Posted By Underwriters Laboratories,
Wednesday, November 01, 2006
Updated: Sunday, February 10, 2013
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Question: One conductor per terminal
I know you can use only one conductor per terminal in a wire connector on a molded case circuit breaker and other distribution equipment unless the equipment is marked otherwise; however, I can’t find where it says that in the White Book. Where can I find that information in the UL White Book?
The 2006 UL White Book is the Companion Tool to the 2005 NEC. The White Book is a very powerful reference source for the AHJ, specifier and the installer, and can be used to answer many of the questions that may arise regarding UL Listed electrical products, if you know how to use the book. Last edition of the UL Question Corner featured the Practical Application of the White Book in the Field, located on page xxxv. To answer this question, we’ll walk through using the White Book to find an answer and let you follow along.
If you are looking for information specific to a type of product, in this case molded case circuit breakers, you should always start your search in the UL Guide Information for the product. The application specific product category Guide Information should be able to answer your questions, if not they will include direction on where to look for additional information.
Since we are looking for molded case circuit breakers let’s look in the Index of UL Product Categories starting on page 359 in the UL White Book. We see that on page 361 there is a reference for the product category "Circuit Breakers, Molded Case and Circuit Breaker Enclosures” located on page 45 of the 2006 UL White Book. Reviewing the Guide Information on page 45 for the product category Circuit
Breakers, Molded Case and Circuit Breaker Enclosures (DIVQ), we see that there is a lot of useful information there; however, there is no information regarding more than one conductor under a wire terminal. There is a heading in the Guide Information titled "Additional Information” that refers us to Circuit Breakers (DHJR) and Electrical Equipment for Use in Ordinary Locations (AALZ).
Following those recommendations, we review the Guide Information for Circuit Breakers (DHJR) located on page 44 in the White Book and see a lot of useful information on terminations, however, not the issue of more than one conductor under a terminal. Circuit Breakers (DHJR) is the main category for all the circuit breaker categories and supplements all the sub-categories Guide Information, such as (DIVQ).
The other category for additional information is Electrical Equipment for Use in Ordinary Locations (AALZ) located on page 6. (AALZ) includes useful information that applies to all product categories for electrical equipment for use in unclassified (ordinary) locations in accordance with the National Electrical Code, (NEC). Instead of repeating this information in the Guide Information of each individual product category, UL created the (AALZ) product category Guide Information as a "Super Guide” with a reference to it in each ordinary location equipment product category Guide Information.
Let’s look at the Guide Information for (AALZ) on page 6 in the White Book and let’s see what information is common to all ordinary location electrical equipment. There is information on Investigation Requirements and Standards, giving a general overview of the scope of Listing investigations and standards used for ordinary location electrical equipment.
(AALZ) includes an explanation of all the environmental enclosure types that appear in NEC Table 430.91 as well as other UL environmental ratings. In addition, general information on Appliances and Utilization Equipment Terminations, Distribution and Control Equipment Terminations as well as other important general information applicable to all ordinary location electrical equipment.
In (AALZ) under the heading for Distribution and Control Equipment Terminations, there is information on what type of conductors and rating of conductors can be used as well as how the terminals will be identified. There is also a subheading
titled "Terminals” which will provide the answer to our question.
"Terminals — Product terminals, including wire connectors and terminal screws, are acceptable for connection of only one conductor, unless there is marking or a wiring diagram indicating the number of conductors which may be connected.”
The UL White Book can be used to answer many of the questions you may have for UL Listed electrical equipment, just take a few minutes to learn how to use the book and you’ll have an encyclopedia of electrical information at your fingertips.
This information can also be obtained from UL’s Online Certification Directory atwww.ul.com/databaseand entering each category code discussed above in the category code search field and click on search. The category code is the 4 letter code after each product category title such as (DVIQ), (DHJR) and (AALZ).
UL Question Corner
Posted By Richard Temblador,
Friday, September 01, 2006
Updated: Sunday, February 10, 2013
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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
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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
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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
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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
Posted By Peter Walter,
Friday, September 01, 2006
Updated: Sunday, February 10, 2013
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Electromagnetic compatibility (EMC) is the ability of electrical / electronic equipment to operate in its installation environment while neither causing nor experiencing electromagnetic interference (EMI). EMI is any interference with normal equipment operation caused by abnormal energy entering the equipment either by conduction though wiring connections or by radiated wave reception. Radiated EMI is also called radio frequency interference (RFI). Conducted EMI is also called high-frequency line noise.
