Posted By Dennis Dorn with introduction by Ken Vannice,
Monday, July 01, 2013
Updated: Thursday, June 20, 2013
| Comments (0)
Entertainment comes from a magical space. Through the mediums of
live and recorded arts, the mind is transported to new levels of excitement,
fantasy, and adventure. As the entertainment industry strives to reach even
higher levels in this magical space, the boundaries of science are constantly
being stretched. The entertainment industry is known to take unconventional
paths to attain magic, but the paths must be safe for the performers, the
support staff, and the audience. Without these people there is no magic.
In the early 1980s, the United States Institute for
Theatre Technology (USITT), the association of design, production, and
technology professionals in the performing arts and entertainment industry
formed 53 years ago, realized that the entertainment industry was working with
a National Electrical Code from the 1920s. Marble slab switchboards and
resistance dimmers requiring hoods to keep the scenery away from the hot
resistance plates were no longer the industry standard or even commonplace.
USITT began to work with the electrical inspection community to update codes
and standards in order to make them safely relevant and workable. The
entertainment industry, in defense of some of its unconventional proposals,
offered that their people were trained professionals. The inspection community
would counter with "How do you know your people are trained professionals?” The
entertainment industry answered the question seven years ago by providing
opportunities for certification.
This article describes the creation of a dual-focused
program created under the rubric of the Entertainment Technician Certification
Program (ETCP). The two spheres currently covered by the program are rigging
and electrical work, as industry leaders determined that these areas are the most
vulnerable to accidents which can lead to serious and sometimes fatal injury.
Recognizing that the area of electrical skills will be
of most interest to IAEI members and readers, this discussion will focus
largely on that subject. However, first a bit of history to provide a context
in seeing how this electrical skills certification program came to be. What
follows is a brief background on how the program began under the auspices of
the Entertainment Services and Technology Association (ESTA).
Establishment of the Entertainment Technician Certification
It was past experience and knowledge regarding the probable
dangers of entertainment production that motivated the board of directors of
ESTA to establish ETCP in March 2003. One goal was to establish a system of
internal industry checks to assure that all reasonable caution is taken in
entertainment venues and that our work force is supervised by lead workers who
meet the criteria of being "qualified individuals.” ETCP was formed with the intention
to attract the top-third of riggers and entertainment electricians who would
oversee the hundreds of thousands of permanent and temporary installations that
occur each year in this country.
Control of ETCP lies directly in the hands of the ETCP Certification
Council, made up of major elements of the North American entertainment world
(see sidebar). Council members represent most of the major trade and
professional associations, key employers, knowledgeable individuals, and the
chairs of the relevant subject matter expert groups that created the
certification examinations. As an aside, in 2012, ESTA merged with its European
counterpart, PLASA, and operates now as PLASA North America. PLASA is the
leading international trade association for those who supply technologies and
services to the event, entertainment and installation industries. PLASA now
maintains the ETCP in North America and the National Rigging Certificate (NRC)
in Europe. The UK and the US have very different standards for how certification
(or qualification) programs are created and operated, so it was necessary for
each program to address their unique legal, liability and geographic
Certification programs are extremely expensive to
develop and maintain, so it was necessary to raise substantial amounts of money
to establish the program. With a cost in excess of a quarter-million dollars to
create just one test, the initial investment was sizeable. Each of the organizations and businesses
holding seats on the Certification Council made significant contributions as
did many members of ESTA. The target goal was always to have the program become
self-sustaining, and at this time the number of candidates (over 1600 certified
to date) has made this hope a reality.
Photo 1. Joe Hatch, ETCP Certified, lighting the Golden Gate Bridge
As stated earlier, initial conversations identified two
disciplines as being of substantial interest and involving a population large
enough to support a certification endeavor: Rigging and Electrical. With its
determination that rigging was the field that involved the most risk, ETCP
first concentrated on that area, but divided the specialty into two distinct
populations: theatrical (auditorium-based performance venues) and arena
(touring shows, circuses, and similar ventures).
The development of certification programs involves an
assessment process that recognizes an individual’s knowledge, skills and
competency in a particular specialty. The oversight body must ensure that all
credentialing programs and their examinations are developed and conducted
according to legally defensible and generally accepted psychometric principles
To assure absolute legitimacy, the process used in the
development of ETCP followed theNational Commission for Certifying
Agencies’ Standards for the Accreditation of Certification Programs. ETCP
was formed and its actions guided by recognized certification experts and
psychomatricians, the latter being the nationally-acclaimed firm, Applied
Measurement Professionals (AMP). A staff person who was trained in statistics
and psychometrics was hired to guide the ETCP office work and support the
Council members. Subject matter experts (SMEs), one group for each emphasis,
were recruited from among the industry’s leading practitioners and work
commenced immediately to identify a body of knowledge that would guide the
development of test questions. For the most part both rigging SME groups used a
parallel time frame and the first set of tests was conducted in 2005. While
these were paper and pencil exams, still given to groups of 10 or more,
nowadays exams are more typically taken by individuals at registered
computer-based testing sites.
Photo 2. ETCP certificate with ID photo
Electrical Skills Certification
The electrical skills exam was unveiled in 2007. Test development followed the same approach, principles
and pricing that was used for the rigging certifications. Again, the focus is
on attracting the top-third of practicing entertainment electricians. This
certification encompasses the installation, interconnection, safe use, and
repair of all portable distribution; utilization of entertainment industry
related electrical equipment; and the safe use of all venue electrical
equipment. Additionally, this certification encompasses the design, layout, and
interconnection of portable electrical distribution equipment, including generation
if necessary, as well as the safe connection of portable distribution feeders
to fixed power sources. Applicants will be expected to know electrical theory
and the safe installation and use of entertainment electrical equipment.
ETCP has prepared candidate
handbooks which describe the entire process in great detail. The candidate
information for all three examinations can be found on the ETCP website, but
the Electrical Skills Handbook can be found at:
Test subject matter content is detailed in an outline located at the center of
the handbook. The handbook notes that each exam includes questions based on
every topic listed, as well as the number of questions that address each
Questions were written based on the principle that
candidates need to be able to know and apply knowledge in three ways:
Recall: The ability to recall or
recognize specific information.
2. Application: The ability to comprehend,
relate or apply knowledge to new or changing
3. Analysis: The
ability to analyze and synthesize information, determine solutions and/or
evaluate the usefulness of a solution.
Any certification program must be
independent of any teaching, coaching activity or knowledge depository. The
content outline, however, provides a scope that candidates can use to evaluate
their personal knowledge and experience and guide their own study (see sidebar
for an abbreviated listing).
The handbook also includes three
sample questions and ETCP has created practice examinations that include 50
representative questions and are available at http://etcp.plasa.org/practice
These practice exams have proven
to be a big confidence booster for candidates who generally have some degree of
test anxiety. To combat some of this concern, The ESTA Foundation provides a
bibliography of texts that might be useful in reviewing for the test and
provides a list of seminars that might be helpful in preparation. Both of these
are available at http://www.estafoundation.org/seminars/resources.htm.
In order to take the test, candidates must meet a criterion of 30
points that can be earned through various means such as undergraduate and
graduate degrees, internships, and similar activities. The most important
element in qualifying to sit for the exam is practical field experience and
even though formal educational credits will help, most of the points must be
derived from work experience. All information submitted on the application must
be verified by employers, institutions, and labor providers.
Certifications must be renewed every five
years, because ETCP wants to encourage continued education in the field. To
this end, ETCP has established a category of ETCP Recognized Trainers, Training
Programs, and Training Providers. These individuals or companies must submit
credentials and syllabi that inform ETCP as to what their programming will
provide in terms that clarify its relevance to renewal candidates.
ETCP Has Influenced the Industry
The idea of hiring the best of the best has
worked its way into numerous contracts at major convention centers and
performance venues across the nation. While there still exists a need for
growth, it is safe to say that the entertainment industry has embraced the
program and made it a lynchpin to further the strength of technician skills and
to encourage ongoing education. There are ETCP Recognized Employers,
Contractors and Labor Providers who sign a Best Practices agreement which
indicates their commitment to use Certified Technicians. These companies and
organizations advertise their proud association with ETCP and the quality of
work and skills ETCP certificants provide.
One of the services provided on the
ETCP website is a North American map which allows someone seeking qualified
workers to find them at the click of a mouse. Clicking on a state or province
will bring up a list of names with company associations, union affiliations, and
certifications, along with the dates certifications were granted and when they
expire. While the majority of certificants hold only one certification, there
are quite a few with multiple credentials and more than a dozen who hold all
We hope that
by informing IAEI members of ETCP’s existence, cooperative efforts may emerge
that will strengthen both organizations’ ability to provide our labor force
with safe work practices and increase their skills as our technology grows more
sophisticated. The number of accidents that has occurred in the last couple of
years has made us aware of both the opportunities and the challenges that face
all of us in the future. With certification, the entertainment industry stands
prepared and actively engaged in making certain that our profession is safe for
participants and audiences alike.
Certification Council MembershipORGANIZATIONAL MEMBERS (10)
PLASABUSINESS MEMBERS (6)
Alliance of Motion Picture and Television
The Broadway League
Canadian Institute for Theatre Technology (CITT)
International Alliance of Theatrical Stage
International Association of Venue
The League of American Theatres and Producers
Themed Entertainment Association (TEA)
United States Institute for Theatre Technology (USITT)
Broadway Across AmericaSME CHAIRS
Cirque du Soleil
Disney Theatrical Productions
Production Resource Group
Electrical Skills – Alan Rowe and Ken Vannice
Rigging Skills – Karen Butler (Theatre)
and Bill Sapsis (Arena)
1. ELECTRICAL SKILLS, 75A. APPLY ELECTRICAL THEORY, 10
• Calculate formulas using electrical principles and alternating current theory and applications B. HANG/RIG OVERHEAD EQUIPMENT, 10
• Apply operational theories of SCR dimmers, basic electronics, and power supplies
• Perform operations and procedures with electrical metering tools, e.g., multimeter, ground tester, DMX tester, network/Ethernet tester
• Calculate weights of electrical equipment C. SET UP ELECTRICAL SYSTEMS, 15
• Specify equipment hanging techniques
• Portable power distribution equipment, generators/transformers
• Lighting equipment and practical set fixtures
• Equipment addressing (e.g., scrollers, dimmers, moving lights)
• Basic special effects (e.g., fog/haze, water, snow, strobes)
• Branch circuit wiring for multiple purposes and safety ground connections
• Tie in feeder cables: bare end and single-pole locking connector
Dennis Dorn is
a professor emeritus of Theatre Technology from the University of
Wisconsin-Madison. He has worked extensively as a consultant, technical
director and set designer and is the co-author of Drafting for the
Theatre, now in its 2nd edition. A USITT member since 1980, Dennis is
active in Institute leadership and activities on both regional and national
levels,having served as an area
commissioner, director-at-large, Certification Council. He was named a Fellow
of the Institute in 2000 and recently received the 2011 USITT Distinguished
Achievement Award in Technical Production.
Ken Vannice is
the co-chair of the electrical skills section of the ETCP. He is the USITT
representative on NEC CMP-15 and is an associate member of IAEI.
