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IAEI News provides educational forums, updates on electrical codes and reports of innovative research to facilitate the development and enforcement of practices designed to drive efficiency and compliance with the highest standards of product development and safety—for the public as well as for electrical personnel. The magazine reaches authorities with power of product specification, approval and acceptance. Published six times a year by the International Association of Electrical Inspectors.

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CEC 2006 – Neutral Grounding Devices, Rules 10-1100 to 10-1108

Posted By Leslie Stoch, Friday, September 01, 2006
Updated: Sunday, February 10, 2013

Rules 10-1100 to 10-1108 of the Canadian Electrical Code provide rules on installing neutral grounding devices (grounding resistors) used for the purpose of controlling the ground fault current or the voltage-to-ground of an alternating current electrical system. These rules have undergone some significant changes in the 2006 edition of the code.

Rule 10-1102 contains the most noteworthy changes. Sub-rule (1) remains unchanged and continues to specify that: "Neutral grounding devices shall be permitted to be used only on a system involving a true neutral or an artificial neutral, where line-to-neutral loads are not served.” Sub-rule (1), as in the past, remains unequivocal — no single-phase electrical loads from a resistance grounded system.

Rule 10-1102, sub-rule (2) is generally unaffected, but contains the words "Where line-to-neutral loads are not served —”, which alerts us to some impending changes in this rule. As in the past, the remainder of the sub-rule remains unchanged. It goes on to say that resistance grounded circuits up to 5 kV may continue to operate on detection of a ground fault provided that:

  • the ground fault current is 10 amperes or less; and
  • a visual or audible alarm is provided to indicate the occurrence of a ground fault.

The 2002 CEC specifically ruled out the above easement for systems above 5 kV, which were required to trip OFF under all ground fault conditions. The new rule provides the same restriction by implication. Another difference, the 2002 CEC limited the current rating of the grounding resistor to 5 amperes ground fault current or less. As you will notice, this has been increased to 10 amperes in the 2006 edition.

Rule 10-1102, sub-rule (3) contains the most dramatic changes, stating that when phase-to-neutral loads are supplied from a resistance grounded electrical system, the power supply must automatically be disconnected when:

  • there is a ground fault; or
  • the system neutral is inadvertently connected to ground; or there is
  • inadvertent disconnection of the grounding resistor from the system neutral or the grounding electrode.

Sub-rule (3) presents a significant departure from earlier versions of the CEC, that prohibited supplying any single-phase loads from a resistance grounded distribution system. The 2006 code opens that door with some conditions. Obviously, the above installation change will need to be supplemented with specialized detection equipment that is capable of detecting all of the above conditions and tripping the upstream overcurrent protection.

But does anyone sense there may be a problem with the wording of this Rule? In my opinion, there is a conflict between sub-rules (1) and (3). You will recall that sub-rule (1) states unequivocally that phase-to-neutral loads are not permitted to be supplied from resistance grounded electrical systems. But sub-rule continues on to spell out the conditions that apply when we intend to do just that. What’s missing from sub-rule (3) are the words "Notwithstanding sub-rule (1)—”. I think we have an oversight that will result in some serious conflicts within Rule 10-1102, and that will certainly precipitate numerous lively debates.

Rule 10-1104 remains unchanged and includes the requirements that grounding resistors:

  • must be approved for the purpose;
  • must be continuously rated unless disconnected on occurrence of a ground fault; and
  • must have an insulation rating of at least the line-to-neutral voltage.

Rule 10-1106 is also unchanged and still requires that grounding resistors:

  • have live parts are guarded;
  • are accessible only to qualified persons;
  • are located to permit the dissipation of heat; and
  • have warning signs at points where there is access to the electrical system neutral.

Rule 10-1108 contains one significant change, but most of the rule remains unaffected. The conductor between the system neutral and the grounding resistor must be:

  • insulated for the system voltage;
  • identified grey or white; and
  • sized to suit the grounding device, but no less than #8 AWG.
  • The conductor between the grounding resistor and the system grounding electrode must be:
  • insulated or bare copper wire;
  • identified green if insulated; and
  • sized to suit the grounding device but not less than #8 AWG.

The only change to Rule 10-1108, where line-to-neutral loads are supplied, the above conductors must match the ampere rating of the grounding device and be no smaller than #12 AWG.

As with all previous articles, you should always consult the electrical inspection authority in each jurisdiction as applicable for a more precise interpretation.


Read more by Leslie Stoch

Tags:  Canadian Code  September-October 2006 

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The 2007 NESC – Part 4

Posted By David Young, Friday, September 01, 2006
Updated: Sunday, February 10, 2013

This article is a continuation of what I see as significant changes that are coming in the 2007 revision of the National Electrical Safety Code.

Photo 1. Bonding of cases and enclosures

Grades of Construction

Table 242-1 has been changed by the removal of the delineations rural and urban. The higher grades of construction that used to apply to urban areas, now apply to all areas. This is a significant change for utilities that used to use the lower grades of construction in rural areas. The grade of construction is used to determine the safety factors that must be used in the strength and loading design of the facilities. In general, the higher the grade of construction, the greater the safety factor and the stronger and more expensive the structure.

Construction and Maintenance Loads

Rule 250A2 has been expanded to emphasize the need to consider temporary loads such as lifting of equipment, stringing conductors, or a worker on the structure or component when designing the strength of the structure.

Load Factors


Photo 2. Fiberglass crossarms

Starting in Rule 253, what was called overload factors is now load factors. The Grade C construction section of Table 253-1 has been expanded to delineate between At crossings and Elsewhere. Footnote 5 now addresses fiberglass (fiber-reinforced polymer) portions of structures and crossarms. The table also has load factors for the new extreme ice and concurrent wind loading (Rule 250C).

