) model building codes.
Non-metallic outlet boxes, which can be used in fire-rated assemblies, are Classified under the category Outlet Boxes and Fittings Classified For Fire Resistance (QBWY), in the UL Electrical Construction Equipment Directory, and under CEYY in Volume 1 of the UL Fire Resistance Directory. This same information can also be found by accessing UL’s online product certification database atwww.ul.com.
This product category covers special purpose boxes for installation in floors, and nonmetallic outlet boxes for installation in ceilings, floor/ceiling or roof/ceiling assemblies, and in wall and partition assemblies in accordance with the National Electrical Code (NEC).
These boxes provide the required fire resistance when installed in specific fire-rated ceilings or walls described for each Classified company. These boxes have also been investigated and found to comply with UL’s electrical requirements. Any Listed metallic or nonmetallic cover plate is suitable for use with these nonmetallic boxes.
This category includes Classifications for nonmetallic outlet and switch boxes for use in fire-resistive rated wall or partition assemblies. The information provided for each Classification includes the model numbers for the Classified products, a description of the rated assemblies, the spacing limitations for the boxes and the installation details.
Nonmetallic boxes are not to be installed on opposite sides of walls or partitions in staggered stud constructions, unless Classified for use in such constructions or unless Wall Opening Protective Materials (QCSN or CLIV) are installed with the nonmetallic boxes.
The minimum horizontal spacing between boxes located on opposite sides of walls of partitions may be reduced through the use of Wall Opening Protective Materials. In both cases, the nonmetallic boxes shall be protected as described in the Classification requirements for the protective materials for use on the specific box.
Nonmetallic outlet boxes Classified for use in fire-resistive designs will be marked on the box with the UL Classification Marking along with the hourly rating (Class 1 or 2HR); and the intended use "F” for floor, "W” for wall; "C” for ceiling; and "F/C” for floor/ceiling. Such boxes are Classified for use in specific fire-resistive designs when installed in accordance with the details described for each Classified company. Always refer to the Classification requirements in the UL Electrical Construction Equipment Directory and Fire Resistance Directories, and the installation instructions for proper installation guidelines.
UL Question Corner
Posted By Clive Kimblin,
Saturday, July 01, 2000
Updated: Monday, February 11, 2013
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The objective of this paper is to increase inspector-awareness of arc-fault circuit interrupters. The significance of AFCIs is discussed in the introduction, and this is followed by a description of recent changes associated with the standard, with the National Electrical Code, and with the availability and application of the technology. Here there is a general discussion of AFCI availability, followed by a detailed description of the Cutler-Hammer line of residential miniature circuit breakers that incorporate branch/feeder AFCIs and a brief description of the technology involved. The operating experience has been excellent, relative to both fire protection and immunity from unwanted tripping. It is concluded that arc-fault circuit interrupters provide a significant fire-safety improvement for dwelling unit electrical distribution systems. They are the residential electrical safety technology of the future.
As explained in an earlier AFCI article in this magazine1, present residential overcurrent protective devices such as miniature circuit breakers (MCBs) are designed to protect circuit conductors by opening automatically before conductor damage is caused by excessive heating. For low current overloads, the breaker trips due to the heating of an internal bimetal. For high current overloads, the circuit breaker trips "instantaneously” due to internal magnetic forces. Because they prevent excessive or dangerous temperatures in the conductors or conductor insulation, these present-day circuit breakers reduce, to some extent, the incidence of residential fires associated with the electrical distribution system.
Data provided by CPSC2 show that about 10 percent of present-day residential fires are associated with the electrical distribution system. This percentage represents 41,600 fires and 370 civilian deaths. Further, these fires cause 1,430 civilian injuries and over $682.5 M in property losses. AFCIs have been specifically designed to supplement the protection afforded by overcurrent protective devices such as circuit breakers, and to make a significant reduction in these numbers.