Codes and standards in the U.S.
In the U.S., there are no codes and standards that specifically and completely cover electromagnetic compatibility of adjustable frequency drives (AFDs).
FCC rules and regulations
Photo 1. Meeting EMC Standards - ABB's ACH550 AC Drive family combines simplicity, convenience, fieldbus connectivity, harmonic mitigation and programmability to a degree not seen in drives before. A built-in EMI/RFI filter guarantees trouble-free ope
Part 15 of the Federal Communications Commission (FCC) rules and regulations covers unlicensed equipment that emits radio frequency energy. Part 15 would apply to any AFD as an "incidental radiator.” The operation of any equipment covered by Part 15 is subject to the general conditions of operation listed under paragraph 15.5. The essential requirements of 15.5 are that the equipment must not interfere with any licensed broadcast, navigation or safety services and must accept any interference caused by other equipment. Under Part 15.13, the manufacturer of an incidental radiator "shall employ good engineering practices to minimize the risk of harmful interference.”
Microprocessor controlled AFDs are also covered by FCC Part 15 as "digital devices.” As commercial or industrial equipment, AFDs are "exempted devices … subject only to the general conditions of operation in 15.5 [described above]…” However, the FCC strongly recommends that "the manufacturer of an exempted device endeavors to have the device meet the specific technical standards [of Part 15].”
Part 15 lists limits for radio frequency voltage conducted to the public utility power lines by digital devices. The range of frequencies covered is 0.15 to 30 MHz. Part 15 also lists limits for the field strength of radiated emissions from digital devices. The range of frequencies covered is 30 MHz and above. At frequencies lower than the radio frequencies regulated by the FCC, voltages conducted to the power lines would be considered to be harmonic distortion voltages. Harmonic distortion issues are covered by IEEE Standard 519.1
Evaluating a drive as an FCC Part 15 digital device
A drive’s microprocessor is not likely to be a significant source of EMI. The most significant potential source of EMI and RFI in a drive is the power switching circuitry. This potential is largely unrelated to the design of the microprocessor or other type of control circuitry. EMI is generated in a drive by switching the output terminals back and forth between the positive and negative sides of the DC bus to synthesize an AC output waveform. Each time the output transistor switches operate, the terminal voltage jumps (in a 480 V drive) from 650 volts of one polarity to 650 volts of the opposite polarity. This nearly instantaneous voltage change has the potential to generate a significant amount of radio frequency energy.
Evaluating the drive as a microprocessor controlled digital device does not correctly target the most significant source of EMI.
Requiring a drive to meet FCC requirements
Since the applicable requirements are not very specific or restrictive, almost any drive could be said to meet the requirements of Part 15 without actually providing a significant level of electromagnetic filtration.
A drive could be required to meet the conducted and radiated emission limits listed in Part 15 for a Class A or Class B digital device, but Part 15 does not contain or specify a testing procedure that is designed for use with drives. Without specifying a suitable testing procedure, any declaration that a drive meets the specified limits might be suspect.
The conducted emission limits listed in Part 15 were revised in 2002 to "harmonize our domestic requirements with the international standards developed by the International Electrotechnical Commission (IEC), International Special Committee on Radio Interference (CISPR)” [see FCC 02-157]. The CISPR 11 standard provides a suitable test procedure for testing drives to verify conformance with these limits.
The radiated emission limits specified by CISPR 22 are lower than the limits listed in Part 15. Accordingly, in 2003, Part 15 was revised to include 15.109(g):
"As an alternative to the radiated emission limits shown in paragraphs (a) and (b) of this section, digital devices may be shown to comply with … (CISPR) Pub. 22 (1997)…” (see FCC DA 03-3848).
CISPR 22 covers digital devices, while CISPR 11 covers industrial scientific and medical equipment. The U.S. Food and Drug Administration encourages manufacturers of electromedical equipment to use CISPR 11.
EU Council Directives
In the European Economic Community, the EU Council Directives set standards for various products. Many of these standards are derived from standards written by the International Electrotechnical Commission (IEC). The EMC Product Standard for Power Drive Systems, EN 61800-3 (or IEC 61800-3), is used as the main standard for adjustable speed drives. This standard contains test procedures that are specifically suitable for drives and the standard is quite comprehensive. It covers both the drive’s electromagnetic emissions and its immunity from received emissions.
IEC 61800-3 defines two installation environments
"The First Environment includes domestic premises. It also includes establishments directly connected without intermediate transformer to a low-voltage power supply network which supplies buildings used for domestic purposes.”