Alternate Load Factors

The alternate load factors in Table 253-2 and the associated strength factors of Table 261-1B shall not be used after July 31, 2010.

Fiberglass Structures, Crossarms and Braces

Rule 261A3 now addresses the strength requirements of fiberglass structures and Rule 261D3 now addresses the strength requirements of fiberglass crossarms and braces. Table 261-1A now gives the strength factors for fiberglass structures, crossarms and braces.

Strength of Climbing and Working Steps

New Rule 261N addresses the strength of climbing and working steps on structures.

Strength of Insulators

Rule 277 has been changed significantly to better define the strength requirements of insulators consistent with the ANSI® C29 standards for insulators.

Emergency Installation of Cables on the Ground


Photo 3. Insulators on a 138 kv line

New Rule 311C allows for the installation of electric and communications cables laid directly on grade during an emergency under special conditions.

Electric and Communications Cables in the Same Duct

New Rule 252E clearly states that electric and communications cables shall not be installed in the same duct unless all of the cables are operated and maintained by the same utility.

Communications Cables in the Same Duct

New Rule 252F allows communications cables to be installed in the same duct as long as the utilities involved are in agreement.

Bonding of Cases and Enclosures

The NESC requirement that all above ground metallic power and communications pedestals, terminals, apparatus cases, transformers cases, etc., be bonded if they are separated by a distance of 6 feet or less has been moved from Rule 350F to new Rule 384C. Many people were not aware of this rule because it was located in the Direct-buried Cable section of the code. It is now where it should be in the Equipment section.

Arc Protective Clothing

Rule 410A3 now requires employers to make an assessment to determine the potential arc energy exposure for all employees who work on or near energized parts or equipment. If the assessment determines a potential employee exposure greater than 2 cal/cm2 exists, the employer shall require the employee to wear clothing or a clothing system that has an effective arc rating at least equal to the anticipated level of arc energy. This goes into effect as of January 1, 2009.

Work in the Vicinity of Communications Antennas

New rule 420Q limits the radiation level a worker may be exposed to when working in the vicinity of communications antennas.

Existing Utility Location Verification

Rule 423D2 now recommends that the location of existing utilities be verified by exposure prior to the use of guided boring or directional drilling methods.


Read more by David Young

Tags:  Other Code  September-October 2006 

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The 2006 UL White Book is much larger than the 2005, what has changed and how do I use the White Book in the field?

Posted By Underwriters Laboratories, Friday, September 01, 2006
Updated: Sunday, February 10, 2013

2006 UL White Book

The 2006 UL White Book is much larger than the 2005, what has changed and how do I use the White Book in the field?

Answer

The 2006 UL White Book has under gone many changes and can be considered THE Companion Tool to the National Electrical Code,N EC. Besides a new name, 2006 Guide Information for Electrical Equipment, White Book and a new look, here are some of the highlights (see page 97).

  • For the first time, UL has added an index of product categories correlated to the 2005 NEC. The index provides a direct link between individual sections within the NEC and corresponding UL product categories that may be applicable to that section of the code. While not every Code section has corresponding Listings, there are over 4100 crossreference entries in this index. This index, which starts on page 311, is very intuitive and simple to use, just look up a particular NEC section number and read across to locate the corresponding UL category code and page number on which the complete guide information for the category is located.
  • In response to suggestions from electrical inspectors, the table of contents that lists all the product categories is no longer divided by UL Directory title, the list is now one comprehensive list of all product categories in the White Book organized alphabetically by four letter Category Code.
  • All seven electrical UL marking guides are now included in Appendix A of the White Book starting on page 389. Those marking guides include Circuit Breakers, Heating and Cooling Equipment, Luminaires, Panelboards, Swimming Pools and Spas, Switchboards and Wire and Cable.
  • We also include the "UL Online Certification Directory Quick Guide” to illustrate how to use UL’ Online Certification Database for verifying UL Listings, as well as a membership application for the IAEI on the last page of the White Book so that any user of the White Book will have easy access to the forms needed to join the premier electrical education organization.
  • A detailed explanation of how to use the White Book has been added as a convenience to those who are not familiar with this publication. This explanation is located in the front of the White Book starting on page xxxv and is titled "Practical Application of the White Book in the Field”. That explanation is reprinted in this column. In addition to the paper copy of the book, there is also an electronic version available on CD that can be downloaded onto your computer.

The electronic version of the White Book is very user friendly and easily searched using the Fast Folio platform, which is the same software used for the NEC and NEC Handbook CD’s. A pdf version of the 2006 White Book is also available as a download on the Regulators page of UL.com at http://www.ul.com/regulators/2006WhiteBook.pdf.

If you would like a complimentary copy of the 2006 White Book or the White Book CD, please see the UL booth at one of the five U.S. IAEI Section meetings this fall or at your local IAEI Chapter meetings or contact UL at https://www.ul.com/auth/regcon.cfm#Contact

Tags:  September-October 2006  UL Question Corner 

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Three New Programs for Motivated Members

Posted By James W. Carpenter, Friday, September 01, 2006
Updated: Sunday, February 10, 2013

Summer is nearly over and the children are back in school. For most of us vacation times are now fond memories. It is back to work until the next opportunity for a relaxation period. Speaking of opportunity, IAEI has joined with Underwriters Laboratories to offer a way for our members to participate in a program that will teach our school children electrical safety. This opportunity gives you a way to give back to your community.

As inspectors, we already are charged with assuring our homes, offices, factories, stores, and persons are safe from hazards arising from the use of electricity. Installers, suppliers, manufacturers, and engineers are also part of this mission. Now we can join together and teach our children about being safe, not just electrically safe, but safe in any circumstances.

