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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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Investment Mistakes to Watch for. . . at Different Stages of Life

Posted By Jesse Abercrombie, Friday, March 01, 2013
Updated: Wednesday, February 13, 2013

As an investor, how can you avoid making mistakes? It’s not always easy, because investing can be full of potential pitfalls. But if you know what the most common mistakes are at different stages of an investor’s life, you may have a better chance of avoiding these costly errors.

Let’s take a look at some investment mistakes you’ll want to avoid when you’re young, when you’re in mid-career, when you’re nearing retirement and when you’ve just retired.

When you’re young …

Mistake: Investing too conservatively (or not at all) — If you’re just entering the working world, you may not have a lot of money with which to invest. But don’t wait until your income grows; putting away even a small amount each month can prove quite helpful. Additionally, don’t make the mistake of investing primarily in short-term vehicles that may preserve your principal but offer little in the way of growth potential. Instead, position your portfolio for growth. Of course, stock prices will always fluctuate, but you potentially have decades to overcome these short-term declines. Since this money is for retirement, your focus should be on the long term — and it’s impossible to reach long-term goals with short-term, highly conservative investments.

When you’re in mid-career …

Mistake: Putting insufficient funds into your retirement accounts — At this stage of your life, your earning power may well have increased substantially. As a result, you should have more money available to invest for the future; specifically, you may now be able to "max out” on your IRA and still boost your contributions to your employer-sponsored retirement plan, such as your 401(k), 403(b) or 457(b). These retirement accounts offer tax advantages that you may not receive in ordinary savings and investment accounts. Try to put more money into these retirement accounts every time your salary goes up.

When you’re nearing retirement …

Mistake: Not having balance in your investment portfolio — When they’re within just a few years of retirement, some people may go to extremes, either investing too aggressively to try to make up for lost time or too conservatively in an attempt to avoid potential declines. Both these strategies could be risky. So as you near retirement, seek to balance your portfolio. This could mean shifting some of your investment dollars into fixed-income vehicles to provide for your current income needs while still owning stocks that provide the growth potential to help keep up with inflation in your retirement years.

When you’ve just retired …

Mistake: Failing to determine an appropriate withdrawal rate — Upon reaching retirement, you will need to carefully manage the money you’ve accumulated in your IRA, 401(k) and all other investment accounts. Obviously, your chief concern is outliving your money, so you’ll need to determine how much you can withdraw each year. To arrive at this figure, take into account your current age, your projected longevity, the amount of money you’ve saved and the estimated rate of return you’re getting from your investments. This type of calculation is complex, so you may want to consult with a financial professional.

By avoiding these errors, you can help ensure that, at each stage of your life, you’re doing what you can to keep making progress toward your financial goals.

Read more by Jesse Abercrombie

Tags:  Featured  March-April 2013 

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Mineral-Insulated Cable Is Re-Classified with 2-Hour Fire-Resistive Rating

Posted By Barry O’Connell, Friday, March 01, 2013
Updated: Wednesday, February 13, 2013

In September 2012, both UL and ULC withdrew certification for Electrical Circuit Protective Systems (FHIT and FHITC) that employed fire resistive cables. This included UL Classified Fire Resistive Cable (FHJR), UL Listed cable with "-CI” suffix (Circuit Integrity), and ULC Listed Fire Resistant Cable (FHJRC). Certification was retained for systems that used protective materials like intumescent wraps, tapes, composite mats, etc.

Fire resistive cables are used for emergency circuits in many applications, including high-rise buildings and places of assembly. Emergency circuits include feeders for fire pumps, elevators, smoke control equipment, fire alarm systems and other similar circuits. These circuits are required by the National Electrical Code and the Canadian National Building Code to have a 2-hour fire rating. This added level of survivability is intended to allow sufficient time for building occupants to exit a building during an emergency and to provide uninterrupted power for fire fighting equipment and emergency communication systems.

There are two types of fire resistive power cable systems: polymer insulated cables that require conduit protection and armored cables that do not. Armored cable types include both mineral-insulated and metal-clad cable. The events that led to the certification withdrawal were based on systems employing polymer insulated cables, not armored cable.

In 2011, UL was informed of an issue with using polymer insulated fire-resistive cables in conduit systems coated with zinc. UL confirmed that a problem existed and issued a notice stating that fire-resistive cables should be used only with components free of zinc. UL expanded their research and conducted extensive additional testing that showed an unacceptable level of variability with all non-armored polymer insulated cables.