Posted By Thomas A. Domitrovich,
Monday, July 01, 2013
Updated: Thursday, June 20, 2013
| Comments (1)
The story of the arc-fault circuit interrupter is an interesting one as it is technical in nature, wrapped in controversy, fueled by passion, and delivers a positive electrical safety impact to the electrical industry. I have read many different articles on this topic and for some time have noted issues with technical details. This article will provide a technical review of the AFCI technology from a standards perspective. You will see how the attempt to simplify a technical message has actually lead us to take liberties that are not technically accurate but help to convey a basic understanding. I will attempt to illustrate what the UL standard requires for a few types of AFCIs to cut through the lingo that has been used to describe the functionality of an AFCI. I am hoping that this article will be your technical resource to ground any discussions around what an AFCI device can or cannot do. I will be referencing UL standards for most, if not all, of the discussion that follows.
Standards versus Outline of Investigations
I can’t begin without addressing a fundamental aspect of UL Listed products that directly pertains to this AFCI discussion. We must first understand what a UL Outline of Investigation (OOI) is before proceeding. Most products you install are supported by a product standard which, in the case of AFCIs, is UL 1699 Standard for Safety ofArc-Fault Circuit Interrupters. A product standard like UL 1699 is an ANSI-approved document that is created through an ANSI process. The ANSI process requires a balanced panel of individuals assuring that no single interest group dominates. UL uses their Standards Technical Panel (STP) to usher this UL standard through the ANSI process. These STPs are similar to the code-making panels that you and I are most familiar with in the NFPA process. Both processes are ANSI-accredited. This balanced panel reviews proposed changes, votes, and ultimately produces an updated consensus standard. The other document I mentioned above, the OOI, is different in that it is not a document that has gone through the same ANSI process described for a UL standard. UL defines the OOI as ". . . a document that contains the construction, performance, and marking criteria used by UL to investigate a product when the product is not covered by the scope of an existing UL Standard for Safety. Outlines are not consensus documents and do not require review by an STP or other external group.” This definition is relevant as you will see later in this article. It is a way that a new product which has no UL standard can quickly come on the market and yet still be evaluated to a predefined test specification. From my experience, the OOI is usually a document that has received industry input from various organizations and just may be the first draft of a future UL /ANSI standard, but has not yet gone through the sometimes lengthy ANSI process.
UL standards contain performance basedtestingthat verifies products will do what the standard intends the products to do and confirms that the product safely performs these duties under the conditions in which it is intended to be applied. Let me explain performance based through an example of a performance based test and a prescriptive requirement. One AFCI test requires cutting into a wire with a sharp blade, causing an arc that must be cleared before a wrap of cotton ignites. This is an example of a performance based test and not a prescriptive requirement. A requirement that all AFCIs must have 30 mA ground fault would be an example of a prescriptive requirement, and one that is not in the standard. UL Standards thrive on performance based test requirements.
UL 1699 Standard and Associated OOIs Background
The origins of UL 1699 can be traced back as far as 1997. The draft requirements of this standard were used as input to the certification of branch-circuit AFCI devices available on the market at that time. Those first devices were initially UL Listed under the Standard for Molded-Case Circuit Breakers, UL 489, and UL Classified for mitigating the effects of arcing faults. UL subsequently pulled together an industry advisory group in the Fall 1998 to develop the draft requirements for the first edition of UL 1699 which was ultimately released in February 1999. The performance based test standard used in the classification of the first AFCIs on the market in 1997 may not have been called an OOI by UL at the time, as they are today, but it indeed resembled the process as we know it.
Today, UL utilizes Standards Technical Panels, (STPs) to usher standards through the ANSI consensus process. The ANSI consensus process has a strict set of guidelines that include important aspects of: Openness, Lack of Dominance, Balance and Consensus Voting.
Products that can be listed to UL 1699 standard requirements include the following:
- Branch Feeder AFCI (Category AVZQ)
- Combination AFCI (Category AWAH)
- Portable AFCI (Category AWDO)
- Cord AFCI (Category AWAY)
- Outlet Circuit AFCI (Category AWCG)
The outlet type AFCI above is not the Outlet Branch Circuit (OBC) AFCI that we have seen mentioned recently. We’ll discuss the differences later. The OBC AFCI is listed to an OOI, "Outline of Investigation for Outlet Branch Circuit Arc-Fault Circuit-Interrupters” and not to the ANSI /UL 1699 standard. The UL White Book discusses all of the above types of AFCI Categories; the OBC AFCI is found in Category AWBZ. Another type of AFCI that is listed to an OOI is the Photovoltaic DC AFCI, Category QIDC, listed to "Outline of Investigation for Photovoltaic (PV) DC Arc-Fault Circuit Protection.” This too can be found in the UL White Book but will not be a focus of this article.
Figure 1. NMB Conductor used in UL 1699 testing.
Figure 2. SPT-2 Conductor used in UL 1699 testing.
UL 1699 Arc-Fault Testing
If you were to purchase a copy of UL 1699 and look through the table of contents, the following are the performance tests conducted on AFCIs:
- Drop and Impact Tests
- Humidity condition
- Leakage Current Measurement
- Voltage Surge Tests
- Environmental Test
- Arc Detection Tests
- Unwanted Tripping Tests
- Operation Inhibition Tests
- Dielectric Voltage Withstand Tests
- Resistance to Environmental Nose Tests
- Normal Temperature Tests
- Operating Voltage Test
- Endurance Test
- Abnormal Operation Test
- Surge current test
- Abnormal overvoltage test
- Short circuit current test
- Terminal lead strain-relief test
- Power-supply cord strain-relief test
- Mechanical tests
- Crushing tests
- Dust test
- Performance of markings
- Reverse line – load miswire test
- Supplemental voltage surge immunity test
As you can see, the performance testing for AFCIs is quite extensive. I will focus on arc detection tests, unwanted tripping tests, and operation inhibition tests. I will also discuss the requirements in the OOI for the OBC AFCI but will leave the PV AFCI for another day.
There are four arc detection tests described in UL 1699. These include the following:
- Carbonized path arc ignition test
- Carbonized path arc interruption test
- Carbonized path arc clearing time test
- Point contact arc test
Not every product listed to UL 1699 has to be tested to the above arc detection tests. Table 1 illustrates the arc detection tests that must be performed for each of the devices that can be listed to UL 1699.
You’ll note the references in the tests above to NM-B and SPT-2 conductors. Not every test is performed on both types of conductors but these are the only types of conductors that are used. They are depicted in figures 1 and 2 respectively. Tests conducted on NM-B are performance tests that verify the tested product can detect and mitigate the effects of arcing faults in the installed wiring of a home. Tests conducted on SPT-2 cords are performance tests that verify the tested product can detect and mitigate the effects of arcing faults in cords, like those connected to receptacles which are usually attached to appliances.
Now let’s take a look at these arc detection tests, one at a time.
1. Carbonized path arc ignition test (figure 3): This test is conducted on NM-B samples only. The outer jacket of the NM-B sample is removed, insulation is removed from one conductor, and this conductor is cut. This area is then covered with electrical tape and loosely wrapped with cotton. A test apparatus is used to create a carbonized arcing path that can be sustained at 120 volts at varying RMS load currents as low as 5 amps. The AFCI must interrupt the circuit before the cotton ignites. Many call this a "Series Test,” but I would much rather refer to this as a "low-current” arcing test since the current is restricted by the load, and is a minimum of 5 A.
Figure 3. Carbonized Path Arc Ignition test sample preparation performed on the Branch Circuit and Combination Type AFCI. This one line diagram illustrates the preparation of the sample to be tested.
2. Carbonized path arc interruption test (figure 4): This test is conducted on both NM-B and SPT-2 samples. To prepare the sample, a cut is made to penetrate the insulation across all conductors. This area is then covered with electrical tape. A test apparatus is used to create a carbonized arcing path that can be sustained at 120 volts. This test is conducted without a connected load, at 100 A and 75 A as delivered by the source. The AFCI must clear the arcing fault if 8 half-cycles of arcing occur within a period of 0.5 seconds. Many refer to this as a "parallel test,” but I would much rather refer to this as a "high-current” arcing test since the current is not restricted by any load and is at a minimum, 75 amps.
Figure 4. Carbonized Path Arc Interruption test sample preparation performed on the Branch Circuit and Combination Type AFCI. This one line illustrates the preparation of the sample to be tested..
3. Carbonized path arc clearing time test (figure 5): This is the sole additional arc detection test required for the combination-type AFCI, beyond that which is required for the branch/feeder type. It is conducted on SPT-2 samples only. The test sample ends are cut and separated. A cut is made to penetrate the insulation across the conductors, and this area is then covered with electrical tape. A test apparatus is used to create a carbonized arcing path that can be sustained at 120 V. As in the carbonized path arc ignition test above, which is only performed on NM-B, a load is used to adjust the RMS load current as low as 5 amps for this test. The AFCI must interrupt the circuit before the times specified in the standard (at 5 A = 1.0 seconds). As noted above, this test is commonly referred to as a "Series Test,” but I would rather refer to this as a "low-current” arcing test since the current is restricted by the load, and is a minimum of 5 A.
Figure 5. Carbonized path arc clearing time test sample preparation. This is the only extra test a combination type AFCI must pass. This one line illustrates the preparation of the sample to be tested.
4. Point contact arc test (figure 6): known as the "Guillotine Test,” here a utility knife blade is utilized to attach a hinged lever arm that is slowly closed onto a test sample such that the blade cuts through the wire insulation causing an arc. Many, at IAEI events saw this test as manufacturers would demonstrate it during meetings. The AFCI must trip if 8 half-cycles of arcing occur within a period of 0.5 seconds. The test is conducted without a connected load at several specified current levels between 500 A and 75 A, as delivered by the source. Both NM-B and SPT-2 samples must be tested. Many refer to this as a "parallel test,” but I would much rather refer to this as a "high-current” arcing test since the current is not restricted by any load and is at a minimum, 75 amps.
Figure 6. Point contact test sample preparation performed on the Branch Circuit and Combination Type AFCI. This diagram illustrates how the steel blade cuts the insulation and causes the arcs in this test.
Figure 7. Illustrates the tests performed and protection provided by the branch feeder and combination type AFCIs as per the UL 1699 Standard. Note that a Branch Feeder AFCI mitigates from high and low arcing currents in installed NMB but only high arcing currents in connected cords. The Combination type AFCI extends the low current arc detection to connected cords.
Table 1 illustrates the fact that the difference between a branch feeder and combination-type AFCI is NOT that one does "parallel” arc detection and the other does "parallel” and "series” arc detection, but rather that the combination-type AFCI extends low-current arc detection to connected cords.
The OBC AFCI
The outline of investigation for the OBC AFCI device, because it is intended to detect arcing and sparking, a basic function of a UL 1699 device, utilized the UL 1699 standard as the basis for its development, referencing it heavily and performing many of the same tests that the combination-type AFCI must perform. Table 2 illustrates the arc detection tests required to be performed by the OBC AFCI. As noted in this table, there is an additional twist to two of the tests listed that make the OBC AFCI unique. Other listed devices are only required to look downstream. A combination AFCI, UL category (AWAH) for example, in the loadcenter, must detect high and low current arcing in all connected downstream NM-B and SPT-2 conductors. It does not look back towards the utility or other branch circuits on the same bus and, in fact, has technology to ensure this does not occur. The outlet-type AFCI, UL category (AWBZ) again this is not the OBC AFCI, must detect high-current and low-current arcing in connected cords (SPT-2) and downstream NM-B conductors connected to its load terminals. This device does not have to detect arcing in the NM-B conductors connected to its line-side terminals, looking back towards the utility.