An arc-fault circuit interrupter, as defined in the National Electrical Code3, is a device intended to provide protection from the effects of arc faults by recognizing characteristics unique to arcing and by functioning to de-energize the circuit when an arc fault is detected. In the embodiment discussed in this paper, the AFCI is integrated into the circuit breaker design, and the resulting integral circuit breaker (Listed to UL 489) and AFCI (Listed to UL 1699) combines conventional wire thermal-protection with the mitigation of arcing effects.
The previous paper1 was published in 1997. Since then, a UL standard has been published 4, AFCI issues have been addressed relative to the National Electrical Code 3, there have been advances in AFCI technology, and increases in both field experience and product availability. The objective of the present paper is to discuss these recent changes. In particular, the paper is intended to increase inspector awareness of this new fire-safety product.
Standards Situation (UL 1699)
The First Edition of UL 1699 was published in February 1999. This standard defines several types of AFCI’s:
• Branch/Feeder Arc-Fault Circuit Interrupter – A device intended to be installed at the origin of a branch circuit or feeder, such as at a panelboard. It is intended to provide protection of the branch-circuit wiring, feeder wiring, or both, against unwanted effects of arcing. This device also provides limited protection to branch circuit extension wiring. It may be a circuit-breaker device or a device in its own enclosure mounted at or near a panelboard.
• Outlet Circuit Arc-Fault Circuit Interrupter – A device intended to be installed at a branch-circuit outlet, such as at an outlet box. It is intended to provide protection of cord-sets and power-supply cords connected to it (when provided with receptacle outlets) against the unwanted effects of arcing. This device may provide feed-through protection of the cord-sets and power-supply cords connected to downstream receptacles.
• Combination Arc-Fault Circuit Interrupter – An AFCI which complies with the requirements for both branch feeder and outlet circuit AFCIs. It is intended to protect downstream branch-circuit wiring and cord-sets and power-supply cords.
The standard also deals with cord AFCIs and portable AFCIs.
There is a great deal of commonality in the test requirements for the three types of AFCIs defined above. Thus they must all recognize parallel (line to neutral) arcing faults in circuits with available short-circuit currents of 75A and above. At these current levels, the intermittent arcs, see Figure 1, associated with damaged or abused cables and wires may be insufficient to trip the circuit breaker either thermally or instantaneously. The main difference between the branch/feeder requirements and the outlet requirements is that the branch/feeder is tested for parallel faults in both the installed wire (Type NM-B) and in commonly used appliance cord (Type SPT-2). The outlet device, however, is tested solely with Type SPT-2 cord.
Figure 1. Typical current waveform observed when a carbon-steeled blade cuts through 16 AWG SPT-2 cord to create a parallel arc.
There is also some commonality in the test requirements for responding to series arcs associated with arcing at a break in a line or neutral conductor. For branch/feeder AFCIs the tests are performed at current levels of 5A and above in Type NM-B cable. The criterion is that cotton above the break point internal to the cable must not ignite. For outlet AFCIs the tests are performed with Type SPT-2 cord, and the time for arc extinction must be less than specified arc-test clearing times.
For the three types of AFCIs, the standard contains similar tests to check that the devices are immune to unwanted tripping. These tests include immunity to (a) transient inrush currents, (b) the waveforms associated with electronic devices, (c) the arcing waveforms associated with the burn out of incandescent lamps, and (d) the waveforms of "safe” arcs associated with the normal operation of electrical devices. Further, there are similar tests to check that the devices will not be masked by circuit conditions.
It is noted that the Canadian Standards Association has a Technical Information Leaflet5 with requirements for AFCIs that closely parallel the UL standard for branch/feeder AFCIs. A more comprehensive CSA standard is presently under development.
The Cutler-Hammer AFCI is of the branch/feeder type and consequently addresses series and parallel faults in the installed wiring; Zone 1 of Figure 2. This is the origin of about 35 percent (6,7) of residential fires associated with the electrical distribution system. In addition, the branch /feeder AFCI detects parallel faults in Zone 2, which represents the appliance cords and loads beyond the outlet, and the parallel faults in Zone 3. It also responds to all arcs to ground in Zones 1, 2 and 3.
