Posted By Michael W. Vallier,
Wednesday, November 01, 2006
Updated: Sunday, February 10, 2013
| Comments (0)
As professional sports venues become bigger and more complex in design and scale, architects and engineers are looking for bold new ideas. Retractable roofs have become a popular feature in those structures because they provide the ability to control the stadium’s interior environment more effectively. Only a select number of companies have the knowledge and expertise to mechanize and control these immense structures, which, themselves, become architectural feats.
Uni-Systems, based in Minneapolis, Minnesota, is just such an expert. Whether it’s a retractable roof, a retractable pitcher’s mound, movable walls or seating, Uni-Systems has established itself as the industry’s premier provider. The company’s impressive resume includes work on Minute Maid Park and Reliant Stadium, Houston, Texas; Miller Park, Milwaukee, Wisconsin; RFK Stadium, Washington, D.C.; and most recently, the Arizona Cardinals’ Stadium, Glendale, Arizona.
Photo 1. New Arizona Cardinals state-of-the-art retractable stadium
Photo 2. Cable drum with bull gear
With its curved roof track, the Arizona Cardinals’ project presented interesting challenges in designing the retractable roof mechanism. Uni-Systems partnered with ABB and selected the ABB ACS800 drive to provide optimum control of the roof’s torque-distribution system.
Building an Architectural Oasis in the Desert; Take the Grass Outside
When the National Football League’s Arizona Cardinals made the decision to construct a new arena several years ago, the desert climate was a major consideration in the design plan. The heat can take its toll on fans and players, alike, and can be detrimental to the playing surface, as well — especially if it’s natural grass. On the other hand, in cooler months, the world-famous climate is perfect for hosting outdoor activities.
The exterior design of the stadium resembles the basic form of the barrel cactus and was created by renowned architect Peter Eisenman, along with HOK Sport. The retractable roof can be closed so the facility can be air conditioned in the hot months, and then opened in the cooler months. The roof’s panels consist of a PTFE (polytetrafluoroethylene) coated woven fiberglass fabric, and are much lighter than a traditional, clad roof. The stadium design includes not only a retractable roof, but also a retractable playing surface.
Photo 3. 8 ACS800 drive control 16 motors per roof quadrant
The innovative, roll-out field will save an estimated $50 million in operating costs, as it is more economical to move the field outside, rather than having the entire roof retract to allow the necessary sunshine to reach the grass. The retractable, natural-grass playing surface is contained in a 16.9-million pound tray that is 234 ft wide by 400 ft long — the first of its kind in North America. All in all, the design of the stadium is so unique that, to date, it’s been featured in a multiple series on "The Discovery Channel.”
Direct Torque Control Provides More Accurate Feedback; Drive Proves Torque at Motor
This roof was different than any that Uni-Systems had previously constructed. According to Lennart Nielsen, Danish master electrician and senior electrical designer with Uni-Systems, one of the most important decisions was selecting motor drives to control the roof’s movement.
"An important factor in choosing the ABB drives was the inherent risks associated with running a roof on a sloped track,” says Nielsen. "This caused us to look for a variable frequency drive (VFD) that would allow us to test the drive torque before each roof motion, to ensure that each drive was operational and capable of a 100-percent torque output. The ACS800 was capable of this, so before each motion, the programmable logic controller (PLC) checks the torque output from the VFDs at 0 Hz, before committing to opening the motor brakes.” Nielsen also says the ABB drives could be installed and operated without the need for closed-loop encoders — a cost-effective option that helped the company meet budget requirements.
Nielsen explains that for other roofs that Uni-Systems designed, if the brakes were to release and the motors didn’t start up for some reason, the roof would simply remain in place. However, at the Cardinals’ new stadium — with its sloped roof track — if the brakes were released and the motors didn’t start up, the roof sections would fall into the parking lot.
Photo 4. Each retractable roof panel is raised and lowered on a steep slope
"The ABB set-up, with their direct torque control, can measure the feedback from the motor much more accurately than a standard drive,” says Nielsen. "And in their control/output algorithms, they can measure the characteristics coming back from a motor at 0 Hz (meaning that they start the energy field but don’t rotate it), and that’s a big reason why we chose them.”
"We wanted to have this capability all the way down to 0 Hz, and none of the manufacturers — except ABB — could guarantee that,” Nielsen continues.
ABB Drives Critical to Roof Functionality
The retractable roof consists of two moveable panels suspended between two parallel tracks — along the east and west sides of the structure. The tracks are curved to follow the roof’s slightly domed profile, which slopes down from its apex at the 50-yard line towards the north and south ends of the building. Each roof panel rests on eight, two-wheeled carriers: four along the west and four along the east side of the roof panel; each set of four carriers forms one quadrant of the entire retractable roof system.
Conventional techniques — such as the powered traction wheels that Uni-Systems used on previous stadium projects — were not an option for the Arizona stadium’s sloped roof. Instead, Uni-Systems designed a system in which each roof panel is tethered by four 1.5 inch-diameter steel cables on each side.
There are two cables running on each side of the roof rail, and each is wound on its own 48-inch-diameter cable drum. The cable drums are arranged with one on each side of the two upper carriers for each roof panel quadrant, and the two lower carriers in each quadrant are not powered. Each cable drum is equipped with a bull-gear along the outer rim, driven by four, geared 7.5 HP, 480 VAC motors with spring-set brakes.
The four motors per drum are controlled by two 20 HP ACS800 VFDs, meaning that each roof quadrant is powered by 16 motors that are controlled by eight VFDs. Accurate control of the VFDs was essential to distribute the load evenly to the roof cables. "It was deemed inadequate to let the roof PLC act as referee for each individual drive via the ProfiBus that was to handle the regular data communications between the PLC, VFDs, and remote I/O,” says Nielsen. "Instead, we use a parallel, fiber-optic communications network between each group of eight VFDs, where one VFD was designated as Master and the other seven as Followers.”
Photo 5. Retractable roof panels nearly closed
Once the roof is moving, it is extremely important to keep a very tight torque-and-speed envelope around each Follower drive in relation to each roof quadrant’s Master VFD,” Nielsen continues. "The ultra-fast switching direct torque control system of the ACS800 provides the means for doing this via the fast intra-VFD fiber-optic network.”
The PLC issues a speed (frequency) command to each of the two Master VFDs (one per side) and the seven Follower drives then match the torque output of the Master drive. Each roof panel’s PLC handles the position alignment between the two quadrants of each roof panel, which receives position feedback from an absolute encoder in each quadrant and from incremental encoders on each cable drum. If a roof side gets more than two inches ahead of the other — the rails are 257 feet apart — the PLC will signal the Master of the leading side to slow down until the two sides are again in alignment.
Since the roof rails are curved, the actual cable load increases as the roof panel moves towards the fully open position and the steeper sections of rail. For optimum motor torque, the VFDs output 60 Hz at the lower half of the rails, and to decrease operating times, 85 Hz on the upper half. Motors operate in both motoring and generating modes — generating when the panels are lowered, and motoring to lift and close the panels.
The ABB drives require no maintenance. They are mounted in air-conditioned enclosures that are on the carriers.
Retractable Roof Quick Facts
- Two retractable roof panels at 1,100,000 lb. each (550 tons)
- Each roof panel’s dimensions: 185 ft. long by 285 ft. wide, 16 ft. deep
- 8 cables (1.5 in. diameter) connect each retractable roof panel to the stadium structure at the 50 yard line (over ½ mile of cable used)
- 32 motors (7.5 HP) power each roof panel (480 total HP for stadium)
- 16 crane wheels (36 in. diameter) support each retractable roof panel
- 595,000 lb. of mechanization equipment used to make the roof move
- 257.5 ft. span of retractable roof over stadium bowl
- Two rail lines with 175 lb./yd. crane rail (over ¼ mile of rail used)
- Maximum travel speed: 25 ft./min. or ¼ mph
- Total travel time: 11.5 min. (10 min. run time, plus 1.5 min. of slow speed for final positioning)
Cable Oscillation Tests Drives Capabilities
During initial testing at the Cardinals’ stadium, Uni-Systems found that natural frequencies in the drive cables caused some oscillation or whipping in the cables as the roof was opened. "And the faster we ran, the more pronounced it was,” says Nielsen. "We saw that the drives actually made it worse. As each cable oscillated, the anchor points of the cables would see a varying torque. The master drive would then react to those changes by increasing or decreasing its torque output. And its torque profile would then be transmitted to the other drives that reacted to it — causing the whole cable system to start into harder and harder oscillations.”
This was an unforeseen challenge, but ABB was there to help develop the solution. ABB engineers visited the site to help Uni-Systems get the drives tuned in to deliver optimum control and eliminate the bounce in the cable as the roof opened. Nielsen says, "Our natural reaction would have been to just open up the tolerances more to allow a larger window around the optimal speed and torque to allow a little bounce without the drives reacting to it. But ABB application engineer Steve Boren went the opposite way and actually made that window extremely small so as not to allow it to react harshly enough to cause the oscillation. So we got everything to smooth out and work extremely well.”
"We simply needed to utilize a standard software feature in the ACS800 which allows for Loadshare (Torque) Followers to have, also, an over-riding speed window about the Master drive’s coordinated speed reference,” Boren said. "Because of the uneven cable stretch, which can be viewed as slip between the driven cable drums, it’s tough to make the drums share the load evenly. But by activating the ACS800’s Speed Window capability in the torque follower drives, and limiting the window (slip) to only 2 rpm on each motor, the cable drums have no choice but to evenly share the load of the immense roof.”
"Our experience with ABB has been very good,” says Nielsen. "It’s not the first time we’ve used ABB drives, but it’s the first time we have used them in one of our stadium projects. ABB has been very responsive as far as both sending personnel out during our prototype testing and getting the drives adjusted for optimal performance on the final product.”
Future Projects Already in the Works
With the Arizona Cardinals’ stadium nearing completion, Uni-Systems and ABB will soon turn their collective attention to several more new NFL stadium projects. Already in progress in Indianapolis, the Colts are replacing the RCA Dome with a new, state-of-the-art retractable roof stadium. "The system required for that roof is much more complex,” says Nielsen. "Instead of a nearly one-to-one, width-to-length ratio, the Colts’ panels are around five-to-one. This has resulted in a five-rail design, rather than a two-rail as in the Cardinals stadium, and twice as many cables and drives. Also in progress is a design for the new Dallas Cowboys’ stadium. Both of these stadiums will use the newer ACS800-U11, or regenerative drive, which was not available when the Cardinals stadium was designed.” The Cardinals stadium design uses stand-alone regenerative drives working with the ACS800 VFDs.
As both Uni-Systems and ABB gain more experience in this niche business, expect even bolder designs in the near future.
Read more by Michael W. Vallier
Posted By Michael Johnston,
Wednesday, November 01, 2006
Updated: Sunday, February 10, 2013
| Comments (0)
There is significant intangible value in many of the things we take for granted. For example, essential resources such as the air we breathe and the water we drink and use are often taken for granted. Society expects these life essentials to be safe, and not much thought is given to how safe they really are. Only when an identified problem surfaces, do people get concerned and fear sets in. The electrical power and lighting that powers society has become a resource that is taken for granted. People generally don’t think twice about the electricity they use until it is not available. Then its lack is inconvenient and creates challenges they are not used to. The coffee has to be brewed in the morning and the TV has to work in the evening, not to mention meals that have to be cooked and laundry that must be washed and dried. Society just expects things to work. Another expectation is that the electrical system within their dwelling or place of business is safe.
Photo 1. An inspector at work
Why Is It Safe?
Did you ever wonder how safe an electrical system really is? Think about the dwelling where you live and the business where you work. Electrical wiring is often buried within the hollow, inaccessible construction of the structure, so it would be difficult to detect deterioration of the electrical wiring. Most people just assume it is safe. Out of sight, out of mind, so to speak, so the question arises, how safe is the electrical system, and what are the reasons it is safe? What impact would it have if it were not safe? Could the building be subject to fire? Could the residents or building occupants be subject to electrical shock or even electrocution? The answer is, when electricity is in the mix, all of these events are possible. So what makes our electrical systems safe? They are safe because of qualified persons installing and qualified electrical inspectors verifying that minimum requirements are met for installations that are essentially free of electrical hazards. This article looks at the value of qualified electrical workers, and specifically the value of qualified electrical inspectors and the unseen job they perform on a daily basis so an expecting society can live safely.
Qualified Electrical Work Force
Photo 2. Generator paralleling equipment
Working in the electrical field requires training, and lots of it. The uniqueness and intricacies of the electrical field warrant extensive training initially for one to become a qualified and competent industry professional and require continuing education. Many states and local jurisdictions have laws that require these qualified workers to be licensed and to maintain their licenses through continuing education. This is essential because the electrical field is so dynamic. New technologies, methods, and products are constantly being introduced and installed. Not only do qualified electrical workers need to stay informed and trained in current technologies and applications, electrical inspectors really do too. Staying current is an essential part of their jobs.
Unsung Heroes — The Electrical Inspectors
The responsibilities of a building safety inspector are enormous, especially so for an electrical inspector. The value of what they do is an intangible, necessary benefit to society. People not only expect the electrical wiring to work, they expect it to never fail, and they definitely expect it to be safe. The services provided by electrical inspectors can be compared to other professions that relate to safety, such as fire department workers, police department workers, and medical workers. The difference is that these aforementioned heroes are very visible to the general public. The services of building safety inspectors are not often visible to the public, but the resulting installation and service it provides is.
Photo 3. Installers work to achieve code-compliance; inspectors verify it
It’s a tough job, but someone has to do it. Does that phrase sound familiar? Think about the responsibilities of a police officer, a fireman, or a doctor. The safety services they provide help protect people and save lives. The services they provide are based on needs at a point in time. When people become ill, they seek the services of medical personnel. If a building catches fire, the fire department will respond, hopefully, in time to save the lives and the building if possible. The police officer responds to speeding vehicles, crimes being committed, and other actions requiring intervention of law enforcement. All of these services are associated with the safety of society, but are provided in a reactionary fashion for the most part. In comparison, the unsung heroes—the electrical inspectors—furnish services that proactively provide environments safe from the hazards of electricity which can injure or kill people just as quickly as do fire or crimes. Electrical inspectors can prevent the smoke from happening, yet they never get much credit. In fact, electrical inspectors usually get negative attention because of the job they must do, such as sometimes rejecting an installation, which is not necessarily the popular thing. So the inspector often gets a bad rap for doing a good job.
