Posted By Thomas A. Domitrovich,
Sunday, July 01, 2012
Updated: Friday, September 07, 2012
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One could argue that due to the technologies on the market, arc flash and other electrical life-threatening events should be rare occasions. But electrical safety is more than just applying a product or sitting through a training class; it’s a regiment of training and procedures implemented in combination with technology that saves lives. There’s no silver bullet for safety. Just like respect, and I don’t mean the respect we should give electricity, safety is earned. Simply attending class and punching your ticket, so to speak, is not enough. An earlier edition of this column gave you a view into arc-flash events from a survivor perspective. One of those individuals attended training classes and was well aware of the dangers of his profession but that was not enough for his safety. You have to implement what you learn. In short, you have to take action. You not only can impact your organization and the projects you work on, you can also impact the codes and standards that set the stage for safety. This article will emphasize your need to work towards safety and to implement what you have learned in your jobs and your lives; it will also help you see how you can get more involved and make an even better and safer electrical industry.
Photo 1. Attending training class is just your first step. You must apply what you learn to realize the value of your education and to keep those skills alive.
Code Development and Adoption
Getting beyond the importance of having codes and standards, we all must do our part and help with their development and adoption. It is important to remember that codes and standards are not developed by the individuals who volunteer to sit on panels; codes and standards are developed by you or people like you that are advocates of safety. Do not lose sight of this fact. It is your input, your proposals, your continued due diligence for safety that creates these documents that we use on a daily basis. The volunteers that sit on code making panels review your input, comment and ultimately either adopt or reject it. What they adopt may be your exact words or some derivative of them. You can’t simply sit back and expect others to improve these documents that you use. Get involved. The NFPA provides you numerous opportunities to propose and comment during a code development cycle on the documents they administer. TheNECjust happens to be one of those documents that you and I use on a daily basis and it just so happens that it is in the middle of a new cycle.NEC2014 is currently being worked on by the 19 code panels that are responsible for all of the chapters of this important document. Your proposals are forming this new document. The Report on Proposals (ROP) document is available at the following URL:www.nfpa.org/70. You can download these documents for free and also download the comment forms to submit comments. NEC 2014 is a baseline for safety and, once released, will be reviewed by states and local jurisdictions for adoption.
Table 1: NEC 2011 Adoption Status with Effective Dates
Don’t be mistaken and think that you only have input to the NEC. You can impact other codes and standards as well. In addition to the numerous NFPA documents, these include but are not limited to the International Code Council (ICC) and Underwriters Laboratories (UL) codes and standards. The codes and standards that you work with on a daily basis have a process for their continued development and a cycle for their revision. Most of these are ANSI documents that follow rules for public input. Your ideas can make these documents even better than they are today.
So let’s take a quick look at the success of NEC 2011 as it moves across the United States. NEC 2011 state-by-state adoption is a very good tale to tell. Table 1 is a list of states who have adoptedNEC2011, including their effective dates. The adoption process for most of these states has been quite uneventful. Some states that have never had a statewide code are in the process of changing that status. Alabama, for example, not shown on the list below as they have most recently adopted NEC 2008 through the adoption of the 2009 International Residential Code (IRC), will now be on a statewide code. It would have been nice to have Alabama adopt NEC 2011 by reference rather than use the IRC version of the document, but it was just not in the cards for that state.
The amendments in these various states are relatively low; especially if you compare them to NEC 2008 adoption success. They range anywhere from removal of GFCI requirements for garage doors and sump pumps (Ohio) to keeping AFCIs on bedroom circuits only (Oregon). AFCI adoption for states on NEC 2011 has been quite successful, with Oregon as the only state that has adoptedNEC2011 keeping AFCIs on bedroom circuits only. That has historically been a practice in that state and old habits are, I guess, just hard to break. The difference between NEC 2011 and NEC 2008 from a financial impact perspective, as reported in an earlier version of this column, is minimal at best. Most of the changes occurred for those areas of the structure that are not basic requirements of a building code. The bigger issue for states these days is not theNECbut rather the energy codes that they must adopt.
The state-by-state adoption of the NEC and other building codes, unfortunately, can be a very political process. A good example of this is currently being played out in the state of Michigan. State-by-state adoption issues have historically been focused on amendments to the proposed code. We’ve typically seen a focus on GFCI, AFCI, selective coordination, tamper-resistant receptacles and other similar sections of the code when it comes to amendments. But just when you thought the controversy would be minimal and adoption of the NEC would go off without a hitch because these areas of the code have little to no change in them, you have a state like Michigan throw yet another kink into your vision by working to extend the adoption process from a 3-year cycle to a 6-year cycle. Pennsylvania is considering the same. Those who try hard to amend the NEC when it is adopted have basically run out of issues to argue. When you have no arguments against a bill at hand, your next strategic move is to implement delay tactics. Many organizations are working together to educate legislatures across the country on why this is not a good idea, but it takes people like you and me to voice our concerns when our state or local jurisdiction decides to make amendments to bare minimum codes. Get involved with your local code adoption process and support timely adoption of the NEC without amendment.
Training and Resources
Training is a fundamental part of safety. It’s not only something you can do on your own but is usually more effective with periodic interaction with other formal programs. If you think that training classes are only good to attend because you need CEU credits for your license, you are mistaken. Seize every opportunity. These training events are not only places where you get your immediate questions answered but also where you build your network of professionals that you can leverage when you have questions later.
Photo 2. IAEI offers many educational opportunities. Attend your local meetings and don’t forget about the Section meetings that occur every year.
Education and networking opportunities are not far away. IAEI provides many opportunities through section meetings and state/local chapter meetings. These events are great opportunities to get updated on latest code changes and code questions, electrical topics like grounding and residential wiring and many other opportunities to network with key individuals.
Trade magazines like IAEI News also provide good information for reference. I personally keep all of my IAEI magazines as well as other trade magazines to which I subscribe filed away not too far from my desk. Another method I use for some periodicals is to snip key articles and file them by topic.
Nothing can replace your network of professionals when it comes to finding answers to your questions. The best place to create that network is at IAEI meetings. Those individuals who attend these meetings love to talk about electrical safety and more often than not are those same individuals that volunteer their time on code panels for the NEC and other key documents we use on a daily basis. Sharing knowledge is the bare minimum we can do to be advocates of safety.
Tools of Safety
There are many products on the market today that can make a difference when it comes to saving life and property from the worst that electricity has to offer. Not all of these tools are products. The following are just a few examples:
Safety Plan — Yes, your safety plan is an important product that you manufacture yourself for your own organization. Just about every presentation and training seminar I personally deliver has time set aside to poll the audience and talk about their safety plan. I’ve had various individuals tell me that they don’t have a safety plan because they do residential work. My response to that is a safety plan is important no matter what market or structure you work in. Put the basics of your plan in your truck to remind yourself on every job. Working de-energized should be at the top of your list.
Personal Protective Equipment (PPE) — PPE is not limited to those big heavy suits that protect you from arc flash. PPE also includes eye and ear protection. We can sometimes forget about these most basic items that protect the most sensitive areas of our bodies. You may not be in front of energized equipment and may in fact be working de-energized but you will still need your eye and ear protection. Every day we experience sound in our environment, such as the sounds from television and radio, household appliances, and traffic. Normally, we hear these sounds at safe levels that do not affect our hearing. However, when we are exposed to harmful noise — sounds that are too loud or loud sounds that last a long time — sensitive structures in our inner ear can be damaged, causing noise-induced hearing loss (NIHL). These sensitive structures, called hair cells, are small sensory cells that convert sound energy into electrical signals that travel to the brain. Once damaged, our hair cells cannot grow back. So how loud is too loud?
110 Decibels: Regular exposure of more than 1 minute risks permanent hearing loss.
100 Decibels: No more than 15 minutes of unprotected exposure recommended.
85 Decibels: Prolonged exposure to any noise at or above 85 decibels can cause gradual hearing loss.
To put this in perspective, the following gives an idea of decibels vs. sound source:
Decibels Sound Source
120 Ambulance siren
110 Chain saw, rock concert
105 Personal stereo system at maximum level
100 Wood shop, snowmobile
90 Power mower
85 Heavy city traffic
60 Normal conversation
40 Refrigerator humming
30 Whispering voice
0 Threshold of normal hearing
Your eyes are yet another sensitive area that must be protected. In many cases, you may not be actually performing the work but still need eye protection. The most basic PPE is not limited to eyes and ears. Don’t forget about your feet and hands and even your knees. Wearing the correct PPE while you work is important no matter what you are doing. Make sure your PPE is up-to-date and on your person — not in the truck.