The OBC AFCI, on the other hand, must detect high-current and low-current arcing on connected cords (SPT-2) and downstream NM-B conductors connected to its load terminals as well as detect low-current arcing in the NM-B conductors connected to its line-side terminals. The line-side arc detection for this device does not include detecting high-current arcing. This additional test of low-current line-side arc detection is in essence looking back towards the source for low-current arcing. An arcing fault that trips an OBC AFCI circuit could be on the load side of the device, in a connected cord, in the downstream NM-B conductors connected to its load terminals or in the line-side NM-B conductors connected to the line terminals of the device anywhere upstream. Figure 8 illustrates the protection coverage of the OBC AFCI device.
Figure 8. Illustrates the tests performed and protection provided by the OBC AFCI device as per the Outline of Investigation for this device.
Figure 9. Point contact test sample preparation with NMB instead of SPT-2 cord as shown in Figure 6.
Unwanted Tripping Tests
In addition to arc detection, it is important that the AFCI device does not needlessly trip. The UL 1699 standard has a section of the document focused on taking a representative AFCI of each rating and ensuring that it does not trip after being tested under various loading conditions including inrush currents, normal operating arcing, non-sinusoidal waveforms, cross talk, multiple loads and even lamp burnout. Tests are performed with various types of appliances from a flat iron skillet to vacuum sweepers and air compressors. Not every manufacturer’s device or model types are tested in these standards.
This testing is quite extensive and, as noted above, includes using tools and appliances you would find in a home. But this is an area where manufacturers go above and beyond to ensure their products perform in the market without unwanted tripping. More than one model or manufacture of an appliance is tested, more combinations of loads, varying models from various brands. It is a fact that if you walk through the AFCI labs of any one AFCI manufacturer, you will find products with which tests are performed that are not in the UL 1699 standard. The answer to why a manufacturer would do this lies in the desire to be the best in the market, to reduce warranty claims, and to maintain customer loyalty to name a few. Each manufacturer strives to have a product that operates with any load on its circuit yet detects the dangerous arcs that may be the source for fires. Other examples of this can be found in efficiency type standards. There is a lot of evidence where manufacturers have gone above and beyond to be the best in their markets. Whether it is to boast better gas mileage than their competition, more efficient transformers or lamps, or even longer lasting batteries, the work that the manufacturer does to have the best product on the market can be viewed as a competitive advantage.
Operation Inhibition Tests
So far we have discussed performance based testing that ensures an AFCI detects arcs and unwanted tripping tests that ensure it detects the bad arc and not the good arcs causing a trip. However, we can’t forget the fact that an AFCI must detect dangerous arcs without being masked by other types of loads on the same circuit. These tests in the UL standard help to ensure dangerous arcs can be detected even in the presence of other loads that may act to mask the arc, preventing the AFCI from doing what it needs to do — open the circuit when an arc fault exists. Scenarios such as electromagnetic interference (EMI), masking loads such as vacuum sweepers, air compressors, switching power supplies, electronic lamp dimmers and more are tested with the AFCI device to ensure its robust arc detection methods operate correctly in these "dirty” environments. High-current and low-current arcs must still be detected when other loads are on the circuit.
Series versus Parallel
The terms series arcs and parallel arcs are used quite heavily in discussions pertaining to AFCIs to describe the types of arcs that are being detected and to describe the differences between types of AFCIs. While it would appear that using these terms helps simplify the complex, we know that from an electrical standpoint this is technically not a correct use of these terms and, depending upon what they are used to describe, may not describe the facts at all.
Let’s first look at the definition of the words "series” and "parallel.” Merriam-Websterdefines series as "a number of things or events of the same class coming one after another in spatial or temporal succession.” This resource defines parallel as "extending in the same direction, everywhere equidistant, and not meeting.” Both of these definitions utilize a relationship or a comparison between two or more objects as the basis for the definition. These two words, in our context, are intended to describe the relationship between two or more elements of an electrical circuit. These terms, when used by themselves, series arc or parallel arc do not identify which element(s) are in series/parallel with another. If you draw a circuit, the terms series and parallel will heavily depend upon how you draw your circuit and reference the components in the circuit. From a technical perspective, these words do not provide clarity.
These terms are also used when describing the difference between a branch-circuit AFCI and a combination-type AFCI. You’ll hear, "A branch-circuit AFCI detects parallel arcs and the combination-type AFCI detects parallel and series arcs.” Plain and simple, this is incorrect. The reason is due to the facts we discussed above. Look at the carbonized path arc ignition test, figure 3, that the branch-feeder and combination-type AFCI must pass. Ask yourself if that is what you envision when someone says series arc. Is that conductor cut and subsequent arc across that conductor cut in series with the load? In this test, the current is limited down to 5 amps by the load because it is performed for both the branch-feeder and the combination-type AFCI devices, saying that the branch-feeder does not detect series arc faults is not an accurate statement per the standard.
If instead of usingseries and parallel we use low-current and high-current, respectively, our explanation is technically accurate and should be understandable. A better way to describe the difference between a branch-feeder AFCI and a combination-type AFCI would be as follows:
"A branch-feeder AFCI offers high- and low-current arc detection for installed NM-B wire and high-current arc detection for connected cords. The combination-type AFCI offers the same level of protection afforded by the branch-feeder AFCI but extends the low-current arc detection to connected cords.”
AFCIs and Ground Fault
In the past, confusion around the definition of a combination-type AFCI left some thinking that the combination-type AFCI was a combination of AFCI and GFCI in the same device. The UL 1699 standard does not include a prescriptive requirement of any level of ground-fault protection. Some AFCI devices do indeed have a level of ground-fault protection which may vary from manufacturer to manufacturer. Ground fault added to an AFCI is there primarily as a means to pass the carbonized path arc ignition performance test included in UL 1699 and described above. (See figure 3). An AFCI device that carries an additional listing to either UL 943 or UL 1053 standards would be considered a dual purpose AFCI device which provides people protection or equipment protection respectively.
The arc-fault circuit interrupter is a device that is technical in nature, wrapped in controversy, fueled by passion, and delivers a positive electrical safety impact to the electrical industry. For examples of found electrical products, bookmark www.afcisafety.org and check it often as there is a document on that web site that provides examples of found electrical problems. Together we can make a difference.
As always, keep safety at the top of your list and ensure you and those around you live to see another day.
Read more by Thomas A. Domitrovich
Safety in Our States
Posted By Ark Tsisserev,
Monday, July 01, 2013
Updated: Thursday, June 20, 2013
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The subject of bonding and grounding is perhaps the mostconfusing to the users of the electrical installation codes.
In fact, I have written on this subject in this very publication, at least two such articles, in the past few years. Nevertheless, I routinely receive e-mails and phone calls with the questions about differences between bonding, grounding and neutral conductors, about differences in use of these conductors under the Rules of the Canadian Electrical Code and about differences in the Code requirements for sizing such conductors. So, let’s provide a bit of clarification again.
1. Bonding conductor
Bonding and bonding conductor are defined in the CE Code as follows:
"Bonding — a low impedance path obtained by permanently joining all non-current-carrying metal parts to ensure electrical continuity and having the capacity to conduct safely any current likely to be imposed on it.
Bonding conductor — a conductor that connects the non-current-carrying parts of electrical equipment, raceways, or enclosures to the service equipment or system grounding conductor.”
Based on these definitions, it is abundantly clear that bonding is a low-impedance path that is deliberately created between all non-current-carrying metal parts of electrical equipment in order to safely conduct any undesirable current (leakage or fault current) that could be inadvertently imposed on these metal parts during use of electrical equipment.
Bonding conductor is such conductor that actually connects these (normally non-current-carrying) metal parts of the electrical equipment (including cable armour and sheath, and metal raceways) with service equipment or with system grounding conductor. Let’s hold for a time being the explanation regarding connection of bonding conductor with the service equipment or with system grounding conductor, and let’s concentrate on a selection of size for a bonding conductor.
Photo 1. Does marking of this bonding conductor comply with the CE Code?
Bonding conductor is not considered to be a circuit conductor, as circuit conductors carry the circuit current under a normal operating condition, and ampacity of circuit conductors is selected in accordance with Rule 8-104 (or with other applicable rules of the Code depending on a type of connected loads such as motor, capacitor or heating loads). However,asa bonding conductor is intended to carry only a fault current, it must be sized so, as to have sufficient ampacity to carry the maximum fault current that could be accidentlyimposed on the non-current-carrying metal parts of a specific electrical equipment (of a specific connected load).
Selection of a bonding conductor size is governed by Rule 10-814(1).
This Rule states the following:
"10-814(1) The size of a bonding conductor shall be not less than that given in Table 16, but in no case does it need to be larger than the largest ungrounded conductor in the circuit.”
Table 16 offers the code users a criteria for selection of a bonding conductor size based on the ampacity of the largest ungrounded conductor in the circuit.
Appendix B Note on this Rule further clarifies this requirement by explaining that raceways permitted by the Code to be used as bonding conductors are deemed to be of adequate size to carry the fault current. This Appendix B Note also explains to the Code users that a bonding conductor provided as an integral component of a cable designed and constructed in accordance with an applicable safety standard (with one of the CSA Part II standards listed in Appendix A of the Code) is also deemed to be of adequate size for the purpose of Rule 10-814(1) to carry the maximum fault current that could be imposed on the non-current-carrying metal parts of electrical equipment connected by that particular cable.
Appendix B Note on Rule 10-814(1) "When a raceway or cable sheath enclosing the circuit conductors is permitted to be used as a bonding conductor for the equipment being supplied, it is deemed to be of adequate size for the purposes of this Rule. The bonding conductor incorporated into a cable assembly is sized in accordance with the relevant Part II Standard. Typically, the bonding conductor size in manufactured cables corresponds to the requirements of this Rule, but in some cases it may differ by one size, usually on the larger side. In any case, the bonding conductor incorporated into a cable assembly is deemed to be of adequate size for the purposes of this Rule.”
So, for example, if three 3/0 AWG copper conductors are selected from a 75 Deg. C column of Table 2 with ampacity of 200 A, and these conductors are installed in a PVC for a connection to,let’s say, a motor, then a copper bonding conductorsized at not less than 6 AWG must be selected from Table 16 based on ampacity ofsuch circuit conductors. If these three circuit conductors are installed in a rigid metal conduit, and this rigid metal conduit is used as a bonding conductor in accordance with Rule 10-618 of the CE Code, then the rigid metal conduit selected as per Table6 of the Code is deemed to be of adequate size to carry the maximumfault current that could be imposed on the metal enclosure of the motor connected to the circuit by these three 3/0 AWG copper conductors.
Photo 2. What should be the color of insulated grounding conductor?
Now is a good time to re-visit the Code definition of bonding conductor "Bonding conductor — a conductor that connects the non-current-carrying parts of electrical equipment, raceways, or enclosures to the service equipment or system grounding conductor,” and review the portion of this definition that describes connection of the bonding conductor to the service equipment or to the system grounding conductor.
Let’s start with connection of a bonding conductor to agrounding conductor. Before we’ll analyze the objective of this portion of definition, we need to clearly understand the meaning of agrounding conductor and grounding electrode.