The I am Safety Smart! program is designed to give children the skills to develop life safety skills. The program has two modules: Ages 5 through 8 (kindergarten – 3rd grade) and ages 10 through 14 (grades 4 – 8). To be an I am Safety Smart! ambassador, one who actually goes into the classroom to teach the children, you must be trained. UL has agreed to train an initial group of people who will serve as coordinators, and train others in the local chapters and divisions. You should have received information about this program by the time you receive this issue of the IAEI News. That information gave specifics about the program. If you want additional information or have questions on how to participate, you may contact one of the officers of your chapter or division. Or you may contact Kathryn Ingley at the International Office atsafetysmart@iaei.org. Printed material has been developed, sample letters to your jurisdiction and school officials, and kits for use in the classroom are ready for chapters or divisions to use in promoting this very exciting program.

This chance for our IAEI inspector and associate members to do what the firemen and policemen have been doing for years in the schools is an excellent way that we can not only teach electrical safety but also show the community the importance of the role of the electrical inspector and installer. Maybe the child will want to grow up to be an inspector and join the IAEI.

Membership in IAEI affords many possibilities to further one’s knowledge, skills, and friendships. The I am Safety Smart! program is just one of the new ways that IAEI members can share their knowledge, skills, and friendship with others and at the same time increase their own knowledge, skills, and friendships.

IAEI is going through a period where membership, as well as participation in any group or association, seems to be not as important as it once was. The many volunteers that provide leadership and guidance for IAEI are wondering and looking for where this leadership and guidance will come from in the coming years. The I am Safety Smart! program will possibly encourage the children of today to be like that electrical person who came to his classroom to teach electrical safety.

Another example of things that your IAEI is doing is the directCONNECT feature on iaei.org. Your guide to electrical regularity has been established on the website to provide information on Code adoption, electrical contractor licensing, journeyman licensing, and inspector certification requirements. The National Electrical Contractors Association (NECA) has furnished us their list of licensing agencies and IAEI has updated it and added additional information. For this guide to electrical regularity to be beneficial, it will need to constantly reviewed, updated, and added too. You can help in this process by providing information, updates and corrections to:directCONNECT@iaei.org.

Another feature on IAEI’s website is the opportunity to put your name on a volunteer list, so that for the next Katrina there will be people that can go and help the local inspection department recover much sooner. That feature has already been used by a jurisdiction in the northeast when the recent floods overtaxed a city’s inspection department. Volunteers were there as soon as help was requested. Thanks to the IAEI disaster volunteers.

As 2006 draws to a close we can reflect on what has transpired over the year. Of the many partnerships and co-sponsored events IAEI has participated in, one event stands out. NFPA hosted a Forum for electrical inspectors from across the U. S. to come together and discuss, not code issues but, common procedures and problems.

For two days, the participants had a chance to network with each other on such topics as: The Status of Electrical Inspection Departments, Approving Electrical Equipment, Disaster Recovery, and the Status of IAEI in the Local Area. Look for more information on that Forum and future forums.

I hope you have made plans to attend a Section meeting near you. It is not too late to join your fellow members to network and learn more about your very important profession. Code discussion is always a hot topic at section meetings and this year is no exception. We are in the midst of the code making cycle. Preparation of comments on the work the NEC Code-Making Panels did at the proposal stage will be on the agendas. Come to the annual section meetings and let your voice be heard. See you there!


Read more by James W. Carpenter

Tags:  Editorial  September-October 2006 

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VFDs for Energy Savings in Hospitals – what they are, how they work, and how they save money

Posted By Mike Olson, Saturday, July 01, 2006
Updated: Sunday, February 10, 2013

What Is a VFD?

A variable frequency drive (VFD) is an electrical device we use to control the speed of a standard three-phase ac induction motor. The number of poles designed into a motor and the frequency applied to the motor determine the motor base speed. We can conveniently adjust the speed of a motor by changing the frequency applied to the motor. You could adjust motor speed by adjusting the number of poles, but this is a physical change to the motor. It would require rewinding, and would result in a step change in the motor’s base speed. So, for convenience, cost-efficiency, and precision, we change the frequency (and voltage). At any given frequency output of the drive, you get a new torque / speed curve from the ac motor.

Saving Energy with Variable Frequency Drives

It is estimated that over 60 percent of the electrical power generated in the U.S. is used to power fans and pumps. Most fans and pumps are of the centrifugal design type. Centrifugal fans and pumps follow the Affinity Laws of pressure, flow and energy consumed.

The Affinity Laws (also called the Fan Laws) state that fan output CFM or flow is directly proportional to the speed of the fan. Static pressure is proportional to the fan speed squared, and fan required HP is proportional to the fan speed cubed. Therefore, according to the Affinity Laws of speed, pressure, and horsepower, to produce 50% airflow, the fan would be run at 50% speed. At this operating point, the fan would produce 25% of rated pressure (0.5 x 0.5 = 0.25), and would require only 12.5% of rated horsepower (0.5 x 0.5 x 0.5 = 0.125 or 12.5%).


Figure 1

There are several methods of obtaining variable air flow from a centrifugal fan. The most common methods used are outlet dampers, inlet guide vanes and variable speed drives. We will use figure 1to illustrate the difference in energy consumed between outlet damper and variable speed flow control. The top curve in the figure is the fan curve. The fan curve represents the pressure and flow-producing characteristics of a given fan. The curves rising from the origin of the X and Y axis are the system curves. The system curves represent the physical air distribution system including the ductwork, filters, balancing dampers, and the fan outlet flow control damper mechanism.