Benefits of Electrical Inspection
Although construction code inspectors are often viewed as a necessary evil, there are significant benefits of a quality inspection program. This article is built around the value of electrical inspection. When one takes a close look at the value of electrical inspection, a few things come to mind. One value is the peace of mind that comes from knowing an electrical system is essentially free from hazards because it was inspected. For many, this is the most important value, but the business of electrical code enforcement provides other monetary values. It might not be viewed as an economic value or advantage, but in the bigger scheme of business, a good electrical inspection and building safety program can result in significant value for consumers.
The Insurance Services Organization (ISO) is concerned with providing accurate assessments of the services jurisdictions provide that result in safer buildings. Where inspection departments are providing quality and sufficient building safety inspection and plan review services, those jurisdictions are awarded a rating that can often result in lower insurance rates. Sounds like a pretty good value, safety, peace of mind, and lower insurance rates. What are the ISO ratings awarded to the jurisdiction in your area? These can be a good indication of whether public safety is deficient and in need of improvements. The fortunate aspect of knowing this information and understanding its impact is that jurisdictions can become proactive so the services they continue to justify provide the desired results.
Another intangible value that electrical inspectors provide is the contribution to the electrical Code development process. The electrical inspector is represented on each NEC code-making panel. The value they provide is asserting the voice of code enforcement in this process to assure that the safety rules produced in each new edition are practical, understandable, and, most importantly, enforceable. The International Association of Electrical Inspectors is committed to supporting this Code development process for these reasons and to promoting electrical safety through uniform application and understanding of the electrical codes and standards. Electrical inspectors also provide value to the product safety standards development through their contributions on the standards’ technical panels and the UL Electrical Council. The electrical inspector provides diligent service to the industry in these two areas, but it all happens out of the limelight. The recognition is not important, the service is. That is why they unselfishly give their time and expertise to this segment of the electrical industry. Electrical inspectors are teachers as well. The job they perform usually results in learning.
The Electrical Safety System
Photo 4. Violations are evident to inspectors
From the beginning, the quest to understand and use electricity has been an adventure. Lives have been lost, injuries sustained, and buildings have burned. Not long after electricity was discovered and refined to a usable status, society was provided with significant evidence of its force and how dangerous and even lethal it can be when not installed and used properly. Insurance companies recognized early on that regulation of electrical installations and the use of electricity were necessary for safety of persons and property. Insurance companies played an important role in the initial development of the National Electrical Code we use today. The North American Electrical Safety system has had an unprecedented role in developing necessary codes and standards relating to the safe electrical installations. Safe electrical installations of today resulted from years of experience and knowledge gained by unfortunate events that led to losses. This is the harsh reality of this powerful force, that society views complacently. The electrical industry has a long history of establishing an unprecedented electrical safety system that is every bit as effective and necessary today as it was in the past. In many cases even more so, as a result of today’s more complex, intricate electrical power systems and their diverse use. The safety afforded by regulation cannot be taken for granted at all.
The electrical safety system is the reason society can live and function in an electrically safe environment. Some essential elements that make up the electrical safety system that provides this protection are the qualified electrical testing laboratories, manufacturers, a qualified electrical work force, and quality electrical inspection of installations, equipment and systems. Each of these entities plays an important role in the safety we are afforded. Without a doubt, safe electrical installations are the result of each of these entities fulfilling its role in the electrical industry. Without all of them working for the same objectives, safety can be, and often is, compromised. It’s something to really consider when asking questions such as how safe is an electrical installation? What are the contributing factors that ensure it is safe?
The Role of Manufacturers
How do electrical product and equipment manufacturers contribute to the electrical safety system? By building quality products that meet or exceed the minimum electrical product safety standards that have been developed and established through research and experience. Time has provided the opportunity to invent and develop electrical products and equipment and often through the school of hard knocks, electrical safety lessons were learned. It’s a shame that lives had to be lost, injuries sustained, and properties damaged or lost along the way, but that is the nature of this powerful force. Electrical equipment manufacturers have come to depend on the established electrical safety system for the success of their business. By manufacturing equipment to meet or exceed minimum electrical standards, there are reasonable assurances that it will provide the level of service anticipated by a wealth of continuous industry needs. By having electrical products evaluated and tested to developed standards, their products become very marketable in an electrical industry that creates such demand. These manufacturers find comfort in the third party evaluation and testing and product certification process because they understand how valuable it is from a liability, marketing, and safety standpoint. It stands to reason that our electrical safety system is very dependant on electrical equipment manufacturers fulfilling their role in producing and certifying products that will meet the minimum standards for safety while providing a supply to the electrical industry.
The Role of Safety Standards Development Organizations
Did you ever wonder what is behind an electrical product certification mark such as UL, CSA, ETL, MET, TUV, or others? These marks of electrical products serve as an indicator to the electrical industry and society that a product meets the safety criteria for which it is intended. There are many qualified electrical testing laboratories in the industry today. It has become big business, and rightly so, with the ever-expanding use of electrical energy. The role of the qualified electrical testing laboratory is to determine that electrical products are essentially safe by verifying they meet the minimum requirements in established electrical safety standards. This awards an electrical manufacturer with recognition as a qualifying contributor to electrical safety. The qualified electrical testing laboratories play an important role in the electrical safety system because their work provides the electrical code enforcement community with a strong basis for their approvals. When inspectors are faced with equipment that does not bear such a mark indicating it meets electrical safety criteria and standards, the approval process is more difficult. Many authorities having jurisdiction base their approvals on the use of equipment that has been safety evaluated by a qualified electrical testing organization, such as those mentioned above. This is an essential part of the electrical safety system and is the common inspector approval criteria utilized where approvals of electrical equipment and installations are sought. From the beginning of electrical history, product safety evaluation and testing has been there and has seen the growth and demands paralleled in this industry. It is logical that the electrical safety system depends on the continuous contributions and services provided by qualified electrical testing laboratories and standards writing bodies.
The Role of Inspectors and Inspection Jurisdictions
Being involved in electrical inspection and promoting electrical safety through quality code enforcement is a noble profession. Many of the qualified electrical inspectors in the business today have evolved from being qualified electrical workers to becoming qualified electrical inspectors. Their contributions to the electrical safety that society enjoys today are taken for granted and expected.
There is no room for complacency when it comes to safe electrical installations. The role of the inspector is vital to the industry and as this industry progresses to include more and more advanced technologies and methods of electrical power distribution, the importance of the electrical inspector and his or her role are self-evident.
The responsibilities of electrical inspectors are focused on safety. That’s why they have chosen that career path. The service they contribute helps people. It is important to recognize that those that are knowledgeable about the electrical field understand the hazards electricity can bring to persons and property if it is not properly installed. Inspectors have a serious responsibility and the consequences of not fulfilling those obligations can be severe. So how important is the role of electrical inspector to the electrical safety system? It is extremely important, yet immeasurable. No one can place a dollar amount on the value of the job the inspector does; but examine the many cases where safety is not put first and the results are property losses and injuries and death. How essential are the services provided by electrical and other construction code inspectors? The answer rests with the consumer. The public wants electrical systems to provide quality service without interruption, and they just expect it to be safe. Therefore, the role and services of the electrical inspector are equally as essential as the visible services and work of the fire and rescue teams and the law enforcement departments. They are unsung heroes and their work is as essential today as it was back in time when society first started working with this powerful force.
IAEI Focus on Electrical Safety
IAEI is committed to electrical safety and the role of the electrical inspector and has been since long before the official establishment of the organization. IAEI continues to promote the uniform understanding and application of electrical codes and standards to installations and systems. This is an essential element of the electrical safety system. The focus of IAEI has always been on safety, and the value of the electrical inspector has always been in the interest of the association. Our industry would not be where it is today, nor would it be as safe, if it were not for the electrical inspectors and the job they do. Although the electrical inspector might not have the front page publicity of police officers, firefighters, and other emergency response team personnel, they are truly equally as valuable because their work is proactively resulting in electrical safety for society in general and, more specifically, for families and the way of life we’ve come to expect.
These dedicated members of the electrical field don’t expect recognition for what they do; they have chosen this career path because in their hearts they know and understand the importance and the need. Electrical code enforcement officials are necessary and the value they provide to society is more than just evident, it is undeniably essential.
Read more by Michael Johnston
Posted By Ed Larsen,
Wednesday, November 01, 2006
Updated: Sunday, February 10, 2013
| Comments (0)
Have you ever been confused about what the markings on circuit breakers mean? Understanding the markings on electrical equipment is a fundamental need to ensure a safe and reliable electrical installation. Circuit breaker marking requirements are established by the requirements found in the NEC and the UL 489 product standard. This article will discuss the most common markings and where they can be found.
The UL 489 product standard for Molded Case Circuit Breakers specifies the information to be marked on circuit breakers and where it is to be located, so let’s discuss what information needs to be marked on the circuit breaker and the location where you will find those markings. Keep in mind the UL® standard specifies minimum requirements. Circuit breaker manufacturers may provide additional information or provide information in a more convenient location.
Photo 1. Markings visible with trims or covers in place
Markings Visible without Removing Trims or Covers
UL 489 requires that some markings be visible without removing trims or covers. This location is typically referred to as the handle escutcheon (see photo 1).
Markings Visible with Trims or Covers Removed
Photo 2. Markings visible with trims or covers removed
UL 489 requires other markings be visible on an installed circuit breaker with trims or covers removed. This location is typically referred to as the face of the circuit breaker (see photos 2, 3, 4).
Other markings which should be visible with trims or covers removed are:
Photo 3. Markings visible with trims or covers removed
Independent trip –
Multi-pole circuit breakers are constructed with either a common trip, where all poles are mechanically tripped when one of the poles trips, or an independent trip construction where only the pole that is involved with the overcurrent condition trips. If a 2-pole circuit breaker does not have an internal common trip feature, then it must be marked "Independent Trip” or "No Common Trip.” NEC 240.20(B) is the foundational requirement for a common trip function in a circuit breaker; however, it also goes on to explain where independent trip is permitted.
For Replacement Use Only not-CTL –The Class CTL (circuit limiting) panelboard has only been in existence for about 25 years, even though the lighting and appliance branch circuit panelboard has been in the NEC for decades. CTL panelboards have a rejection means designed to reject more than the appropriate number of circuit breakers that can be installed in the panel. The marking "For replacement Use Only Not CTL Assemblies” means that the circuit breaker does not have CTL rejection provisions and is intended for replacement in older equipment pre-dating the CTL requirements for circuit breakers and panelboards. Circuit breakers with this designation should not be installed in a panelboard marked "Class CTL Panelboard” since that would be a violation of the listing of the assembly [NEC 110.3(B)].
Markings Found in Other Locations
The markings we will discuss below may appear in any location except the back of the circuit breaker. These markings include:
40°C –This marking indicates the maximum ambient temperature in which the circuit breaker can be applied at its marked ampere rating without rerating the ampacity of the circuit breaker. This marking is required for thermal-magnetic circuit breakers and is optional for electronic trip circuit breakers unless they are only suitable for a 25°C ambient, in which case they must be marked 25°C. When the ambient temperature rises above 40°C, the designer may need to consult the manufacturer to obtain rerating information (see item 4 in photo 3).
Class CTL –Circuit breakers marked Class CTL have a rejection means designed into the circuit breaker. Class CTL panelboards or assemblies, in conjunction with Class CTL circuit breakers, prevent more circuit breaker poles from being installed than the number for which the equipment is rated.
HACR type –This marking indicates the circuit breaker is suitable for use with the group motor installations typically found in heating, air conditioning and refrigeration equipment. TheNEC2005 no longer has this marking requirement. The electrical industry determined that circuit breakers are considered suitable for use with such equipment without any further testing, therefore, the HACR marking is no longer required on air conditioning and refrigeration equipment or on circuit breakers for use in these applications. The requirement for this marking has also been removed from the UL 1995 product standard for HVAC equipment (see item 3 in photo 1).
Maximum wire size –Circuit breakers are typically marked with a wire range, however that marking is not mandatory. If the circuit breaker cannot accept the next larger wire size required for the ampere rating, then the maximum wire size must be marked in any location except the back (see item 5 in photo 3).
Separately shipped connectors –If connectors are not factory installed on a circuit breaker, then it must be marked with the proper connectors or terminal kits required in any location except the back (see item 8 in photo 3).
Ground-Fault Protection for People
The GFCI function, as part of a circuit breaker, provides ground-fault protection for people and has a number of unique marking and instruction requirements.
Test function –The GFCI has a test function that requires action upon installation and on a monthly basis. GFCI circuit breakers must have a test button or switch that must be labeled in a location accessible without removing trims or covers in order to facilitate monthly testing.
"Class A” marking –A "Class A” ground-fault device is intended to protect people. The Class A marking indicates that the trip threshold of the GFCI is between 4 mA and 6 mA. This marking may be in any location except the back.
Instructions –All GFCI circuit breakers must include instructions for the installer plus instructions on the use of the test function. A hangtag or self-adhesive label must also be provided, instructing the user to test the GFCI at least monthly. Inspectors should check to see that the tag or label has been properly installed.
Ground-Fault Protection for Equipment
Circuit breakers may also include a ground-fault protection for equipment (GFPE) function that, like GFCIs, has a number of unique marking and instruction requirements.
Test function –GFPE circuit breakers may have a test button or switch that may be labeled in a location accessible without removing trims or covers in order to facilitate testing.
Trip level –GFPE circuit breakers must be marked with their trip threshold in milliamperes in a location accessible without removing trims or covers.
Instructions –All GFPE circuit breakers must include instructions for the installer.
Circuit breakers may also include arc-fault protection (AFCI) that, like GFCIs, also has a number of unique marking and instruction requirements.
Device identification –AFCIs must also be identified appropriately. Branch/feeder or Combination type AFCIs must be so marked in a location visible when the trims or covers are removed. This is an important marking to note as we move into 2008, asNEC-2005 requires Combination AFCIs in bedrooms effective January 1, 2008 (NEC 210.12).