Figure 2. Division of the residential wiring into four zones.
Code Situations (NEC, Vermont and CEC)
Arc-fault circuit interrupters were included, for the first time, in the 1999 edition of NEC 70 (The National Electrical Code). They are referenced in Section 210-12 of Article 210 which deals with branch circuits. There we find:
210-12(a) Definition – An arc-fault circuit interrupter is a device intended to provide protection from the effects of arc faults by recognizing characteristics unique to arcing and by functioning to de-energize the circuit when an arc fault is detected.
210-12(b) Dwelling Unit Bedrooms – All branch circuits that supply 125 volt, single phase, 15 and 20 ampere receptacle outlets installed in dwelling unit bedrooms shall be protected by an arc-fault circuit interrupter(s). This requirement shall become effective January 1, 2002.
It must be noted that, in order to protect a complete branch circuit, as required by the 1999 NEC, the device must be located in or adjacent to the load center where the branch-circuit overcurrent protective device is located.
During the proposal stage for the 2002 edition of the NEC, there were many additional proposals to extend the application of branch/feeder AFCIs and to include AFCIs at the outlets. At the moment, it seems probable that branch/feeder AFCI protection will be mandated for all bedroom outlets rather than solely for bedroom receptacle outlets. Other proposals to extend branch/feeder coverage to additional dwelling unit rooms and, for example, to hotel guestrooms and limited care facilities will continue to be discussed through the comment period. From proposals submitted for the 2002 NEC, it also seems likely that branch/feeder AFCI protection will be extended to the bedroom outlets of mobile homes and manufactured homes.
With respect to the state of Vermont, branch/feeder AFCIs will be mandated for all 120V circuits serving receptacle outlets in dwelling unit living areas and bedrooms. The effective date is January 1, 2001. The application of branch/feeder AFCIs to dwelling unit bedroom circuits is also under active discussion relative to the Canadian Electrical Code, Part 1.
At the present time, branch/feeder AFCIs have been announced by four of the major US manufacturers of residential miniature circuit breakers (MCBs). These products are effective8. With respect to Cutler-Hammer, there is a complete line of UL Listed single-pole, 15A and 20A MCBs that contain the additional function of AFCI, see Figure 3. There are also single pole MCBs that contain both UL Listed AFCI and ground-fault circuit interrupter (GFCI) functions. Further, the AFCI function has been incorporated into two-pole Listed circuit breakers that are also classified for mitigating the effects of arcs, and which provide protection in shared neutral circuits.
Figure 3. Photographs of the line of MCBs with AFCI
It should be noted, as indicated in Figure 4, that these MCBs, with AFCI function, are completely interchangeable with conventional Cutler-Hammer MCBs. Their connection in the loadcenter is identical to present-day MCBs with GFCI function, namely with a wire connection to ground, and their cost is also similar to an MCB with integrated ground-fault protection.
Figure 4. Diagram showing the interchangeability between MCBs, with branch/feeder AFCI capability, and conventional MCBs
Operation of the Cutler-Hammer AFCI
A block diagram of a single pole AFCI appears in Figure 5. The load current sensor output is fed to an arc signature filter whose output is responsive to the magnitude of the arcing currents. Normal "non-arc” related current components are filtered out. The signal is then amplified and fed to a logic block that distinguishes between dangerous arcing events and normal circuit transients, including the waveforms associated with incandescent-lamp-burnout. In the event of a dangerous arc, the logic block provides an output that will trip the breaker. This logic block has a second input from a ground-current-sensor amplifier. If this logic input exceeds a preset 30 milliamp trip threshold, a trip signal is provided. This arc-fault circuit interrupter (listed to UL 1699) is also available in combination with ground-fault circuit protection (listed to UL 943). In this embodiment, the ground-fault sensor is set at five milliamps for personnel protection and a grounded neutral sensor is included. Individual test buttons are provided for both the AFCI and GFCI functions. It is noted that the value of a residential circuit breaker including both AFCI and GFCI technologies was recognized by UL in the Recommendations Section of their 1995 Report to CPSC9.