In figure 1, point 1 represents full or design flow with the outlet damper in the full open position. In the example shown, this corresponds to approximately 25-brake horsepower (BHP) in energy required to deliver 100% flow at 100% rated pressure. Point 2 represents a 75% flow condition with the outlet damper partially closed. Due to pressure loss across the outlet damper, the pressure downstream of the damper decreases. This pressure/flow condition corresponds to approximately 23 BHP of energy required. Finally, point 3 represents a 50% flow condition by further closing of the outlet control damper with the corresponding flow decrease and increasing head across the nearly fully closed damper. This pressure/flow condition corresponds to approximately 20 BHP of energy required.

This control method is sometimes referred to as "riding the fan curve.” As shown in figure 1, outlet damper control and riding the fan curve result in a small reduction in BHP at the reduced flow rates. We are supplying energy (kW) to the fan motor to develop pressure, only to bleed the pressure off with a head drop across the restricting outlet damper. This method of control can be compared to driving a vehicle with one foot on the accelerator and the other foot on the brake. To slow the speed of your vehicle, one applies more brake and leaves the throttle wide open, rather than lifting off the throttle!

VFDs Avoid Traditional Brake Control; Provide Optimal Energy Usage

A much more efficient system would employ a VFD to operate the fan motor. In a VFD system, the speed of the fan motor is reduced, thereby reducing the amount of airflow. Simply locking the outlet dampers at fully open position and supplying a VFD can retrofit an outlet damper system to a variable speed system.

The electrical signal that was used to control the damper position can now be used as the speed reference signal for the VFD. With variable speed operation, each speed creates a new, different fan curve. Running a fan at reduced speed produces a new fan curve roughly parallel to the full-speed design curve (figure 2).

Figure 2

With VFD fan control, if 75% airflow is required (point 2), as in the previous example, the drive would run the motor at 75% speed. From figure 2, one can see that the point 2, 75% flow rate now requires only 10.5 BHP. Similarly, for the 50% flow condition, using variable speed control now requires approximately 3 BHP. With outlet damper control, the same operating condition required approximately 20 BHP!

To put these potential savings into perspective, we will assume the following operating conditions for the example 25-HP fan above. Assume this is a hospital supply fan application and therefore this fan runs 24 hours per day, 7 days per week, 365 days per year or 8760 annual hours of operation. We will further assume a standard bell curve duty cycle of reduced flow operation as follows: 100% flow for 2.5% time; 90% flow for 7.5% time; 80% flow for 10% time; 70% flow for 15% time; 60% flow for 22% time; 50% flow for 22% time; and 40% flow for 21% of the 8760 total hours.

Using the Affinity Laws and the above assumptions results in the following required kWHs (kilowatt hours) per year for constant speed, outlet damper control—171,975 kWHs per year. With the same assumptions and variable speed fan control, the fan would require only 53,430 kWHs per year. Finally, assuming that this hospital pays an average of $0.10 USD per kWh (including basic kW rate and demand charges), the outlet damper control method would require $17,198 USD per year to operate the supply fan. VFD control would require $5,343 USD per year for the same flow/operation of the supply fan. Total savings would therefore be $11,855 USD per year for this example application.

Even with very liberal estimates for VFD first cost and installation costs, the above example would lead to less than one-year payback. While rules of thumb are always dangerous, in the author’s opinion, with typical/prevailing U.S. electrical energy costs, most centrifugal fan and pump applications above 10 HP will have a two-year or less payback. Figure 3 shows in graphical form the amount of energy savings (reduced power consumption) that can be realized using a VFD.


Figure 3

How to Spot a Good VFD Potential Application

Since hospitals are typically a 24/7 operation, most fan and pump applications in hospitals are potential variable speed candidates. Simply stated, any HVAC system that spends a large amount of its total operating hours at less than peak load is a potential candidate for VFD retrofit.

One easy method for discovering variable speed opportunities is a fairly simple, walk-around-type inspection. Each time you are in a mechanical room, note the position of the outlet damper or inlet guide vane damper actuator. If the actuator is usually substantially closed, this is probably a good candidate (figure 3). A similar inspection could be accomplished on the pumps in the facility. If the pumps use throttling or bypass valves, note the position of their associated valves. Once again, if the valves are partially closed most of the time, this is probably a good retrofit candidate.

Of course, there are more sophisticated ways for spotting potential retrofit candidates such as taking flow and power measurements and comparing these figures to the rated flow and power of the system under study. Also, there are many independent companies that will perform energy savings estimates for facility managers.

Potential hospital fan and pump VFD applications include supply and return fans; fan coil units; DX units; exhaust fans; cooling tower fans; liquid coolers; condenser fans; secondary chilled water pumps; and domestic and hot water pumps. In addition, there is a growing trend of applying VFDs on primary chilled water and condenser water pumps. In short, any fan or pump in the hospital is a potential candidate for variable speed control.

Other Important VFD Benefits

In addition to energy savings, VFDs provide other benefits to the electrical systems they reside upon and the mechanical equipment they control. For example, when an ac motor is "line started” on utility power, it will require 600 to 800% of its rated current (inrush current) while it is accelerating. An ac motor started by a VFD will be limited to 110% inrush current worst case. In addition, PWM VFDs will dramatically increase power factor seen by the utility. A fan using outlet dampers at 40% flow may have a motor true power factor of 40% or less. With the same motor on VFD power at the same 40% flow, the utility would typically see an 80% or better true power factor.

From a mechanical benefit standpoint, bearings run at reduced speeds typically last much longer than their full speed counterparts. Also, drives inherently "soft start” the driven mechanical equipment. This soft start extends not only the life of the motor and bearings, but also drastically reduces belt wear and tear. Cooling tower gear boxes that are stressed by across-the-line utility starting will experience much less wear and tear when soft started with a VFD. Also, cooling tower "short cycling” will be avoided by VFD control, further extending the life of the gear box. Finally, the mechanical linkages controlling outlet dampers, inlet guide vanes or throttling valves require routine maintenance and are prone to stick or fail. Many VFDs have been installed on in-flight vane axial control fans simply to eliminate the complex mechanical linkages—and their associated high maintenance costs—with these types of flow control.