Test function –AFCI circuit breakers must have a test button or switch that must be labeled in a location accessible without removing trims or covers in order to facilitate testing.
Instructions –All AFCI circuit breakers must include instructions for the installer.
Circuit Breaker Markings Ensure a Safe Electrical Installation
So why are all of these markings on circuit breakers? Without them, it would be nearly impossible to install or inspect an installation for the appropriate performance ratings and fundamental electrical connections. When designing or completing an installation, key items to review are:
1. Are the voltage, continuous current, and interrupting ratings appropriate for the application?
2. Does the application require SWD or HID ratings?
3. Is the wire type and size appropriate for the circuit breaker?
4. Is the circuit breaker suitable for the equipment in which it is installed? Have other protective functions such as GFCI or AFCI been provided as required by the NEC?
5. Is the temperature rating of the circuit breaker suitable for the application?
The UL Marking Guide for Molded Case Circuit Breakers is a valuable resource to understand circuit breaker markings that may further explain these and other markings in detail. If you have questions about CB markings not answered here, consult the Marking Guide or the manufacturer to assist in an NEC-compliant installation.
Read more by Ed Larsen
Posted By Michael Weitzel,
Wednesday, November 01, 2006
Updated: Sunday, February 10, 2013
| Comments (0)
In most areas of the country, building construction is booming, and there is a huge need for and use of temporary construction power. As electrical inspectors and installers in the field, we either inspect, install, or otherwise work with these types of installations frequently, if not daily. That being the case, it can be easy to become too comfortable with electrical equipment that is commonplace and all around us. We may often be a little complacent regarding temporary electrical power. Installations with compromised Code requirements would never be allowed, but often are accepted in temporary service installations for expediency, because "That’s the way we’ve always done it,” or because others aren’t addressing the issue, or even because of the attitude that is prevalent in many minds in the construction trades — It’s only temporary! Keep your shirt on! Or as our Aussie friends say, No worries!
Temporary services can create challenges for installers and inspectors. This article focuses on temporary services, temporary service equipment short-circuit current ratings, common Code violations that may be found in temporary service installations, and the need for comprehensive inspections every time a service is installed, whether temporary or permanent.
Photo 1. Typical Temporary Service
Figure 1. Service equipment installed close to a transformer with large kVA capacities require suitable equipment short-circuit interrupting ratings.
Common Code violations indicate that there is somewhat of a lax attitude toward temporary power services. Hazards exist every day on construction sites. Let’s not add to the problem! Some perils are obvious, such as the possibility of a fall from an upper level of a high-rise building. Others may be just as real, but not as apparent. One such item is short-circuit protection and ratings of temporary electrical service equipment. The classic example is a temporary service rated 200 amperes or less, that is supplied from a 500 kVA or larger transformer and located immediately next to the service equipment, with a very short length of service conductor (see figure 1).
Photo 2. Temporary service
In this case, a ground fault in the electrical service equipment could result in high levels of fault current flowing into equipment that most often does not have a sufficient interrupting rating, possibly causing an explosion and/or damaging life and property. This type of installation would not comply with NEC 110.9 and 110.10, yet is commonplace. Many types of accidents occur on construction sites. A ground fault could easily occur when a temporary service is struck and knocked down by construction equipment. Overhead conductors may be snagged by a truck or forklift mast, etc., even if all Code minimum clearances were complied with. But not to worry; after all, it’s only temporary, right?
This is an issue, however, that many jurisdictions have not addressed. Again, it appears that there is an attitude of complacency. Is that a good reason not to require at least the minimum level of code-compliance? Some may ask, Where’s the ‘body count’? Remember that not every Code rule exists because of a death or injury, though that does get people’s attention, at least for a while. The rule may be totally appropriate, and necessary to a safe installation. Another concern is that requiring electrical equipment for temporary services to have adequate interrupting ratings would result in an uproar from the construction community, because of the additional cost for equipment with higher fault-current ratings. The minimum requirements of the Code apply whether the service is temporary or not. Appropriately rated equipment can be added, and the job can be done without a huge expense, though you are practically guaranteed to hear, We’ve never had to do that before! That’s true in many cases. But electrical systems and installations have improved greatly over the years for safety and usability, as has the NEC; and as an industry, we are learning all the time, or should be, as our trade is constantly changing. It should be noted that the calculations found in figure 2 are based on an infinite current supply from the serving utility.
Figure 2. Calculations based on an infinite current supply from the serving utility
The Code does not place any less importance on proper short-circuit protection and adequate ampere interrupting capacity of overcurrent protective devices and equipment ratings for temporary services as compared to permanent service installations. The question is, do we?
It is important to remember that chapters 1 through 4 of the NEC apply to temporary services. Section 590.2(A) states that "Except as specifically modified in this article, all other requirements of this Code for permanent wiring shall apply to temporary wiring installations.”
Table 1. Common code violations found in temporary service installations
Because of the heavy workload that many jurisdictions have, it’s often easy to feel rushed or get in a hurry when inspecting temporary services. The thought may prevail, It’s only temporary, it’s not a big deal. Such assumptions are risky, and can be dangerous. The need to inspect carefully each temporary service every time it is placed on a jobsite cannot be overlooked, even if you have previously inspected it, perhaps many times before. Even if the installation looks safe, there could be hidden hazards that may not be apparent. Also, things can happen to the equipment between the time it was first inspected and when it is used again on the next jobsite.
In some jurisdictions, electric utilities may provide — and their line crews may also install — temporary services. In such cases, it is possible that no electrical inspection is performed or required, or the persons inspecting may be professionals in their field but not trained electrical inspectors that understand the hazards and know what to look for to assure a safe installation that is code-compliant. The question is, are these types of installations truly safe?
If temporary construction power installations are within your responsibility, please consider the following suggestions: Good working relationships are important, but it’s wise not to make assumptions that because you know the contractor and/or may have inspected this particular piece of equipment before, that the equipment is still safe and meets at least the minimum Code standards. There may be hidden concerns or damage that you or they have no idea exists. Damage to electrical equipment can easily occur, for example, where the temporary power pole is removed by a backhoe that pulled it out of the earth. In the process, the service grounded (neutral) conductor was pulled on very hard, which destroyed the neutral and ground bar in the service equipment. In other cases, the service ungrounded conductors were completely pulled out of their terminations in the service equipment or meter base, or made very loose.
Another example is supply-side grounded and ungrounded conductors being connected to the wrong terminals of service equipment, which if energized will give off enough fireworks to remind you of the 4th of July! Many temporary service installations are installed by non-electrical personnel that often don’t realize what is needed or required for electrical safety. All they know is that "the boss said to put the pole in” and, by golly, that’s what they’re doing. And, usually, all the builder or owner is concerned about with his service is, How quick can you get this thing approved, and get me my power? Sound like the real world to you? It is common in field construction trades to have varying skill levels and awareness of electrical safety. Many non-electrical construction trades people really don’t have a good idea of what is electrically safe or not, and what items — especially subtle errors — may place their safety and others around them at risk.
OK, at this point you may be saying, Hey, give me a break! If there were conductors pulled out of lugs, I’d catch that in a heartbeat. Yes, you probably would catch the obvious stuff, but what about those more subtle things that can be deadly if ignored or bypassed because you have a huge inspection schedule, a limited amount of time, and you promised contractors that you’d be at their jobsites soon but you’re already running late? Most of us have "been there, and done that.” We enjoy being out in the field, being a part of what’s going on, and helping people. However, when it comes to safety, and signing our name to an inspection approval or citation, we need to take the time even when we don’t think we have it. Every installation is important, even if it’s a temporary one.
I have personally experienced situations where a construction laborer moved the ground rod from one temporary service that was approved and energized by the utility, to another lot location in the subdivision for a new temporary service. Hey, the power is on, it must be okay! The man didn’t do it maliciously, he simply had no idea of the importance of grounding, or how a lack of it could affect his own safety! Installers have the responsibility to comply with NEC 110.7, Insulation Integrity, and assure that their electrical installation is free from short circuits and ground faults. Installers also must continue to be encouraged to look over their work and check it as needed before calling it in for inspection. As electrical inspectors, we visibly inspect the installation, drawing on our experience, training, and Code knowledge for compliance with adopted codes and standards. Quality electrical inspections are a vital part of safety for persons and property arising from the use of electricity.
One proposal for NEC-2008 intends to improve safety on construction sites. Proposal #13-11 creates new Section 445.20, which will require GFCI protection for all 125 and 125/250-volt, single-phase, 15-, 20-, and 30-ampere receptacle outlets that are part of portable electric generators. It may surprise you that this has not been previously required in the Code, but it’s true.
Table 1 provides some common Code violations often found on temporary services. This is intended to be a useful guideline, but not an all inclusive checklist. Others items may apply to specific installations or geographical areas.
Installing a temporary service on a jobsite means that many more inspections will follow on the same site. As subsequent inspections are made, changes to the temporary service installation that had previously been approved may develop because of damage or abuse. Finding support posts knocked over, grounding electrode conductors cut in half or damaged, or other types of physical damage is not uncommon. The electrical permit holder has responsibility for the safety of the temporary service installation. However, as we become aware of unsafe situations regarding the temporary service electrical equipment, we need to alert the permit holder as soon as possible.
In summary, we have focused on temporary services, their equipment short-circuit current ratings, common Code violations found in temporary service installations, and the need for comprehensive inspections every time a temporary service is installed.
There is an apparent need in the field to be more aware of electrical safety for temporary electrical service installations. In general, the only difference between a temporary electrical service and a permanent one is the length of time that it exists. Making sure that service equipment has the proper ratings for the short-circuit current available at the equipment, and that every temporary service installation is thoroughly inspected will go a long way toward electrical safety.
Read more by Michael Weitzel
Posted By Ron Janikowski,
Wednesday, November 01, 2006
Updated: Sunday, February 10, 2013
| Comments (0)
Each code cycle, members of the code-making panels have the opportunity to review countless code proposals. Every now and then, a proposal to develop a new article is received. The Technical Correlating Committee (TCC) then has to determine its merits and assign a code panel, based on their assigned Code sections, to review and select which chapter in the Code would be the appropriate location for the new article. This year was no exception. Panel 12 was assigned to review a proposed new Article 626, Electrified Truck Parking Space Equipment As a principal member of CMP-12 and member of the task group assigned to this new article, I was excited to work on an article that could potentially revolutionize the long-haul commercial trucking industry and help reduce our dependence on foreign oil.
Photo 1. Shurepower stanchion-mounted pedestal
Figure 1. States with idling regulations
By way of introduction to the members of CMP-12, this code proposal was developed by the Truck Stop Electrification (TSE) Committee of the National Electric Transportation Infrastructure Working Council (IWC), sponsored by the Electric Power Research Institute (EPRI). The TSE Committee is a multi-industry group of professional volunteers, involving truck manufacturers, TSE designers and implementers, component manufacturers, utilities, and members of the National Association of Truck Stop Operators, Society of Automotive Engineers (SAE), Environmental Protection Agency, Department of Energy, Department of Defense, Institute of Electrical and Electronics Engineers (IEEE), Electric Power Research Institute (EPRI), and others, working together to develop the TSE infrastructure.
The panel was asked to consider the following statistics:
- U.S. DOT hours-of-service (HOS) regulations, revised in August 2005, require long-haul drivers to rest a minimum of 10 hours after driving 11 hours. The approximately 1.4 million heavy-duty long-haul trucks on the road typically idle 10–12 hours per night, 300 nights per year.
- Trucks emit over 0.3 tons of nitrogen oxides and 21 tons of carbon dioxide each year while burning 1 to 1.3 gallons of fuel for each hour of idling.
- Idling trucks collectively burn 3.7 billion gallons of diesel fuel annually at a cost of more than one trillion dollars to the industry. That number increases as the cost of fuel increases. Other areas of concern are engine wear and tear and noise.
Photo 2. IdleAire's cab control center
Over the past several years, the attention of regulatory agencies and environmental groups has focused on reducing truck idling. Developing a standardized, safe and efficient means of reducing fuel consumption and emissions has been the goal. As of today, more than twenty states and cities have already adopted legislation to reduce the number of hours a truck idles.
Today, approximately 500,000 truck parking sites exist in the United States, with an additional 200,000 sites in non-dedicated parking areas and loading sites around the country. Less than one percent of these sites now provide any electrified parking space equipment.
Stiffer 2007 and 2010 emission standards for trucks also enhance the need to develop a means to reduce idle time while still providing for the "creature comfort” services.
Photo 3. Example of Shurepower equipment
The challenge is to develop specific electrical code rules that address the very specialized needs of trucks as they stop for their required downtime and connect to electrified truck parking space equipment. Truck stop electrification (TSE) equipment must provide an alternative for providing heat, A/C, and electrical power in the truck cab with the engine off. Once the connectivity issues of standardization, consistency and safety are in the Code, truck manufacturers can start to supply on-board standardized electrical equipment to mate with the off-board equipment the NEC governs. Article 626 will outline standard NEMA configurations, wiring methods and demand factors for the geographical areas of the country to make it economically viable to users. The infrastructure will be a major undertaking but federal grants and funds are available.
Figure 3. Anticipated growth in shorepower capable trucks
Another challenge is the initial hesitance of truckers to change their habits. Education, regulations and fleet owners can help change habits.
Future challenges have also been identified as the ability to power the truck refrigeration units (TRU). Approximately 10 percent of the trucking fleet has TRU units. Article 626 will be a good starting point as the industry comes on board with standard configurations. Future code proposals will tweak the code as new technology and standardization of the OEMs come on-board. It has also been discussed to have NAFTA-wide coverage for US, Canada and Mexico.