2. Grounding conductor
The CE Code defines grounding conductor and grounding electrode as follows:
"Grounding conductor — the conductor used to connect the service equipment or system to the grounding electrode.
Grounding electrode — a buried metal water-piping system or metal object or device buried in, or driven into, the ground to which a grounding conductor is electrically and mechanically connected.”
Based on these two definitions, it should be clear that agrounding conductor at service equipment is such aconductor that connects aservice equipment enclosure to the grounding electrode and, via a grounding electrode, toground (toearth). This means that a service equipment enclosure (to which all other non-current-carrying metal parts of electrical equipment are connected by a bonding conductor) is reliably connected to ground (earth) by means of a grounding conductor and grounding electrode. Italso means that through this connection to ground/earth, all bonded non-current-carrying metal parts of electrical equipment are not only connected together (i.e., they are not only kept at the same potential), but they are actually bonded to ground (i.e., they are reliably kept at the potential of ground). It means that the purpose of a grounding conductor between the service enclosure and a grounding electrode is to always keep the equipotential plane established by the equipment bonding — at the potential of ground.
What about a system grounding conductor? In a typical solidly grounded system usually derived by a secondary of a utility or a customer-owned transformer or by a generator, a neutral point of the system is connected to ground via a system grounding conductor and a grounding electrode. This neutral point is also permitted to be connected to the enclosure of a transformer or a generator.
Photo 3. Does identification of the neutral conductor meet the CE
So, how should a grounding conductor be sized? The answer to this question depends on the answer to another question: doesa grounding conductor carry a fault current?
Let’s review this question. When a fault current is imposed on a non-current-carrying metal part of electrical equipment which is bonded by a bonding conductor, this fault current is brought back to the service equipment by the bonding conductor sized in accordance with Table 16. What will be the effective path of a fault current back to the electrical power supply source in order to facilitate operation of the overcurrent protective device? Will this path be provided by a grounded service conductor which connects the bonded enclosure of the service equipment with the grounded neutral point of the source (with the grounded neutral point of the transformer or generator), or will it be provided by a grounding conductor and earth back to the neutral point of the source?
Of course, the effective ground fault current path will be provided only via a grounded service conductor and, for the purpose of facilitating operation of the overcurrent protective device, the fault current will never reach the source via a grounding conductor. This means that a grounding conductor does not carry a fault current for the purpose of facilitating operation of the overcurrent protective device. Of course, it does not. This is the reason that Table 17 has been removed from the CE Code, and Rule 10-812 states the following requirement for a grounding conductor sizing:
10-812 Grounding conductor size for alternating-current systems and for service equipment (see Appendix B) "The size of the grounding conductor connected to a grounding electrode conforming to Rule 10-700 shall be not smaller than No. 6 AWG.”
Appendix B note on Rule 10-812 offers the following clarification of this requirement:
"Appendix B Note on Rule 10-812 "It is intended that the size of a grounding conductor for a solidly grounded alternating-current system connected to a grounding electrode need not be larger than No. 6 AWG. The majority of fault current will be taken by the service grounded conductor of the system back to the source, and a grounding conductor sized not less than No. 6 AWG would be sufficient to carry any portion of the fault current that will flow through it.”
Let’s now elaborate on a "grounded service conductor” which will carry the fault current back to the source from the bonded service equipment. Usually such grounded service conductor is a neutral conductor.
3. Neutral conductor
Neutral is defined in the CE Code as follows: "Neutral — the conductor (when one exists) of a polyphase circuit or single-phase, 3-wire circuit that is intended to have a voltage such that the voltage differences between it and each of the other conductors are approximately equal in magnitude and are equally spaced in phase (see Appendix B).”
Appendix B provides the following clarification on this definition:
"Neutral — By definition, a neutral conductor of a circuit requires at least three conductors in that circuit. However, in the trade, the term "neutral conductor” is commonly applied to the conductor of a 2-wire circuit that is connected to a conductor grounded at the supply end. Care should therefore be taken in the use of this term when applying the Code.”
Neutral is acircuit conductor. However, neutral is identified (i.e., grounded) circuit conductor. Ina 3-phase, 4-wire circuit, or in a single-phase, 3-wire circuit, neutral conductor carries only unbalanced current. In a typical 2-wire circuit, neutral (identified) conductor carriesa full load current.
In fact, Subrules (3) and (4) of Rule 4-004 of the CE Code help the Code users in understanding the function of a neutral conductor in a circuit as follows:
"Rule 4-004(3) A neutral conductor that carries only the unbalanced current from other conductors, as in the case of normally balanced circuits of three or more conductors, shall not be counted in determining ampacities as provided for in Subrules (1) and (2).
Rule 4-004(4) When a load is connected between a single-phase conductor and the neutral, or between each of two phase conductors and the neutral, of a three-phase, 4-wire system, the common conductor carries a current comparable to that in the phase conductors and shall be counted in determining the ampacities as provided for in Subrules (1) and (2).”
Rule 4-022 provides guidance to the Code users regarding the minimum allowable size selection of a neutral conductor:
"Rule 4-024 Size of neutral conductor(1) The neutral conductor shall have sufficient ampacity to carry the unbalanced load. (2) The maximum unbalanced load shall be the maximum connected load between the neutral and any one ungrounded conductor as determined by Section 8 but subject to the following: (a) there shall be no reduction in the size of the neutral for that portion of the load that consists of (i) electric-discharge lighting; or (ii) non-linear loads supplied from a 3-phase, 4-wire system; and (b) except as required otherwise by Item (a), a demand factor of 70% shall be permitted to be applied to that portion of the unbalanced load in excess of 200 A. (3) The size of a service neutral shall be not smaller than the size of a neutral selected in accordance with Subrule (1) and shall (a) be not smaller than No. 10 AWG copper or No. 8 AWG aluminum; and (b) be sized not smaller than a grounded conductor as required by Rule 10-204(2), except in service entrance cable or where the service conductors are No. 10 AWG copper or No. 8 AWG aluminum. (4) In determining the ampacity of an uninsulated neutral conductor run in a raceway, it shall be considered to be insulated with insulation having a temperature rating not higher than that of the adjacent circuit conductors.”
But which Code requirement recognizes neutral conductor as a bonding conductor when the neutral conductor is installed betweentheneutral point of a solidly grounded system at the power supply sourceand the grounded enclosure of the service equipment?
The answer could be found in Rule 10-204(2) of the CE Code. Rule 10-204(2) "Where the system is grounded at any point, the grounded conductor shall: (a) be run to each individual service; (b) have a minimum size as specified for bonding conductors in Table 16; (c) also comply with Rule 4-024 where it serves as the neutral”;
This Code rule clearly recognizes the fact that the grounded conductor installed between the source of a solidly grounded supply system and the service is actually a bonding conductor, as it will carry the fault current between the bonded service enclosureand the source [see paragraph (b) above]. This rule also states that in addition to being a bonding conductor (and being sized as per Table 16) this grounded service conductor must be sized as per Rule 4-024 when it serves as a neutral conductor. Rule 10-624(4) specifically recognizes the fact that a grounded service conductor (regardless whether it is used as a neutral or just as a bonding conductor between the source of the solidly grounded supply and the service equipment) is permitted to bond the service equipment, thus re-enforcing its purpose by the Code of carrying the fault current between the service equipment and the source. Rule 10-624(4) states:
"The grounded service conductor on the supply side of the service disconnecting means shall be permitted to be connected to the metal meter mounting devices and service equipment, and where the grounded service conductor passes through the meter mounting device it shall be bonded to the meter mounting device.”
Hopefully, this exercise of reviewing functions of bonding, grounding and neutral conductors and criteria for selecting appropriate sizes of these unique conductors will help to further clarify the subject of bonding and grounding. However, as usual, in each case of design and installation, the respective AHJ should be consulted in discussing specific issues related to this subject.
Read more by Ark Tsisserev
Posted By Underwriters Laboratories,
Monday, June 24, 2013
Updated: Thursday, June 20, 2013
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Has there been any progress made on changes to UL2196 and ULC-S139? Are the standards still active? Are there any new certifications?
Yes to all three questions. Initial research has been completed and a joint U.S. and Canada standards working group of the consensus based technical committee has been formed to determine what upgrades in requirements are necessary to deliver a single, harmonized bi-national standard. The group will focus on a strategy to address installation variables, sampling requirements for testing, and the need for any further research.
UL and ULC continue to maintain an active certification program for fire resistive and CI cable. While UL and ULC authorization for certification was initially discontinued in September of 2012, an interim program was quickly developed and we re-established certification in December of 2012. UL and ULC have been working closely with manufacturers to fully understand how variables impact performance of cables and systems. The interim program focuses on three key factors:
1. The need to establish repeatability, which includes testing of five samples of cable with all of the necessary system components
2. Whether representative testing may be possible in some cases if the critical variables of the fire resistive and CI cable system are understood (i.e., conductor size, conduit type, fitting, etc.) and a worst case configuration can be determined
3. An enhanced follow-up services process designed to evaluate continued compliance
To date, two cable manufacturers have achieved certification under the interim program. These cables systems appear under UL’s Product Category, Electrical Circuit Integrity Systems (FHIT). A MI Cable achieved a two-hour Fire Rating and is covered under System Number 1850. The second cable is a MC Cable with a one-hour fire rating under System Number 120. More are expected in the near future. You can view these systems online at www.ul.com/database and enter FHIT at the category code search field.
We will continue to provide updates related to the above on the Fire page of the UL Code Authorities web page (ul.com/fireratedcables). Please contact Bob James (firstname.lastname@example.org)or Al Ramirez (email@example.com)with any questions or comments.
2011 NEC 410.16(C)(5) states that "Surface-mounted fluorescent or LED luminaires shall be permitted to be installed within the storage space where identified for this use.” Are there any luminaires certified (Listed) for this use and how are they identified?
Yes, there are some certified (Listed) luminaires that have been evaluated for use in a clothes closet. UL has certified luminaires that are transparent closet rod tubes with an integral fluorescent luminaire for this use under the product category Fluorescent Surface Mounted Luminaries (IEUZ) located on page 180 in the 2013 UL White Book. In addition, UL has certified a transparent closet rod tube with an integral LED luminaire for this use under the product category Low-Voltage Lighting Systems, Power Units, Luminaires and Fittings (IFDR) located on page 189 of the 2013 UL White Book. These luminaires have been evaluated and found to operate with surface temperatures sufficiently low so as to not present a risk of ignition to fabrics or materials that may be in contact with them, even under conditions where ventilation of the luminaire is inhibited by these materials. The luminaires are permitted to be marked "Suitable for Installation in the Storage Area of a Clothes Closet.” These product categories can also be viewed on UL’s Online Certification Database at www.ul.com/database and enter IEUZ or IFDR at the category code search field.
In addition to the luminaire evaluation, the rod/luminaire is subjected to a 4 times rated loading test, so that if it is rated for 50 lbs. it has undergone a 200 lb. loading test.
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UL Question Corner
Posted By David Clements,
Wednesday, May 01, 2013
Updated: Thursday, April 25, 2013
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In its simplest terms, branding is who we are, how others feel about us, and how industry and the public view us as an organization. Every time a prospective member, a potential customer or the general public contacts us, by whatever means, they formulate an opinion of us which creates our brand.