While these mechanical and electrical side-effect benefits of VFD control are many, they are often ignored because they are harder to quantify from a dollar and cents standpoint than the kWh savings which can be dramatic and easily measured. However, these side-effects are real and can often save as much as the efficiency improvement savings.

Other Important VFD Application Considerations

The need for controlling the level of harmonic current in power distribution systems is widely recognized as an important factor in selecting and applying adjustable speed drives and other non-linear load equipment. With the large amount of possibly sensitive, electronic life safety equipment prevalent in the modern hospital environment, administrators should be aware of possible harmonic and EMI/RFI noise implications.

IEEE Standard 519-1992 explains the reasons for limiting harmonics and recommends limits to be applied in various situations. The harmonic currents drawn by a load cause extra heating in all of the power distribution equipment that supplies the load. Harmonic voltages are generated by the action of the harmonic currents flowing in all of the impedances in the system. Harmonic voltages cause additional harmonic currents to flow in equipment that does not ordinarily draw harmonic currents. Harmonics may interfere with the operation of some sensitive equipment.

Harmonic Mitigation Alternatives

Line chokes and dc bus chokes are the most common harmonic mitigation devices for VFDs. Inductors (chokes) offer very little resistance to continuously flowing dc current, but the flowing current causes a magnetic field that stores energy and opposes any increasing or decreasing current. Either line chokes or dc bus chokes may be provided by the drive manufacturer as a built-in standard feature or made available as a built-in optional feature.

A swinging choke design has recently been released that provides decreased harmonic currents, especially at part-load conditions. Since VFDs spend most of their operating hours at part-load conditions, the swinging choke development is expected to provide substantial benefits to HVAC VFD users (figure 4).


Figure 4

Limiting Harmonic Currents Reduces the Drive’s Total RMS Input Current

The swinging choke assures that the drive’s input current will never exceed the output current supplied to the motor. The rated input current marked on the drive’s nameplate is the same as the rated output current. This means that there is no need to oversize the branch-circuit wiring, disconnecting means and up-stream protection to comply with the National Electrical Code and that the drive meets the EN/IEC 61000-3-12 Standard Limits.

Limiting the harmonics generated by an individual piece of equipment frees power system capacity for adding future equipment. When each piece of new equipment includes this simple, cost-effective, built-in feature, the user reduces the risk of needing to retrofit harmonic limiting measures in the future.

(As a recommendation to specifiers, it is recommended that for the hospital environment, consulting engineers and hospital administrators should insist that all VFDs be supplied with 5% impedance line reactors, or better yet, swinging chokes.)


Figure 5

EMI / RFI and the EU Council Directives

Electromagnetic compatibility (EMC) is the ability of electrical/electronic equipment to operate in its installation environment while neither causing nor experiencing electromagnetic interference (EMI). EMI is any interference with normal equipment operation caused by abnormal energy entering the equipment either by conduction though wiring connections or by radiated wave reception. Radiated electromagnetic interference is also called radio frequency interference (RFI).

In the European Economic Community, the EU Council Directives set standards for various products. The EMC Product Standard for Power Drive Systems, EN 61800-3 (or IEC 61800-3) is used as the main standard for VFDs. This standard contains test procedures that are specifically suitable for drives and the standard is quite comprehensive. It covers both the drive’s electromagnetic emissions and its immunity from received emissions.

Recommendations to Specifiers

For drives with the most comprehensive electromagnetic compatibility, specifiers should require drives to meet the IEC 61800-3 Electromagnetic compatibility standards and emission limits for Restricted Distribution and installation in the First Environment. Drives that meet the above requirements will typically meet the technical requirements of FCC Part 15 including the emission limits for a Class A digital device.

Summary

This paper has discussed the energy savings possibilities when using VFDs on fan and pump applications. It has given the end user a simple method of identifying potential VFD retrofit applications. The paper has presented a brief introduction to harmonic distortion with an explanation of some reasons and methods for limiting harmonics. A swinging choke has been described as the key component of a recently developed method for limiting harmonics generated by a VFD and provided recommendations for specifiers. Finally, EMI/RFI considerations and recommendations have also been discussed for the hospital environment.


Read more by Mike Olson

Tags:  Featured  July-August 2006 

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Article 675 – Electrical Driven or Controlled Irrigation Machines

Posted By Robert McCullough, Saturday, July 01, 2006
Updated: Sunday, February 10, 2013

Welcome to the Rodney Dangerfield of NEC articles! Irrigation machines? Most of you will labor your entire electrical careers without ever having seen one of these, let alone inspect or wire one. Back in 1973, proposal number 115 was submitted to code-making panel 11 by the Technical Subcommittee on Electrically Driven Center-Pivot Irrigator Systems. This proposal was to add a new article 675 to put in place requirements that dealt with the unique characteristics of this type of equipment. It is no surprise that it was proposed for Chapter 6; if this isn’t special equipment, I don’t know what is. The simple fact was that trying to apply the general rules of the Code to these machines was not adequate. We’re not talking about just a lawn sprinkler here, we’re talking about a lawn sprinkler on steroids. The supply end of the machine may be over a quarter-mile from its transformer, feeder or service equipment and the machine itself may be over a quarter-mile long. Couple that with the fact that these things move and are operating in the middle of literally tons of water and you have a very special set of circumstances to consider.

The panel’s action was to hold this on the docket and a task committee was appointed to review the new article. The results of the task committee’s action then appeared in NEC-1975.

One point to keep in mind is that this article only covers the machine itself for the driver motors or control or signaling circuits. Some machines are driven hydraulically and use 30 volts or less control circuits. Electric pump motors that supply the water to the irrigation machine are covered in the general requirements of the Code.