Ground-Fault Circuit Interrupters (GFCI) — This technology has been around for quite some time and has saved many lives. Job sites that have temporary power have requirements in the code that specifically call out GFCI protection. These requirements are there for a reason. But you don’t have to stop at the bare minimum code requirements. GFCI can provide protection on more than just those circuits in a home that have been called out in theNEC. Going above and beyond is not a code violation.
Arc-Fault Circuit Interrupters (AFCI) — These products too have been around for quite some time and have prevented fires and found many wiring mistakes / damaged conductors and a good number of damaged appliances. This is an unforgiving technology that can detect wiring problems. You do not have to only include these on the circuits that have been identified in the NEC. They can be applied on any 15-A and 20-A circuit and will find the wiring problems that can be detrimental to the occupants of the structure. It’s that electrical inspector that you leave in the load center that keeps an eye out for problems.
Arc Reduction Technologies — Earlier in this article I said, "One could argue that due to the technologies on the market today, arc flash and similar events should be rare occasions.” In addition to GFCI and AFCI solutions on the market, there are many solutions now available that work to reduce the energy on a system when a fault occurs. The NEC now has Section 240.87 that specifically calls out these technologies, or approved equivalent, for certain installations. You can always go above and beyond when it comes to implementing these technologies. Zone selective interlocking (ZSI) and arc flash reduction switches have been used for many years in industrial power systems for certain markets. Now the code is beginning to recognize the value of these technologies and requiring them under certain conditions.
Arc-Resistant Electrical Equipment — Those big grey boxes we live and work with on a daily basis are also now being designed to channel arc-flash energy up and out as opposed to directly in front of the gear where we typically stand and walk. A little thought during the design process can make a big difference down the road when it comes to safety. A little education and awareness go a long way.
Handheld safety equipment — We can’t forget those tools that make it possible to detect problems and also indicate what is energized, keeping us out of harm’s way. These handheld devices are great tools but just as with any product, if you do not apply them correctly, they can be dangerous. Reading instructions and being diligent about how they are used is critical. Misapplied meters and other equipment, handheld or not, may result in disaster. Remember to read the instructions and apply all of your products correctly. These products can be a great asset to your organization. From Infrared cameras to meters, there is a broad range of solutions available that can help detect wiring problems and system issues. They are worth the investment.
The above is just a sample of the various types of solutions available on the market. Simply having these products on your project or in your truck does not mean they will achieve the expected goal. They must be utilized appropriately and included in your safety plans and procedures to be effective.
Procedures in Practice
As noted earlier, electrical safety is more than just applying a product or sitting through a training class; it’s a regimen of training and procedures implemented in combination with technology that saves lives. We can be very knowledgeable and have all of the best safety solutions employed in our facility. We may even have the best that PPE has to offer hanging in a closet or in a bag that is readily accessible. If you don’t make the first move and flex all of this horse power, that investment was all for naught. You must get moving and work to make a safe environment for youself and those around you. Be an advocate of safety by doing the bare minimum — share your knowledge with those around you. Spreading your knowledge just may save a life or keep someone out of the hospital.
As always, keep safety at the top of your list and ensure you and those around you live to see another day. If you have any tips or ideas you would like to share, please feel free to send them to me at firstname.lastname@example.org. I look forward to your input to these articles and guidance for future articles
Read more by Thomas A. Domitrovich
Safety in Our States
Posted By Leslie Stoch,
Sunday, July 01, 2012
Updated: Friday, September 07, 2012
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You probably noticed a number of important changes from 2009 to the 2012 edition of the Canadian Electrical Code. Section 4 – Conductors has taken the lion’s share of the changes. Rule 4-004 has received a good deal of attention. This article discusses and compares some of the similarities and differences between the 2012 version of Rule 4-004 – Ampacity of Wires and Cables and its 2009 predecessor.
Beginning with underground conductors, the 2009 Canadian Electrical Code rule for calculating the allowable ampacities for underground conductors, direct buried or in raceways went right to the point (minimum conductor size #1/0 AWG and allowable ampacities calculated in accordance with the IEEE 835 standard). A "see Appendix B” note led us to an interpretation of the standard — the diagrams and ampacity tables in Appendices B and D. The 2009 rule offered no clues as to what to do about wire sizes smaller than #1/0 AWG or conductor arrangements different from the Appendix B diagrams.
The new Rule 4-004 addresses these earlier limitationsas follows:
Rule 4-004 refers us directly to the conductor configuration diagrams in Appendix B and the allowable ampacity tables in Appendix D;
It tells us what to do if we decide to arrange underground conductors in configurations different from those shown in Diagrams B1 to B4 — allowable ampacities are to be based on the IEEE 835 standard calculation method; and
It tells us what to do for conductor sizes smaller that #1/0 AWG — use Tables 2 or 4 or the IEEE 835 standard calculation method.
Rule 4-004 of the 2009 CEC specified allowable ampacities for single-conductor cables in free air.For cable spacing at least the diameter of the larger adjacent cable, we could use Tables 1 or 3 to determine allowable ampacities for copper and aluminum conductors. For up to 4 single-conductor cables in contact with each other, Tables 1 and 3 ampacities needed to be corrected in accordance with Table 5B. With more than 4 cables in contact, the rule led us to the lower allowable ampacities of Tables 2 and 4.
For single-conductor cables in free air, Rule 4-004 of the 2012 CEC is identical to the 2009 version for spacing apart of at least the diameter of the larger adjacent cable.
But here is where the similarity between the 2012 and the 2009 CEC ends:
For single conductors between 25% and 100% of the larger adjacent cable diameter, we must now use Tables 1 or 3 with correction factors from Table 5D.
For up to 4 single-conductor cables spaced less than 25% of the larger adjacent cable diameter, we must now use Tables 2 or 4 with correction factors from Table 5B.
For more than 4 single-conductor cables spaced less than 25% of the larger adjacent cable diameter we must now use Tables 2 or 4 with correction factors from Table 5C for total number of conductors. (Table 5C correction factors do not apply to runs shorter than 600 mm).
I would be remiss in not mentioning a very important change —new Rule 4-006. This rule requires that when equipment (such as circuit-breakers) is marked for maximum termination temperatures, allowable ampacities must be based on the corresponding conductor temperature columns in Tables 1 to 4. Remember, this applies to both ends of every conductor or cable. If the equipment is unmarked, the 90° C ampacity column applies.
As with earlier articles, you should always check with electrical inspection authority in each jurisdiction for a more precise interpretation of any of the above.
Read more by Leslie Stoch
Posted By Underwriters Laboratories,
Sunday, July 01, 2012
Updated: Friday, September 07, 2012
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Is the XO bonding jumper strap provided in certified (Listed) dry type core and coil transformers used in typical commercial installations adequately sized?Answer
Dry type coil and core transformers typically found in commercial installations are certified by UL under the product category Power and General-Purpose, Transformers Dry Type (XQNX), located on page 452 of the 2012 UL White Book and also on UL’s Online Certification Directory at www.ul.com/database and enter XQNX at the category code search field.
Dry type transformers can have two bonding jumpers installed. One bonding jumper is for grounding the transformer steel core to the enclosure where the core is electrically isolated by the sound dampening pads that are typically made of rubber. This bonding jumper is covered by the requirements in UL 1561, the Standard for Safety for Dry Type General Purpose and Power Transformers 600 Volts or less, and must remain in place.
The other bonding jumper, that may or may not be supplied by the manufacturer, is installed between the XO terminal and the enclosure. This second bonding jumper is identified from the National Electrical Code as the "system bonding jumper.” UL 1561 does not contain requirements to install or size the system bond jumper between the XO terminal and the enclosure or equipment grounding bus. The evaluation of the transformer for Listing, therefore, does not include an evaluation of the size or adequacy for the system bonding jumper; it is really an item optionally provided by some manufacturers. For the same reason, if this bonding jumper were removed because the system grounding and bonding was done elsewhere as allowed by NEC 250.30, the UL Listing of the transformer is not affected. Since the size of the system bonding jumper is based on field-installed feeder conductors for the derived system, it would be difficult to determine the correct size of the system bonding jumper that is to be installed at the factory. If the inspector determines the supplied system bonding jumper does not meet the Code minimum based on the actual installed feeder conductors, then they can require it to be replaced with a suitable system bonding jumper meeting all the requirements from the NEC.