"Second Environment includes all establishments other than those directly connected to a low-voltage power supply network which supplies buildings used for domestic purposes.”
IEC 61800-3 defines sale or distribution to two levels of customer competence
"Unrestricted distribution is a mode of sales distribution in which the supply of equipment is not dependent on the EMC competence of the customer or user for the application of drives.”
"Restricted distribution is a mode of sales distribution in which the manufacturer restricts the supply of equipment to suppliers, customers or users who separately or jointly have technical competence in the EMC requirements of the application of drives.” The installer must install the drive in conformance with the instructions provided in the installation manual.
Edition 2 of IEC-61800-3
The terminology of product standard IEC-61800-3, edition 2, differs somewhat from edition 1. Categories C1 through C4 replace distribution terminology.
Additional information is available in two ABB publications:
- Technical Guide No. 2, EU Council Directives and Adjustable Speed Electrical Power Drive System
- Technical Guide No.3, EMC Compliant Installation and Configuration for a Power Drive System
Recommendations to specifiers
For drives with the most comprehensive electromagnetic compatibility, specifiers should require drives to meet the IEC 61800-3 EMC standards and emission limits for Restricted Distribution, and installation in the First Environment. Manuals should be required to include instructions for installing the drive equipment so that it meets the specified emission limits as installed.
Drives that meet the above requirements will typically meet the technical requirements of FCC Part 15, including the emission limits for a Class A digital device.
1 FCC information and documents are available at www.fcc.gov and/or links from www.fcc.gov to the Government Printing Office web site.
Read more by Peter Walter
Posted By Jesse Abercrombie,
Friday, September 01, 2006
Updated: Sunday, February 10, 2013
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If you’re an investor, especially a business owner in the higher tax brackets, you’ll want to pay close attention to some of the provisions of a bill that President Bush signed into law on May 17.
The new legislation extends the lower tax rates on capital gains and stock dividends, temporarily removes restrictions on transfers from traditional to Roth IRAs, and raises the exemption level on the alternative minimum tax (AMT). Clearly, the new laws can have a big impact on your investment strategies over the next few years.
Let’s take a look at the tax law changes and see how they might affect you.
Extension of 15 percent rate on dividends and capital gains
Until a few years ago, dividends were taxed at your personal income tax rate. But changes in tax laws resulted in a 15 percent tax rate on dividends through 2008. I had an appointment with a prospective client this week, who thought he would have to pay taxes at 30+ percent because of how capital gains were taxed years ago. Information about the extension of 15 percent made his day. This rate has now been extended through the end of 2010. Also, the maximum long-term capital gains rate will remain at 15 percent through 2010; this rate, too, was slated to expire at the end of 2008. For taxpayers in the 10-percent and 15-percent brackets, long-term capital gains will be taxed at 5 percent for the 2006 and 2007 tax years and at 0 percent for 2008–2010. Clearly, these changes give you some incentives to look for high-quality, dividend-paying stocks and to hold your stocks for at least one year—long enough to receive the best capital gains rate when you sell. Some stocks have paid, and increased, dividends for 25 straight years or more. These companies are typically well-run businesses that strive to reward their investors. (Keep in mind, though, that no company is obligated to pay dividends and may lower, or discontinue, dividends at any time.) And never hold on to a stock because you don’t want to pay capital gains taxes. You may regret that move if it is a volatile stock.
Removal of restrictions on conversions to Roth IRA
Starting in 2010, you can convert your traditional IRA to a Roth IRA, regardless of your income level. Currently, only taxpayers with adjusted gross incomes of $100,000 or less can make this conversion. The amount you transfer will be included in your gross income, so you’ll have to pay taxes on it, but you can spread the taxes out over two years if you make the rollover in 2010. This traditional-to-Roth conversion may benefit you in at least two important ways. First, qualified withdrawals from a Roth IRA are not taxable. And, second, you won’t have to start taking distributions from your Roth IRA at age 70-1/2, as you must with a traditional IRA and a 401(k).
Increased Alternative Minimum Tax exemption
For many years, many taxpayers have been shielded from the AMT by its large exemption, but this exemption has not been adjusted for inflation, so, as wages and earnings rise each year, more and more people will be subject to the AMT. Recent cuts in income tax rates also mean that more people may face the AMT. The new tax bill provides AMT relief by raising the amount of the exemption to $62,550 for joint filers, $42,500 for singles and $31,275 for married persons filing separate returns. This new exemption level applies only to the 2006 tax year, so when 2007 rolls around, watch for the results of new legislation. By the way, if your advisor recommends tax free bonds to you, make sure that they are not subject to AMT. If they aren’t, they are no different than a taxable bond.