The new article contained rules for determining the current rating of the machine, its disconnecting means, and branch-circuit protection. For the most part, these rules were rooted in Article 430 but modified to meet the typical characteristics of the machines. Special attention was paid to the type of wiring used to interconnect the various driver motors on the machine, and the article sets forth the construction requirements for the cable required to be used in 675.4. This is an irrigation cable or an irrigation cable assembly as covered in Underwriters Laboratories categories (OOFY) or (OFJZ). Other cables or assemblies may be used in lieu of listed irrigation cable but must meet the construction requirements of 675.4(A). The specific type of cable was chosen as the interconnect method because, as mentioned in the substantiation, other types of conduits and cables have been tried and were found to be impracticable. Remember, these machines are moving over uneven terrain, are subject to flexing, operate in the presence of many different types of chemicals and fertilizers, are subject to freezing and thawing, and of course are right in the middle of the watering operations.

Other rules modified some specific provisions in Article 430 just due to the nature of these beasts. For example, 675.10(A) dealing with overcurrent protection for several motors on one branch circuit allows for motors up to 2 horsepower and up to 30-ampere branch circuit protection rather then the one horsepower and 15- or 20-ampere protection that is required in 430.53(A). The original technical subcommittee determined that due to the circuit lengths involved, the prospective fault current at the downstream controllers was greatly reduced and the requirements of 430.53(A) were more restrictive than necessary for these installations.

Another consideration that was placed in the article was to require an equipment grounding conductor to be sized not less than the power conductors feeding the equipment on the machine. This was done to provide a low-impedance return path given the lengths involved.

Still another modification of Article 430 involves how the current rating of the machine is determined. Section 675.7 tells us that where intermittent duty (of the motors) is not involved, the provisions of Article 430 apply. Where intermittent duty is involved, the methods set forth in 675.7(A) and (B) are to be used. Those methods are based on tests and operating experience and take into account the inherent diversity of motor operations when the machine operates in a circle. Remember these are the driver motors and to move the machine in a circle the inboard motors will not be operating for the same period of time as the outboard motors.

One last consideration that sometimes gets overlooked is the provision of 675.15 that requires a machine with a stationary point to have a grounding electrode system complying with Part III of Article 250 connected to the machine at the stationary point for lighting protection.

All in all, the article has seen very few changes since its inception and the rules developed continue to provide for a safe and practical installation. The next time you are flying over the Southwest and look down at those half-mile green circles, you can thank Article 675 for them.


Read more by Robert McCullough

Tags:  Featured  July-August 2006 

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The 2007 NESC – Part 3

Posted By David Young, Saturday, July 01, 2006
Updated: Sunday, February 10, 2013

This article is a continuation of what I see as significant changes that are coming in the 2007 revision of the National Electrical Safety Code.®

Direct embedded metal poles as ground electrodes

New Rule 094B7 addresses the conditions under which a direct embedded metal pole is considered an acceptable ground electrode.

Maximum ground resistance of ground rods on single-grounded (ungrounded or delta) systems

The present Rule 096D requires the ground resistance of individual ground rods on a single-grounded system to be not more than 25Ω where practical. It also states that if the ground resistance of an individual rod exceeds 25Ω a second rod must be installed in parallel with the first one. The 2007 wording requires the ground resistance of individual ground rods of single-grounded systems to meet the requirements of Rule 096A and not exceed 25Ω. Rule 096A states that "Grounding systems shall be designed to minimize hazard to personnel and shall have resistances to ground low enough to permit prompt operation of circuit protective devices.” It also states that if the resistance of a single rod cannot meet these requirements, other methods of grounding as described in Rule 094B shall be used to meet the requirements. Rule 094B lists the various types of grounding electrodes including driven rods, buried wire, strips, or plates, pole-butt plates and wire wraps, concentric neutral cable, concrete-encased electrodes and direct embedded metal poles.

Guarding of the secondary grounding conductor when primary and secondary neutrals are interconnected with a spark gap

One way of reducing stray voltages or currents on multi-grounded systems is to isolate the primary and secondary neutrals at the source transformer with the use of a spark gap or a device that performs an equivalent function. These devices are commonly called neutral isolators. Rule 097D addresses such applications. The present rule requires separate grounding conductors, one for the primary neutral and one for the secondary neutral, extending to the respective ground rods which must be separated at least six feet apart. One or both of the grounding conductors must be insulated for 600 volts. The 2007 edition now requires the secondary grounding conductor on a pole to be guarded in accordance with Rule 093D2.

Bonding of communications systems to electric supply systems

When electric supply systems and communications systems are grounded on a joint use structure, Rule 097G presently recommends, with the word "should,” either a single grounding conductor be used for both systems or the separate grounding conductors should be bonded together. The 2007 wording now requires this with the word "shall.”

Access to electric supply stations by unqualified persons

Rule 110B2 now allows access to electric supply stations by unqualified persons as long as they are escorted by qualified personnel. The present rule only allows access by qualified personnel.

Grounding of anchor and span guys

The present Rule 215C2 requires all uninsulated anchor and span guys to be effectively grounded if they are attached to a supporting structure carrying any supply conductors energized at more than 300V, or if vulnerable to accidental energization by such conductors due to a slack conductor or guy. The new wording requires all uninsulated anchor and span guys to be effectively grounded.

Grounding of span wires carrying luminaires, traffic signals, trolley or electric railway contact conductors

New Rules 215C3 and 4 require all span wires carrying luminaires, traffic signals, trolley or electric railway contact conductors to be effectively grounded unless they have insulators meeting the requirements of Rules 279B and 215C 5 and 6 respectively.

Insulators in anchor guys, span guys, and span wires

New Rules 215C5 and 6 address the use of insulators in anchor guys, span guys, and span wires in lieu of grounding.