About Underwriters Laboratories: Underwriters Laboratories® (UL) is an independent product safety certification organization that has been testing products and writing Standards for Safety for over a century. UL evaluates more than 19,000 types of products, components, materials and systems annually with 20 billion UL Marks appearing on 66,000 manufacturers products each year. UL's worldwide family of companies and network of service providers includes 68 laboratory, testing and certification facilities serving customers in 102 countries. UL is also the only National Certification Body (NCB) for PV in North America and an OSHA-accredited Nationally Recognized Testing Laboratory (NRTL). For more information, visit www.UL.com/newsroom.
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UL Question Corner
Posted By David Clements,
Sunday, July 01, 2012
Updated: Friday, September 07, 2012
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Never underestimate the value of networking face-to-face! Despite the various ways of communicating — phones, email, instant messaging, social media, faxing, snail mail, telegram, or carrier pigeons — the "time spent interacting in the presence of or in the same location as another or others”1 is still the most productive and valuable. In fact, it is becoming priceless — and rare.
The American Sign Language Association uses "Four Hugs a Day,” a teaching song that demonstrates not only how to sign but also the importance of personal interaction. Inevitably, personal interaction leads to a sense of community, which, in turn, leads to cohesiveness and a common purpose.
IAEI offers face-to-face time to each member and his/her family through the annual section meetings and local chapter and division meetings. From the amount of handshaking and backslapping at these meetings, it is obvious we’ve developed good relationships and a sense of mutual respect and trust, all which are the foundation of community.
As a community, IAEI discusses, first and foremost, the code — face-to-face. Sometimes we get passionate and forceful; sometimes we disagree; sometimes we agree to disagree on code proposals or interpretations of a specific rule. Face-to-face provides the opportunity to debate and discuss inspection challenges, presentations, new ideas and new products.
As a community, IAEI decides which code proposals we will support, based always on whether this change will enhance and increase safety.
As a community, IAEI challenges the merits and safety of new products — representatives, engineers, inspectors, city officials, authors, presenters and whoever is involved face these challenges. Each person is expected to make his or her points clear and concise and in alignment with the code.
As a community, IAEI celebrates the successes and achievements of individual members as well as chapters, sections or divisions; the passage of code proposals; the enrollment of new members.
As a community, IAEI mourns the misfortune, loss or death of any member. We care about those who are ill or facing challenges and we reach out to them.
As a community, IAEI makes the Great North American Educational Adventure. Not all of us can make each event, but we attend as often and as many as we can because we meet up with our friends and their families. We laugh, joke, study, eat, and learn from each other. The program for this year’s educational adventure includes a number of code training sessions and trade shows.
Here are the times and venues for this adventure:
Southwestern Section, DoubleTree Mission Valley, San Diego, CA
Northwestern Section, Hilton Garden Inn, Missoula, Montana
Western Section, Holiday Inn City Center, Fort Smith, Arkansas
Canadian Section, Sheraton Parkway, Toronto, Ontario
Eastern Section, Providence Marriott, Providence, Rhode Island
Southern Section, Astor Crowne Plaza, New Orleans, Louisiana
As a community, IAEI is a group of people interacting with one another remotely and face-to-face and with intense interest in electrical safety. The community affects each other’s abundance, distribution, and career development in the sense that we pass along job openings, recommendations, and share our knowledge of the electrical industry. Whether our units are small and local, state-wide, or regional or global — together we are cohesive and have a common purpose. Together we are stronger than we are individually, especially when we maximize the ability to meet face-to-face.
If you are planning to attend one of the section meetings, or a local chapter or division meeting you will not be disappointed.
If you are not able to attend due to lack of financial support from your employer, approach your supervisor or manager and explain the benefits of being or becoming a member of IAEI and the importance of staying abreast of code and standards and the importance of networking with your peers face-to face.
1 American Heritage Dictionary
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Posted By Stephen J. Vidal,
Tuesday, May 01, 2012
Updated: Friday, September 07, 2012
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Electric machines are very useful and efficient devices which operate through a variety of control circuits. These control circuits are made up ofinputdevices that sense a condition or situation andoutputdevices that make adjustments to change the situation. The symbolic language for this process is calledladder logic. Many of the diagrams used resemble the steps of a ladder; hence, the addition of the word "ladder” into the title.
It is important also to discuss the termlogic. In the study of digital electronics, devices are used that operate in either anonstate or anoffstate. A specialized branch of mathematics called Boolean algebra analyzes this relationship with two numbers — a zero , which represents theoffstate; or a one , which represents theonstate. These two numbers comprise the binary number system.
The most common logic functions areand,orandnot. Think of a single-pole light switch in your home that controls a 100W light bulb. The switch can either beoff oron. Now imagine we place two single-pole switches in series to control the same 100W light bulb. In this condition, switch 1andswitch 2 both have to beon to light the 100W bulb; this is an example of anandoperation (see figure 1). Logic relates to ladder diagrams because input functions in series constituteandoperations, while input functions in parallel constituteoroperations.
Two Types of Ladder Diagrams
Two-wire control circuits
Figure 1. "And” Circuit
You will encounter two types of ladder diagrams: the two-wire control circuit and the three-wire control circuit. The two-wire control circuit is shown in figure 2. This circuit is used to start a motor for some industrial process. The components in a two-wire control circuit are a maintained contact switching device (S1), a relay coil (M1), and the thermal overload relay contact (OL). The sequence of operations is fairly simple when S1is closed, the coil of magnetic motor starter M1 is energized and the motor starts, provided the running overload current is within the value of the overload relay OL. To stop the motor, S1 is simply opened.
Three-wire control circuits
The three-wire control circuit is shown in figure 3. Again this circuit is used to start a motor for some industrial process. The components in a three-wire control circuit are a momentary push-button (STOP), a momentary push-button (START), a normally open relay contact (M1), a relay coil (M1), and the thermal overload relay contact (OL). The sequence of operations here is a little more complex. When the start button is pressed, the coil of magnetic motor starter M1 is energized and the motor starts, provided the running overload current is within the values of the overload relay OL. However, there is one very important difference: a normally open contact of magnetic motor starter M1seals around the start button to latch the circuit. To stop the motor, the STOP button is pressed which, in
Figure 2. Two-wire control circuit
turn, breaks the latch and de-energizes the coil of magnetic motor starter M1; the motor stops.
If you review the traditional ladder diagram of a standard three-wire control circuit as shown in figure 3, you will notice several components: a normally closed stop button, a normally open start button, a normally open relay sealing contact, a relay coil, and a normally closed thermal overload relay contact. This figure also resembles a step ladder with each rung of the ladder representing a specific input or output function, and it demonstrates where the term ladder diagram comes from. Figure 4 provides additional common symbols used in ladder diagrams and motor control circuits.
Momentary contact and maintained contact devices
What components make up a ladder diagram? There are several types of input devices and output devices. For the purpose of this article, we will focus on conventional electromechanical devices. Input devices can first be classified as momentary contact and maintained contact devices. Momentary contact devices are spring-loaded and are classified as normally open and normally closed devices. The designation "normally” refers to the state of the device
Figure 3. Three-wire control circuit
in its resting position when no external stimulus is acting upon it. The contact arrangement of switching devices can also be classified as SPST, SPDT, DPST, DPDT, 3PDT, etc. The first two letters refer to the number of "poles,” and the last two letters refer to the number of "throws.” For example, SPST refers to a single-pole, single-throw contact. 3PDT refers to a three-pole, double-throw contact. A fractional manual motor starter useful for single-phase motors, 1HP and lower, can either be a SPST for 120-V applications, or DPST for 240-V applications. A green start button is an example of a normally open momentary push-button, while a red stop button is an example of a normally closed momentary push-button.
Maintained contact devices are not spring-loaded; they remain in either an on state or an off state. They can also be classified as normally open and normally closed. An emergency stop is an example of a maintained contact device. Temperature sensing devices commonly used are thermostats and thermocouples. A thermostat relies on the thermal expansion/contraction of a bimetal, while a thermocouple relies on a principle known as the Seebeck effect. Two dissimilar metal wires are joined together in a loop with one end being the hot junction and one end being the cold junction. A difference of potential is generated in the loop in response to temperature change. Each of these devices sense temperature change and then presents a contact closure for use in a control circuit.