So, there you have it—news you can use about the new tax laws. Consult with your investment professional and tax advisor to see how you can benefit from these changes.
For any questions or comments, please contact Jesse Abercrombie, investment representative, 972-241-8059.
Read more by Jesse Abercrombie
Posted By Ryan Johnson,
Friday, September 01, 2006
Updated: Sunday, February 10, 2013
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In September 2005, the California Public Utilities Commission (CPUC) announced "the most ambitious energy and efficiency campaign in the history of the utility industry in the U.S.,” when introducing a three-year, $2 billion funding plan for energy efficiency programs. This campaign is designed to help energy customers utilize the large number of energy efficiency programs that are available in California.
These initiatives help energy customers, energy providers and the state. Naturally, less consumption means lower energy bills for consumers. The state, through the CPUC, has an interest in making sure that the utilities have enough power to meet demand. The utilities benefit because lower energy demands mean the investor-owned utility companies have less power to generate and, therefore, less need to build more power plants.
Beyond the financial toll involved in the building of more power plants, there is also an environmental concern that is being addressed. The CPUC, in a statement announcing the program, estimates that new energy efficiency programs will "eliminate the need to construct three large power plants over the next three years, and reduce global warming pollution by an estimated 3.4 million tons of carbon dioxide by 2008, which is equivalent to taking about 650,000 cars off the road.”
Edison Has an IDEEA
With efficiency in mind, Southern California Edison (SCE) introduced the Innovative Designs for Energy Efficiency Applications (IDEEA) program in 2004. This initiative looks outside of the utility industry for new ideas to promote energy efficiency.
"SCE had been involved in the promotion of energy efficiency and energy conservation since 1911,” says Steven Long, the non-residential program manager at SCE, "but we had never solicited outside parties for such a program before.”
"In 1998,” Long added, "the CPUC started this idea of the third-party program. They handled most of the responsibility for the projects while utility companies like SCE administered purchase orders. Now, we are soliciting and administering our own programs through third party implementers.”
Since 2004, SCE has openly solicited suggestions for energy efficiency initiatives from manufacturers, distributors, importers and many other non-utility parties. SCE’s IDEEA program is an avenue for introducing new and promising technologies, an innovation in program delivery, targeting of niche markets, or ideas for more effective marketing and rebate programs.
Several of these submissions are chosen each year for pilot programs. If one pilot proves to be exceedingly successful, then SCE will try to mainstream it. "We see the IDEEA program as a sort of program design R & D shop, an innovation incubator,” says Bill Grimm, a manager for non-residential energy efficiency programs at SCE.
Last year, 13 of the 140 proposals submitted for IDEEA were selected for the program. One pilot program helps dairy farms install new fan technology, which reduces energy costs while keeping the cows cool (helping them produce more milk). Another program involves the development of an 80 percent efficient power supply for desktop computers. This IDEEA initiative is promoting this new technology prior to the adoption of the new computer efficiency standard by Energy Star.
A Focus on Cold Cathode Lighting
One current IDEEA program provides rebates to purchasers of cold cathode fluorescent lamps (CCFL). While cold cathode technology is not new, it was only recently that this technology has been utilized to replace incandescent lighting in many applications. Many customers are still unaware of cold cathode and the benefits it can provide when compared to incandescent or regular fluorescent lighting.
Cold cathode fluorescent is similar to normal fluorescent (or "hot cathode”) in many respects. Unlike traditional fluorescent lamps, however, cold cathode lamps have the ability to dim without any special dimming ballasts. The real advantages of cold cathode are seen when comparing CCFLs to incandescent lamps. Cold cathode lamps can operate using as much as 65–80% less energy than comparable incandescent lamps and can last 20 times longer, or more.
The cold cathode program was conceived by Energy Controls & Concepts (ECC), a company specializing in lighting efficiency design consultation. SCE selected this program for IDEEA and awarded ECC a one million dollar contract. ECC has served as the program implementer for this enterprise.
The cold cathode lamps used in the program were provided by Litetronics International, Inc. "We were glad to be a part of Southern California Edison’s plan to promote cold cathode,” says Greg Lechtenberg, regional sales manager for Litetronics. "This was a great opportunity to introduce consumers to an emerging lighting technology.”