Where We Are Today
To date, two companies have taken the lead in engineering and installation of TSE sites. IdleAire1 and Shurepower2 have existing installations currently open, with other sites under construction. IdleAire uses an overhead gantry system to supply HVAC, phone, electric, CATV, and internet services to the truck cab. Shurepower delivers reliable single-phase 220 and 120-VAC power along with high-speed Internet, phone and cable TV services through an all-weather stanchion-mounted underground power pedestals. IdleAire has 225,000 parking spaces under contract throughout the southern tier of states. Shurepower has installations throughout the state of New York, with other installations in the planning stages. The anticipated growth in shorepower capable trucks is expected to skyrocket to more than 500,000 units on the road by the year 2014. As on-board systems become the standard and additional states regulate idle time, the infrastructure will have to keep up with demand. The southern tier of states will demand more HVAC cooling, with the northern tier of states and possibly Canada requiring infrastructure to provide cab heating and outside receptacle outlets for block/fuel heaters. The trucking industry in today’s digital age mandates that drivers have the capacity to communicate with dispatch through not only telephone but also high speed Internet capable interfaces. Several sites have wireless Internet hot spots. These services are currently available by scanning a credit card at the site or pay/control kiosk on the grounds. Current costs are very favorable compared to the cost of fuel.
Photo 5. Example of Shurepower equipment installation
Figure 4. Loading dock equipped with TSE hookup
It has been exciting to work on a new Code article that will help preserve and clean up our environment as well as reduce our dependence on foreign oil. This article, which was accepted in principle at ROP meetings last December, is still a work in progress. The task group responsible for the final document has had several conference calls as well as one on-site meeting in Atlanta, Georgia, to visit existing and new TSE sites. As of this date, no standardized provisions for truck refrigeration units (TRU) exist. As the code cycle proceeds, TSE providers will have some guidance to provide the correct electrical systems to connect the TRU units.
1 IdleAire Technologies Corporation, 410 N. Cedar Bluff Road, Suite 200, Knoxville, TN 37923
2 Shurepower, LLC, 153 Brook Road, Rome, New York 13441
Read more by Ron Janikowski
Posted By Jesse Abercrombie,
Wednesday, November 01, 2006
Updated: Sunday, February 10, 2013
| Comments (0)
If you follow the news regularly, you will see many different reports on the state of the economy. Government officials and economists closely watch these reports — and, as an investor, maybe you should, too.
Here are a few of the most important economic indicators to consider:
Employment Situation Report
This monthly report, issued by the Bureau of Labor Statistics, shows the unemployment rate, new jobs created, the average weekly hours worked and the average hourly earnings. Economists and policymakers watch this report closely because employment drives consumer spending — a key factor in economic growth. Furthermore, low employment figures can cause the Federal Reserve to lower interest rates, while high employment figures can signal an overheated economy, which may lead the Fed to raise rates. Higher interest rates can have an effect on all your investments. When rates rise, it is more difficult for companies to borrow to expand their businesses, which can hurt their stock prices. Also, higher interest rates will likely cause the value of your bonds to drop.
Around the middle of every month, the Commerce Department releases a report on housing starts for the previous month. Economists consider housing starts to be a leading indicator of recessions and recoveries — and both those events can have an impact on interest rates.
Advance Monthly Retail Sales
Each month, the Census Bureau reports on retail sales for the previous month. This indicator tracks the merchandise sold by companies, large and small, within the retail industry. Each month’s report shows the percent change from the previous month. This indicator can affect some important areas of the financial markets, particularly retail stocks.
Consumer Price Index (CPI)
Released mid-month by the Bureau of Labor Statistics, the CPI is considered the most widely used measure of inflation. Basically, the CPI tracks the monthly change in price of a "basket” of consumer goods and services. Generally speaking, the financial markets anticipate the CPI will rise at an annual rate of 1 percent to 2 percent; any larger increase is seen as a signal of inflation heating up too much. (Keep in mind that the "core rate” of inflation excludes food and energy prices, which are often volatile.)
Producer Price Index (PPI)
Generated each month by the Bureau of Labor Statistics, the PPI is not as commonly used as the CPI, but it is also considered a reasonably good indicator of inflation. The PPI is essentially a basket of various indexes covering a wide range of industries, including manufacturing and agriculture. Because the PPI includes goods being produced, it is often seen as a "forecast” of future CPI reports.
When it comes to investing, no one has a crystal ball. But by paying close attention to these and other economic indicators, your investment professional can acquire valuable information that may well help you make the right moves at the right time.
If you wish to follow these indicators yourself, look at http://www.fxstreet.com/news/economic-indicators/ or http://www.economicindicators.gov/.
Read more by Jesse Abercrombie
Posted By Richard Temblador,
Friday, September 01, 2006
Updated: Sunday, February 10, 2013
| Comments (0)
The traditional distinction between MC and AC cable applications is changing because of a new interlocked armor ground Type MC cable. In the last few years, contractors have been using Type MC cable for branch circuits because of the installed-cost savings MC delivers. Now, a new form of Type MC —MCAP™ cable — promises to reduce installation time further. In addition, the new cable can also be utilized in applications formerly reserved for Type AC cable, increasing productivity.
For both those reasons, MCAPcable and its health-care-facility version, HCF MCAPcable, are likely to be encountered by inspectors in the field. This article will update you with the latest information and background regarding the new cable, as well as provide the information you will need to recognize it and determine proper installations.
Although the new product resembles ordinary Type MC or AC cable, it differs in several respects that will be noticeable during an inspection (see figure 1).
Figure 1. Cable differences
What Is MCAPCable?
MCAPcable is Type MC cable constructed with THHN copper insulated circuit conductors and interlocked armor that is listed and identified for grounding. Prior to Alflex being acquired by the Southwire Company, the cable was originally referred to as MC SMART. After considering potential cable applications, Southwire decided to change the product name to MCAPcable to better reflect the all-purpose aspect of the product. The "AP” in MCAPstands for All-Purpose, which means that MCAPcable can be used in both MC and AC cable applications. The dual use is permitted because the armor of MCAP cable is listed and identified as a suitable equipment grounding path, unlike conventional MC.
Here’s How the Armor Ground Path Works
A full-sized bare aluminum grounding conductor, located outside the Mylar tape covering, is in direct contact with the interlocked armor throughout the entire cable length. This allows the armor of MCAPcable to serve as an equipment grounding conductor with full UL® and NEC® compliance. The MCAPcable armor ground path is equivalent to the green copper ground in conventional MC cable. Unlike Type AC cable, the bare aluminum ground conductor increases based on the size of the copper circuit conductors just like the green ground in conventional MC Cable. For example, an MCAPcable with 10 AWG copper circuit conductors would contain an 8 AWG aluminum grounding conductor (see figure 2).
Figure 2. Interlocked armor ground MC
Armor Ground Yields Productivity Benefits
UL-listed and NEC-compliant, MCAP and HCF MCAPcables provide an innovative built-in armor ground that eliminates the need to make up equipment grounding conductors in every outlet box, luminaire, and panel. One immediate benefit for contractors is that with MCAPcable, there’s no need for separate equipment grounding conductor connections inside the box. This may sound like a small detail, but MCAPcable can make a big difference in the contractor’s installation time and total installed costs.
With MCAPcable, contractors save time in every box, outlet, light fixture and panelboard, over and over again. Where contractors install hundreds — or thousands — of cables, outlet boxes, and luminaires in a project, the time savings can really add up. Branch circuit make-up productivity can jump by 20 to 30 percent. That’s why you’re likely to see MCAPcable on the job site.
Figure 3. 5-step installation process
Installation Instructions Provided with Every Reel and Coil
Installation instructions are required by UL to be provided with every reel and coil. When MCAPcable is installed, the installer cuts the aluminum grounding conductor flush with the armor, then secures the cable into a fitting listed for the new cable. The listed fitting provides a bonding connection between the armor and the box. An effective ground-fault current path is established because the armor is equivalent to the green insulated equipment grounding conductor in a conventional MC cable.
With self-grounding wiring devices, no equipment bonding jumper between the device and the box is needed. If the wiring device is not self-grounding, a bonding jumper from the device to the box is required. See figure 3 for the 5-step installation process.
The use of the armor as an equipment grounding conductor path distinguishes MCAP cable from conventional MC cable.
Listing Process for Cable and Fittings Now 100% Complete
The new armor ground system in MCAPcable is the culmination of several years of development, testing, UL standard changes, and UL listing. To give a sense of the time required to move a new electrical product through the approval processes, an early article about MCAPcable (formerly MC SMART) appeared in this magazine in May 2004.1 At that time, nearly four years of development had already gone into the design. Some of the descriptive information in this article is based on that earlier piece.
Figure 4. HCF MCAP cable is the first interlocked armor MC cable that meets NEC requirements for redundant equipment grounding conductor paths in health care facilities.
Since that article, additional changes have taken place in both the product and the related documentation. Some of those changes were based on comments from inspectors who were involved in UL’s Standards Technical Panels.
- The UL-listed method for terminating the aluminum grounding/bonding conductor changed. Folding back and placing the aluminum ground under the fitting was revised to cutting off the aluminum ground flush with the armor to eliminate potential interference with the fitting cable securement means.
- UL 514B Standards for Fittings was revised to include references, listing criteria, and marking requirements for "interlocked armor ground MC Cable.” This process alone took a year and a half, and involved close coordination between the cable manufacturer and the fitting manufacturers.
- UL Guide Information for MC Cables, MC Cable fittings and Metallic Outlet boxes have also been updated to reflect the new interlocked armor ground MC Cable Listings, markings and grounding over 250 volts. MC Cable Fittings listed for use with cable Type MCI-A under category PJOX are suitable for bonding over and under 250 volts. See excerpts from the UL guide information provided below.
- All boxes with eccentric or concentric knockouts listed under category QCIT are suitable for grounding and bonding over and under 250 volts. See excerpts from UL Guide information provided below.
UL White Book Information
The following key excerpts regarding MCAPhave been taken from UL’s Online Certification Directory and can be found on UL’s website,www.ul.com.
UL Online Certifications Directory
"Cable with interlocked armor that has been determined to be suitable for use as a grounding means has interlocked aluminum armor in direct contact with a single, full-sized, bare aluminum grounding/bonding conductor. This cable is marked to indicate that the armor/grounding conductor combination is suitable for ground.”
"Cable with an interlocked armor that is intended as a ground path is marked ‘armor is grounding path component,’ and is provided with installation instructions.”
UL Online Certifications Directory
Metallic Outlet Boxes
Concentric or Eccentric Knockouts
"All boxes with concentric or eccentric knockouts have been investigated for bonding and are suitable for bonding without any additional bonding means around concentric (or eccentric) knockouts where used in circuits above or below 250 V and may be marked as such.”
UL Online Certifications Directory
Metal-clad Cable Connectors, Type MC
"This category covers … (b) metal-clad interlocking armor ground cable” (MCAPand HCF MCAPcables.)
"Metal-clad connectors for use with metal-clad interlocking armor ground cable … are considered suitable for grounding for use in circuits over and under 250 V and where installed in accordance with … National Electrical Code.”
As an alternative to conventional AC cable, MCAPcable yields significant benefits. To begin with, it reduces termination steps, compared to AC (see table 1).
- More conductors than AC
Types AC and AC cables for health care facilities are limited to four current-carrying conductors. MCAPand HCF MCAPcables have no limits on the number of conductors in a cable. That means you may see multiple neutrals and home run cables where MCAPcable is used, even in health care facilities.
- Equipment grounding conductor capacity
The armor of MCAPcable delivers 350 percent more effective ground-fault current path capacity than AC. This is based on the UL maximum permitted armor resistance for MC and AC cables. With the addition of a green insulated grounding conductor, HCF MCAPcable meets NEC 517.13 requirements for health care facilities.
- No bushings, less support than AC
Because MCAPand HCF MCAPcables are Type MC products, they require no anti-short bushings where the armor has been cut. For more information regarding the use of anti-short bushings, refer to NEMA’s Engineering Bulletin No. 90, "Use of Anti-Short Bushings for Terminating Type MC Cable” (available atwww.NEMA.org). In addition, they require less securing and supporting than Type AC cables. Like conventional MC, MCAPand HCF MCAPcables need support only every six feet, compared with 4.5 feet for the AC constructions.
Table 1. Comparing AC termination steps with MCAP
First Interlocked Armor Type MC Cable for Health Care Facilities
HCF MCAPcable is the first interlocked armor MC cable that meets NEC 517.13 requirements for redundant equipment grounding conductor paths in health care facilities, and, as noted above, HCF MCAPcable has a 350 percent better ground-fault current path in the armor than the armor of AC cable suitable for use in health care facilities. Figure 5 shows a comparison of HCF MCAP cable with AC cable suitable for use in health care facilities.
Figure 5. Pre and post cable identification
Identification of MCAPCable
Coils of MCAPcable will be shrink-wrapped and color-coded to identify gauge and voltage. This will make it easier to identify MCAPcable and to distinguish it from AC and standard MC. Every package of MCAPcable will carry an identification tag that indicates the cable type and the information that the armor and grounding conductor combined are an effective ground-fault current path. The tag also provides installation instructions.
For post-installation identification, the white neutral (ungrounded) current-carrying conductor of MCAPcable is marked "armor is equipment grounding path component.” The conductor marking makes it easy to identify MCAP cable after installation (see figure 5.)
Initial Cable Availability Includes Common Conductor Sizes
Inspectors will see MCAPand HCF MCAPcables first in branch circuit sizes from 14 to 10 AWG, with 120 V and 277 V conductor colors. Other conductor combinations will be available later.
MCAPand HCF MCAPcables are rated for 90ËšC dry locations and for use in cable trays. They are also classified for use in one-, two- and three-hour through penetration systems. The UL Online Certification Directory provides more detail on these applications.
Table 2. Fittings UL approved for MCI-A/MCAP cable applications
Listed Fittings and Boxes Are Now Available
Fittings used with MCAPand HC MCAPcables must be listed for use with MCAPcable, or for use with interlocked armor ground MC cable, and are marked for use with
Type MCI-A cable. Tables 2 and 3 show a list of approved fittings and boxes.
Field Inspection Guidelines for MCAPcable
Here is a list of details to verify for when inspecting installations of MCAPand HC MCAPcables.
- Aluminum ground conductor cut flush with armor
- MC Cable Fitting packaging marked MCI-A
- Installation instructions are followed based on instruction tag included with every package of MCAPcable.
- Bonding jumpers are required on non-self-grounding devices only.
- Post installation identification via white neutral (ungrounded) current-carrying conductor is marked "armor is equipment grounding path component.”
- Support required every six feet.