For example, one of the most successful brands was Tiger Woods, the first "billion dollar athlete.” Tiger, the golfer, was known and loved worldwide; a family man, he was known equally well for his work with underprivileged children and for his foundation. Corporations avidly sought his endorsements. Then an exposure of infidelity dramatically shattered his brand and, to some degree, the brand of those who endorsed him. With his recent wins re-positioning him as one of the world’s top golfers, will it also be a factor in recreating his brand?
Lance Armstrong, the cyclist, won the Tour de France for seven consecutive years, fought cancer, and returned to win again and again. He introduced the collaboration of sponsors, and corporations jockeyed to become sponsors. He also founded charities. Again, the public fervently supported him; he had over four million followers on Twitter. Then the deep dark secret of performance-enhancing drug use crashed his brand and changed the public’s perception of and attitude towards him. Of course, his brand is damaged right now.
Who we are and how others feel about us may also be called character, credibility, and reputation. Character is the combination of moral and other traits which makes one the kind of person one actually is. Credibility is the quality of being believable or worthy of trust. Reputation is the regard in which a person or group is held, especially by the community or the general public.
These elements of branding apply not only to individuals but to governments, businesses, and associations. In order to influence the world, a government must be true to its character and must maintain its credibility. When senators, politicians, and other government officials, acting from self-interest, depart from the country’s character and standards of government, the government loses credibility both at home and abroad.
You may recall that in 1982, Johnson & Johnson faced a major crisis due to someone’s tampering with extra-strength Tylenol capsules once they reached the market shelves; an unknown suspect(s) put cyanide into the Tylenol capsules, which resulted in the death of seven people in Chicago. This event was a potential major blow to the Johnson & Johnson brand. Although Johnson & Johnson knew they were not responsible for the tampering of the product, they assumed responsibility of ensuring public safety first and recalled all of their capsules from the market. The way Johnson & Johnson handled this crisis not only saved lives, but it saved their brand from damage. The public relations industry played an important role in managing the risk that could have damaged Johnson & Johnson’s reputation. Afterward, many companies followed their lead in dealing with major crises. However, others didn’t learn the lesson, such as in the case of Exxon Oil spill.
Starbucks and Apple customers generally develop a powerful and visceral emotional attachment to their brands. Could it be that these companies are exactly who they claim to be, and that they deliver what their customers want? It is certainly true that each of these companies jealously guard their reputations and the consistency of their brands. They obviously have learned that every little thing matters.
Has IAEI learned that? Let’s look at ourselves and ask two simple questions: Who are we? and What do others think of us? Confusing taglines and multiple logos do not make IAEI; character, credibility and reputation do. These elements are important:
Who are we really? IAEI is a group people who have chosen to work together toward the common goal of safe and compliant electrical installations. Do we understand that "we” means "all of us,” not just our officers or staff? Do we stand firmly on our moral and ethical beliefs? Are we joyful, excited, and forward-looking? Passion is contagious; therefore, it is essential that we truly enjoy and believe in what we do and stand for. If we do, others with the same passion will want to be part of our association and will talk about IAEI in a positive manner.
What are our skills and expertise? We must clearly and specifically identify what we do best and what are our core strengths. The more we focus on what we do best, the more efficiently we do it and the more likely we are to succeed.
What are our vision, goals, and strengths? We should not pattern our goals after those of other associations or groups. The goals must be our own and must be supported by our strengths. We must have our own identity, unique from others.
Over the next several months the International Office will be identifying ways to increase our brand recognition. In the meantime, every little thing matters! Never underestimate the affect that you, as an individual, have on the overall brand of IAEI.
Read more by David Clements
Posted By Underwriters Laboratories,
Wednesday, May 01, 2013
Updated: Friday, April 26, 2013
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Can I use any UL Listed grounding lug evaluated to UL 467 for grounding a photovoltaic (PV) panel or supporting rack system? What devices are evaluated for grounding and bonding PV modules and mounting racks to comply with 2011 NEC Section 690.43(C), (D), and (E)?
No, UL certified (Listed) grounding and bonding devices are not automatically evaluated for grounding or bonding PV modules unless the Listed PV module or panel’s installation instructions identify that device as suitable for grounding or bonding its modules. Grounding and bonding lugs are evaluated for compliance with the Standard for Safety for Grounding and Bonding Equipment, UL 467, and are certified (Listed) under the product category Grounding and Bonding Equipment (KDER) located on page 224 in the 2013 UL White Book and online at www.ul.com/database by entering KDER at the category code search field.
The Guide Information for this product category indicates that grounding and bonding equipment intended for use in PV systems is additionally investigated in combination with the PV module/panel (see QIGU) to the applicable requirements for such products. Installation instructions provided with the PV system identify the specific grounding and bonding device that has been investigated and intended for use with that system. PV panels are certified (Listed) under the product category Photovoltaic Modules and Panels (QIGU) located on page 339 in the 2013 UL White Book and also online at www.ul.com/database and enter QIGU at the category code search.
Each PV panel or module and its frame and mounting systems is different, made of different materials and configurations so that a grounding or bonding device that has only been evaluated for compliance with UL 467 alone has not been evaluated for use in PV systems and doesn’t address the special conditions of grounding and bonding each uniquely constructed PV module frame to the wiring system and the module supporting racking systems. UL 467 alone doesn’t address the different weather conditions and conditions of mechanical loading such as the panels themselves and snow and wind loads that can affect the integrity and reliability of the grounding and bonding systems of PV systems over time.
Grounding and bonding devices as well as mounting and racking systems specifically evaluated for PV systems are UL certified (Listed) under the product category Mounting Systems, Mounting Devices, Clamping Devices and Ground Lugs for use with Photovoltaic Modules and Panels (QIMS) located on page 343 in the 2013 UL White Book and also online at www.ul.com/database and enter QIMS at the category code search field.
Products certified under the QIMS product category are evaluated for compliance with the Outline of Investigation for Rack Mounting Systems and Clamping Devices for Flat-Plate Photovoltaic Modules and Panels, UL Subject 2703. This category covers photovoltaic (PV) mounting systems, mounting devices, clamping devices (which may be for bonding and/or mechanical loading) and ground lugs intended for use with specific PV modules and panels and specified module frames and mounting structures as identified in the individual Listings. Both mounting systems and clamping devices may be investigated for mechanical mounting alone, or mechanical mounting and ground bonding as identified in the individual Listings. Ground lugs may be investigated for use with specific PV modules, specific PV module frames, or specific mounting-system rails.
The installation of these mounting systems, clamping devices or bonding devices is intended to be in accordance with ANSI/NFPA 70, National Electrical Code, in addition to any applicable building codes. Authorities having jurisdiction should be consulted as to conformance with applicable building codes, including the class of roof covering.
The devices certified under this category can be identified by the UL Listing Mark on the product that identifies it as one of the following product names: "Photovoltaic Mounting System,” "Photovoltaic Module Clamping Device,” "Photovoltaic Mounting Device,” "Photovoltaic Bonding Device,” "Photovoltaic Mounting and Bonding Device” or "Photovoltaic Ground Lug.” The word "photovoltaic” may be abbreviated "PV.”
The installation instructions will identify the panels, modules and racking systems as appropriate for which they have been certified. That information can also be found on UL’s Online Certification Directory at www.ul.com/database and enter QIMS at the category search field, then click on the specific manufacturer. The certification information will detail the specific installation criteria of what the devices are certified (Listed) for, as well as the products they are certified for use with.
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UL Question Corner
Posted By Joseph Wages, Jr.,
Wednesday, May 01, 2013
Updated: Friday, April 26, 2013
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My First Tunnel
Remember your first tunnel? I do; but now, it not only involves me but also my wife and children. Driving through the tunnel has become an event my family and I look forward to when we travel to the state of Alabama. The tunnel I speak of runs beneath Mobile Bay. My first encounter came at age sixteen, while I was on vacation with the Rankin Family to the white beaches of Gulf Shores, Alabama. Even though I will never forget that vacation and the fun I had on the beach and while fishing in the gulf, the tunnel really got my attention.
At first, it was alarming that we would be traveling in an automobile through a small shaft under a large body of water; I was concerned that if something happened and all that water came rushing in, we would all die. But an interesting distraction happened while we were in the tunnel: happy-go-lucky kids, in numerous vehicles, were all honking their horns while inside the tunnel. This small act relieved a lot of the tension in me, and before I knew it we were out of the tunnel on the other side of the bay.
I still encounter tunnels on a daily basis. In the Dallas area, I have passed through roadway tunnels as well as through tunnels associated with the public transit system (DART). In the Northeast, I have experienced the Big Dig tunnel in the Boston, Massachusetts area. Driving back to Northwest Arkansas to visit family and friends I pass through the Bobby Hopper Tunnel, the first tunnel in Arkansas to go through a mountain and the connection to the River Valley with the enchanted area of the state known as Northwest Arkansas.
From the roadway tunnels that pass under interstate highways to smaller tunnels that allow for pedestrian and bike flow under a busy intersection, tunnels are everywhere. These locations serve a purpose that allows for safer and easier travel to millions of people around the world. They are also examples of great engineering and architectural achievements that span throughout world history.
Photo 1. Tunnel under a major intersection for pedestrian/ bike traffic. Notice signage above the entrance stating, "Keep Right Through Tunnel.”
Tunnels and the NEC
So, with tunnels comes a need for lighting and, in some cases, ventilation; but where does one go to find guidance toward the installation requirements for these areas? How do we decide which type of wiring method, device or luminaire to install in these locations? Are these areas subject to physical damage? What does the NEC have to say about these locations? Does the terminology that the NEC and the public use even have the same meaning?
Defining a Tunnel
When dealing with this subject one must know what defines a tunnel. In the NEC we typically find definitions in Article 100, but this is not the only place a definition can be found. Definitions that relate to a particular article are found in the .2 locations within the article. Upon searching, we find that there is no definition of tunnels within the NEC. This leads me to Webster’s Dictionary for their help.
When used as a noun, a tunnel is defined as a passageway through or under something, usually underground (especially one for trains or cars); example, "The tunnel reduced congestion at that intersection.” This definition seems to be addressing the two topics I mentioned in this story: we have passed under a large body of water and then under a busy city intersection. But what can we find within the NECtowards installation guidance and practices when there is no definition of these locations? More searching and a word search of the NEC finds the word "tunnel”; but in reading that section in Article 110, it appears that this applies to installations of "over 600 volts.” This code language does not help me apply the requirements to the pedestrian tunnels I want to discuss.Additionally, what guidance can we find toward what types of conductors and conduit methods are acceptable in these locations? Are these areas considered as dry, damp or wet locations? This is something that must be addressed now before we purchase materials, install the electrical devices, call for an inspection, and then face an inspector who ultimately has the final say. His or her decision might not be the same as ours, and could cause additional work, expense, and unnecessary hard feelings.
A tunnel can mean different things to different individuals. I recently passed a drainage culvert under a highway. A smaller culvert is not a tunnel to me, but to a beaver it becomes a great and safe passageway from one side of the road to the other. Based on the above definition, the culvert could be defined as a tunnel. It is noteworthy for the reader to be aware that there have been electrical conduits installed in what one might consider a culvert.
Photo 2. View of trails converging at the tunnel entrance.