Motion Sensing Devices
Photoelectric controls and proximity controls
Figure 4. Common symbols [N.O. means normally open; N.C. means normally closed
Motion sensing devices commonly used are photoelectric controls and proximity controls. Early versions of photoelectric controls had an incandescent lamp transmitter and a cadmium sulfide photocell receiver. Modern versions of the photoelectric control have pulsed infrared transmitters and solid state photo-detector receivers. They work on the principle of beam interruption to sense motion and then present a contact closure to the control circuit. Proximity controls sense motion when an object passes by the sensing target on the device. They can detect metallic as well as non-metallic objects. They operate on the principles of magnetism and capacitance, and then present a contact closure to the control circuit. Limit switches are the most versatile device in terms of motion detection. They are available in a variety of operator mechanisms and contact arrangements. They work on the principle of physical contact between an object and the operator mechanism to present a contact closure to the control circuit.
Liquid level sensing devices
The most commonly used liquid level sensing device is the float switch, which operates on the principle of buoyancy. The float is suspended in a liquid bath and as levels of the liquid rise and fall, the float moves. This movement of the float presents a contact closure to the control circuit.
Pressure sensing devices
The most commonly used pressure sensing device is the pressure switch. The diaphragm, or bellows, in a pressure switch monitors the change in pressure and presents a contact closure to the control circuit.
Other types of input devices include the foot switch, the selector switch, or even the contact of a control relay or a timing relay. These are all mechanical devices that present a contact closure to the control circuit.
Outputs of the control circuit can be relay coils, pilot indicating lights, audible devices, etc. To use the generic term relay coil, we need further classification into magnetic motor starter, contactor, and relay. A magnetic motor starter is a relay with a coil and contacts as well as running overload protection by means of thermal overload relays. Bi-metallic thermal overload relays are units made of a heater coil that heats a coil of wire to a specified temperature based on overload current, and a bimetal unit that expands/contracts and operates a contact. Solder pot thermal overload relays use a similar heater coil and a eutectic solder that melts under overload conditions and correspondingly turns a ratchet wheel to operate a contact. The contact arrangement on the thermal overload relay is normally closed but will open under excessive current conditions and de-energize the coil of the magnetic motor starter and consequently disconnect the motor. Contactors are also relays that switch high-load currents but do not provide running overload protection via the thermal overload replay. Control relays are usually designed to switch small control circuit currents. Common types of timing relays are on-delay (delay on operate), off-delay (delay on release), interval delay, and repeat cycle delay. Time delay relays are used for timing in control circuit.
Pilot indicating lights
Pilot indicating lights are used to provide visual indication of a function or verify that a certain operation is either on or off.
Audible sounding devices
Audible sounding devices are used to indicate trouble with a process or alert the user to a particular situation.
Standard motor control circuits will be covered in the next issue.
Read more by Stephen J. Vidal
Posted By Alan Manche,
Tuesday, May 01, 2012
Updated: Friday, September 07, 2012
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GFCI and AFCI protection have both become fundamental safety devices in electrical systems. Understanding the basics of ground-fault protection for people, and arc-fault protection for 15- and 20-amp branch circuits in dwelling units can ensure that your installations are code-compliant and help you in troubleshooting a circuit. As of the time this article was written (late January 2012), the NFPA code-making panels have met to consider proposals for the 2014 NEC. While the 2014 NEC code development process still has a long way to go, a number of GFCI and AFCI proposals are in the works, once again revising where these devices get installed. We’ll discuss a few of them along with some product standard and technology changes.
AFCIs and GFCIs
What is a GFCI?
Do you feel like you have a full understanding of how ground-fault protection works? If not don’t worry about it; we hope this discussion with help you and your co-workers further understand the basics.
There are two different types of ground-fault protection required in the NEC, ground-fault protection for people and ground-fault protection of equipment. Both work in a similar manner, but the protection levels are quite different. We will focus on ground-fault protection for people, provided by a device called a ground-fault circuit interrupter (GFCI). Article 100 in theNECincludes a definition for GFCIs.
Ground-Fault Circuit Interrupter (GFCI). A device intended for the protection of personnel that functions to de-energize a circuit or portion thereof within an established period of time when a current to ground exceeds the values established for a Class A device.
Informational Note: Class A ground-fault circuit interrupters trip when the current to ground is 6 mA or higher and do not trip when the current to ground is less than 4 mA. For further information, see UL 943,Standard for Ground-Fault Circuit Interrupters.
The Informational Note describes two very important performance criteria for GFCIs, namely that they will not trip if the leakage current to ground is less than 4 mA and will definitely trip if the leakage current is 6 mA or higher. The 4 mA level is necessary to prevent unwanted tripping due to the natural leakage in appliances, tools and other connected loads, and in the wiring itself.
Figure 1. Effect of current on the human body
The 6 mA must-trip level is important due to the amount of electrical current a human body can withstand without serious physical harm. Although physical effects will vary from person to person depending on whether they are male or female, an adult or a child, in general people will be able to sense electrical currents as low as 1 mA. At about 10 mA they may not be able to "let go” if they come into contact with an energized conductor. Current flow as low as 30 mA may cause breathing difficulty and heart fibrillation in small children. Fibrillation is almost certain for currents in the 100–200 mA range and current over 4 A will cause heart paralysis and tissue burning (see figure 1).
The ANSI/UL 943 standard defines the requirements for GFCI performance in the U.S. and is a tri-national standard, meaning that it is harmonized with CSA C22.2 No. 144.1 in Canada and ANCE NMX-J-520 in Mexico.
How does a GFCI work?
Figure 2. If there is an imbalance, an electronic circuit will determine if the leakage is enough to necessitate an interruption of the current flow.
The operation of a GFCI is really quite simple. It compares the amount of current going out to the load with the amount of current coming back from the load. In a single-phase device both the hot and neutral conductors pass through a current transformer (CT). This is why the load neutral conductor must be connected to a GFCI circuit breaker. If the current going out to the load equals the current coming back, there is no leakage to ground and the output from the CT is zero, but if there is an imbalance, an electronic circuit will determine if the leakage is enough to necessitate an interruption of the current flow, see figure 2.
In a two-pole GFCI circuit breaker, if single-phase (120 V) loads are to be served, both of the hot conductors, and the neutral conductor, must pass through the CT; therefore, the load neutral conductor must be connected to the circuit breaker, see figure 3. Three-pole (three-phase) GFCI circuit breakers are only suitable for protection of a three-phase load; hence, only the three-phase conductors must pass through the CT.
The white "pigtail” wire on a GFCI circuit breaker serves two functions. It completes the connection to the panel neutral bar for the neutral load conductor and also completes the power supply circuit for the electronics. This means that even in installations where there is no load neutral conductor, the white pigtail wire must still be connected to the neutral bar in the load center or panelboard in order for the electronic ground-fault protection circuit to function. (Note: Some manufacturers may offer circuit-breaker GFCIs with a plug-on neutral connection rather than a pigtail.)
What different types of GFCIs are available?
GFCIs are available in two different forms, circuit breakers and receptacles. Circuit-breaker GFCIs are dual listed as UL 489 circuit breakers and UL 943 ground-fault circuit interrupters, see figure 4. Receptacle-type GFCIs are listed as UL 943 ground-fault circuit-interrupter receptacles. The receptacle portion of the device must meet the requirements of UL 498.
In circuit breakers, the main circuit breaker contact(s) perform the interruption task when a ground-fault of sufficient magnitude is detected. In receptacles, a set of contacts performs the interruption task.
The terminals of circuit-breaker GFCIs are marked "Line” and "Load,” so they are not suitable for backfeeding. The terminals of receptacle-type GFCIs are similarly marked to insure that when properly wired the GFCI will also protect downstream receptacles should the installation so require.
Where are GFCIs required?
Figure 3. In a two-pole GFCI circuit breaker, if single-phase (120 V) loads are to be served, both of the hot conductors, and the neutral conductor, must pass through the CT; therefore, the load neutral conductor must be connected to the circuit breaker.