Figure 5. A block diagram of a single pole AFCI
A block diagram of a two-pole Listed circuit breaker also classified for mitigating the effects of arcs appears in Figure 6. The design basically consists of two single pole AFCI designs as described in Figure 5 with a common logic trip output signal. The response to arcs to ground is set at 30 milliamps. There are individual AFCI test circuits for each of the poles.
Figure 6. A block diagram of a two-pole Listed circuit breaker also classified for mitigating the effects of arcs
More than 10,000 Cutler-Hammer MCBs with AFCI protection are presently operating in the field. The total operating time is more than 150 million hours. During that period there have been no reports of unwanted tripping issues. More importantly, there have been cases of reported fire prevention. For example, there have been cases of the detection of arc tracking at the base of two-wire lighting fixtures. These fixtures were typically located in the dining room, and arc tracking near the base of the bulb had led to a parallel arc. Other examples include the initiation of an arcing fault in a TV set, supplied by a two-wire cord, due to water dripping from a hanging plant, and the detection of arcing within junction boxes. Additional discussion of effective branch/feeder AFCI protection appears in a recent NFPA paper 10.
At the present time, branch/feeder AFCIs will provide protection to 120-volt dwelling unit bedroom circuits. These circuits are indeed associated with a large number of residential electrical distribution system fires11. However, other residential locations also have a high incidence of electrical fires11, and it is therefore to be expected that branch/feeder AFCIs will find application for many additional residential circuits.
The AFCI function can also be expected to extend to the higher voltages (e.g. 240 volt, 277 volt and 480 volt) associated with commercial and industrial electrical distribution systems.
It is also noted that the aerospace industry12 is interested in AFCI technology relative to the protection of onboard electrical wiring.
Arc-fault circuit interrupters represent the application of new technology to an old problem; namely, the need to improve fire safety in residential electrical distribution systems. Standards have been developed for the requirements of these devices, and branch/feeder AFCIs are available from many manufacturers. National, Canadian and state electrical code issues are being addressed, and the field experience with branch/feeder AFCIs has been excellent. AFCIs are the technology of the future with a fundamental focus on safety.
1. Arc-Fault Circuit Interrupters: New Technology for Increased Safety, J. C. Engel, R. J. Clarey, and T. M. Doring, IAEI News, October 1997.
2. 1996 Fire Loss Estimates, US Consumer Product Safety Commission Report, 1998
3. National Electrical Code, NFPA 70, 1999.
4. Arc-Fault Circuit Interrupters, UL 1699 Standard for Safety, First Edition, February 28, 1999
5. CSA Publication of Technical Information Letter (TIL) No. M-02, Interim Requirements for Arc-Fault Circuit Interrupters, September 30, 1999.
6. What Causes Wiring Fires in Residences?, L. Smith and D. McCoskrie, Fire Journal, pp. 19-24, January/February 1990.
7. The U.S. Home Product Report, 1992-1996, (Appliances and Equipment), K. Rohr, NFPA Fire Analysis and Research Division, February 1999
8. Preventing Home Fires: AFCIs, Consumer Product Safety Review, Volume 4, #1, Summer 1999
9. "Technology for Detecting and Monitoring Conditions that Could Cause Electrical Wiring System Fires”, Report Prepared by Underwriters Laboratories (UL Project Number NC233, 94ME78760) for the Consumer Product Safety Commission (Contract Number CPSC-C-94-1112), September 1995
10. AFCIs Target Residential Electrical Fires, G. D. Gregory, NFPA Journal, pp. 69-71, March/April 2000.
11. Residential Electrical Distribution Fires, L. Smith and D. McCoskrie, US Consumer Product Safety Commission Report, December 1987.
12. Arc-Fault Circuit Interrupters, J. McCormick, M. Walz, J. Engel, P. Thiesen and E. Hetzmannseder, Proceedings of the Conference on Advances in Aviation Safety, Paper 2000-1-2121, Daytona Beach, Florida, April 2000.
Read more by Clive Kimblin