These findings led to the conservative decision to withdraw all certifications, including armored cable systems, even though there was no indication that similar issues existed with either metal-clad or mineral-insulated cables. Shortly thereafter, however, UL offered an interim test program to manufacturers of fire-resistive cable for possible re-certification of existing products.

After UL/ULC withdrew all fire resistive cable certifications, a joint meeting of the UL Standard Technical Panel on Fire Resistive Cables and the ULC Standards Committee on Fire Tests was arranged. The meeting took place on October 24, 2012, in Ottawa, Canada, where the committee reviewed available information and agreed to form task groups to evaluate and update the fire resistance test standards for cable systems. This process will include additional testing and review, and a revised standard is likely to take at least two years to complete.

Because mineral-insulated cable construction is completely different from the cable-in-conduit technology under investigation, UL/ULC worked with Pentair Thermal Management to reinstate Pyrotenax mineral-insulated cable as a 2-hour fire-rated cable system. The process included reviewing MI cable designs in detail, detailed technical explanations of the critical design factors related to mineral-insulated cable’s fire resistance, and extensive fire tests, in accordance with the interim test program performed at the UL facility in November and December of 2012.

On December 21, 2012, UL and ULC re-established certification of fire-resistive cables used in electrical circuit integrity systems. The first system to be included is Pyrotenax Mineral Insulated Cable, and it has been assigned a new identification: System No. 1850. Information can be found at in the Online Certifications Directory.

Read more by Barry O'Connell

Tags:  Featured  March-April 2013 

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Application and Installation Requirements for Exit Signs: What, Why, and How

Posted By Ark Tsisserev, Friday, March 01, 2013
Updated: Wednesday, February 13, 2013
This subject, similar to many other issues that relate to the application and installation of electrically connected life safety system, is far from being fully understood by the designers, installers and regulators.

And certain provisions of the legally mandated documents do not help the Code users.


Let’s elaborate: provisions for installations of exit signs are governed by Rule 46-400 of the Canadian Electrical Code (CEC).

This Rule states the following requirements:

"46-400 Exit signs

(1) Where exit signs are connected to an electrical circuit, that circuit shall be used for no other purpose.

(2) Notwithstanding Subrule (1), exit signs shall be permitted to be connected to a circuit supplying emergency lighting in the area where these exit signs are installed.

(3) Exit signs in Subrules (1) and (2) shall be illuminated by an emergency power supply where emergency lighting is required by the National Building Code of Canada.


Appendix B Note on this Rule offers the following clarification:

"Rule 46-400

This Rule applies only to exit signs connected to an electrical circuit. Other requirements for exit signs, including those not connected to an electrical circuit, may be found in Section 3.4.5 of the National Building Code of Canada.

Rule 46-400(2)

The circuit supplying emergency lighting could be ac or dc. The National Building Code of Canada requires that exit signs be illuminated continuously while the building is occupied. Caution should be taken to ensure that a circuit supplying both emergency lighting and exit signs is not controlled by a switch, time clock, or other means.”

So far, requirements of the CEC appear to be straightforward, and the users of the electrical installation code clearly understand that in accordance with the scope of Section 46, these requirements are only applicable when such exit signs are "required by the National Building Code of Canada” (by the NBCC).

Photo 1. Old type exit sign—with the word "exit”

Photo 2. New type exit sign—with the green running man


As the NBCC is the "driving force” in respect to the application of exit signs, let’s take a look at the relevant provision of the NBCC.

Sentence of the NBCC states the following requirements for location of exit signs:

" Every exit door shall have an exit sign placed over or adjacent to it if the exit serves

a) a building more than 2 storeys in building height,

b) a building having an occupant load of more than 150, or

c) a room or floor area that has a fire escape as part of a required means of egress.”


Sentences and (7) provide additional requirements for location of exit signs as follows:

"6) Where no exit is visible from a public corridor, from a corridor used by the public in a Group A or B major occupancy, or from principal routes serving an open floor area having an occupant load of more than 150, an exit sign conforming to Clauses (2)(b) and (c) with an arrow or pointer indicating the direction of egress shall be provided.

7) Except for egress doorways described in Sentence, an exit sign conforming to Sentences (2) to (5) shall be placed over or adjacent to every egress doorway from rooms with an occupant load of more than 60 in Group A, Division 1 occupancies, dance halls, licensed beverage establishments, and other similar occupanciesthat, when occupied, have lighting levels below that which would provide easy identification of the egress doorway.”

So far – so good, as these NBCC provisions advise the code users of all possible locations where exit signs would be required.


Now, let’s take a look at what NBCC tells the Code users regarding performance of the required exit signs.