TheNECand Canadian Electrical Code (CEC) require GFCI protection in a large number of applications. The fundamental GFCI requirements are found in Section 210.8 of the NEC, although many other sections require them as well. Suffice it to say wherever electricity may be supplied in a potentially wet location, such as kitchen countertops, near sinks or outdoors, there is a good chance that GFCI protection is required there. A key revision to the 2011 NEC introduced a requirement for GFCIs to be readily accessible for monthly testing. Make sure you keep those receptacles located so as to not create an issue with this new requirement. If you are using a GFCI circuit breaker installed in a panelboard, this revised language is a nonissue.
What’s on the horizon for GFCI Protection?
A proposal to add an auto-monitoring function to the UL 943 GFCI standard is currently being considered by the industry. If adopted, this proposal will require that a GFCI be able to test itself, with the exception of the contact opening function. If a failure is detected, the GFCI will open the contacts (if possible) and deny power to the load. This new function was requested by the US Consumer Products Safety Commission because too few people regularly test their GFCIs. But even with auto-monitoring, users will still need to periodically test their GFCIs to insure that the contact opening function continues to work properly.
What is an AFCI?
Article 100 in theNECincludes a definition for AFCIs.
Arc-Fault Circuit Interrupter (AFCI).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.
The ANSI/UL 1699 standard defines the requirements for AFCI performance in the U.S. While CSA does certify AFCIs, a CSA standard has yet to be approved.
How does an AFCI work?
The operation of an AFCI is far more complex than that of a GFCI. Note that the NEC Article 100 definition states that an AFCI recognizes characteristics that are unique to arcing. Unfortunately, there is no single characteristic that is unique to hazardous arcs, so an AFCI must look for multiple characteristics, usually occurring at the same time or within a short period of time, to determine whether or not to interrupt the current flow. This usually involves monitoring both the current and the voltage.
Figure 4. Circuit-breaker GFCI certification label
We are using the term hazardous arcs in order to distinguish from operational arcs that naturally occur in an electrical system such as when switches or motors are operated. This greatly complicates the protection task. Not only must the AFCI detect whether arcing is taking place, but it must determine whether it is an operational arc or hazardous arc.
Because of this, the UL 1699 standard is unlike the GFCI or overcurrent protection device standards. In those standards, the device must operate when a specified level of current has been exceeded for a specified period of time. The UL 1699 standard, on the other hand, requires that various types and lengths of cable be intentionally damaged so as to create a hazardous arcing condition that must either be interrupted in a specified period of time or before a fire indicator is ignited.
Further, the UL 1699 standard requires that unwanted tripping tests be conducted using various loads that naturally arc or generate waveforms that might be mistaken for hazardous arcing. Masking tests are also conducted to insure that loads do not interfere with the ability of the AFCI to detect hazardous arcs.
Like in a GFCI, both the hot and neutral load conductors must be connected to the AFCI, and as is also the case with GFCIs, the white "pigtail” wire completes the connection to the panel neutral bar for the load neutral conductor which is terminated on the circuit breaker and also completes the power supply circuit for the electronics. (Note: Some manufacturers may offer AFCIs with a plug-on neutral connection rather than a pigtail.)
What different types of AFCIs are available?
AFCI circuit breakers of 15- and 20-amps are available for installation in load centers and panelboards. They are dual listed as UL 489 circuit breakers and UL 1699 arc-fault circuit interrupters (see figure 5).
Single-pole AFCI circuit breakers are available for 120-V branch circuit protection. Two-pole versions are also available from some manufacturers for the protection of 240 V loads (with common trip) or 120 V shared neutral loads (without common trip).
UL also lists AFCIs and leakage-current detector-interrupters (LCDIs) as a part of cord sets for use on appliances such as window air conditioners to meet the requirement in NEC 440.65.
While UL has a standard (UL 1699A) for outlet branch-circuit arc-fault circuit interrupters (OBC AFCI) and has listed one or two products, as of this writing none are commercially available.
In circuit breakers, the main circuit breaker contact(s) perform the interruption task when an arc fault is detected. In OBC AFCIs or cord-type AFCIs and LCDIs, a set of contacts performs the interruption task.
The terminals of circuit-breaker AFCIs are marked "Line” and "Load,” so they are not suitable for backfeeding.
When AFCI circuit breakers were first introduced, only the branch/feeder type was available. A branch/feeder type AFCI provides protection for parallel arc-faults that occur line-to-line or line-to-ground. The 2005NECrequired the use of combination-type AFCIs beginning January 1, 2008. Subsequent editions of theNEChave required the use of only combination-type AFCIs.
Figure 5. Circuit-breaker AFCI certification label
The UL 1699 standard requires that a combination-type AFCI provide protection against both parallel and series arc-faults. Series arc-faults are those that might occur due a break in a line or neutral conductor.
The certification label on the circuit breaker will identify if it is a branch/feeder or combination-type AFCI (see figure 3). The color of the test button is also a way to identify if a circuit breaker is a GFCI, branch/feeder or combination AFCI; however, as the standards do not define test button colors, each manufacturer has their own scheme for GFCI and AFCI test button colors.
Speaking of test buttons, it is important that users periodically test their AFCIs by pushing the test button.
Where are AFCIs required?
Section 210.12(A) of the 2011 NEC requires arc-fault protection of all 15- and 20-A 120-V branch circuits in dwelling unit "family rooms, dining rooms, living rooms, parlors, libraries, dens, bedrooms, sunrooms, recreation rooms, closets, hallways, or similar rooms or areas.” Section 550.25 requires AFCI protection in the same rooms in modular and mobile homes. An OBC AFCI may be installed at the first outlet in a branch circuit if a steel wiring method is used to protect the home run or if the home run is imbedded in at least 2 inches of concrete (see 210.12 Exceptions 1 and 2). Exception 3 allows AFCI protection to be omitted if a fire alarm circuit is encased in a steel wiring method.
Section 210.12(B) requires AFCI protection where a 15- or 20-A 120-V branch circuit "is modified, replaced, or extended.”
AFCIs and the 2014 NEC
A couple of key revisions to the NEC-2014 AFCI requirements are being considered by Code-Making Panel 2. The expansion of arc-fault protection to 15- and 20-A branch circuits serving kitchens and laundry rooms has been proposed. It is common to find AFCI protection on at least one of the kitchen branch circuits today when the dining area, which is required to have AFCI protection, is also serving the kitchen.
There is also consideration being given to permit a branch-circuit breaker to provide parallel arc-fault protection for a home run feeding an OBC AFCI installed in the first outlet without being enclosed in a steel wiring means or in concrete. A number of key conditions are essential for this protection system to work based on a recently issued UL research report:
- The instantaneous trip level of the circuit breaker must not exceed 300 A.
- The home run must have a limitation on its maximum length.
- The first outlet box must be identified.
The most significant challenge for this proposal may land in the lap of the contractor and electrical inspector. Will you be able to effectively meet and enforce these parameters? How will you know which circuit breaker has the appropriate instantaneous trip level? (Today, the instantaneous trip level of a branch-circuit breaker is not controlled by a standard and, therefore, can range well above the maximum 300-A level. Indeed, some applications require a higher trip level in order for the loads to operate.) The Code Panel rejected the fundamental requirement for a circuit breaker used in this application to have a Listed marking indicating suitability. How will you know the home run length? How will you know that the OBC AFCI was installed in the first outlet? You may want to review this proposal and provide your thoughts through an NEC comment to the Code Panel.
GFCIs and AFCIs continue to provide the protection envisioned by the electrical industry when they were first introduced in the 1960s and 1990s respectively. Here are a few items to consider as we wrap up this discussion:
- Having a fundamental understanding of the basic functionality of GFCIs and AFCIs will ensure you are not only properly protecting people and the circuit but it also gives you the foundation to figure out why the GFCI or AFCI opened.
- When a GFCI or AFCI opens, always ask the question, "What was it protecting against?” Dismissing the opening as a nuisance trip for either a GFCI or AFCI fundamentally means you just closed the breaker or receptacle back into the same potential hazard if you didn’t address it.
- The requirements for GFCIs and AFCIs continue to be revised in the NEC. Make sure you are keeping up-to-date on the latest requirements.
- Stay engaged with the future development of GFCI and AFCI requirements in the NEC. Provide your input by submitting a comment to NFPA.