A word search for the word "tunnel” was conducted for the 2011 NEC. The majority of the hits occurred in Article 110, Part IV, Tunnel Installations over 600 Volts, Nominal, but the installations I am interested in are applications under 600 volts. I had one other hit for tunnels in Section 210.6, Branch Circuit Voltage Limitations. This was for 600 volts between conductors and dealt with permanently installed auxiliary equipment for electric discharge lamps for luminaires. This is still not helpful for my installation. However, this information would be beneficial for the installation of a "utility” tunnel and would be very much applicable. This sort of tunnel would be installed between two buildings and used in conjunction with other utilities for the routing of their systems.
Wet, Damp or Dry Location?
How do we determine if a tunnel is a wet, damp or dry location? It is highly advisable to schedule a meeting with the local authority having jurisdiction (AHJ) for his/her viewpoint before you begin your project. While visiting various pedestrian tunnels I have observed several wiring methods. I have encountered set screw and compression EMT connectors and fitting. I have seen EMT conduit installed with one-hole straps to the wall of the tunnel. I have also seen installations of EMT conduit supported by unistrut with unistrut straps.
It appears to me that there are many interpretations of the tunnel area as it pertains to a wet, damp or dry location. We must also remember that changes in environmental conditions may change the condition of our tunnel. Heavy rains may change a typically dry condition to a wet or damp location. This must be considered when you choose the wiring method for these locations.
So who are these individuals that fill the role of an AHJ? The AHJ has final approval for your electrical project and is burdened with a tremendous responsibility for the safety of the public. This involves both property and personnel associated with various locations. These individuals are typically experts within their fields and highly respected. Let’s refresh ourselves on the NEC definition of the AHJ:
Authority Having Jurisdiction (AHJ). An organization, office, or individual responsible for enforcing the requirements of a code or standard, or for approving equipment, materials, an installation, or a procedure.
Informational Note: The phrase "authority having jurisdiction,” or its acronym AHJ, is used in NFPA documents in a broad manner, since jurisdictions and approval agencies vary, as do their responsibilities. Where public safety is primary, the authority having jurisdiction may be a federal, state, local, or other regional department or individual such as a fire chief; fire marshal; chief of a fire prevention bureau, labor department, or health department; building official; electrical inspector; or others having statutory authority. For insurance purposes, an insurance inspection department, rating bureau, or other insurance company representative may be the authority having jurisdiction. In many circumstances, the property owner or his or her designated agent assumes the role of the authority having jurisdiction; at government installations, the commanding officer or departmental official may be the authority having jurisdiction.
As we can see from the definition, an AHJ can be made up of different individuals. Who wears that hat depends on the location you are working in. Become familiar with the local AHJ, as this person can become your greatest asset towards installing a compliant electrical installation. The AHJ will use his/her experience and expertise to make a determination of what is best for that particular situation. But the AHJ will also take into consideration three definitions within the NEC to help mold that decision.
Photo 3. An access point to an underground utility tunnel
Proper Interpretation and Enforcement Starts with Understanding Definitions
Let’s look at the definitions we are to consider when making decisions about these locations. To begin, let’s go to Article 100 in the 2011 NEC. We need to review the definitions that are going to help us make this decision.
Location, Damp. Locations protected from weather and not subject to saturation with water or other liquids but subject to moderate degrees of moisture. Examples of such locations include partially protected locations under canopies, marquees, roofed open porches, and like locations, and interior locations subject to moderate degrees of moisture, such as some basements, some barns, and some cold-storage warehouses.
Location, Dry. A location not normally subject to dampness or wetness. A location classified as dry may be temporarily subject to dampness or wetness, as in the case of a building under construction.
Location, Wet. Installations underground or in concrete slabs or masonry in direct contact with the earth; in locations subject to saturation with water or other liquids, such as vehicle washing areas; and in unprotected locations exposed to weather.
Again, it must be stressed that these locations within tunnels are subject to the interpretation of the AHJ. Let’s revisit photo four; it could be argued that this is a damp location. It could also be considered a wet location. According to the definitions, this area could be subject to moderate degrees of moisture or, in some instances, saturation with water or other liquids. In this installation, the AHJ determined that this area meets the requirements of a dry location and allowed the wiring method shown in the picture. Right or wrong, it is the judgment of the AHJ and has been approved.
Photo 4. A "4 by 4 Combo Box” at the entrance (interior) of a tunnel. Notice corrosion on screws (inset photo).
Photo 5. Electrical installation on the exterior of the tunnel is considered a "wet” location.
In photo five, we see an installation on the exterior of the tunnel location. This area has been deemed a wet location from the definition stated above. It is noteworthy that an area does not have to be located outside to be considered a wet location. An example of an interior location that could be considered a wet location would be a poultry processing facility, which is subject to saturation from high pressure washdowns at the end of various shifts. This environment requires the electrical contractor to install the correct electrical devices and components that will "survive” as well as function properly under such conditions.
Luminaire Types within Tunnels
Luminaire types within fixtures must also follow the guideline of the above definitions as well as their manufacturer’s installation instructions. Protection of the lamp must also be considered due to the environment and also due to vandalism that sometimes occurs. Lighting is extremely important for the safety of the user of the trail/sidewalk system. Unsavory individuals with malicious and/or dishonorable intentions sometimes lurk in dimly lit areas. Properly lit areas help to deter the would-be unsavory individual from unleashing his devious intentions.
Lighting also allows for people to see in the tunnels. Walkers, joggers and bicyclists need lighting in these locations to avoid possible injuries due to collisions. It goes without saying that these requirements are also necessary for tunnels that allow for vehicular movements as well. One could only image the calamity that would result from improperly lighted tunnels.
Photo 6. Types of luminaries used in tunnels
Ventilation is an important consideration for life safety and for dissipation of heat from various electrical devices. Heat produced by transformers or lighting ballasts could accumulate and contribute to unfavorable conditions within these locations. Again, each tunnel is different. A small tunnel, as pictured above, top right, would not have many items that would produce a lot of heat. Being relatively short allows for the air to move freely through the tunnel. The absence of motor vehicle use does not allow for the entrapment of dangerous vapors. In larger tunnel installations, there exist many heat producing devices and ventilation would need to be considered. Ventilation will also allow for air exchanges that are necessary to remove moisture and to allow for air exchanges within these areas. Because these areas are subject to repair and alteration by qualified persons, their safety must be considered.
Roadway Tunnels Are Another Animal Altogether
Roadway tunnels are governed by another important document, which addresses lighting, ventilation and other electrical concerns that are not addressed within the NEC. These locations are still referred to as "tunnels” and deserve mention in this article.
NFPA 502 is a safety standard that covers roadway tunnels as well as other highway structures. Within this document, Chapter 12 is dedicated to the electrical systems found in these locations.
NFPA 90 lists several items that shall be connected to the emergency power system. Emergency lighting is one of these items, as one might think. Total darkness for emergency response personnel in the likelihood of an emergency would not be acceptable. Signaling features such as tunnel closure and traffic control and exit signs are to be on the system too. The other remaining items include: emergency communication, tunnel drainage equipment, emergency ventilation, fire alarm and detection, closed-circuit television, and video and firefighting equipment.
Emergency power for road tunnels is required to conform to Article 700 of NFPA 70 for certain categories of tunnels as described in Table 7.2 in NFPA 502. This part deals with fire protection and fire life safety requirements in these locations.
NFPA 502 is an interesting document. It reinforces that not all electrical requirements can be found in the NEC. Other documents must be consulted regarding specific installation practices. Please consult the NFPA website at www.nfpa.org for more useful information concerning this and other publications.
My journey through tunnels has addressed many issues, and has been a brief overview or things to consider. There are many terms that one must be familiar with before conducting an electrical installation or inspection for a tunnel. The types of locations and who makes these determinations are crucial in the success of your installation. A decision must be made as to what type of tunnel one is dealing with before you can begin the work. The three discussed have specific requirements based on their location.
I hope you take a few moments to observe the workings of the common tunnel. I think you will be surprised at some of the electrical requirements that must be considered. Think about some of the decisions that need to be addressed for these locations. Good communication between the installer and the AHJ will help with an understanding of the requirements of the NEC and of other documents. Tunnels can provide years of enjoyment and safety for individuals within your community. Together we can make sure they will be functioning correctly for years to come.
Read more by Joseph Wages, Jr.
Posted By Howard Herndon,
Wednesday, May 01, 2013
Updated: Friday, April 26, 2013
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The rooftop temperature adders in NEC310.15(B)(3)(c) were first included in the 2008 NEC. The proposal to include this requirement was based on a study that showed increased temperatures in conduits on rooftops in direct sunlight. However, there remained unanswered questions for the Southern Nevada Chapter of IAEI; they live with extreme temperatures, and yet installers and inspectors have not seen evidence of failure related to rooftop installations. Since the impact on conductor sizing due to this requirement is significant in the Southern Nevada area, the Chapter funded an experiment to gather more information about rooftop electrical installations exposed to direct sunlight.
In conjunction with SouthWest Electritech Services, a third party independent electrical testing firm, Chapter members designed a test setup to determine if actual electrical installations on rooftops experienced the damage to conductors reported to Code-Making Panel 6 in the 2008 NECdevelopment process. The conductor sizes used were based on NECrequirements, but without the temperature correction factors required by 310.15(B)(3)(c).
Test Setup Installation and Data
In order to capture data during the hottest part of the year, the test setup was installed July 7, 2012; data was collected and analyzed for a two-month period. The test period captured data during the hottest days of 2012, which was reported to be the hottest summer on record for Las Vegas. Licensed electricians installed the electrical conductors and thermocouples. Southwest Electritech Services employees installed the data loggers, current meters and recording software.
The test installation was located on a facility that is a two-story warehouse with office area on the first floor (occupying about 25% of the first floor). The construction is concrete tilt up with a wood truss built up roof, using asphalt rolled roofing. The second story was not in use throughout the duration of the testing, and therefore was not conditioned.
Photo 1. Rooftop installation for temperature experiment in Las Vegas
Temperature data was collected in three conduit locations. Since the electrical equipment was already in place, an additional 20 feet of EMT was added to each circuit (photo 1) to allow for the installation of the monitored conductors and thermocouples. The runs were installed running east to the west in a location chosen to get maximum sunlight exposure during the hottest portion of the day.
Two thermocouples were installed in conduits with wire that was unloaded and attached to an evaporative (swamp) cooler in two different conduit sizes. Another thermocouple was installed in a conduit with wire that was loaded and attached to an air conditioner. The thermocouples were carefully installed in such a way as to contact the conductor installation and in no way be in contact with the EMT itself (photo 2).
Photo 2. Thermocouple installation
The first setup had five 12 AWG conductors with THHN/THWN-2 insulation. These were installed in 10 feet of 1/2″ EMT and the return run in 3/4″ EMT. A thermocouple was installed in each of these runs. Also, a thermocouple was installed inside the disconnect of the evaporative cooler these conductors fed, and then one thermocouple was installed to measure outside ambient temperature at approximately 48″ above the roof surface, near the top of the cooler. The conduits were supported on industry manufactured roof support block approximately 6″ above the roof surface (photo 3).