Sentence (2) of Article mandates the following performance requirements for exit signs:

"(2) Every exit sign shall

(a) be visible on approach to the exit,

(b) except as permitted in Sentence (3), consist of a green pictogram and a white or lightly tinted graphical symbol meeting the colour specifications referred to in ISO 3864-1, "Graphical symbols – Safety colours and safety signs – Part 1: Design principles for safety signs in workplaces and public areas,” and

(c) conform to the dimensions indicated in ISO 7010, "Graphical symbols –Safety colours and safety signs – Safety signs used in workplaces and public areas,” for the following symbols (see Appendix A):

i) E001 emergency exit left,

ii) E002 emergency exit right,

iii) E005 90-degree directional arrow, and

iv) E006 45-degree directional arrow.”


Sentence (3) of Article now mandates that internally illuminated exit signs must be illuminated continuously (and that such continuous illumination is required not only when a building is occupied, but at all times). This Sentence appears to allow two options for the internally illuminated exit signs: to be illuminated by being connected to an electrical circuit or by being able to provide "self-illuminating” capabilities, as follows:

"(3) Internally illuminated exit signs shall be continuously illuminated and

(a) where illumination of the sign is powered by an electrical circuit, be constructed in conformance with CSA C22.2 No. 141, "Emergency Lighting Equipment,” or

(b) where illumination of the sign is not powered by an electrical circuit, be constructed in conformance with CAN/ULC-S572, "Photoluminescent and Self-Luminous Signs and Path Marking Systems.”


It is also interesting to note that Sentence now recognizes externally illuminated exit signs that are illuminated not by being connected to an electrical circuit but by displaying self-illuminating properties as follows:

"(4) Externally illuminated exit signs shall be continuously illuminated and be constructed in conformance with CAN/ULC-S572, "Photoluminescent and Self-Luminous Signs and Path Marking Systems.”


Finally, the NBCC appears to confuse the users by the following statement in Sentence

"(5) The circuitry serving lighting for externally and internally illuminated exit signs shall

(a) serve no equipment other than emergency equipment, and

(b) be connected to an emergency power supply as described in Article”


This apparent confusion is manifested by the fact that Sentence (4) does not appear to mandate illumination of externally illuminated exit signs by external lighting being connected to an electrical circuit (it appears to rely on self-illuminating properties of such externally illuminated exit sign); however, Sentence (5) references the "circuitry serving lighting for externally and internally illuminated exit signs.” To add to this confusion, Sentence (5) mandates that this circuitry must serve "no equipment other than emergency equipment.” Does it mean that this exit sign circuitry must serve such emergency equipment as a fire pump or firefighters’ elevator? This NBCC statement appears to be inconsistent with provisions of Rule 46-400 of the CEC quoted above as follows:

"46-400 Exit signs

(1) Where exit signs are connected to an electrical circuit, that circuit shall be used for no other purpose.

(2) Notwithstanding Subrule (1), exit signs shall be permitted to be connected to a circuit supplying Emergency lighting in the area where these exit signs are installed.”


So, let’s summarize the information presented above:

Exit signs are part of electrically connected systems mandated by the NBCC.

Article of the 2010 edition of the NBCC has been clarified by removing wording "while building is occupied” from the requirements for the internally and externally illuminated exit signs to be continuously illuminated. Such clarification removed ambiguity on this essential safety requirement and allowed the users of the NBCC to appreciate significance of continuous illumination of exit signs in accomplishing fundamental safety objective in fire protection. NBCC introduced new signage on exit signs, by replacing the word "EXIT” by the green pictogram of a running man, as such pictogram meets provisions of the ISO standard.

However, Article of the NBCC has also been revised – to recognize "Photoluminescent and Self-Luminous Signs” that are designed and constructed in conformance with the ULC standard S572 as the exit signs that meet the performance requirements of Sentence; Sentence and Sentence of the NBCC.

These NBCC Articles mandate the following performance requirements:

" Minimum Lighting Requirements

(1) An exit, a public corridor, or a corridor providing access to exit for the public or serving patients’ sleeping rooms or classrooms shall be equipped to provide illumination to an average level not less than 50 lx at floor or tread level and at angles and intersections at changes of level where there are stairs or ramps.