Read more by Alan Manche
Read more by Ed Larsen
Posted By Daniel R. Neeser,
Tuesday, May 01, 2012
Updated: Friday, September 07, 2012
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Overcurrent protective device interrupting rating (IR) and equipment short-circuit current rating (SCCR) are key considerations for the safety of commercial and industrial electrical systems. If inadequate overcurrent protective device IR or equipment SCCR is present, a serious potential safety hazard exists. As a result, the NEC and Occupational Safety and Health Administration (OSHA) have added requirements that draw attention to this issue that are resulting in changes to equipment design and specification.
This article focuses on equipment SCCR marking requirements with an emphasis on proper equipment installation requirements according to the NEC.
Unlike the product standards, theNECidentifies the overcurrent protective device IR and equipment SCCR marking requirements. More importantly, it also addresses the installation requirements for proper application of overcurrent protective device IR and equipment SCCR.
It’s important to understand the difference between the IR of overcurrent protective devices (such as fuses and circuit breakers) versus equipment SCCR (such as devices, appliances, apparatus and machinery).
Figure 1. The NEC requires marking of the interrupting rating on a current-limiting fuse per NEC 240.60(C)
IR is defined in the 2011 NEC Article 100 as "the highest current at rated voltage that a device is identified to interrupt under standard test conditions.” Therefore, IR simply is the highest current that an overcurrent protective device is rated to safely clear. According to NEC 110.9, the IR of the overcurrent protective device must be no less than the current available at the equipment’s line terminals.
The NEC requires the marking of the interrupting rating of fuses per NEC 240.60(C) and circuit breakers per 240.83(C) [see figure 1].
Short-Circuit Current Rating
The 2011 NEC Article 100 defines SCCR as "the prospective symmetrical fault current at a nominal voltage to which an apparatus or system is able to be connected without sustaining damage exceeding defined acceptance criteria.” Therefore, SCCR simply is the highest current that equipment is rated to safely withstand.
NEC 110.10 requires that the equipment SCCR "be selected and coordinated to permit the circuit protective devices to clear a fault, and to do so without extensive damage to the electrical equipment of the circuit.” Notice thatNEC110.10 indicates that a specific circuit protective device (fuse or circuit breaker) might be required to provide proper protection.
NEC 110.10 also says the protective device must protect the equipment fromextensivedamage. Therefore, damage can occur to equipment after a fault, but it can’t result in a shock or fire hazard outside of the enclosure.
Figure 2. This is an example of marked SCCR on an industrial control panel nameplate
The acceptable damage criteria for SCCR testing and evaluation in product standards is another topic for an in-depth discussion not covered in this article. Typically, acceptable damage might render the assembly or a component in the assembly as useless. The main objective of the product standard SCCR acceptable damage level, however, is to prevent a shock hazard or a fire outside the enclosure.
If a violation of NEC 110.9 or 110.10 occurs, and the fault current exceeds the IR of the overcurrent protective device or the SCCR of equipment, a catastrophic and violent failure of the overcurrent protective device or equipment can occur.
OSHA 1910.303(b)(4) and 1910.303(b)(5) contain similar language to NEC 110.9 and NEC 110.10, so both newandexisting overcurrent protective devices and equipment must have adequate IR and SCCR.
SCCR Marking Requirements
In the past, equipment such as HVAC, industrial control panels and industrial machinery was considered "utilization equipment” and was overlooked regarding proper SCCR and the ability to withstand fault currents. To correct this issue, the 2005NECadded new requirements for marking equipment SCCR to correlate with the product standards.
The 2005 NEC added SCCR marking requirements for motor controllers in NEC 430.8; HVAC equipment in 440.4(B); industrial control panels in 409.110; and industrial machinery in 670.3(A).
In addition, 409.110(3) and 670.3(A) also contained fine print notes (changed to information notes in the 2011 NEC) that UL 508A, Supplement SB was an approved method for determining equipment SCCR for industrial control panels and industrial machinery (see figure 2).
Figure 3. This demonstrates the available fault current and proper application of equipment SCCR.
In the 2008 NEC, Section 409.110 was changed to add an exception that SCCR wasn’t required to be marked on industrial control panels that contain only control components to correlate with the requirements of UL 508A. Therefore, if the industrial control panel contains only control circuit components (components that don’t supply loads such as motors, lighting, heating, appliance or receptacles), then an SCCR marking is not required.
SCCR Installation Requirements
Changes to theNECSCCR equipment-marking requirements were designed to help draw attention to the withstand capabilities of equipment and, combined with the existing requirements of NEC 110.10, prevent installation of underrated equipment.
In the 2011 NEC, additional requirements were added for industrial control panels and industrial machinery that complement and reinforce the requirements ofNEC110.10. Specifically, a new section, 409.22, was added to require that an industrial control panel not be installed where the available fault current exceeds its SCCR as marked in accordance with 409.110. Similar wording was added for industrial machinery per a new section in NEC 670.5.
The added text in 409.22 and 670.5 draws attention to the fact that industrial control panels and industrial machinery must be designed and manufactured with an SCCR that is adequate for the installation.
Therefore, if equipment such as an industrial control panel is being installed in an industrial facility, the system designer must communicate the maximum fault current to the equipment supplier so the supplier can design the equipment with SCCR no less than the fault current where installed in accordance with NEC 409.22 and 110.10.
The process would be similar for HVAC equipment in commercial and industrial building facilities, although not specifically stated other than the requirements of NEC 440.4(B) and 110.10.
Another requirement highlighting proper equipment ratings was added in the 2011 NEC. A new section, 110.24, requires commercial and industrial service equipment to be marked with the maximum available fault current, and to be remarked if modifications of the electrical installation resulted in an increase of the maximum available fault current. The intent of this change was to assure compliance withNEC110.9 and 110.10 for service equipment (see figure 3).
The 2011 NEC changes discussed in this article have helped increase awareness of available fault current and proper equipment SCCR by system designers, installers and AHJs. In many jurisdictions, AHJs have responded to these changes by requiring the available fault current to be documented at equipment and by red-tagging equipment if found with an inadequate SCCR. Because of this, system designers and installers are identifying the fault current at equipment and communicating these requirements to equipment manufacturers.
System designers and installers also are realizing that once the equipment is installed with inadequate SCCR, there are no easy fixes. The only options are equipment modification and recertification or reduction of fault current (through use of additional conductors, isolation transformers or reactors).
Additionally, equipment might be relocated within a facility or to another facility that has increased fault currents, causing additional concerns for flexibility of application for equipment. This can result in costly delays and increased equipment cost.
As a result, equipment suppliers now are being requested to provide equipment with high SCCR. This, in turn, brings equipment design changes to meet the requirements for high fault-current installations.
For more information on industrial control panels and SCCR, see Section 4 of the Cooper Bussmann "Selecting Protective Devices” handbook. Download it free by clicking on the "register for free download links” and submitting the required information athttp://bit.ly/SPDhandbook.
Read more by Daniel R. Nesser
Posted By Don Offerdahl,
Tuesday, May 01, 2012
Updated: Friday, September 07, 2012
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The NEC Code-Making Panels met to act on NEC proposals in January 2012. The results can be found at:http://www.nfpa.org/AboutTheCodes/AboutTheCodes.asp?docnum=70&tab=nextedition.
This is the time to bring comments to the electrical industry by using your IAEI membership. Under the NFPA rules, anyone can submit a comment under his or her own name. IAEI encourages that and does not restrict, in any way, anyone wishing to make such submissions.
If the individual also wishes to have IAEI endorsement, in addition to submitting the comment himself or herself, then that person must work through the local chapter or division to start the process. IAEI encourages the chapters and divisions to work cooperatively to develop good code comments. These groups can discuss and refine the proposed language and be sure the technical substantiation is complete and that it solidly supports what is being proposed. Comments may start with a voice of one, but they get stronger and gain power with support and input of many. When accepted by the chapter, it will be submitted to the section as a chapter-accepted IAEI comment. When chapters and divisions have their meetings, this is when the membership of the chapter or division needs to act on any comments to move forward.
The next step is at the section level. Based on policies set by each section, chapters and divisions can submit their proposals to the section for consideration. The Section Codes and Standards Committee will complete a review and then make a recommendation to the membership at the section meetings in September and October of this year. The section needs to receive these comments in time to meet two deadlines.
The first deadline is so the Section Codes and Standards Committee will have the opportunity to review, meet, discuss, and provide a recommendation to the membership to vote on. Most of the sections have set dates in the August timeframe, so check with your section secretary to find out what the deadline is.