Photo 3. Height above rooftop
The second installation was connected to a 5-ton rooftop mounted all-in-one A/C unit that was in use for the duration of the test (photo 4). This unit supplies cooling to the first floor offices of the facility. It was found that this unit frequently ran for over 3 hours at a time, giving us good data on the conductors feeding it. Measuring temperature readings on the insulation of the loaded conductors provided a real world application (photo 5). Since the A/C was the only load on these conductors and ran for more than three hours at a time, it was a good test of an installation with continuous loading and without diversity.
Table 1. Highest recorded temperatures for each thermocouple in conduit
Table 2. Highest recorded temperatures for thermocouple in disconnect and junction box
Photo 4. AC label
This installation consisted of two 6 AWG THHN/THWN-2 conductors with a 10 AWG equipment grounding conductor, installed in 1″ EMT, again on the same type of roof supports as the first installation. For this installation, a thermocouple was installed in one of the runs of the 1″ EMT, one was installed in the junction box about 18″ above the rooftop and the outside thermocouple was installed about 6″ above the rooftop so that it would have a western exposure.
Intellirent, a company specializing in electrical test equipment, provided certified, calibrated data loggers and current meters, as well as the computers and software used to download and analyze the data. Data was collected every 60 seconds by each of the data loggers for each of the measurement points (photo 6). This produced a great deal of data. In order to report meaningful information, the highest temperatures recorded each day were compared to nationally reported ambient temperature values obtained from the NOAA database. This comparison resulted in a maximum daily differential temperature.
Photo 5. Current meters
Photo 6. Data logger and software
Ambient temperature data was also collected with the thermocouples installed in two locations on the roof. In general, these ambient thermocouples recorded temperatures higher than that reported by NOAA. Since installers and inspectors will typically depend on nationally reported data, we chose to use the NOAA data to calculate the differentials. This resulted in a worse case differential than if the measurements from the ambient thermocouple installed on the rooftop were used.
During the experiment, it was found that on an actual rooftop in Las Vegas in an actual installation of conduits with wires (both loaded and unloaded), the temperatures measured did not approach the temperatures predicted by the adjustment requirements in Section 310.15(B)(3)(c). On the contrary, the average temperature differential recorded was 15°F for unloaded conductors in conduit. Since the conduits were installed approximately 6″ above the rooftop, the adjustment factors required by the values in the 2011 NEC Table 310.15(B)(3)(c) would require an adder of 30°F, twice the actual measured values.
Additionally, it was observed during this real world rooftop test that the loaded conductors never exceeded the operating temperature of the conductors or terminations during the testing. Since the originally stated reason that the additional temperature correction was added to the code was the premise that conductors would exceed their rated temperature, this testing shows that the premise was false. The highest recorded temperature was 148°F for fully loaded conductors. The maximum ambient temperature on that day was 114°F according to NOAA, resulting in a differential of 34°F for loaded conductors in conduit operating at the maximum load recorded on the air conditioning circuit (37 amps). Much of this differential was due to the heat generated by the current flowing through the conductor, not the heating of the conduit by sunlight exposure.
The conductors are rated at 194⁰ F and the connections are limited to 167⁰ F. Comparing these limitations to the measured temperatures indicates that even should the temperature be more extreme or if there was additional load placed on the circuit, the conductors and connections are unlikely to exceed their rated temperature.
2014 NEC Proposal 6-29 requested even higher values for temperature correction - for this installation, 50⁰ F would have been required. CMP-6 decided in the Comment phase to reject Proposal 6-29 in Panel Comment 6-14a. This decision was based in part on the information gathered during the experiment described in this article, which was presented to CMP-6 at the ROC meeting in December 2012.
The test results indicate that the added temperature correction values in 310.15(B)(3)(c) are unnecessary for rooftop electrical installations in the Las Vegas area. Since Las Vegas is one of the hotter areas in the country, it is likely that the correction factors are unnecessary for other areas, as well. These findings support the statement submitted by IAEI CMP-6 principal John Stacey with his negative vote to 2014 NEC Comment 6-16, which stated that "The requirement in Section 310.15(B)(3)(c) increases cost with no benefit to the safety of people or the protection of equipment, and this requirement should be removed in its entirety.”
Read more by Howard Herndon
Posted By Leslie Stoch,
Wednesday, May 01, 2013
Updated: Friday, April 26, 2013
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The Canadian Electrical Code’s long-winded definition of grounding is shown as: "a permanent and conductive path to the earth with sufficient ampacity to carry any fault current liable to be imposed on it, and of sufficiently low impedance to limit the voltage rise above ground and to facilitate the operation of the protective devices in the circuit.” This article discusses a number of permissible grounding requirements and methods covered by the Canadian Electrical Code.
As you no doubt noticed, the definition covers a lot of ground (excuse the pun), as it includes all of the electrical code requirements, including that grounding must:
- be permanent and continuous;
- carry available fault currents without failure;
- have sufficiently low impedance to ensure
- that voltage rise during a ground fault will
- not cause damage to components such as sensitive electronic devices; and
- ensure that fuses and circuit-breakers react
- quickly enough to prevent electrical failures,
- fires and shock hazards.
In some cases, the Canadian Electrical Code does not require that all electrical circuits be solidly grounded. In others, the CEC prohibits it. Rule 10-108 specifies that circuits supplying electrical arc furnaces (such as a scrap metal melting furnace) need not be grounded. Rule 10-110 specifies that circuits supplying cranes operating above highly flammable fibres in Class III hazardous locations must not be grounded. This provision reduces the probability of arcs and sparks along the crane rails and the current collector, thereby limiting the risk of a flash fire. Rule 10-112 permits ungrounded circuits supplied by a transformer incorporating a grounded faraday shield between the primary and secondary windings when permitted by other rules or in special cases to prevent electrical accidents (underwater swimming pool speakers, for example).
We are all at ease with solidly grounded electrical systems. They provide the benefit of limiting system voltages to ground and minimizing voltage stress on wiring and electrical equipment insulation. Solidly grounded systems may experience high ground fault currents, but when correctly arranged, faults are quickly detected and removed by fuses or circuit-breakers before there is damage. In an industrial environment, shutting down during a ground fault may be impracticable, and therefore other grounding methods are recognized in the Canadian Electrical Code. Rule 10-106(1) requires that except where otherwise specified, 120/240-volt and 120/208-volt AC systems or circuits that include a neutral conductor must be grounded.
Ungrounded delta systems don’t require shutting down during a single-phase ground fault since they have no reference to earth. However, they come with risk of equipment damage as well as personal safety risks when a second phase becomes inadvertently grounded. In addition, overvoltages tend to shorten the lives of electrical equipment. Rule10-106(2) requires that ungrounded delta systems must be equipped with ground fault detection devices such as ground indicating lights to ensure that inadvertent grounds are removed as quickly as possible. But you know what happens to those — the indicating lights burn out and are not promptly replaced, leaving people and equipment at risk.
A nice compromise is resistance grounding which permits operation during a single-phase ground fault. Resistance grounding offers a number of important advantages. It limits ground fault currents by connecting a grounding resistor between the electrical system neutral and the system ground electrode and thereby:
- minimizing damage to electrical wiring and equipment;
- reducing mechanical stresses;
- reducing arc flash and arc blast hazards ;
- controlling overvoltages; and
- no shutdown required during a ground fault.
Finally, effective grounding helps ensure that faults are quickly removed. Rule 10-500 defines effective grounding. Sound familiar? But what’s this about "impedance sufficiently low”? Appendix B provides an answer: impedance of the ground fault path should be sufficiently low so as to permit at least five times the setting of the circuit overcurrent devices to flow during a ground fault. For example, for a 400-ampere circuit, at least 5 times 400 amperes or 2000 amperes must be allowed to flow during a ground fault.
As with earlier articles, you should always check with the electrical inspection authority in each Province or Territory as applicable for a more concise interpretation of any of the above.
Read more by Leslie Stoch
Posted By Randy Hunter,
Wednesday, May 01, 2013
Updated: Friday, April 26, 2013
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Article 250 is the largest article in the National Electrical Code. It is often the most dreaded by those new to the code, and sometimes even by those who have dealt with the code for years. Some of the terminology is confusing and conceptually difficult to follow. In keeping with the Combination Inspector emphasis of this series of articles, we will cover those items which I have previously taught to inspectors who weren’t electrical by trade. In doing so, we will not cover every section of Article 250, but concentrate on those that are used most commonly by multi-trade inspectors.
Photo 1. Here is a very small sampling of some of the devices designed for grounding connections. Please note the bottom right device will bond the grounding electrode conductor to an enclosure or raceway.
Photo 2. This shows a sampling of bonding jumpers that are provided by the factory for main bonding jumpers in panels.
The scope of this article covers general requirements for grounding and bonding of electrical installations. First, we have two definitions that we need to consider in order to help us understand the principles of grounding. Effective grounded-fault current path is an intentionally constructed, low-impedance electrically conductive path designed and intended to carry current under ground-fault from the point of a ground fault on a wiring system to the electrical supply source and that facilitates the operation of the overcurrent protective device or ground-fault detectors on high impedance grounded systems. Ground-fault current path is an electrically conductive path from the point of a ground fault on a wiring system through normally non-current-carrying conductors, equipment, or the earth to the electrical supply source. Both of these are best understood as the emergency path the current takes in the event of a ground fault (which is a short from an ungrounded conductor to ground). If we have a good path, then the high current flow back to the source should operate the overcurrent device and shut down the system.
As you probably noticed, the main difference is that one is an intentionally constructed path, which is what we hope to have, and the second is any path in which the current may flow. To give a real life example of this, I remember getting a service call to a house which had smoke coming out of the walls. As luck would have it, I was very close and beat the fire department to the site. The first thing I did was shut off the main at the service and the smoke started to lessen. By the time the fire department got to the house, there was hardly any visible smoke coming out of the walls, just the smell of burning wood. The fire department broke open a hole in the wall and the plaster reinforcing wire lath had been burning its way into the wood studs, just like one of the old wood burning kits we used to have as kids. The only electrical device near this part of the dwelling was an air conditioner compressor unit. I opened the junction box of the unit and the grounding wire wasn’t connected. If it had been connected, there would have been a low impedance path that carried the current back to the breaker and caused it to open. However, one ungrounded conductor had shorted out and the only path for the fault current was through the copper refrigeration lines to the wall where they contacted the metal lath wire and energized it, causing it to heat up to the point of burning the wood framing. Without a good fault-current path back to the overcurrent device, the device just sees an additional load, but not enough to make it trip in a timely fashion.
Photo 3. The bare copper conductor here is the grounding electrode conductor that has been connected to the concrete- encased electrode (rebar) stubbed up from the building footing.
Where grounding starts
Now that we understand why we need good grounding paths, let’s start back at Part III Grounding Electrode System and Grounding Electrode Conductor, since this is where grounding starts, with a good connection made to the earth. The connections to the earth are called electrodes, and the code describes eight different types of electrodes. We will only cover the concrete-encased electrodes and ground rods, since they are the ones most commonly used in construction today. Details are found in 250.52(A)(3) for the concrete-encased electrode. This is the preferred electrode for any new construction, and it performs very well due to the fact that the concrete continues to extract moisture from its surrounding soil and has great contact with the earth simply due to its weight.
The second most common is rod or pipe electrodes, which are covered in 250.52(A)(5). Ground rods are very common and make a good connection to the earth due to the fact they are required to be 8′ in length and reach deep enough into the earth. This is the best option when adding a grounding electrode system to a facility where you can’t incorporate a concrete-encased electrode.