(2) The minimum value of the illumination required by Sentence (1) shall be not less than 10 lx. Emergency Lighting

(1) Emergency lighting shall be provided to an average level of illumination not less than 10 lx at floor or tread level”



" Emergency Power for Lighting

(1) An emergency power supply shall be

(a) provided to maintain the emergency lighting required by this Subsection from a power source such as batteries or generators that will continue to supply power in the event that the regular power supply to the building is interrupted, and

(b) so designed and installed that upon failure of the regular power it will assume the electrical load automatically for a period of

(i) 2 h for a building within the scope of Subsection 3.2.6.,

(ii) 1 h for a buildingof Group B major occupancy classification that is not within the scope of Subsection 3.2.6., and

(iii) 30 min for a buildingof any other occupancy.”


Thus, such recognition of self-illuminated exit signs is articulated in Sentences and (4)(b) of the NBCC, and as the result of this recognition the NBCC no longer mandates that the self-illuminated exist signs conforming to ULC S572 have to be illuminated from lighting connected to the electrical circuit.


When the internally illuminated exit signsconstructed to the CSA safety standard C22.2 No.141 are connected to an electrical circuit in accordance with Sentence and in conformance with Rule 46-400 of the CE Code, the above referenced NBCC illumination performance requirements will be met. It means that under a normal power supply condition electrically connected exit signs will be continuously illuminated, and in the event of a normal power failure, the emergency power supply source will be provided to these electrically connected signs in accordance with the requirement of Sentence of the NBCC. Such emergency power supply source will be able to provide continuous illumination of these electrically connected exit signs for a period mandated by the NBCC in accordance with the type of a building.

In addition, electrical connection of the internally illuminated exist signs will allow to conform with all applicable provisions of Sentence of the NBCC (i.e. to comply with the ISO 3864-1 for a green pictogram and a graphical symbol), as each electrically connected internally illuminated exit sign complies with the CSA standard C860, "Performance of internally lighted exit signs.”

However, when "Photoluminescent and Self-Luminous Signs” (that are designed and constructed in conformance with the ULC standard S572), are installed in a building under provisions of Sentence, ability of each such "internally illuminated” exit sign to comply with provisions of the ISO 3864-1 for a green pictogram and a graphical symbol, and with provisions of the NBCC for a minimum of 10 lx of illumination under a power failure condition for a period up to 2 hours, is highly questionable, as the ULC S572 has no reference to the above stated NBCC performance requirements.

In addition, there is no requirement in the ULC S572 to mark these "Photoluminescent and Self-Luminous Signs” with the ULC certification monogram indicating that these self-illuminated exit signs conform to this ULC standard.

Thus, the users of the NBCC (designers, installers and regulators) would not have objective, consistent, transparent and measurable criteria for understanding whether such signs, in fact, meet the safety objectives of the NBCC for the illumination level and for the time period required for illumination at the NBCC prescribed level under power failure condition.

As was indicated above, Sentence of the NBCC creates confusion to the Code users, as this Sentence recognizes the signs constructed to the ULC S572 as also being "externally illuminated.”

This NBCC Sentence does not mandate an electric power supply source – to externally illuminate such signs in order to allow these signs to rely on their self-illuminating properties after the source of external illumination disappears.

It should be noted that the scope of the ULC S572 considers these signs to be furnished with "photoluminescent and self-luminous” properties (i.e., signs that are being illuminated by means of the internal self-illuminating attributes, but only after a source of ambient lighting to which these signs are exposed under normal conditions, disappears).

In fact, the following definition is provided in the ULC S572 "SELF-LUMINOUS — Illuminated by a self-contained energy source other than a battery, such as radioactive tritium gas. Operation is independent of external power supplies or other external forms of energy.”

Sentence simply outlines the requirements for circuitry serving lighting for externally and internally illuminated exit signs, but there is no requirement in Article for the externally illuminated exit signs – to be illuminated by the lighting in the area where such signs are installed. And it was already noted that the wording of paragraph is questionable, as it mandates "circuitry serving lighting for externally and internally illuminated exit signs serve no equipment other than emergency equipment.”

In light of the fact that the emergency equipment is not defined by the NBCC but is described in Article, the Code users might be under impression that the circuitry serving lighting for externally and internally illuminated exit signs could also serve such emergency equipment as fire pumps, fire fighters’ elevators, smoke control and smoke venting fans.

The writer of this article has advised the NRC staff that confusion related to this wording must be expediently removed from the Code, as this wording conflicts with 32-206 and Rule 46-400 of the CEC and with requirements of NFPA 20.

Electrically connected exit signs must be supplied only from a dedicated circuit or from a circuit that supplies emergency power to the lighting in the area where such exit signs are installed. Failure to recognize this fact in the NBCC will compromise the fire safety objective of the Code.