The second deadline is for the IAEI International Codes and Standards Committee. This committee needs all comments that might become IAEI-endorsed to be at the IAEI International Office on or before September 1, 2012. This date is set so the Codes and Standards Committee can review the comments and then take final action once all the sections have completed their actions.
It is important to understand that the role of the Codes and Standards Committee is to review what was submitted and to make recommendations, based on the merit of the submission, to accept to go forward or to reject, and not to write comments.
The international president, in accordance with the international bylaws, has appointed the members to the International Codes and Standards Committee. This committee will receive comments from the sections only. Comments cannot be submitted by individuals to the international level. If the section acts favorably to forward comments submitted to them for consideration as an IAEI organizational submission, then the committee will review the comments in their entirety and if found acceptable will have the CEO/executive director submit the IAEI-endorsed comments to NFPA.
IAEI has two representatives on each code panel and they will be instructed to be advocates for IAEI proposals and comments as submitted by the international CEO/executive director. Having a voice at the panel ensures that the proposal gets considered and discussed fully by the panel.
Now is the time to get involved with your local chapter or division.Being involved with the code change process is one of the benefits of being a member of IAEI and getting involved now can make your job easier and more productive in the future.
Most section comments due. Verify what your section deadline is.
September 1, 2012 5 p.m. CST
Comments to be IAEI-endorsed due at International Office
October 17, 2012
NFPA closing date for NEC comments
Read more by Don Offerdahl
Posted By Steve Douglas,
Tuesday, May 01, 2012
Updated: Friday, September 07, 2012
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Section 4 of the Canadian Electrical Code covering conductors has seen ten revised subrules, eleven new subrules and one new rule for the 2012 CE Code. The most significant change to Section 4 is the addition of new Rule 4-006. Similar to Article 110.14 of the National Electrical Code, Rule 4-006 limits the maximum allowable ampacity of a conductor to be based on the lesser of the temperature rating of the conductor or the maximum termination temperature marked on equipment. By default, equipment without a termination temperature marking is considered 90°C. As an example, an installation with three current-carrying 500 kcm RW90 copper conductors in a raceway terminating on a breaker with a maximum termination temperature of 75⁰C would have an allowable ampacity based on the 75⁰C column in Table 2, resulting in an allowable ampacity of 380 amp. The reason for this change was to recognise the size of conductor used during temperature testing of the equipment, and to harmonise with the requirements in the National Electrical Code. In conjunction with this change, Rules 6-310 and 12-108 have been modified to allow splicing of conductors to satisfy Rule 4-006. The next question is, what is the minimum length of conductor required to satisfy the requirements of Rule 4-006? The answer can be found in CSA Standards C22.2 No 4 Enclosed and Dead-Front Switches, C22.2 No 29 Panelboards and Enclosed Panelboards, and C22.2 No 244 Switchboards. All three of these standards have the same requirement of 1.2 m.
Subrules (1) and (2) of Rule 4-004 have been revised, making the underground allowable ampacities for conductors of 1/0 or larger in the Appendix D tables mandatory for installations matching the configuration drawings in Appendix B. For installations not matching the configurations in Appendix B, the requirements for IEEE 835 calculations have been assigned to Item (e).
New Subrules (9) and (10) have been added to Rule 4-004 to address allowable ampacities of single conductor cable with cable spacing less than 100%. Where more than four single-conductor cables in free air, with spacing less than 25%, are installed, new Subrule (12) directs code users to Tables 2 or 4, and to the correction factors in Table 5C for the allowable ampacity.
New Table 66 for the maximum allowable ampacity of bare or covered conductors in free air has been added; a new Subrule (21) to Rule 4-004 states the allowable ampacity shall be as specified in Table 66.
Rules 4-010, 4-012, 4-020, and 4-040 have been reworded as part of a series of proposals to direct code users to Section 4 when determining the specific conditions of use of conductors and cables found in Tables 11 and 19 with respect to moisture, corrosive action, temperature, degree of enclosure, and exposure to mechanical injury.
The induced voltages and currents in metal armour or sheath of single conductor cable requirements from Rule 12-3022 from the 2009 CE Code, along with the note from Appendix B, have been moved to Rule 4-010. The intent of this move was to have all these similar requirements in the same rule of the code.
Additional limitations to the allowable reductions for the size of neutral conductors found in Item (2)(a) of Rule 4-024 now include the portion of the load that consists of non-linear loads supplied from a 3-phase, 4-wire system such as dimmers, computers, microprocessors, and most other electronic loads.
The last change in Section 4 adds requirements for diesel locomotive (DLO) cable. DLO cable is an extra flexible cable that can have conductor sizes not seen in the CE Code until now, such as 535 kcm, 777 kcm, etc. Rules 4-040 and 4-042 now allow DLO cable 1/0 and larger marked as a TC cable to be installed in cable tray. Precautions do need to be made when terminating the DLO cable. Due to the fine stranding of the cable, it must terminate in connectors specifically approved for these cables. Allowable ampacity for the cable can be found in new Table 12E.
Read more by Steve Douglas
Posted By Randy Hunter,
Tuesday, May 01, 2012
Updated: Friday, September 07, 2012
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Article 220 is a cornerstone of theNational Electrical Codewhich gives us the information we need to properly size the circuits which will provide power to each part of our electrical system. Fundamentally, it is the section of the code which requires the most detail, and during certification testing it is usually one of the most dreaded. Good organization and some basic math skills are required to properly perform the calculations found in Article 220.
Photo 1. Oven
First, the ground rules:the scope (220.1) explains that this article provides the requirements for calculating loads. Part 1 deals with general requirements for calculation methods, Part 2 deals with the calculations for branch-circuits, Parts 3 and 4 give us the methods for feeders and services. Last but not least is Part 5, which gives us the method for calculating loads for farms.
Photo 2. Store signage
Continuing with the ground rules, 220.3 explains that certain other articles will give specifics for specialized applications, and these other articles are outlined in Table 220.3. They are in addition to or will modify some of the items in Article 220. The next ground rule has to do with math, that being what do we do when we perform calculations and have a fraction of an ampere. The code states that if you have a fraction of .5 amps or more, you round up to the nearest whole ampere. If you have less than .5, you simply drop the fraction (round down) [220.5(B)].
The usual place to beginis with the basic lighting load for any occupancy. As every facility requires lights, this is a good place to start. Table 220.12 provides a list of different types of occupancies and the basic requirement in volt-amps per square foot. The square footage is based on the outside dimensions of the building, dwelling unit, or other area. In dwellings we have some areas which we disregard, and these would be open porches, garages or unused or unfinished spaces not adaptable for future use. This last item may be subject to the interpretation of the authority having jurisdiction. It is possible that some of the values in Table 220.12 may be modified in the future as we continue to develop new lighting or design methods and energy codes are enacted.
The values in Table 220.12 deal with lighting and outlets used for general illumination. There are two footnotes to this table, and they deal with dwelling units, banks and office buildings.
The first footnote refers us to 220.14(J) for dwellings, which states that receptacles for
Photo 3. Store signage
dwelling units need no additional load calculations to the overall service size as long as they are the ones covered in: 210.11(C)(3) for bathrooms; 210.52(E) and (G), which deal with minimum receptacles required for outdoors and basements, garages, or accessory building (sheds, etc.); and the last area included in the general load, which is 210.52(A) and (B) for general use receptacles which are the convenience outlets we see around the walls in dwelling units, guest rooms or guest suites. As you may surmise, these are the receptacle outlets which generally do not have large loads and are typically sporadically used. Due to the diversity of the usage of these outlets, they get lumped into the load under general lighting calculations. Every time I mention in a class that we don’t use every outlet or light in our house at the same time, I always get the response from students that I should see their house. Either they have teenagers who turn things on and not off, or their spouses love to have every light on in the house. We laugh and move on; then we discuss diversity later in this section when we start to do the calculations.
In banks and office buildings we have a similar allowance,220.14(K), which states that the receptacle loads will be calculated using the larger of two different methods. First, we can use a value of 180 VA per each receptacle yoke (remember, we covered the term yoke in one of our previous articles). This value is covered in 220.14(I) which gives us the general rules for calculations on receptacle outlets. The other option is to simply add 1 VA per square foot of the facility, which would increase the per-square-foot VA for banks and office buildings up to 4.5 VA per square foot. So depending on the actual number of receptacles on the plans, we will have to perform the calculation both ways to see which comes out with the higher calculated load, then use the larger of the two figures.