- MCAPand HCF MCAPcables are allowed in
— Branch circuits
— Exposed or concealed dry locations
— Cable trays
— Places of assembly
Educational Efforts Are On-Going
Southwire Company, manufacturer of MCAPcable is actively engaged in efforts to educate and increase awareness of this new form of MC cable with contractors and the inspection community. Additional information is available on the manufacturer’s Web site atwww.Southwire.com.
1New Products Don’t Grow on Trees!,Trainor, Thomas and Johnston, Michael J.,IAEI News, May-June, 2004, pp. 36 – 45.
Read more by Richard Temblador
Posted By Michael Johnston,
Friday, September 01, 2006
Updated: Sunday, February 10, 2013
| Comments (0)
In the July/August issue, we provided a glimpse of some of the more significant changes proposed and accepted for NEC-2008. This article is a continuation of that review. Once again, it is important to stress that this is a look at what was proposed and acted on by the code-making panels through the proposals stages of the NEC-2008 development process. These changes could be affected by public comments to the initial committee actions on these proposed revisions. The established deadline for public comments to the proposed changes is October 20, 2006 (5:00 p.m. est).
More Code-Wide Revisions
Photo 1. Disconnecting means capable of being locked in the open position. The provision for locking or adding a lock to the disconnect remains with the switch whether the lock is installed or not.
This first series of changes has to do with Code rules that include the words "capable of being locked in the open position.” Approximately thirty locations throughout the NEC use this wording in the requirements. The concept in all of these instances is the same and is related to safety for workers. Generally, where the Code requires a disconnecting means, it is required to be in sight from, or within sight from the equipment it controls. The term In sight from (within sight from, Within Sight) is defined in Article 100. In many of these disconnect location rules, there is also an allowance (usually by exception) that indicates the disconnecting means could be located out of sight from the equipment if the disconnect is capable of being locked in the open position. However, the wording differs from section to section. New concepts were introduced by CMP-11 in NEC-2005 that clarified the objective (intent) of that requirement. This resulted in a provision for locking or adding a lock to the disconnecting means to be installed on or at the switch or circuit breaker used as the disconnect and for the provision to remain in place with or without the lock installed (see photo 1). This is an important safety requirement for workers. It is logical that, for more consistent and uniform application of this rule, the language should be the same in the various rules that include this provision.
Revision: 240.86(A) Selected Under Engineering Supervision in Existing Installations
Figure 1. Engineered series rated overcurrent device combinations
The concepts in Section 240.86(A) were introduced in NEC-2005 and recognized a method of applying an engineered series rated combination of overcurrent protection that is selected under engineering supervision for existing installations only. This section has been revised this cycle to require specific field marking on equipment applied in engineered series rated combinations. An additional sentence has been added to clarify the operating characteristics of devices applied in combinations selected and applied under the provisions of this section. The new sentence reads as follows: "For calculated applications, the engineer shall ensure that the downstream circuit breaker(s) that are part of the series combination remain passive during the interruption period of the line side fully rated, current-limiting device.” Although application of this provision is not common, the revisions to this section provide needed details clarity for professionals choosing to apply it in existing installations (see figure 1).
Revision: 250.32(B)(1) Exception
Figure 2. Grounding at separate buildings or structures
Section 250.32(B)(2) has been incorporated as an exception to Section 250.32(B)(1) and will apply to existing installations only. The revisions to this section are consistent with the efforts of Code-Making Panel 5 to continue to migrate away from the use of the grounded conductor for grounding on the load side of the service disconnecting means. The original proposal was to delete Section 250.32(B)(2) completely which would not have left any language that could be applied to existing installations. The changes in this section also restrict the application to existing installations only. The conditions specified in Section 250.32(B)(2) for use of the grounded conductor for grounding equipment were already restrictive in nature for new designs and installations contemplating its use. The effect of this revision is users having to develop designs and installations of feeders or branch circuits that include an equipment grounding conductor in accordance with the requirements of 215.6 and 250.32(B)(1) for all feeders or branch circuits installed to supply separate buildings or structures. This change should help reduce the number of designs that purposely invite the possibilities of inappropriate neutral-to-ground connections that can, and often do, happen later, which is uncontrollable by any NEC rule. Existing installations meeting the requirements of Section 250.32(B)(2) in previous editions of the NEC would be allowed to remain operational. However, the restrictive conditions of the new exception [former 250.32(B)(2)] still have to be met and are subject to approval of the applicable authority having jurisdiction (see figure 2).
Revision: 250.94 Bonding for Other Systems
Figure 3. Intersystem bonding termination
This section has been completely revised by additional specific requirements for intersystem bonding and grounding terminations. The existing text has been retained and rewritten into an exception to the new requirements. This revision is one of several correlated changes (100 Definitions, 250.94, Chapter 8 Articles) to improve the requirements related to intersystem bonding and grounding of communication systems. The effect of this change inserts a requirement for a dedicated and well-defined location for terminating the bonding and grounding conductors on a specific set of terminals or a bonding bar provided for that purpose. The proposed termination would have sufficient capacity to handle multiple communication systems (telecom, satellite, CATV) on premises, but not less than three terminals are required. Specified locations for these termination points for the intersystem bonding termination is a key part of the revision. The termination means is required to be secured (electrically and mechanically) to the meter enclosure located at the service equipment enclosure or at the grounding electrode conductor (see figure 3).
New Section: 310.15(B)(2)(c) Conductors Exposed to Sunlight on Rooftops and Table 310.15(B)(2)(c)
Figure 4. Conductors exposed to sunlight on rooftops
A new requirement in subdivision (c) has been added to Section 310.15(B)(2). In addition, a new companion Table 310.15(B)(2)(c) has been added to this section. To correlate with this change, the existing FPN 2 to Section 310.10 has been deleted in NEC-2008. This new requirement for ampacity correction due to ambient temperature results from extensive study, fact-finding efforts, and collected data that demonstrated valid concerns about excessive heat exposure for conductors and cables installed on rooftops in the sunlight. Full details are contained in the test report entitled Effect of Rooftop Exposure on Ambient Temperatures Inside Conduits, November 2005. The studies clearly warranted new requirements for ampacity correction factors for such installations. In electrical installations of conduit, tubing, and cable that are on rooftops and exposed to the sunlight, temperature value factors in accordance with new Table 310.15(B)(2)(c) are now required to be added, and vary based on the height the wiring method is installed above the roof surface. For example, if a conduit is installed 300 mm (12 in.) above a rooftop in an ambient temperature of 122ºF, then 30º is required to be added to the anticipated maximum ambient temperature in which the conduit is installed. In this case, the value of 152ºF must be used for temperature-correction-factor-application adjustments from the applicable table in 310 (see figure 4).
Revision: 314.27(D) Boxes at Ceiling-Suspended (Paddle) Fan Outlets
Figure 5. Boxes at ceiling-suspended (paddle) fans
A new last sentence adds specific requirements regarding the type of box that must be installed when two or more switched ungrounded conductors (switch legs) are roughed in to the box. The new requirement calls for a box that is listed for sole support of a ceiling-suspended paddle fan. This requirement applies to all occupancy types as it is currently worded. This affects the rough-in stages of all electrical installations where ceiling-mounted outlet boxes are installed and more than one switch leg is provided to the outlet. It is commonly understood that in many residential occupancies and some commercial occupancies, luminaires are sometimes replaced by a ceiling-suspended paddle fan at some time after the initial installation, but rarely are the proper listed boxes installed to accommodate the fan support requirements in the NEC. This new requirement takes a proactive approach through a rule that should help reduce the number of ceiling-suspended paddle fan installations that would be supported solely by boxes that are not designed or suitable for providing adequate support (see figure 5).
New Article: Article 355 Reinforced
Thermosetting Resin Conduit: Type RTRC
Figure 6. Reinforced thermosetting resin conduit: Type RTRC
Requirements for reinforced thermosetting resin conduit: Type RTRC have been included in the Code as Article 355. In NEC-2002, Article 352, Rigid Nonmetallic Conduit (RNC), included PVC, RTRC, and HDPE products. However, for NEC-2005, High Density Polyethylene Conduit: Type HDPE was separated from these other conduit types and located in new Article 353. This action left two very dissimilar products grouped together as rigid nonmetallic conduit under Article 352, and technically eliminated HDPE as an acceptable wiring method in all applications where rigid nonmetallic conduit was specified. The separation of PVC and RTRC conduit and the change in title to Article 352 and new definition of Rigid Polyvinyl Chloride Conduit in Article 352 are specific to PVC conduit and fittings. Types HDPE and RTRC are covered under separate articles, correcting this situation by better defining the installation and construction specifications for each nonmetallic conduit type. The new Article 355 includes three parts as follows: Part I General, Part II Installation, Part III Construction Specifications (see figure 6).
Revision: Article 382 Nonmetallic Extensions
Figure 7. Concealable flat nonmetallic extensions
Article 382 has been revised to incorporate provisions for concealed flat nonmetallic extensions. A new definition of this type of concealable flat nonmetallic extension has been added in 382.2. The article has been expanded to include specific product listing requirements in 382.6. Sections 382.10 and 382.12, covering Uses Permitted and Uses Not Permitted, have been revised and expanded to incorporate requirements and restrictions for concealable flat nonmetallic extensions. A new Part III has been added to Article 382 and provides specific construction specifications for concealable flat nonmetallic extensions. New technologies, consumer electronics devices such as flat panel televisions and custom audio systems, along with ever-changing lifestyles have increased the need for additional power outlets and the desire to place power or lighting outlets where needed to obtain functionality as well as an aesthetically pleasing environment. Often these changes are poorly accommodated through the use of extension cords that are easily damaged, misused and can lead to electrical hazards. This new type of concealable flat nonmetallic extension incorporated into Article 382 provides a safe and reliable alternative for existing occupancies that can reduce the misuse of extension cords, overload power taps, and so forth (see figure 7).
Revision: 406.8(B) Wet Locations
Figure 8. Receptacles in wet locations exposed to the elements
Action by CMP-18 responds to substantiation that demonstrates a need for receptacles installed in these locations to be suitable for the elements they are subjected to over time. The sentences, "The receptacle shall be a listed weather-resistant type. This listed weather-resistant requirement shall become effective on January 1, 2011.” have been added to Sections 408.8(A), 408.8(B)(1), and 408.8(B)(2). Substantiation indicated that deterioration and other detrimental conditions have a negative effect on receptacles, and often result in the receptacle faces becoming brittle and breaking. Even though the NEC has made significant progress in the cover requirements for receptacles installed in wet and damp locations, receptacles are still often exposed to varying degrees of moisture, UV, and impact under detrimental conditions (low and high temperatures). These products have not been constructed or evaluated to being exposed to these conditions. An appropriately listed weather-resistant receptacle (able to withstand the elements) addresses the associated safety hazards and concerns of suitability of electrical products for outdoor use. Statistical data has substantiated the need for a more weather-resilient device in spite of the use of protective covers. The inclusion of the proposed additional text in conjunction with the existing code language would address this dangerous condition and noted failure rates. A new last sentence added to these sections provides device manufacturers ample notice to ensure product availability when the requirements become effective (see figure 8).
New Section: 406.11 Tamper-Resistant Receptacles in Dwelling Unit
Figure 9. Tamper-resistant receptacles required in dwelling units
Action by CMP-18 on proposal 18-40 results in a new requirement in Article 406 addressing receptacles installed in dwelling units. The new definition of dwelling unit provides clarity for users as to the extent of this new requirement. This new section adds a requirement that all 15- and 20-ampere receptacles installed in outlets required under Section 210.52 for dwelling units be a listed tamper-resistant type. Substantiation provided with the proposal clearly identified a concern about the number of injuries to and electrocution of children when foreign objects are inserted to receptacles. The substantiation provided by The U.S. Consumer Product Safety Commission’s (CPSC) National Electronic Injury Surveillance System (NEISS) indicated that during a 10-year period, from 1991 to 2001, over 24,000 children in the United States were injured when they inserted foreign objects into electrical receptacles. Every year, an average of at least 2,400 children are injured when tampering with electrical receptacles. Patient information is collected from each participating NEISS hospital for every emergency visit involving an injury associated with consumer products. From this sample, the total number of product-related injuries treated in hospital emergency rooms nationwide can be estimated. The number of injuries to children related to insertion of foreign objects into electrical receptacles is significant and has demonstrated the need to require more protection. Tamper-resistant receptacles are presently required in rooms, bathrooms, playrooms, activity rooms, and patient care areas of pediatric wards and provide a level of protection against this type of injury to children. The effect of this change extends the tamper-resistant receptacle requirement to all 125-volt, 15- and 20-ampere receptacles in all areas specified in 210.52 for dwelling units (see figure 9).
Revision: 408.36 Overcurrent Protection
Figure 10. Panelboards no longer limited to 42 overcurrent devices
Sections 408.36(A) and (B) and the associated exceptions have been restructured into one section with three exceptions. Under this revision, the differentiation between power panelboards and lighting and appliance branch-circuit panelboards has been removed. Existing subdivisions (C), (D), (E), and (F) of this section have been re-identified as subdivisions (A), (B), (C), and (D), respectively. Sections 408.34 and 408.35 which included definitions of power panelboard and lighting and appliance branch-circuit panelboard have both been deleted as a result of these revisions to Section 408.36. The revisions to this section essentially remove the 42 overcurrent device limitations for panelboards and also result in requirements that now address power panelboards and lighting and appliance panelboards in the same fashion. The newly created Exception No. 1 is based on the 2005 exception to 408.36(B) which is intended to recognize a long-standing practice of allowing a small panel to be used as service equipment, with large line-to-line loads leaving at this point and a smaller feeder entering the building to supply what formerly was called a lighting and appliance branch-circuit panelboard. The limitations now contained in this exception prevent the extension of this limited practice to what could otherwise become a split-bus panelboard with an unlimited number of overcurrent devices in the future. The six-circuit limit mirrors the customary service limitation contained in 230.71. Exception No. 2 corresponds to the 2005 language at 408.36(A) [see figure 10].