The writer of this article has recommended to the NRC staff the following:

1. Until ULC S572 is revised so, as to recognize performance requirements of the NBCC for illumination levels and the time period to provide such illumination levels by self-illuminating properties of the sign, to demonstrate compliance with the referenced NBCC performance requirements in specific tests reflected in the standard and to mandate marking by applying a certification monogram stating that each such sign is designed, constructed, tested and certified to the ULC S572 – to remove any references to self-illuminated exist signs and to the ULC S572 from the NBCC ASAP. Failure to do so will compromise fire safety.

2. To revise Sentences (3); (4) and (5) of Article to read as follows:


"(3) Internally illuminated exit signs shall:

(a) be continuously illuminated;

(b) be connected to an electrical circuit; and

(c) conform to the CSA standard C22.2 No. 141.

(4) Externally illuminated exit signs shall be continuously illuminated by electrical circuits supplying lighting in the area where these exit signs are installed.

(5) Electrical circuits illuminating of exit signs described in Sentence (3) or (4) shall be:

(a)used for no other purpose; and

(b)connected to an emergency power supply as described in Article”

Meanwhile, designers and installers of exit signs (if non-electrically connected exit signs are chosen for installation) should contact the relevant AHJ’s – to discuss all potential concerns.

Read more by Ark Tsisserev

Tags:  Canadian Perspective  Featured  March-April 2013 

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Improving Electric Vehicle Charging Stations

Posted By Donald E. Bowen, Jr., Friday, March 01, 2013
Updated: Wednesday, February 13, 2013
As the popularity of electric vehicles (EVs) continues to expand, the demand for charging station availability is also increasing at a rapid rate. EV infrastructure has quickly and quietly sprouted in many urban areas throughout the U.S. and along many interstate highways.

The advanced investment of this pathway infrastructure will continue to play a vital role in the adoption of EVs into our transportation system. However, continued integration of electric vehicles by consumers is dependent on the availability and ease of use of charging facilities.

Although the location and status of each unit may be identified through websites as well as applications on mobile devices, significant inconsistencies remain in the physical appearance, location, and access to this equipment. Electrical codes dictate the standards for materials, installation procedures, and connection to the electrical grid, but the user interface including physical access, signage, use limitations, area demarcations and cost are largely unregulated or standardized and are subject to the discretion of the facility owner. However, a few states have already devised guidelines to combat this problem. A wide range of regulations and policies in the states of California, Washington, Hawaii, Minnesota, Virginia, and Oregon stipulate everything from vehicle charging rates to the exact placement of EV charging systems, parking space dimensions, and signage.

Photo 1. Convenience is important.

For over a year I have been utilizing a wide variety of charging station facilities and have experienced a number of impediments which hinder the convenience of recharging my Chevy Volt. Many hotels, restaurants, supermarkets, and parking facilities have installed EV equipment, an amenity which is rapidly becoming a business imperative in the corporate world. Nonetheless, charging stations have not yet reached widespread prevalence in the most convenient locations. Areas where people are engaged in commerce for a period of hours, such as malls, golf courses, theaters, or transportation facilities, represent significant new opportunities for EV charger installation.

Photo 2. Signage is extremely important.

The vast majority of the charging units that I’ve used were identified through a mobile device prior to departing for unfamiliar destinations. Mobile applications such as PlugShare provide the locations of both private charge stations (which require advanced permission) and publicly available options. Vender specific mobile apps alert you to the location and availability of charging stations equipped solely by their company. Mobile apps usually provide the specific address of the host facility, conditions for use, user comments, level of charge capacity (120v or 240v), directions, and photographs to aid with navigation to the charging facility.

Photo 3. Accessibility is important.

Based on my use and observations of dozens of charging stations, I have compiled a list of Best Practices for facility owners and real estate managers to consider.


Signage is extremely important to locate and then operate the charging equipment. It should be large and well lit at night to avoid the need to search for EV charging stations, especially when entering a parking lot or garage. The vast majority of facilities that offer this amenity have limited instructional signage to direct vehicle operators to designated spaces.

Optimum content for signage:

reservation of parking spot for electric vehicles only

name and phone number of

organization responsible for operation and upkeep

time limitations

level of amperage

user fee or rates

consequences of violation of either time limit or type of vehicle:

"Violators will be towed at owners expense” towing company and telephone number days and hours of operation


An effective method of identifying a charging facility and its designated equipment is the demarcation of individual spaces using easily identifiable EV symbols with bright green paint either on the entire parking space or within one of several plug-in EV logos. Similar to the blue demarcations of handicap parking spaces, green designation of EV parking spaces assists with identification by EV operators and serves as a deterrent or vibrant reminder to conventional vehicle operators. The Seaport Hotel in Boston provides a fantastic example of a clean, well lit, properly designated charging facility.