Insulators used to limit galvanic corrosion

New Rule 215C7 addresses the use of insulators in anchor guys to limit galvanic corrosion. By the way, when was the last time you checked anchors for corrosion? The NESC in Rule 214A2 requires inspection "at intervals experience has shown to be necessary.” If you have never inspected, you don’t have experience. More and more utilities are reporting failures of anchors due to corrosion.

Rounding of calculation results

There are many locations in the NESC where calculations must be made to determine clearances. New rule 230A4 requires the resultant of the calculation to be rounded up to the same level of decimal places as the basic value shown in the rule or table, regardless of the number of significant digits of individual values required to be used in the calculation.

Water slides and other fixed pool-related structures

Table 234-3 now addresses the minimum clearances of water slides and other pool-related structures in the same category with diving platforms.

Installation of electric supply and communications cables installed in the same riser duct or u-guard on a pole

New Rule 239A2 states that electric supply and communications cables cannot be installed in the same riser duct or u-guard on a pole unless all of the cables are operated and maintained by the same utility.


Read more by David Young

Tags:  July-August 2006  Other Code 

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Tricky Rules

Posted By Leslie Stoch, Saturday, July 01, 2006
Updated: Sunday, February 10, 2013

Several of the rules in the Canadian Electrical Code are quite complicated, and it requires our close attention to get them right. This article discusses two of those rules, 28-604 for motor disconnects and 4-004 for underground conductor ampacities.

One of the trickiest CE Code rules to follow and interpret correctly is Rule 28-604 Location of Disconnection Means, which prescribes the locations of motor disconnects. Rules 28-604(1) and (2) deal with the location of disconnects for motor circuits. Rule 28-604(3) and (4) cover disconnections of motors and motor controllers.

Rule 28-604(1) specifies that a motor circuit disconnect (circuit-breaker or switch) must be located at a point of supply (such as a motor control centre or distribution panel). The rule goes on to state that when the motor circuit disconnect also serves as the disconnect for the motor and its controller, the motor circuit disconnect must be located within 9 m and within sight of the motor and its controller.

However the disconnect may also be located beyond 9 m and out of sight of the motor and its controller if the motor circuit disconnect is arranged so that it can be locked OPEN, and is labeled to identify all of the loads that it supplies. But, there is also an exception. Rule 28-602(2) specifies that when a draw-out circuit-breaker is used to isolate a high voltage motor (above 750 volts), the draw-out circuit-breaker must be within 9 m and within sight of the motor and its controller.

Rule 28-604(3) tells us that, except for air conditioning and refrigeration, the disconnect for a motor and its controller must be located within 9 m and within sight of both the motor and its controller.

Rule 28-604(4) provides an alternative to this requirement, stating that when a motor circuit disconnect cannot be locked OPEN, and an across-the-line manual motor starter is used as a disconnect, the starter may be located beyond 9 m and out of sight of the motor as long as the starter can be locked OPEN and is designed to safely interrupt the motor locked rotor current. This option applies only when installing a disconnect within 9 m and within sight is impracticable.

Another complicated requirement, Rules 4-004(1)(d) and 4-004(2)(d) provide the allowable ampacities for copper and aluminum underground conductors #1/0 AWG and larger. The rules are supported by sketches and tables. Great care is required to ensure the rules are interpreted correctly. Points to watch out for:

1. The permissible underground cable configurations are located in Appendix B. The tables that provide allowable ampacities relating to the cable configurations are located in Appendix D. It would be easier if both the cable sketches and their related tables were placed in the same electrical code appendix, preferably on pages opposite each other.

2. There are four sets of underground cable configurations in Appendix B, in single and parallel conductor arrangements, directly buried and in underground duct banks.

3. There are 16 tables that provide maximum allowable ampacities, four for each set of cable configurations as follows:

  • Eight A tables for single and multiple conductors that supply noncontinuous loads or continuous loads when not connected to any electrical equipment that contains fuses or circuit-breakers
  • Eight B tables for single and multiple conductors that supply continuous loads that may be connected to electrical equipment that contains fuses or circuit-breakers
  • The above arrangement also provides separate tables for copper and aluminum conductors

I have made up the following tables in the hope that they might simplify interpretation of the rules for underground conductors.

Table A covers:

  • Continuous loads other than connected to a service box, fusible switch, circuit-breaker or panelboard; or
  • Noncontinuous loads connected to a service box, fusible switch, circuit-breaker or panelboard.

Table A

Table B covers:

  • Continuous loads connected to a service box, fusible switch, circuit-breaker or panelboard

Table B

As with previous articles, you should always consult with the electrical inspection authority in each jurisdiction as applicable for a precise interpretation of any of the above.


About Leslie Stoch: Leslie Stoch, P. Eng, is principal of L. Stoch & Associates, providing electrical engineering and ISO 9000 quality systems consulting. Prior to that, he spent over 20 years with Ontario Hydro as an electrical inspection manager and engineer. Les holds a B. S. in electrical engineering from Concordia University in Montreal.

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Tricky Rules

Posted By Leslie Stoch, Saturday, July 01, 2006
Updated: Sunday, February 10, 2013

Several of the rules in the Canadian Electrical Code are quite complicated, and it requires our close attention to get them right. This article discusses two of those rules, 28-604 for motor disconnects and 4-004 for underground conductor ampacities.

One of the trickiest CE Code rules to follow and interpret correctly is Rule 28-604 Location of Disconnection Means, which prescribes the locations of motor disconnects. Rules 28-604(1) and (2) deal with the location of disconnects for motor circuits. Rule 28-604(3) and (4) cover disconnections of motors and motor controllers.