Revision: 422.51. Cord- and Plug-Connected Vending Machines
Figure 11. GFCI protection for vending machines
In the NEC-2005 development process, a new section 422.51 was added that requires cord- and plug-connected vending machines that are manufactured or re-manufactured on or after January 1, 2005, to include ground-fault circuit interrupter protection that is an integral part of the attachment plug or otherwise provided in the cord within 300 mm (12 in.) from the attachment plug. The new requirement results in revisions to the product standards [UL 541-2005 (refrigerated) and UL 751-2005] for vending machines. For older vending machines that were manufactured before this new requirement, the protection must be provided by connection to a GFCI-protected receptacle outlet. This new NEC-2005 requirement generated several questions and concerns about what a vending machine really is. Action by CMP-17 on proposal 17-27, results in new language in Section 422.51 that provides users with basic criteria as to what constitutes a vending machine. The additional information should provide the needed clarity for installers and Code enforcement authorities that results in more uniform and consistent application of the protection requirements in this rule. The new FPN following this section provides users with a handy reference to the applicable product safety standard for vending machines (see figure 11).
Revision: 501.10(B)(7) Class I, Division 2 Wiring Methods
Figure 12. RTRC and schedule 80 PVC in Class I, Division 2 locations
Action by CMP-14 responded favorably to proposal 14-33 to expand the wiring methods listed in 501.10(B)(1) to include reinforced thermosetting resin conduit (RTRC) and schedule 80 PVC conduit. Substantiation provided with proposal 14-33 indicated that there were situations where corrosion concerns for metallic methods could affect the installation. It was also pointed out that there are already current allowances in the NEC (under specific conditions) for nonmetallic wiring methods in Class I, Division 2 locations. The result was the creation of a CMP-14 proposal (14-33a) that incorporates these two nonmetallic wiring methods into this section. This type of wiring in Class I, Division 2 locations is limited to use only in industrial establishments with restricted public access, where the conditions of maintenance and supervision ensure that only qualified persons service the installation, and where metallic conduit does not provide sufficient corrosion resistance. Although this section has been expanded to include Type RTRC and PVC conduit as wiring methods in Division 2 locations, restrictions provided in this new item (7) have inherent limitations on the use of nonmetallic wiring methods in Class I, Division 2 hazardous locations (see figure 12).
New Section: 513.3(C)(2) Aircraft Painting Hangars
Figure 13. Aircraft painting hangar rules in the NEC
Section 513.3(C) has been revised and restructured into a list format to meet the NEC Style Manual requirements. A new (C)(2) has been added to this section, providing area classification for aircraft painting hangars. Previous editions of the NEC did not include hazardous area classification for aircraft hangars used for painting. NFPA Standard 409-2005 has been revised to specifically separate the hazardous locations near aircraft for aircraft paint hangars from those of general maintenance. Aircraft paint hangars, while constructed like huge paint booths, do not have the same dimensional clearances found in traditional paint booths. The shape of the aircraft creates clearances far greater than that found in any other painting system. This creates a level of safety not found in traditional paint booths and supports hazardous location classification that is less than the entire hangar. The new definition of aircraft painting hangar provides clear descriptive information about what constitutes an aircraft painting hangar to facilitate appropriate application of the area classification boundaries provided in the new provisions in Section 513.3(C)(2). These revisions provide designers, installers, and enforcers with necessary information that establishes the extent of the Class I, Division 2 or Zone 2 locations where aircraft is painted in hangars (see figure 13).
New Article: Article 519 Control Systems for Permanent Amusement Attractions
Figure 14. Control systems for permanent amusement attractions
CMP-15 responded favorably to a proposal to incorporate a new Article 519 in Chapter 5 that addresses control systems for permanent amusement attractions. Previous editions of the Code did not provide rules that could be applied to these types of installations. While Article 525 provides general requirements for electrical installations at carnivals, fairs, circuses, and similar events, it applies only to those entities that are portable. The new article provides specific rules applicable to control power sources and conductors, including associated control wiring in or on all structures that are part of a permanent amusement attraction, as indicated in the scope of the new article. The article is divided into three parts: General, Control Circuits, and Control Circuit Wiring Methods. The new article should provide users with rules that can be applied to these specialized installations and systems that are unique and permanently installed (see figure 14).
New Article: Article 585 Critical Operations Power Systems (COPS)
Figure 15. Critical Operations Power Systems
The new article is the result of work by the NEC Technical Correlating Committee Task Group on emergency and standby power systems for Homeland Security. Code-Making Panel 20 was re-formed for the NEC-2008 development process. The primary assignment from the NEC Technical Correlating Committee for CMP-20 was to develop a new article that addresses power systems or circuits that are critical, and considered vital to remain operational in the event of disruption of power. Recent terrorist events and natural disasters, including the World Trade Center attack, the 2005 hurricane season, most notably Hurricane Katrina, have brought to light the need to assess the adequacy of current requirements in the NEC that address mission critical facility electrical infrastructure protection and reliability. Such systems may be installed throughout an entire facility or may be limited to specific areas depending upon the nature of the operations and where they are to be conducted within a specific facility. An important aspect of proper and consistent application of this new article requires understanding which entities are responsible for determining facilities that qualify for critical operations power systems. The scope of the new article provides guidance about which authority has the responsibility for making these determinations. The new article includes five parts: General, Circuit Wiring and Equipment, Power Sources and Connection, Overcurrent Protection, and System Performance and Analysis (see figure 15).
New Article: Article 626 Electrified Truck Parking Space Equipment
Figure 16. Electrified Truck Parking Space Equipment Photo courtesy of Georgia Power
Action by CMP-12 results in the addition of a new Article 626. This article resulted from the work of the Truck Stop Electrification (TSE) Committee of the National Electric Transportation Infrastructure Working Council (IWC), sponsored by the Electric Power Research Institute (EPRI). The TSE Committee is a multi-industry group of professional volunteers, involving truck manufacturers, TSE designers and implementers, component manufacturers, utilities, and members of the National Association of Truck Stop Operators, Society of Automotive Engineers (SAE), Environmental Protection Agency, Department of Energy, Department of Defense, IEEE, EPRI, and others, working together to develop the TSE infrastructure. Over the past several years, the attention of regulatory agencies and environmental groups has focused on means to reducing truck idling, thereby reducing emissions and fuel consumption. More than twenty states and cities have already adopted legislation to reduce the number of hours a truck idles. Developing a standardized, safe and efficient means of reducing fuel consumption and emissions is the primary objective. This new article provides users with rules that can be applied to electrical installations and systems designed for supplying electrical power and services to trucks while they are parked. This new article includes provisions similar to those that already exist in Articles 550 and 551 that also include requirements for permanent power facilities (see figure 16).
Revision: 700.9(B) Wiring
Figure 17. Emergency system wiring separation requirements
The general requirements and concepts behind Section 700.9(B) relate to separation between emergency circuits from other than emergency loads, unless in accordance with the allowances provided in this section. Action by CMP-13 results in a new list Item (5) in Section 700.9(B). This additional text clarifies that the original separation requirements from the source to the loads, or from the source-distribution overcurrent protection to the loads, is to be required unless modified by any of the provisions in items (1) – (5). The revised text will further clarify that it is permitted to supply any combination of emergency, legally required, or optional loads from a single feeder, or from multiple feeders, or from separate vertical sections of a switchboard that are supplied by either a common bus or individually. The use of an overcurrent protective device at the standby source or for the equipment is related to reliability and design. While the new requirements in (5)(b) maintain the highest degree of reliability, the exception to (5)(b) will also permit the use of an overcurrent device at the source or for the equipment. The coordination of the overcurrent protection at the source or for the equipment with the downstream overcurrent protection requirement in this exception will maintain the highest degree of reliability possible while allowing protection for conductors and equipment. The revised text in the main paragraph clarifies that circuits supplying emergency loads are not to be combined in panelboard enclosures with circuits supplying other loads (see figure 17).
New Section: 800.156 Dwelling Unit Communications Outlet
Figure 18. Dwelling unit communications outlet
While it is a common practice to include communications systems wiring and outlets in dwellings, there have not been any mandatory requirements in the Code for such wiring or outlets. This new section requires at least one communications outlet and associated wiring to be installed in all new construction of dwelling units. It is very common to include several communications outlets in dwelling unit construction. Substantiation provided with the proposal indicated that at least one communications outlet in the home is needed for many reasons, but most important is for emergency services such as a simple call for police, fire or rescue squad. In addition to the problem it solves for communications needs for occupants of a dwelling, the proposal is also targeted at safety of technicians and emergency responding personnel while enhancing the five key NFPA strategies to reduce fatal home fires. The new definition of dwelling unit in Article 100 helps clarify where this requirement must be applied. Direction for installers is also included in this new requirement that calls for the rough wiring for this communications outlet to be routed to the service provider demarcation point of the dwelling unit (see figure 18).
Care and attention to detail have been taken to provide accurate and informed insight into the proposed changes to NEC-2008. This article includes various revisions and new requirements as well as a look at some new articles that possibly will appear in the new NEC. The information provided in this article is based on proposed changes and the code-making panel actions to the proposals at this stage of the NEC development process. The revisions and information in this article could be affected by public comments to the proposed changes. Public comments on the proposals are encouraged. The NEC is a work in progress, a work that involves all of us. It is a better Code each cycle because of the dedication and commitment by many.
Read more by Michael Johnston
Posted By Thomas P. Lanzisero,
Friday, September 01, 2006
Updated: Sunday, February 10, 2013
| Comments (0)
Hazard-based product safety standards are now under development, and this hazard-based approach is likely soon to affect other product/equipment safety standards as well as installation codes.
What is this hazard-based approach? How could it impact safety standards for equipment and installations? Are there relevant applications in electrical safety and practical examples for electric shock and protection?
Hazard-based safety standards can offer clear safety objectives and means to meet them. A hazard-based approach provides us with another way to reduce risk of harm by addressing each hazard. This approach would determine which undesirable effects are to be avoided; the susceptibility to them, their conditions and causes; and appropriate protection against them. A hazard-based standard would identify the objectives of protecting against each specific undesirable effect, and directly relate them to appropriate protection requirements and limits. How does this apply to electrical safety?
Figure 1. Hazard leads to harm (undesirable effect/injury) if interaction exceeds body susceptibility to that effect.
We’re all concerned with electrical safety; we benefit from it and may contribute to it in one way or another. Safety in the U.S. is addressed in standards such as ANSI C2 National Electrical Safety Code for utility distribution to the building; NFPA 70 NationalElectrical Code(NEC) for premises installation; NFPA 70E Standard for Electrical Safety in the Workplace; and OSHA requirements (29 CFR 1910 Sub-part S) for the workplace; as well as product requirements such as UL/ANSI safety standards covering construction and performance of systems, equipment, devices, components, materials, in addition to safety-critical programmable logic and software.
But what is safety? Safety may be considered as freedom from unacceptable risk of harm.1 The lower the severity and likelihood of harm, the lower the risk and the greater the safety. Safety is relative, not absolute, with a primary objective to reduce risk to an acceptable level.
Figure 2. Risk of harm is reduced if protective mechanisms reduce hazard and/or interaction.
The primary objective of electrical safety is to reduce relevant risks to an acceptable level, particularly concerning fire, arc flash and shock hazards. We know electrical energy can be hazardous, even lethal. But many of us may have experienced what we consider electric shock, at levels that were fortunately low. We may know shock by experience, but what is electric shock, what is the harm, how is it caused, and how is it prevented?
In this context of electrical safety, let’s consider electric shock as any undesirable physiological effect due to the flow of current through the body. The harm is the undesirable effect, whether or not a direct injury results. The severity of these effects increases with current levels or duration of time and depends on the susceptibility of body parts in the current pathway. Increasingly higher current causes increasingly severe effects, for example from sensation to involuntary reaction, to strong muscular effects, difficulty in breathing and inability to let go, to ventricular fibrillation and death.
Figure 3. Example body current pathways: hand-to-hand and hand-to-feet (grounded circuit and body).
The susceptibility to these physiological effects is described in IEC Technical Specification 60479.2 This is a basic safety publication that describes the effects of current and the threshold levels at which these effects are likely to begin across the population. In addition, some touch voltage thresholds have been determined that correspond to certain current thresholds, physiological effects and varying body impedance, in a separate proposed draft. This can also provide a better understanding of conventional contact voltage limits (such asNECClass 2) and the underlying conditions that should apply to them, such as skin contact area and moisture, and suitability of startle reaction current levels with regard to contact circumstances.
Figure 4. Electrical shock hazard leads to harm (undesirable physiological effect / injury) if body susceptibility to that effect is exceeded. Susceptibility is based on current for a duration.
Based on research data and analysis, these international technical reports include significant US contribution, and are developed by experts in science and engineering disciplines such as physiology, electrical engineering and other relevant fields. Such technical information forms the foundation for this hazard-based approach to codes and standards for safety. It also forms the technical basis for many existing and developing requirements on electric shock and protection, with suitable safety factors between limits and the physiological thresholds of susceptibility.
Hazard-Based Approach: Safety Standards and Codes
A hazard-based approach for safety standards provides a different way to establish a very clear connection between protection requirements and the undesirable effects, such as injury, to be avoided. Likewise, the undesirable effects would be clearly identified and linked to the protective mechanisms in the requirements. Limits to protect against the harm need to be appropriate, based on technically correct analysis and application of data on physiological thresholds of susceptibility, and with safety factors suitable for the level of risk.
Figure 5. Reducing the risk of electric shock: Body Impedance can limit current below susceptibility to harm (undesirable physiological effects) - but only under the right conditions such as with a low voltage source.
So what is a hazard, how does it cause harm, and how do we protect against it? Simply put, a hazard is something that can cause harm. As an example, a residential Class 1 branch circuit can cause electric shock injury or death to persons that interact with it, directly or by way of wiring, devices or equipment. A hazard-based approach seeks to reduce risk of harm by addressing each hazard. It would first determine the specific harm to be avoided and the susceptibility to it, then analyze the causes of the harm, and then focus on appropriate protection against it.
Determining the harm to be avoided would address each undesirable effect, such as specific injury under set circumstances, and particularly the susceptibility to the harm. Analyzing the causes of harm would cover the mechanisms, factors, conditions and cause-and-effect relationships, and would then identify the source as hazardous. Focusing on appropriate protection would identify and then prioritize protective mechanisms that are effective, reliable and practical.