Convenience will also play a significant roleas the purchase of EVs becomes more widely accepted. Unobstructed access to EV charging stations may seem logical, but I have found that a number of parking facilities have limited or prohibited access. Some restrict access by means of "residents only” or "Do Not Enter” signage, as seen at the Handover Parking Garage in Portsmouth, NH. I had a particularly difficult time tracking down one charging station noted on a mobile app when, after an extensive investigation effort, I was informed that the charging station was located in an underground parking garage referred to as Harbour Front Centre in Toronto, Canada. No trace of evidence on the ground would lead one to conclude that this charging facility even existed. A construction fence prohibited access and only through the kind-hearted assistance of facility staff did it become known that the garage was not even scheduled to open for another two weeks!

Photo 3. Lenox Hotel is the first privately owned, privately funded, company in the city of Boston to install a visible-to-the-public, electric vehicle curb-side charging station. Hotel and restaurant guests can receive complimentary valet parking along with free charging for their electric vehicle.


Accessibility measures may allow disabled persons a greater chance to operate an electric vehicle in a safer and more convenient environment. The first of every 25 EV charging spots, or any available and convenient space should be reserved exclusively for the use of disabled persons. This requires a parking space at a diagonal or perpendicular to the curb with ample space around the charging equipment as well as a barrier-free route of travel. Close proximity to the entrance of the building will allow equal opportunities to all electric vehicle drivers. Accessibility should also include sidewalk clearance for pedestrian passage if in a public area.


Charging station maintenance and protection should be put in place. Charging equipment may either have a retractable cord or a clear place to hang the cord at an appropriate height above the ground. Curbs, wheel stops, or steel bollards prove useful in protecting EV charging stations, especially those placed near an angled or perpendicular parking spot.


EV charging spots must clearly mark their policies and procedures in regards to payment or fees. If requiring a card reader, this device should be clear of obstruction, visible, and at easy level for reach. Free EV charging spots may promote energy efficiency or entice new customers or clients to the business providing the service. These free spots should be well promoted and clear for the driver to understand.


Public education is highly recommended to inform occupants, tenants and visitors of the availability and location of charging stations. This information should be available through websites for individual companies and facility owners. The public is far more likely to consider EVs if awareness of EV infrastructure and equipment is increased. In my opinion, the public charging stations available at City Hall in Boston have increased public awareness more than any other charging stations in New England due to their high profile location and near-constant use.


Use enforcement of EV parking spaces is necessaryto prevent conventional gas powered vehicle operators from occupying EV charging stations. Enforcement may pose challenges, given that the spaces are often in preferred areas, and are desirable due to proximity to elevators and stairwells, building access and pedestrian walkways.


As electric vehicle popularity soars, charging station availability through policing of time limitations will be critical to continued expansion. In addition to education of policies through proper signage, communication of charge completion is one method of insuring that idle equipment does not go to waste. The On-Star app for my Chevy Volt emails me upon complete charge or any premature disruption.

Illumination of parking space(s) is extremely helpful for the payment and use of charging stations. Despite vehicle safety considerations such as the illumination of the J1772 EV plug connection, dimly lit surroundings can make it difficult to identify charging equipment and designated spaces.


As our transportation system evolves, these recommendations will maximize the potential use and benefit of EV charging stations. The adoption of such amenities serves as a strategic differentiator between forward thinking businesses and those who choose to fall behind in a competitive environment. Minimizing the time and effort necessary to utilize charging stations will improve integration of EVs into our transportation system, reducing both our reliance on foreign oil and our carbon emissions. Widespread and well-executed EV infrastructure will provide the groundwork for a stronger economy and healthier environment for our country now and for future generations.

Read more by Donald E. Bowen, Jr.

Tags:  Featured  March-April 2013 

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Parallel Conductors Revisited

Posted By Leslie Stoch, Friday, March 01, 2013
Updated: Wednesday, February 13, 2013
High ampacity services and feeders are often installed with conductors in parallel to reduce pulling tensions and for easier handling. I’m sure you are already aware that a long list of conditions comes with permission to parallel conductors. This article reviews the requirements of Rule 12-108 Conductors in Parallel along with some significant changes for such installations now provided in the 2012 Canadian Electrical Code.