Rule 28-604(1) specifies that a motor circuit disconnect (circuit-breaker or switch) must be located at a point of supply (such as a motor control centre or distribution panel). The rule goes on to state that when the motor circuit disconnect also serves as the disconnect for the motor and its controller, the motor circuit disconnect must be located within 9 m and within sight of the motor and its controller.

However the disconnect may also be located beyond 9 m and out of sight of the motor and its controller if the motor circuit disconnect is arranged so that it can be locked OPEN, and is labeled to identify all of the loads that it supplies. But, there is also an exception. Rule 28-602(2) specifies that when a draw-out circuit-breaker is used to isolate a high voltage motor (above 750 volts), the draw-out circuit-breaker must be within 9 m and within sight of the motor and its controller.

Rule 28-604(3) tells us that, except for air conditioning and refrigeration, the disconnect for a motor and its controller must be located within 9 m and within sight of both the motor and its controller.

Rule 28-604(4) provides an alternative to this requirement, stating that when a motor circuit disconnect cannot be locked OPEN, and an across-the-line manual motor starter is used as a disconnect, the starter may be located beyond 9 m and out of sight of the motor as long as the starter can be locked OPEN and is designed to safely interrupt the motor locked rotor current. This option applies only when installing a disconnect within 9 m and within sight is impracticable.

Another complicated requirement, Rules 4-004(1)(d) and 4-004(2)(d) provide the allowable ampacities for copper and aluminum underground conductors #1/0 AWG and larger. The rules are supported by sketches and tables. Great care is required to ensure the rules are interpreted correctly. Points to watch out for:

1. The permissible underground cable configurations are located in Appendix B. The tables that provide allowable ampacities relating to the cable configurations are located in Appendix D. It would be easier if both the cable sketches and their related tables were placed in the same electrical code appendix, preferably on pages opposite each other.

2. There are four sets of underground cable configurations in Appendix B, in single and parallel conductor arrangements, directly buried and in underground duct banks.

3. There are 16 tables that provide maximum allowable ampacities, four for each set of cable configurations as follows:

  • Eight A tables for single and multiple conductors that supply noncontinuous loads or continuous loads when not connected to any electrical equipment that contains fuses or circuit-breakers
  • Eight B tables for single and multiple conductors that supply continuous loads that may be connected to electrical equipment that contains fuses or circuit-breakers
  • The above arrangement also provides separate tables for copper and aluminum conductors

I have made up the following tables in the hope that they might simplify interpretation of the rules for underground conductors.

Table A covers:

  • Continuous loads other than connected to a service box, fusible switch, circuit-breaker or panelboard; or
  • Noncontinuous loads connected to a service box, fusible switch, circuit-breaker or panelboard.

Table A

Table B covers:

  • Continuous loads connected to a service box, fusible switch, circuit-breaker or panelboard

Table B

As with previous articles, you should always consult with the electrical inspection authority in each jurisdiction as applicable for a precise interpretation of any of the above.


Read more by Leslie Stoch

Tags:  Canadian Code  July-August 2006 

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Should Changes at “The Fed” Affect How You Invest?

Posted By Jesse Abercrombie, Saturday, July 01, 2006
Updated: Sunday, February 10, 2013

It’s been a long time since someone other than Alan Greenspan has served as chairman of the Federal Reserve Board of Governors. In fact, Greenspan has been at his current job since 1987. But in a few weeks, we’ll see a "changing of the guard” as Ben Bernanke takes the helm at the Fed. This is big news for economists and policymakers, but what about individual investors in the electrical business? How will you be affected by the emergence of a new Fed chairman?

Before you can answer that question, you need to be somewhat familiar with what the Federal Reserve does, particularly its ability to contract or expand the money supply. For example, if the Federal Reserve feels that inflation is heating up, it may raise the federal funds rate, a key short-term interest rate. This causes borrowing to become more expensive, so consumers are more likely to save money, instead of spending it. In theory, this reduction in demand will lead to less upward pressure on prices, thereby bringing inflation under control. Lately, inflationary fears have been on the minds of the Federal Reserve’s governors, because the Fed has raised the federal funds rate 12 times from June 2004 through November 2005.

Of course, Alan Greenspan could not take these actions by himself; he needed to get agreement from the other Federal Reserve governors. The same will be true with Ben Bernanke. Nonetheless, the Federal Reserve chairman does wield considerable power; when testifying before Congress, Greenspan’s mere words had the power to move markets.

Still, as an investor, you probably shouldn’t place undue emphasis on what the Federal Reserve chairman says, or what actions the Fed takes. You need to look beyond short-term events and make moves that can help you in the long run. Here are two ideas to consider:

Consistently diversify your holdings

When the Federal Reserve raises interest rates, some industries, such as housing and construction, may be adversely affected, while others, such as healthcare and energy, may actually benefit. But you’d find it almost impossible—and quite costly—to constantly juggle your portfolio in response to rising or falling interest rates. Consequently, you’ll be much better off by building a diversified portfolio containing many different types of stocks, along with other investments, such as bonds and certificates of deposit. Over time, you may need to "rebalance” your portfolio to make sure that it is properly diversified and that it still reflects your risk tolerance and time horizon.

Build a bond ladder

When interest rates rise, the prices on your existing bonds will fall. That’s because no one will pay you full price for a bond that offers a lower rate than bonds that are just coming on the market. To build a bond portfolio that offers benefits in all interest-rate environments, you may want to create a "bond ladder” consisting of bonds of varying maturities. When market rates are high, you’ll have short-term bonds coming due to reinvest. And when market rates are low, you’ll still have your longer-term bonds—which typically pay higher rates—working for you.

By following these basic suggestions, you can help stay on track toward your financial objectives—no matter what’s happening at the Federal Reserve.


Read more by Jesse Abercrombie

Tags:  Featured  July-August 2006 

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