A hazard-based analysis can provide a clear, straightforward model for an otherwise complex problem. It’s a tool we use to analyze a problem and prioritize its solutions — to solve a problem in the right way. It emphasizes and supports the need to first analyze, then evaluate, test and validate.
Figure 6. Reducing the risk of electric shock: Source impedance can limit current below susceptibility to harm (undesirable physiological effects) - but only under the right conditions such as with a limited current source.
Hazard-based product safety standards are now being developed by organizations including Underwriters Laboratories and the International Electrotechnical Commission (IEC), for equipment such as information technology, telecommunications and consumer electronics. The objective is to put this theory into practice to meet the safety objective of reducing risk: to address each hazard and its mechanism for harm, in order to address the mechanisms for protection. This type of hazard-based approach is likely soon to affect other product/equipment safety standards as well as installation codes.
A hazard-based approach identifies a hazard such as parts energized by a branch-circuit supply source capable of causing harm upon interaction with persons (electric shock) or property (fire). This interaction results in injury if a person is coupled with this energy at a magnitude, rate and duration that exceeds the threshold of susceptibility, the ability to sustain or withstand it without injury or other undesirable physiological effects. The more severe or likely the injury, the greater the risk.
Protection from harm involves a means to control, reduce, limit or prevent interaction with this hazardous electrical energy source — to reduce the magnitude, rate or duration below the susceptibility threshold. You may have heard the order of priority to reduce this risk expressed as "Eliminate the hazard, guard against the hazard, or warn about the hazard.”
Figure 7. Reducing the risk of electric shock: Source impedance to ground can limit current below susceptibility to harm (undesirable physiological effects) - but only under the right conditions such as with a source that is isolated from ground
Protective mechanisms need to be effective and reliable to mitigate the hazards and reduce the level of risk under all likely conditions of the application throughout the expected life of the product.
All likely conditions — wanted and unwanted — must be anticipated and considered. This includes conditions of normal use and reasonably foreseeable misuse and abuse. Fault conditions are simply unwanted conditions, states or events that may contribute to the harm being considered. Analysis tools such as fault trees are sometimes used to outline the relationships between the factors that contribute to harm — particularly critical paths — and to help design protective mechanisms in the right order of priority. This may highlight the effect of certain external factors that must also be considered. Multiple faults must also be considered. As an example, one fault could precipitate another, or one fault could exist (undetected, indefinitely) and then another fault could occur at the same time.
Hazard-Based Application: Electric Shock— Some Basic Examples
A hazard-based approach can provide a different way to address electric shock harm to a person. Recall that a person interacting with a hazardous energy source is coupled with its energy, resulting in injury if the magnitude, rate and duration exceed certain thresholds. In the case of electric shock, this coupling is caused by contact, and in the form of current that flows for a duration through the impedance of the body. The electrical circuit through the body is completed by two separate contacts: one to the source of current and one to its return. For example a person could make hand-to-hand contact across line–neutral in a circuit, or hand-to-foot contact with a hand on the line-side of a circuit and a foot in contact with ground (concrete floor, water pipe, other grounded parts, etc.), to which the return circuit (neutral) is referenced.
Figure 8. Reducing the risk of electric shock: Additional series impedance can limit current below susceptibility to harm (undesirable physiological effects) - but only under the right conditions such as with insulation / isolation in equipment
Electric shock harm is considered as any undesirable physiological effect due to current that exceeds the threshold of susceptibility for the involved body parts. The harm is based on susceptibility to current and duration, and protection is therefore based on limiting that current or duration. What about voltage? Voltage can be addressed simply by its ability to drive current as limited by impedance, and this is addressed below under subhead Low Voltage Source.
Consideration of Unwanted Conditions
All likely conditions — wanted and unwanted — must be considered. Fault conditions, even multiple conditions, may be unwanted but must be anticipated. As an example, circuits can be miswired, resulting in unintended wiring configurations of branch circuits, receptacles, and connected loads, and leading to unwanted supply source conditions such as no grounding, reversed polarity and open neutral. Open grounding or reversed polarity could exist undetected and long term. Open neutral conditions may not exist undetected as long (indicated by unenergized loads), but consideration is still warranted.
These conditions can increase the risk of electric shock. Leakage current normally flows from the supply source through resistive and capacitive paths returning to accessible conductive parts and ground. But if the grounding connection is open (green wire in the equipment or in the supply), this leakage current is now touch current, available to flow through a person who simply needs to contact accessible metal on the equipment (enclosure) and ground (concrete floor, water pipe, other grounded parts, etc.). In addition, if the neutral connection to the equipment is open, some circuitry normally at neutral (ground) potential will be raised to line potential. As N-G capacitance is typically symmetrical with L-G capacitance, this condition will double the leakage current and further increase the risk of shock.
These conditions therefore form the basis for typical product leakage/touch current testing requirements as in UL/ANSI 101. Products are tested to applicable leakage current limits under these unwanted but anticipated conditions to ensure that the protection against electric shock is effective.
Harm: Susceptibility to Current and Duration
Figure 9. Reducing the risk of electric shock: GFCI can limit current and time below susceptibility to harm (undesirable physiological effects such as inability to let-go or ventricular fibrillation).
For some common Class 1 residential branch circuit applications (240/120 Vac rms, 60 Hz), the following time/current thresholds of physiological susceptibility from IEC TS 60479 provide a frame of reference for the population. The reference is a common current pathway, left hand-to-both feet. Susceptibility may differ with different pathways, as well as factors such as dc, frequency, waveshape and others not included here. Recall that limits in standards and guidelines generally need to be separated by safety factors from the physiological thresholds for injury, with greater risk warranting greater safety factors. Values are given in ac rms, but certain effects involving muscle stimulation may be more closely associated with peak voltages, so the equivalent peak voltages for clean sinusoidal waveforms are also shown. Some examples follow.
The physiological threshold for startle reaction is 0.5 mA AC rms (0.7 mA peak) independent of duration. These effects increase with current and current density over the area of contact. This is also a commonly used leakage / touch current limit in many product standards. If below this level, physiological effects include [possible] perception but usually no [significant] startle reaction.
Note that startle and related effects may not be direct injuries, but could result in injury in certain applications and circumstances simply as a consequence of an unexpected or undesirable physiological effect. This may indirectly cause injury, but injury nonetheless. The harm is the undesirable effect, whether or not an injury is directly caused by the body current.
The physiological threshold for muscular reactions such as immobilization, difficulty in breathing and inability to let-go can be as low as 5 mA AC rms (7 mA peak) dependent on duration. These effects are generally undesirable and could result in injury in certain applications and circumstances. If below this threshold, physiological effects include "[likely] perception and involuntary muscular contractions…but usually no harmful electrical physiological effects.” 2
The physiological threshold for ventricular fibrillation is as low as 35–40 mA AC rms (approx 50 mA peak) dependent on duration, but based on current that may last a few heart cycles (seconds) or more. This threshold current also depends heavily on pathway through the body, and may be higher (such as hand-to-hand) or lower (such as chest-to-hand).
If below this threshold, physiological effects include "strong involuntary muscular contractions, difficulty in breathing, reversible disturbances of heart function, [and] immobilization, [with] effects increasing with current magnitude, but usually no organic damage is to be expected.” 2
Above this threshold, "pathophysiological effects may occur such as cardiac arrest, breathing arrest, and burns or other cellular damage. Probability of ventricular fibrillation [increases] with current magnitude and time.” 2
Note that these are only examples of the many effects of current for branch-circuit applications. Other harmful effects are also possible, depending on factors such as pathway and affected organs and body subsystems.
Hazard-Based Application: Electric Shock Protection—Some Basic Examples
The hazard-based approach provides a different way to address hazards that can cause harm, as well as protective means that can reduce risk of harm, such as electric shock. The safety objective is to avoid certain undesirable physiological effects, and the protection requirements need to address directly the susceptibility to these effects. As electric shock harm is based on susceptibility to current and duration, then protection is based on limiting the current or duration. To protect against a specific effect, the current or duration must be limited below the level that could cause that effect.
Protection: Limiting the Current or the Duration
Current is limited by impedance, but whether we can rely on body impedance, source impedance or some other series circuit impedance depends on the circumstances. Recall that the needed current limitation must be based on the physiological effect to be avoided and the corresponding current threshold (0.5 mA for reaction, 5 mA for let-go, etc.). Note that voltage is simply addressed here by its ability to drive current, but limited by impedance. Current duration (time) can also be limited, such as by specifically designed protective devices. Again, the limitation must be appropriately below the thresholds (time/current) for the specific physiological effects to be avoided. Recall also that protective mechanisms need to be effective and reliable, as well as appropriate for the application. Some examples follow.
Limiting the Current with Body Impedance (Low Voltage Source)
Body impedance consists of internal body resistance that varies with the current pathway, and skin impedance (resistive/capacitive) that varies with skin contact area and moisture condition, frequency and voltage. Note that skin impedance consists of two contacts for entry and exit of current though the body. Body impedance is also ultimately proportional to the current itself as the two skin contact impedances may differ, and vary as a function of the voltage across them.
Let’s look at variation with voltage. Body impedance is high by nature, primarily due to skin impedance. At very low voltages, this impedance remains high enough, on the order of kilohms to adequately impede the flow of current below critical thresholds.
For example under ordinary conditions such as hand contact with equipment and foot contact with ground, NEC Class 2 circuits would not have the potential to reduce our skin impedance and body impedance, and the current able to flow would not be likely to cause effects more severe than reaction. Notable differences include relatively larger contact area, and damaged or wet skin (note lower NEC Class 2 limits for wet contact).
In order for voltage to be low enough to protect against electric shock, the body impedance must be high enough to limit the body current to acceptable levels — under all likely circumstances and conditions of contact. As body impedance decreases as a function of the voltage across the body, the higher the voltage, the lower the body impedance. At lower voltage, the body impedance is higher, but other factors need to be considered including skin contact area and moisture condition.
Limiting the Current with Source Impedance (Current-Limiting Source)
A supply source may have adequate impedance in the normal current-carrying path. A current source has source impedance so much higher than the remaining circuit impedance that different loads (from a normal electrical load, to a body, to a short circuit) do not appreciably change the current. This source impedance would need to be high enough to limit the available body current to acceptable levels, such as below the 0.5 mA AC threshold for reaction.
This source impedance may also exist in the path to ground, such as in a ground-isolated secondary supply. This may provide protection by limiting fault current that may flow in the grounding path through a person contacting the supply and ground.
But in order for such isolation to be an acceptable protective mechanism, it must be effective and reliable in the application. Adequate isolation from ground (protective earth) can be very difficult to maintain for a product due to interaction with users, interconnection with other equipment and contact with other parts and the surrounding environment. Moreover, if this isolation is compromised it is rarely detected or indicated except for special cases involving suitable monitoring and protection circuitry for isolation from ground (for example a line isolation monitor for isolated power systems required in applications such as Health Care Facilities covered by Article 517 of the NEC.
Limiting the Current with Additional Series Impedance
At residential Class 1 branch circuit voltages (240/120 V), the skin impedance is dramatically reduced, and total body impedance approaches only the internal body resistance on the order of 500 Ohms. With this low body impedance and the low source impedance inherent to a branch circuit (voltage source), there is little to impede the current below hazardous levels.
However, there could be other series impedance to limit this current, by intention or by chance. Of course, such protection is a common part of equipment and installations, provided by insulation and isolation, as well as training, work practices and behavior. In many cases suitable personal protective gear such as insulating gloves or insulated tools may be used. Chance impedance could involve increased body resistance due to very small and dry contact areas (fingers, hands), even for a shorter current pathway such as across the same hand. There could also be additional resistance provided by clothing (shoes, etc.) or the environment (dry wood floor, carpet, etc.) depending on the current pathway and circumstances of contact. No one would expect to rely on chance impedances for safety, but this helps explain why some have been fortunate to interact with a hazardous source without the severe consequences that are possible.
Limiting the Current Duration (Time)
In addition, there are other protective mechanisms that limit the current as well as the duration of current, reducing the severity and the likelihood of injury under different conditions. One example is a ground-fault circuit interrupter (GFCI) that detects current differential between the line and neutral conductors. Under high-impedance fault conditions the GFCI shall trip on differential current of nominally 5 mA within approximately 5 seconds (within milliseconds in practice), protecting against muscular reactions such as immobilization, difficulty in breathing and inability to let-go. Under low-impedance ground-fault conditions (short circuit), instantaneous fault current could be much higher, but the GFCI will very rapidly enter the trip mode, required to trip within milliseconds, well below the short-duration threshold for ventricular fibrillation and protecting against it.
Of course there’s much more to all this, but these were just a few basic examples of applying a hazard-based approach to electrical safety and protection against the risk of electric shock.
This hazard-based approach is now in use and likely to impact safety standards and codes. This basic overview and the electric shock application examples should shed some light on how this hazard-based approach can apply to electrical safety. A hazard-based standard would identify the objectives of protecting against each specific undesirable effect, and directly relate them to protection requirements. Limits to protect against the harm need to be appropriately based on physiological thresholds of susceptibility, with safety factors suitable for the level of risk. This hazard-based approach provides us with another way to address hazards that can cause harm, in order to address protection mechanisms that can reduce the risk of harm.
1 ISO/IEC Guide 51, Safety aspects — Guidelines for their inclusion in standards
2 IEC Technical Specification 60479-1, 4th ed., Effects of Current on Human Beings and Livestock – Part 1: General Aspects (by IEC TC64 MT4), a Basic Safety Publication and IEC 60479-2: Effects of current passing through the human body – Part 2: Special aspects.
Read more by Thomas P. Lanzisero
Posted By Bert McAlister,
Friday, September 01, 2006
Updated: Sunday, February 10, 2013
| Comments (0)
When the city of Detroit hosted the biggest sporting event of the year, Super Bowl XL, the Buildings & Safety Engineering Department (B&SED) played a vital role in its safe operation. Super Bowl XL was the catalyst for a major downtown revitalization and the grand finale of several major events for which our department had the responsibility for safety inspections. Within the last year, Detroit hosted the Major League Baseball All-Star Game at Comerica Park, the summer festival season, the 2006 North American International Auto Show at Cobo Center, and Motown Winter Blast II in conjunction with the Super Bowl.