Rule 12-108 specifies that, except for neutrals, control and instrumentation circuits, parallel conductors must not be smaller than 1/0 AWG copper or aluminum. No doubt this requirement is designed to limit use of parallel conductors to such circumstances where this wiring method is truly needed. We already know, the rule contains numerous precautions to ensure conductors in parallel are loaded as equally as possible, to prevent unbalanced loading, overheating and subsequent failures.

To ensure that conductors are loaded evenly, Rule 12-108requires that parallel conductors must have the same characteristics including identical sizes, types of insulation, methods of termination, wiring materials, lengths, orientation and without any in-line splices. Appendix B shows us the required conductor configurations. These special arrangements are designed to minimize differences in inductive reactance and sharing of load currents. The wire and cable manufacturer should be consulted if it becomes necessary to employ conductor arrangements different from those given in Appendix B.

Furthermore, Rule 12-904 requires that when parallel conductors are in cables or raceways, each cable or raceway must contain an equal number of conductors from each phase and the neutral. Each cable or raceway must also be of the same material and physical characteristics to ensure that conductor impedance differences are minimized. There are some very good reasons for this requirement. Should we for example, attempt to install parallel conductors in different conduit types (say PVC and steel), we would find unequal loading in the paralleled conductors for the reasons discussed above.

But now new challenges await us with changes to this rule. As you are by now aware, some of our earlier expectations are now being tested as the 2012 Canadian Electrical Code has made two important modifications to the above requirements:

Sub-rule (2) specifies that a single splice in each parallel conductor is permitted to meet the requirements of Rule 4-006 Temperature Limitation. You will recall that this rule requires that: "where equipment is marked with a maximum termination temperature, the maximum allowable ampacity of the conductor shall be based on the corresponding temperature column from Tables 1, 2, 3 and 4.” You will also recall that this rule applies to both ends of the conductor. If for example we are using 90° C rated wiring to connect to circuit-breakers marked with a maximum 75° C temperature rating, we would normally base our conductor ampacities on the 75° C columns of Tables 1 to 4. However, this newly minted change also allows us to splice on a larger wire size to meet the maximum wiring connection temperatures specified by Rule 4-006, thereby permitting use of the 90° C temperature rating. Although permissible, it’s still not a great idea, as each splice is a potentially weak link.

Sub-rule (3) specifies that: "in parallel sets, conductors of one phase, polarity or grounded circuit conductor shall not be required to have the same characteristics as those of another phase, polarity or grounded circuit conductor.” This opens the door for parallel conductors of one phase to be of a different wire size, material (copper or aluminum), length, insulation type and termination method as long as the parallel conductors of each phase have the same characteristics. I suspect that this change was designed to make things easier for repairs rather than for the initial installations.

As with past articles, you should always consult with the electrical inspection authority in each province or territory for a more precise interpretation of any of the above.

Read more by Leslie Stoch

Tags:  Canadian Code  Featured  March-April 2013 

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Does UL List (Certify) Paint Spray Booths?

Posted By Underwriters Laboratories, Friday, March 01, 2013
Updated: Wednesday, February 13, 2013

Does UL certify paint spray booths? Does UL provide a field evaluation service for paint spray booths?


UL certifies (Lists) paint spray booths under one of two categories, depending on whether fire protection systems are provided as part of the paint spray booth. The two categories are Paint Spray Booths without Fire Protection Systems for Use in Hazardous Locations (QEFA) and Paint Spray Booths with Fire Protection Systems for Use in Hazardous Locations (QEFY), both are located on page 317 in the 2012 UL White Book or online at (enter either QEFA or QEFY in the category code search field).

These categories cover paint spray booths for liquid and powder coating finishing processes as defined in Article 516 of NFPA 70, National Electrical Code (NEC) and in NFPA 33, Spray Application Using Flammable or Combustible Materials. Some booths may utilize electric heating, gas, gas-oil or an oil-fired heating system for drying. The type of heating employed is indicated in the individual certifications.

These paint spray booths are intended for field assembly indoors in accordance with instructions furnished by the manufacturer and the information marked on the equipment. They are intended to be installed and used in accordance with applicable requirements in NFPA 33 and Article 516 of the NEC. Paint spray booths located within a commercial garage are to be installed as defined in Article 511 of the NEC.

UL can only perform a field evaluation on a UL certified paint spray that has been modified after installation. Even these evaluations can be very challenging, depending on the nature of the modifications that were made.