This program offered customers rebates on cold cathode fluorescent lighting when it was used in applications that would produce significant energy savings and on-peak demand reduction. After customers had replaced their incandescent lighting with cold cathode fluorescent lamps, the installation had to be 100 percent inspected by ECC with a percentage of the work also subject to SCE inspection. SCE and ECC would then approve customers to receive a rebate, in most cases for the entire cost of the lamps.
A Call for New Submissions
Jonathan Baty, vice president of technology at ECC, is encouraged by the "very successful” cold cathode program. He notes that Southern California Edison "wants more people to adopt CCFLs.” Grimm says three of the IDEEA programs will be moving forward in 2006–2007 in some fashion. The cold cathode lighting technology has been added to SCE’s Business Incentives and Services Program as an itemized measure with an incentive of $2.00/lamp.
Lechtenberg was glad to see the program moving forward, stating, "When something new comes along, even if it’s a better product, people are reluctant to try it. I think programs like this really open people’s eyes to the fact that by making a few changes, they can end up saving a lot of money.”
SCE is now preparing for another year of IDEEA and the new InDEE (Innovative Design for Energy Efficiency) Program solicitations. A request for IDEEA/InDEE proposals was sent out on May 10, 2006. Through IDEEA, SCE has made it a priority to introduce and promote new energy saving technology. Baty feels that IDEEA has been an extremely beneficial undertaking, saying, "Southern California Edison’s goal is to find technology that reduces operating costs and conserves energy without compromising performance. Through IDEEA they are certainly succeeding.”
Read more by Ryan Johnson
Posted By Leslie Stoch,
Friday, September 01, 2006
Updated: Sunday, February 10, 2013
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Rules 10-1100 to 10-1108 of the Canadian Electrical Code provide rules on installing neutral grounding devices (grounding resistors) used for the purpose of controlling the ground fault current or the voltage-to-ground of an alternating current electrical system. These rules have undergone some significant changes in the 2006 edition of the code.
Rule 10-1102 contains the most noteworthy changes. Sub-rule (1) remains unchanged and continues to specify that: "Neutral grounding devices shall be permitted to be used only on a system involving a true neutral or an artificial neutral, where line-to-neutral loads are not served.” Sub-rule (1), as in the past, remains unequivocal — no single-phase electrical loads from a resistance grounded system.
Rule 10-1102, sub-rule (2) is generally unaffected, but contains the words "Where line-to-neutral loads are not served —”, which alerts us to some impending changes in this rule. As in the past, the remainder of the sub-rule remains unchanged. It goes on to say that resistance grounded circuits up to 5 kV may continue to operate on detection of a ground fault provided that:
- the ground fault current is 10 amperes or less; and
- a visual or audible alarm is provided to indicate the occurrence of a ground fault.
The 2002 CEC specifically ruled out the above easement for systems above 5 kV, which were required to trip OFF under all ground fault conditions. The new rule provides the same restriction by implication. Another difference, the 2002 CEC limited the current rating of the grounding resistor to 5 amperes ground fault current or less. As you will notice, this has been increased to 10 amperes in the 2006 edition.
Rule 10-1102, sub-rule (3) contains the most dramatic changes, stating that when phase-to-neutral loads are supplied from a resistance grounded electrical system, the power supply must automatically be disconnected when:
- there is a ground fault; or
- the system neutral is inadvertently connected to ground; or there is
- inadvertent disconnection of the grounding resistor from the system neutral or the grounding electrode.
Sub-rule (3) presents a significant departure from earlier versions of the CEC, that prohibited supplying any single-phase loads from a resistance grounded distribution system. The 2006 code opens that door with some conditions. Obviously, the above installation change will need to be supplemented with specialized detection equipment that is capable of detecting all of the above conditions and tripping the upstream overcurrent protection.
But does anyone sense there may be a problem with the wording of this Rule? In my opinion, there is a conflict between sub-rules (1) and (3). You will recall that sub-rule (1) states unequivocally that phase-to-neutral loads are not permitted to be supplied from resistance grounded electrical systems. But sub-rule continues on to spell out the conditions that apply when we intend to do just that. What’s missing from sub-rule (3) are the words "Notwithstanding sub-rule (1)—”. I think we have an oversight that will result in some serious conflicts within Rule 10-1102, and that will certainly precipitate numerous lively debates.
Rule 10-1104 remains unchanged and includes the requirements that grounding resistors:
- must be approved for the purpose;
- must be continuously rated unless disconnected on occurrence of a ground fault; and
- must have an insulation rating of at least the line-to-neutral voltage.