Photo 1. Ford Field, site of Super Bowl XL
Super Bowl XL
On November 1, 2000, the National Football League owners unanimously approved the city of Detroit to host Super Bowl XL at Ford Field on February 5, 2006. This would mark the second time the Super Bowl would come to the Detroit area, the first game being Super Bowl XVI in 1982 at the Silverdome in Pontiac, Michigan. Roger Penske, one of the most successful racing car and track owners in the world of motorsports, was appointed chairman of the Super Bowl XL Host Committee. The Super Bowl Host Committee itself was created to join business, community, political, and economic resources throughout the region for a common goal — "to showcase a revitalized Detroit when the world comes to its living room.” And showcase it did!
Photo 2. Phil Clark is the chief electrical inspector and Bert McAlister, supervising electrical inspector
The groundbreaking ceremony for Ford Field, a $500-million-dollar, 65,000-seat domed stadium was held November 16, 1999, and the first Lions regular season home game was played there September 22, 2002. Ford Field is a state of the art facility designed specifically for football games, but has also hosted concerts, conventions, trade shows and other events. However, some alterations were required to prepare for the big game. Additional accommodations had to be made for the legions of press both inside and outside of the stadium, increased concessions, special NFL events, and of course the halftime extravaganza. Alterations to the existing building power distribution system as well as temporary wiring required scores of electricians within a short time frame.
Photo 3. From left to right: Durand Capers, Cameron Cummings, Richard Helm, Mark Kreim, and Vince Cooley.
The Super Bowl draws fans and media from all over the world. Usually the event is held in a Sun Belt city with a large existing/convention tourism infrastructure. In cities such as Los Angeles, Miami, etc., existing tourist attractions minimize the need for temporary venues. But how do you provide entertainment in the week leading up to the game when the host city is in the Midwest and the event is in the middle of winter? Enter the Motown Winter Blast festival.
Motown Winter Blast II was developed to create an innovative backdrop to Super Bowl XL. Some of the venues included a 200-ft long snow slide, four outdoor music stages, a marketplace featuring 35 or more vendors, the Taste of Detroit featuring 22 outdoor restaurants, vehicle exhibits, and much more. Setup for this 12-city block wintertime festival began on January 21st, and the event opened to the public on Thursday, February 2, 2006, and ran to Sunday, February 5, 2006.
Photo 4. Several of the many portable distribution boxes used as part of the temporary wiring system for the Winter Blast Festival
The city of Detroit Buildings & Safety Engineering Department, Mr. Amru Meah, director, consists of construction and property maintenance functions. The Electrical Division is part of the Construction Division and consists of Chief Electrical Inspector Phil Clark, two supervising electrical inspectors, 13 field electrical inspectors, and an electrical plan reviewer. The level of experience of our inspectors range from 13 very experienced years to two years for our newest inspector.
The field inspection staff is divided into districts throughout the city with a wide diversification of occupancies and types of inspections, from dwelling units to high-rise buildings, theatres, stadiums, hospitals, factories and other industrial establishments. All of our electrical inspectors were involved in inspecting special events including traveling carnivals, weekend festivals, and exhibition shows, the largest being the North American International Auto Show, which utilizes more than 700,000 square feet of exhibition floor space in the Cobo Conference Exhibition Center.
Planning, Preparation and Training
Photo 5. Workers apply temporary light fixtures on top of a sign in the middle of Woodward Avenue
There was a long preparation process for Super Bowl XL that began shortly after Detroit’s selection as the host city. However, things really started coming together right after the Thanksgiving holiday in 2005. Meetings hosted by the Super Bowl Committee were held on a regular basis at Ford Field. This brought together the major organizers, volunteer groups, first responders, vendors, contractors, and inspection agencies. Mr. Clark decided that one supervisor and six electrical inspectors would be assigned to the Super Bowl/Winter Blast special events. Fortunately two of the inspectors, Durand Capers and Mark Kreim were the field inspectors during the construction of Ford Field. Their background knowledge and experience would prove invaluable in the weeks ahead.
Photo 6. Several of the many portable distribution boxes used as part of the temporary wiring system for the Winter Blast Festival
Even with the experience level of our inspectors, a training program was needed to help prepare them for an event of this magnitude. The state of Michigan Public Act 54 requires all registered building officials, plan reviewers, and inspectors to be familiar with changes to the applicable codes administered and enforced within the jurisdiction of the enforcing agency employing the applicant, and with pertinent laws, and to furnish satisfactory evidence of attending local in-service training and education programs on an ongoing basis. I developed, submitted and received approval from the state of Michigan Bureau of Construction Codes for the course of instruction "Special Event Inspections” for continuing education units during the current inspector registration cycle. This training program and our inspections were based on the 2002 National Electrical Code, which was currently adopted and enforced in the state of Michigan.
Photo 7. A typical outdoor portable power distribution arrangement - a primary disconnect for the transformer, a 480-120/208 volt transformer, and a secondary portable power distribution unit. This entire assembly bore a listing mark from Underwriters Lab
To maximize the use of our resources, we needed to streamline our procedures as much as possible. A checklist was developed based on the most common code violations documented while inspecting other major events, and based on the projected weather conditions. This concept not only minimized the write up time, but information and instructions could be directed to contractors and business owners very rapidly.
Special Event Ordinance
The city of Detroit adopted a Special Event Ordinance for Limited Duration Licenses & Permits for the 2006 Super Bowl. The enforcement period was from January 2 through February 10, 2006. This ordinance provided for three specific activity zones: the Clean Zone, Entertainment Zone, and Overlay Zone. These zones determined what kinds of activities could take place within them, the permit requirements, and duration of the occupancy permit. The clean zone, the minimum 300-foot secure perimeter immediately surrounding Ford Field, is perhaps in part a requirement of the post 9/11 era that requires much heavier security concerns, credentials and controlled access.
Photo 8. A panelboard in a NEMA 1 enclosure sits on top of other electrical equipment rated for indoor use unprotected outdoors. The cord sets as well were not listed for wet locations.
Limited Duration Permits could be issued by B&SED for temporary structures (i.e., tents, scaffold stages, etc.) within these zones. All temporary structures were subject to conditions established by B&SED. In addition, several buildings in the entertainment and overlay zones were still under renovation. Some of these buildings had vacant storefronts developed into "white boxes” for future use. The ordinance allowed these storefronts to be used as temporary sites for activities such as entertainment programming, the sale and service of food, beverages, and merchandise. All such sites had to comply with applicable building, fire, health, and safety codes and were inspected by the B&SED, the Fire Department, and the Department of Health and Wellness Promotion prior to the start of the activity periods of the Super Bowl. Temporary certificates of occupancy were issued by the B&SED for all such occupancies in compliance with the codes.
Photo 9. The listing mark applied on a secondary portable power distribution unit. The marking indicates this assembly includes a 150 kVA transformer, is not to be installed where accessible to the public, is suitable for damp locations, and is rated for
Super Bowl activities were not confined just to Ford Field. The "NFL Experience” took place at the Cobo Conference Exhibition Center. The Media Center was in the General Motors Headquarters Renaissance Center Complex. The 2006 NFL Tailgate Party was held in the largest temporary structure hosting an event: a 183,384 square foot tent. Over a three-week period, a two-square-block parking lot was cleared and five massive tents were erected as one structure on the site. This temporary structure included 4,779 square feet of entertainment stages and a 50´ x 70´ ice skating rink, which were supplied by three vehicle-mounted generators.
Photo 10. Front view of the portable power distribution unit in photo 9
During the week leading up to the Super Bowl, there were at least 30 known spinoff events taking place in the city. A major source of information for obtaining the location of these events was the media. We collectively scanned the newspapers, listened to radio and television news broadcast on a daily basis for information. Shared information within our department was essential as well. Information was updated a daily basis from permit applications, contractor/vendor inquiries and other similar sources.
Just about everywhere you turned downtown, someone was giving a party. There were also several major events outside of the downtown area including the Motor City Touchdown and the ever-popular Playboy Party at Detroit City Airport, approximately nine miles from Ford Field. Both events were held at an airport hangar, which underwent a temporary makeover including temporary wiring, vehicle-mounted generators, stage lighting, etc.
Photo 11. Cords, cables and cable connectors lying in the street.
Building owners, tenants, and contractors were scrambling to get ongoing construction projects completed in time for the business opportunities associated with the Super Bowl. Our inspectors were inspecting these projects, some of them on a daily basis, in addition to the special event inspections. In some cases, our inspection teams would be waiting on a window of opportunity to accommodate some of the scheduled Super Bowl related activities. Mr. Clark and I formed an impromptu special response team to visit both the construction and special event sites to assess and resolve some of the more challenging situations. We were on call from our inspectors, contractors, as well as business owners.
Our electrical permit fee schedule has provisions for temporary wiring as well as sporting/special events, both indoor and outdoor. The permit for indoor locations is based on each 100,000-square feet of floor space and includes all electrical equipment. The permit for outdoor locations starts out with a flat fee, and there are provisions for each additional hour of inspection time above that. Each venue was assessed on an individual basis, but we tried to adhere to the special event permits for consistency. During the Super Bowl period, we processed and made inspections on 51 electrical permits including sites in the activity zones, and other associated events.
Photo 12. The only temporary utility service utilized for the Super Bowl/Winter Blast Festival, this installation was located in a protected corner of a parking lot. The logistics required for the utility shutdown and tap, proximity to the utilization equ
Since most of the events associated with the Super Bowl were going to be outdoors, or in or on temporary structures, electrical equipment and how it was installed was a primary concern. NEC Article 525, Carnivals, Circuses, Fairs, and Similar Events, governed most of the electrical installations that we inspected. NEC-2002, 527, Temporary Installations, [NEC-2005, 590] was applied in permanent buildings and structures utilizing temporary wiring. NEC 400, Flexible Cords and Cables, and Article 250, Grounding, were also on the most often enforced list.
Without a doubt, the most common violation on our checklist was Section 250.30, Grounding Separately Derived Alternating-Current Systems. With the exception of one utility service, the sources of electrical power for the outdoor temporary installations were generators. The way they were installed and used met the definition of separately derived systems. Most of these generators were mounted on vehicles, and did not meet the requirements of Section 250.34(B) to allow the frame of the vehicle to be used as the grounding electrode. Ground rods were the electrodes of choice for these installations and our inspectors were busy prodding some of the contractors to install them.
The source voltage produced by most of these generators was 480 volts, which required the use of transformers. Here again is another separately derived system that required an approved grounding electrode system. In many cases our inspectors were tasked with trying to obtain code compliance in some unique situations. For instance, how do you provide a grounding electrode system for a transformer located in the middle of the roof of a building? Or for a generator located in a concrete parking lot? Mr. Clark and I encouraged flexibility where practical to meet the intent of the code if not the letter of the code. Some examples would be connections to the grounding electrode system for a utility light pole. Also, fire hydrants could be used a means of connecting to a metal underground water pipe in direct contact with the earth for more than 10 feet.
Cords and their use, or misuse, was a primary concern especially for the Motown Winter Blast. In addition to the typical abuse from pedestrian and small vehicle traffic, winter weather was a concern especially if the cords were in the path of snow removal equipment. Section 525.20 requires flexible cords or cables to be listed for extra hard usage. Where not subject to physical damage, they can be listed for hard usage. Where used outdoors, flexible cords and cables shall also be listed for wet locations and shall be sunlight resistant.
Another problem with flexible cords and cable installations occurs when they were passed through openings in outlet boxes, disconnecting means, or similar enclosures without protection by bushings or fittings. There were numerous instances when a flexible cord was installed through an opening in the bottom of an electrical enclosure without an appropriate fitting. In addition to being a violation of NEC 400.14, this could cause tension or strain to be transmitted to joints or terminals, a violation of Section 400.10.
There were no less than four temporary outdoor performance stages utilized during the Motown Winter Blast. In addition, temporary indoor stages were constructed inside of several buildings to be used for live performances at Super Bowl parties, by the media for sports shows, interviews, etc. Although these stages were all temporary structures, they nevertheless used stage and studio lighting equipment. NEC Section 520.10 allows the temporary use outdoors of portable stage and studio lighting equipment and portable power distribution equipment, provided qualified personnel supervise the equipment while energized and barriered from the general public. This includes equipment that is not listed for wet or damp locations with the pretense for this being qualified personnel can de-energize and protect the equipment in the event of rain or snow.
NEC Section 110.26(F)(2) requires that all outdoor electrical equipment, rated 600 volts, nominal, or less, shall be installed in suitable enclosures and shall be protected from accidental contact by unauthorized personnel. Both the Winter Blast and Super Bowl utilized generators, transformers, and power distribution boxes for the temporary wiring installations. For the most part, the installers did well in minimizing potential hazards from the public. However, in some cases the metal fencing or barriers were used to enclose the electrical equipment created another code violation—NEC Section 110.26(A)(1) by encroaching on the required depth of working space in the direction of equipment or live parts.
After the Game
As the old saying goes, "what goes up must come down.” In this application all sites that had temporary wiring had to be revisited to ensure that all such wiring had been removed, and where applicable, all previously existing wiring methods restored in an appropriate manner. The February 8th deadline for the reopening of all streets, and the February 10th expiration date of the Limited Duration Permits helped to keep this from being a long drawn out process. In addition, our fee schedule for temporary wiring includes a fee for one-hour inspection time to cover the re-inspection cost.
This was by far the most significant event I’ve been involved with in my 23 years with B&SED. Overall, things went well. If I had to do it all over again would I do anything different? Absolutely! For one, I would’ve contacted the inspection department in Jacksonville, Florida, the host city for Super Bowl XXXIX shortly after the game. Ironically, I was in Jacksonville the week after their big game heading to Mayport, FL and two weeks of sea duty on the USS John F. Kennedy (CV-67).
One of the biggest stumbling blocks for our department was the inability to obtain credentials to access into the clean zone and Ford Field, a definite must for the week preceding the game. The issuance of credentials required background checks, and for whatever reason we did not start the process in time. Also high on my list of "we should haves” is we should have contacted the host facility (Ford Field) much sooner to formulate a plan for testing the emergency system.
Our inspectors worked extremely hard under very challenging circumstances, especially the week prior to the game. But, given the opportunity to do it again, we say bring it on!
Read more by Bert McAlister