Photo 4. Store window
This is a pretty good place to mention something that causes confusion to everyone regarding performing load calculations. The figures in the NEC for load calculations are volt-amperes (VA); however, when you look at much of the equipment or electrical appliances, you will find the values in either amperes or watts. So what’s the conversion for watts or amperes to VA? If we have a value in amperes, then we simply multiply the amperes by the voltage to get the VAs. Now what’s the relationship of watts to VAs? To keep things simple (and considering that most of the common loads in dwelling units are small and have a power factor of 1), for the purposes of this article and the calculations we are going to review, we will assume that we don’t have any power factor issues. Therefore, we are going to use the term VA as an equal to a watt for the purpose of this article.
The rest of Table 220.12 will provide the general lighting loads for various other types of occupancies; this is just the basic starting point for the facility. Once you’ve calculated this figure, we then have to add in the other loads that may be found in the facility. Section 220.14, Other Loads, addresses the procedure to be followed for these other loads. First, in (A) we find that we are going to calculate any load not covered in the following specific paragraph at the ampere rating of that piece of equipment.
Photo 5. Store window
In (B) we find the dwelling unit dryers and electric cooking appliances.The values to use for dryers are found in Section 220.54, where it states that the load for dwelling unit dryers shall be 5000 watts (VAs) or the nameplate rating, whichever is larger. I’ve seen a lot of residential calculations and dwellings completed, and I’ve yet to see a dryer load larger than 5000 watts. Especially at the plans check stage, when generally the dryer hasn’t even been purchased, it would be impossible to know exactly what the dryer load would be, so we always just use the 5000 watt figure. If you are doing a condominium project or apartment building, we would have several dryers within the same facility and, therefore, on the same service. If we were to take all these at 5000 watts, we would have huge electrical services. However, when you start to analyze the possibility of all of the units operating at the same time, we realize that it makes sense to apply a demand factor. The demand factors for household dryers are found in Table 220.54. If you have 10 dryers, you apply a 50% reduction to the total dryer load; if you have 43 or over, you are allowed to use a 25% factor.
Now for electric cooking appliances, we are referred to Section 220.55, which refers us to a table if the appliance is over 1750 watts. Now I have to warn you, this is one of the most confusing parts of the code to teach. I daresay that this is the one area where most certification tests trip up those attempting to do these calculations. I always hear the stories that certain master’s tests have a large apartment building and you have to figure the service size. If you will look at Table 220.55, you will see down the left side a column of the number of electric cooking appliance in the dwelling you are working in. We then have columns A, B and C. If you read the heading of the table, it tells you to go to Column C, unless you qualify to use Note 3, which is located at the bottom of the table. Quite often, the notes under this table get overlooked as they are small print and people mistake them for an Informational Note. However, the notes are critical and save you from having to oversize a service if you happen to be able to take advantage of them. I will warn you to read them carefully. There are conditions that will allow you to use columns A and B if you have cooking appliances that fit into the sizing requirements found there, and this can be beneficial on large facilities which will have efficiently sized units. Typically, Column C is used, and if you have a combination range oven then it is a maximum demand factor of 8 kW; if you have two units, then 11 kW, and so on. If you have a very large unit over 12 kW, then Note 1 has the information on how to use an adder for each kW over 12.
Photo 6. Dryer
For those taking any type of certification testing, this is likely to be the hardest part of the code. We all dread the large multi-family load calculation that has 50 units with 3 kW ranges and 75 units with 6 kW ranges, and then 5 suites with 15 kW appliances. As you can see, you would be jumping from column to column (and reading the notes) just to perform a calculation that would not result in an oversized service. In real life, if you miss by a little and get the service a little oversized, it is no big deal. However, when taking a test where you are faced with a multiple choice answer format, you can appreciate the difficulty and pressure inherent in finding exactly the right answer.
Moving on to a new calculation in 220.14(C),any motor loads will be added according to the requirements in 430.22, 430.24, and 440.6. Paragraphs (D) and (E) deal with luminaires and heavy-duty lampholders; however, this is not usually seen in most calculations since the lighting is typically included in the square footage figure from Table 220.12. The requirements for sign and outline lighting are located in (F), which states that a minimum value of 1200 VA shall be calculated for each required branch circuit specified in Section 600.5(A). This is the one item that often gets overlooked when doing load calculations for small business, such as strip mall tenants. Section 600.5 requires at least one sign circuit be calculated for each business which meets the criteria therein. Similarly,
Photo 7. Refrigerator
show windows are related to businesses which have glass fronts, and these locations have a load requirement per each linear foot of show window. This value is 200 VA, and again it is often overlooked when plans are prepared for these types of locations. Just note that it is a required outlet(s), because one of the first things added by this type of business is often a hanging sign in their show window that says "OPEN.”
The last item for us to cover in 220.14 is fixed multioutlet assemblies.These are the surface-mounted outlet strips which are manufactured in strips of varying sizes and lengths, with many options as to the spacing of the receptacles in these units. These are very convenient to use where you have a high concentration of electrical devices which all require power, and you don’t want to constantly plug and unplug these devices. It could be an area where you might have several printers, a fax machine, postal machine, laminator, electric stapler and paper cutter, etc. As you can imagine, this would be a huge inconvenience to be forced to connect each device every time you need to use one, and it would be an expensive endeavor to have a receptacle added for each new device. For these situations, factory assembled multioutlet strips are made which only require a single connection point and provide great versatility for the number and spacing of receptacles. How do we figure the load for these, as we really don’t have any control of what will be plugged in after the facility is completed? We have to determine whether the anticipated use will have devices connected which will be used at the same time or not. If it is unlikely the appliances will be used simultaneously, then each 5 feet or every fraction thereof will be calculated at 180 VA. If the connected devices are expected to be used at the same time, then we must calculate these at 180 VA per foot or fraction thereof. Now you be the AHJ and tell me how you would handle this. Frequently, the assumption is made that the units will have simultaneous use and therefore the general calculation is 180 VA per foot.
Photo 8. Washer
The last paragraph in 220.14 is (L), which is a catch-all titled "Other Outlets,” and it simply states that other outlets not covered in 220.14(A) thru (K) shall be calculated based on 180 VA per outlet.
The next part of Article 220, Part II, deals with "Loads for Additions to Existing Installations.” This is in 220.16, and in part (A) we deal with dwellings units and break it down to two sections. First, if we are adding a structural addition or wiring a previously unwired portion of an existing dwelling over 500 square feet, then we calculate this as per 220.12 or 220.14. If we are doing a structural addition or wiring, say, a portion of a basement which was unfinished, then this would apply. The second part deals with new circuits or extension of circuits, and the calculations will again be done according to 220.12 and 220.14. In part (B) we cover other than dwelling units, and here loads for new circuits or extensions to existing circuits shall again be calculated according to 220.12 and 220.14. So we have three different conditions, but they all send us back to the basic sections of the code for the methods of doing load calculations for new loads. To put this in simple terms, you take the basic calculation for the original load and then add the new loads to be connected. However, if it is a small project, then quite often when additions are done the designer simply draws a new set of plans that shows the new work by clouding it. Then the designer will do a complete new calculation for the addition, which may allow for further demand reductions according to what the new work consists of.
The last requirement of Part II is 220.18, Maximum Loads. This states the total load shall not exceed the rating of the branch circuits. If you are dealing with motors, air-conditioning, or refrigeration equipment, then we have to refer to the related articles for motors (Article 430) or Article 440 for the A/C or refrigeration equipment. For inductive, LED or lighting loads that have ballast, transformers, driver, or power supplies, the loads will be based on the total amperes of the units and not on the wattage of the lamps. The reason for this is that power supplies and ballast are units which convert from one level of energy power to one specifically designed for the lamps and, therefore, some of the energy consumed is lost in this conversion. As such, the power consumed by the device is what we use for calculation purposes. The last part of 220.18 relates to the range loads and tells us it is permissible to apply demand factors for ranges according to Table 220.55, which we have covered above.
In the next installment, we will continue on with Part III of 220, which starts with feeder and service load calculations. We will do some very basic calculations and discuss the demand factors which apply for certain facilities.
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