There are other electrodes covered in 250.52 (which you should take time to read), but I will mention one that is fading from use, and that is metal underground water pipe. For decades, it was the most common source of grounding electrode; however, with the advances made in water system products, it was found that if a facility had a metal water line that failed, it was being replaced by a non-metallic system. When that occurred, we lost our grounding electrode. Even in new housing construction, I haven’t seen a metallic water pipe feeding a residence in two decades. If you review 250.53, you will find the installation methods for each of the grounding electrodes mentioned above.
One item to note is a change made in the 2011 edition of the NEC for 250.53(A)(1) related to rod electrode installations. In the 2008 NEC 250.56, it stated that a rod, pipe or plate electrode that didn’t measure 25 ohms or less would have to be supplemented by an additional electrode. In the field, this meant an inspector had to have some assurance that one device would measure 25 ohms or less, but how do you do that? Does the inspector test it? Generally no, so it was up to the contractor to prove it met this code requirement. In practice it saved time and multiple trips to the site if the contractor simply installed two rods and then didn’t have to worry about the measurement at all. So in the 2011 NEC 250.53(A)(2), it states you will install two rod electrodes, and then there is an exception which allows one rod if you prove it meets the 25 ohms or less requirement. This is a good example of how the code is often modified to match what is actually the general practice in the field.
Photo 4. This is an example of 250.104, bonding of other systems. This is gas piping which goes throughout the house and may have the possibility of becoming energized and therefore shall be bonded.
Connecting to items to be grounded
So now that we have our actual connection to the earth, we have to connect it to those items we are trying to ground. To do this we use a conductor called the grounding electrode conductor. The grounding electrode conductor is covered in 250.62 through 250.68. First, this conductor must be made of a material resistant to any corrosive conditions to which it may be exposed. This could be various things, such as a corrosive soil, fumes within a building, or any other conditions that may damage it. Again, if we lose this connection to the electrode, we have totally lost our grounding system.
Article 250.64 is where we find the details on the installation of the grounding electrode conductor. Covered is how to secure and protect it, and depending on the size, it may need some physical protection such as a raceway. Please note that if protected by a metallic raceway, and the raceway isn’t continuous from the equipment to the grounding electrode, then the raceway must be bonded at each end to the grounding electrode, see 250.64(E). The reason for this is really pretty simple: the impedance of the conductor and the raceway are different and the current will travel at different speeds from one end to the other, so if they are not bonded and there is an air gap at one end or the other, it will arc. Repeated arcing will cause damage to the electrode conductor. It must be securely fastened to the surface on which it is carried and can be run through framing members. It shall be installed in one continuous length without a splice or joint; however, if it absolutely has to be spliced, there are four very specific ways to do it in 250.64(C). Remember this is a crucial element to the safety of the electrical system, and anytime we have a splice or connection we have created a possible failure point, so we try to avoid any conditions which may create a weak point.
Photo 5. In both of these photos, the grounding electrode conductor is the bare copper. It is being terminated on the grounded terminal location in these residential main services. Note the aluminum bussing that continues into the meter section in each of these photos to connect directly to the utility-grounded service conductor, which meets the main bonding jumper requirement.
Also please note 250.64(D), which has allowances for a single electrode and conductor to be tapped to serve several service-entrance enclosures located in close proximity to one another. Now for one of the key elements of the grounding electrode conductor — how do we size it? In Article 250.64(D)(2) we find that each electrode conductor is to be sized according to 250.66, and there we find that generally it is sized according to Table 250.66, which lists the size of the service conductors on the line side of a service and then shows us the size of the grounding electrode conductor. The sizing is based on the size of the conductors feeding the service, since we don’t have an overcurrent device on the service conductors. Refer to Table 250.66 and also review the notes, which cover the methods for multiple sets of conductors.
Now for three applications where we don’t need to use the table and that are covered in 250.66(A), (B) and (C): these deal with conditions where we have a single conductor which is the sole connection to the grounding electrode for rod, pipe, plate, concrete-encased and ground-ring electrodes. In these sections we find a new maximum size conductor requirement for each of these types of electrodes. For example, on a concrete-encased electrode you are not required to use a conductor larger than a 4 AWG copper conductor, no matter what the size of the service. I must caution you that if the design professional has designated a larger conductor, you would be obligated to follow his requirements. Remember that the code is a minimum and can always be exceeded.
Connecting to the grounded service conductor
So now that we have the electrode and the electrode conductor, what do we do with it? In 250.24 Grounding Service-Supplied Alternating-Current Systems, we find the answer. First, in 250.24(A) System Grounding Connections, we discover that the grounding electrode conductor shall be connected to the grounded service conductor. As simple as it sounds, this is one of the most critical requirements of the code. The connection can be done in various ways as outlined in 250.24, so please follow along in the code as we go.
This should be the only point where we connect together the grounded conductor, the grounding electrode conductor and the equipment grounding conductors. This is generally done at the main service disconnecting means of a service, utilizing what is called a main bonding jumper [see 250.24(B) and 250.28]. Failure to make this connection can lead to various issues, the least of which will be voltage fluctuations that may damage connected equipment.
Once we move past the service main location, we are not to connect the grounded conductor (remember this is generally referred to as a neutral) to any grounding conductors; this is covered in 250.24(A)(5). If you do, you will create parallel ground fault return paths that may not push the overcurrent device to react in a timely fashion. Or, if you are downstream of a ground fault sensor in either a GFCI or GFP device, it will cause the device to trip.
Connecting to equipment grounding conductor
From the service, the path continues in Part VI Equipment Grounding and Equipment Grounding Conductors. In 250.110 we learn that exposed, normally non-current-carrying metal parts of fixed equipment supplied by or enclosing conductors or components that are likely to become energized shall be connected to an equipment grounding conductor. In the remainder of 250.110 and in 250.112, 114 and 116, we see some specific requirements for various types of equipment. The types of equipment grounding conductors are outlined in 250.118, and the most common would naturally be a wire-type conductor. However, you will also notice within the article that various types of raceway also meet the grounding requirements. I will not go into details of any one of these specific methods, please review for yourselves.
We need to cover 250.119 Identification of Equipment Grounding Conductors, and here we find that these conductors can be bare, covered or insulated. If covered or insulated, they shall be identified with a continuous outer finish that is either green or green with one or more yellow stripes, except as permitted elsewhere in 250.119. Those exceptions make an allowance for conductors larger than 6 AWG, which normally doesn’t come in green from the factory. We are allowed to re-identify using three options: stripping the insulation or covering, coloring or marking at the termination points. Also covered in (B) and (C) are allowances for multiconductor cablesand flexible cords.
Our next concern with equipment grounding conductors is how to properly size them. In 250.122, it states that we shall size them according to Table 250.122. This table is based on the overcurrent device that is protecting the circuit. Basically, the larger the circuit ampacity size the larger the conductor that is required to handle the fault current back to the source and to cause the overcurrent device to operate. A couple of items need to be mentioned here; one is that if the ungrounded circuit conductors are increased in size for any reason, then the related equipment grounding conductor shall be proportionally increased. This might happen if voltage drop requires a larger phase conductor, since the larger conductors will have a higher fault current capacity and we have to compensate for that with a larger equipment grounding conductor.
The other item is found in 250.122(F) Conductors in Parallel, which states that in each raceway where an equipment grounding conductor is used it must be sized in accordance with the other rules in 250.122. So if you have six PVC conduits for a parallel run, you will have to install an equipment grounding conductor in each conduit, and each must be sized according to Table 250.122. However, in the body of 250.122 we find language which states that it will never have to be larger than the ungrounded conductors.
Photo 6. This is another example of bonding piping systems. On the left the water main is bonded, and in the upper left insert we have a poor example of bonding as the connection isn’t making direct contact due to the tape. On the right, I found a fire sprinkler riser at a gas station canopy and was wondering where they made the bonding connection.
Now that we have the equipment grounding conductors run where needed, what do we do with them? The purpose of the equipment grounding conductor is again to connect any normally non-current-carrying metallic parts that may become energized in order to provide what I call the emergency electrical relief system, which is needed to open the protective devices. In Part VII Methods of Equipment Grounding, you will find the details for such things as receptacles, certain boxes, ranges and dryers to name a few; again, please review these more completely on your own.
Connecting metallic items
Bonding is covered in Part V, starting at 250.90. Bonding is simply the connection of metallic items to ensure that we have a connection to the earth. Earlier we mentioned the main bonding jumper within the service, but now we are connecting other parts of the system for the purpose of ensuring electrical continuity to safely conduct any fault current that may be imposed. In 250.96, 97, and 98, we cover the most common bonding items we need to check for on our inspections.
Bonding of enclosures, raceways, cable trays and various other items (including around loosely jointed fittings) need to be addressed. One of the most common points is at factory knock-outs where we just don’t have a good ground path. So how do we size these jumpers? It depends on if you are working on the supply side of a system or on the load side. If you are on the supply side, then you use 250.66, based on the ungrounded conductor size. On the load side, we would use 250.122, which is based on the overcurrent device size. This distinction points out a very good general rule of thumb, which is that if you have an overcurrent device upstream, go to Table 250.122; if there is no overcurrent device, go to Table 250.66.
The last bonding items are in 250.104 and 106, which cover the bonding of piping systems, exposed structural steel and lightning protections systems. Review these requirements and make sure you are getting these items properly bonded in your areas. Often this is overlooked or not properly done as we sometimes tend to get casual about these items.
Connecting to separate buildings
One item which seems to be most overlooked (in housing construction especially) is 250.32 Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s). At each separate building or structure you should make sure you have a grounding electrode installed. I know this may sound bold, but let me explain. Often these types of projects start small, and you think you are going to have a single circuit, so you use the exception. Then the plan changes and now there are multiple circuits, and it is difficult to later install an electrode. In my local area, the home builders just decided to automatically install a concrete-encased electrode no matter what the original intended use of the separate structure. At times they would only intend them as a workout room, but then they could be converted to a casita (a small house) with a bathroom and cooking equipment, so it was just easier to stub up a rebar as a grounding electrode whether we needed it or not. A little planning ahead sometimes saves a lot of headaches later on.
Insuring reliable connections
The last items to cover are found in 250.8, 10 and 12. Notice that we started at the electrode and worked our way up, and these last requirements cover methods to insure good reliable grounding and bonding connections. This includes such things as the type of components to be used, even down to the types of screws. Ground clamps, which are devices for connecting conductors to various types of building materials, shall be approved for the use and may require protection, so you will have to review the listing and installation instructions on these. Through the years, probably one area of the most creative invention has been in the grounding and bonding process. There are so many products out there and electricians don’t always have access to the proper devices and therefore try to become designers, manufacturers and installers of some of the most unique methods. If it looks a little weird, ask for the literature that should have come with the components. Lastly, we must make these connections to clean surfaces, and that may require the removal of paint or other surface coating to ensure a good metal to metal connection.
This concludes the high level coverage of Article 250. I tried to do it in a logical inspection process from the bottom up, literally. Just remember to open the code book and review it with this article, and remember that grounding is the emergency safety line. Everything electrical will generally work just fine if the ground isn’t done right, but when we have some type of abnormal issue, it is the grounding installation that saves us. This is one of the most important portions of any inspection.
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