Rule 10-1106 is also unchanged and still requires that grounding resistors:
- have live parts are guarded;
- are accessible only to qualified persons;
- are located to permit the dissipation of heat; and
- have warning signs at points where there is access to the electrical system neutral.
Rule 10-1108 contains one significant change, but most of the rule remains unaffected. The conductor between the system neutral and the grounding resistor must be:
- insulated for the system voltage;
- identified grey or white; and
- sized to suit the grounding device, but no less than #8 AWG.
- The conductor between the grounding resistor and the system grounding electrode must be:
- insulated or bare copper wire;
- identified green if insulated; and
- sized to suit the grounding device but not less than #8 AWG.
The only change to Rule 10-1108, where line-to-neutral loads are supplied, the above conductors must match the ampere rating of the grounding device and be no smaller than #12 AWG.
As with all previous articles, you should always consult the electrical inspection authority in each jurisdiction as applicable for a more precise interpretation.
Read more by Leslie Stoch
Posted By David Young,
Friday, September 01, 2006
Updated: Sunday, February 10, 2013
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This article is a continuation of what I see as significant changes that are coming in the 2007 revision of the National Electrical Safety Code.
Photo 1. Bonding of cases and enclosures
Grades of Construction
Table 242-1 has been changed by the removal of the delineations rural and urban. The higher grades of construction that used to apply to urban areas, now apply to all areas. This is a significant change for utilities that used to use the lower grades of construction in rural areas. The grade of construction is used to determine the safety factors that must be used in the strength and loading design of the facilities. In general, the higher the grade of construction, the greater the safety factor and the stronger and more expensive the structure.
Construction and Maintenance Loads
Rule 250A2 has been expanded to emphasize the need to consider temporary loads such as lifting of equipment, stringing conductors, or a worker on the structure or component when designing the strength of the structure.
Photo 2. Fiberglass crossarms
Starting in Rule 253, what was called overload factors is now load factors. The Grade C construction section of Table 253-1 has been expanded to delineate between At crossings and Elsewhere. Footnote 5 now addresses fiberglass (fiber-reinforced polymer) portions of structures and crossarms. The table also has load factors for the new extreme ice and concurrent wind loading (Rule 250C).
Alternate Load Factors
The alternate load factors in Table 253-2 and the associated strength factors of Table 261-1B shall not be used after July 31, 2010.
Fiberglass Structures, Crossarms and Braces
Rule 261A3 now addresses the strength requirements of fiberglass structures and Rule 261D3 now addresses the strength requirements of fiberglass crossarms and braces. Table 261-1A now gives the strength factors for fiberglass structures, crossarms and braces.
Strength of Climbing and Working Steps
New Rule 261N addresses the strength of climbing and working steps on structures.
Strength of Insulators
Rule 277 has been changed significantly to better define the strength requirements of insulators consistent with the ANSI® C29 standards for insulators.
Emergency Installation of Cables on the Ground
Photo 3. Insulators on a 138 kv line
New Rule 311C allows for the installation of electric and communications cables laid directly on grade during an emergency under special conditions.
Electric and Communications Cables in the Same Duct
New Rule 252E clearly states that electric and communications cables shall not be installed in the same duct unless all of the cables are operated and maintained by the same utility.
Communications Cables in the Same Duct
New Rule 252F allows communications cables to be installed in the same duct as long as the utilities involved are in agreement.
Bonding of Cases and Enclosures
The NESC requirement that all above ground metallic power and communications pedestals, terminals, apparatus cases, transformers cases, etc., be bonded if they are separated by a distance of 6 feet or less has been moved from Rule 350F to new Rule 384C. Many people were not aware of this rule because it was located in the Direct-buried Cable section of the code. It is now where it should be in the Equipment section.
Arc Protective Clothing
Rule 410A3 now requires employers to make an assessment to determine the potential arc energy exposure for all employees who work on or near energized parts or equipment. If the assessment determines a potential employee exposure greater than 2 cal/cm2 exists, the employer shall require the employee to wear clothing or a clothing system that has an effective arc rating at least equal to the anticipated level of arc energy. This goes into effect as of January 1, 2009.
Work in the Vicinity of Communications Antennas
New rule 420Q limits the radiation level a worker may be exposed to when working in the vicinity of communications antennas.
Existing Utility Location Verification
Rule 423D2 now recommends that the location of existing utilities be verified by exposure prior to the use of guided boring or directional drilling methods.
Read more by David Young