Performing field evaluations on a paint spray booth that will be installed in a Classified hazardous location is very difficult because subassemblies or components have not undergone full certification testing prior to a field evaluation. There are many aspects of the installation such as ventilation, filters, dead air space validation, and potential destructive testing that would be required for assemblies to properly determine compliance with the applicable standard. Therefore, UL does not provide a field evaluation service for paint spray booths that have not been previously UL certified as a paint spray booths.

For information on initiating a Field Evaluation, please go to or contact UL Customer Service at 877-ULHELPS (877-854-3577) and select prompt number 2.


I have seen Listed (certified) roof top HVAC units that incorporate a receptacle for maintenance personnel to use while servicing the unit that are not ground-fault circuit interrupter (GFCI) protected. Are these receptacles required to be GFCI-protected in the UL Standard? Are they required to be covered by a wet location "while in use cover,” e.g., a "bubble cover”?



Roof top HVAC units are certified (Listed) under the product category Heating and Cooling Equipment (LZFE) located on page 239 in the 2012 UL White Book and online at and entering LZFE in the category code search field. These products are evaluated for compliance with UL 1995, the Standard for Safety of Heating and Cooling Equipment. Effective October 2014, UL 1995 will require a ground-fault circuit interrupter (GFCI) on all 125 or 250V, single phase, 15 or 20A receptacles intended for general use installed on heating and cooling equipment for outdoor use.

The receptacles will also be required to be of the weather-resistant type, and receptacles installed in wet locations shall be subjected to the rain test or have an enclosure that is weatherproof, whether or not the attachment plug is inserted (bubble cover).

In addition, receptacles connected to the line side of a unit disconnect will be required to have a separate disconnect.

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Tags:  Featured  March-April 2013  UL Question Corner 

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The Calling of an Inspector

Posted By Steve Foran, Friday, March 01, 2013
Updated: Wednesday, February 13, 2013
The first time I came eye to eye with a 600-volt system was during the commissioning of a new amusement park. To me, the utility engineer, it was a low voltage system but not so to the customer and indeed 600 volts is a high voltage.

It was unusual for our utility to get involved in the commissioning of commercial businesses but the amusement park had some very large motors, in particular the flume ride motor. Although I can’t remember its horsepower, a full voltage start would almost look like a dead short circuit to the power system. Even with the starter controls on the motor, the amusement park ended up having restrictions on the number of times they could start the motor to eliminate the impact of voltage flicker on nearby customers.

Who is not familiar with the convenience of modern electricity — flick the switch and "on” goes the power? Yet there are relatively few people who understand the complex interconnectedness of a power system that enables us to turn on the switch, whether to a bathroom light or a flume ride. It’s true, isn’t it?

As an electrical inspection professional, you are part of this system.

Inspectors operate within an equally complex interconnected sub-system of people and processes that extend beyond the inspector’s workplace. This network includes colleagues from around the country or the globe, local and federal regulations, utilities, municipalities, businesses, electricians, and property owners in the communities you serve.

And the ultimate purpose of the electrical inspector is two-fold: first, to ensure electrical systems are safe; second, to facilitate the connection of end-use devices and systems that serve humanity.

Melodramatic? Maybe. True? Absolutely!

The impact of this perspective is significant. It elevates the work of electrical inspection to a calling. You may already see your work as a calling because of your responsibility to protect the safety and security of people and property. But I see your calling as something much larger.

Homes and schools are heated or cooled, factories are powered, food is prepared, hospitals are lit, technology is enabled and so much more all because of the safe reliable delivery of electrical energy.

Your calling as an electrical inspector is central to the well-being of humanity. Although it is seldom top of mind, but everything you do as an inspector on a daily basis, either directly or indirectly makes a difference in our world — all in support of this calling. Everything.

Seeing electrical inspection work as a calling is challenging. The complexity of the electrical system makes it hard to see the difference our actions make. And as is frequently the case, self-limiting beliefs about the nature of our work diminish our awareness to the point where the impacts of our actions are invisible to us. For those who do not overcome these challenges, the meaning of electrical inspection work is easily reduced to a mundane series of pass-fail transactions.

Like the flume motor that has the potential to trip upstream protection on the power system or to annoy nearby customers if started too frequently, your actions, in some way impact everyone with whom you are connected. This is true whether you see the impact or not. But unlike the flume motor, you can know you make an impact even without seeing the impact.

It is absolutely critical to have a healthy, realistic pride both in one’s work and in the impact of one’s work. And it is up to electrical inspection professionals like you to spread the word about the Calling of being an Electrical Inspector.

Read more by Steve Foran

Tags:  Featured  March-April 2013 

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Manual Motor Controllers and Self-Protected Combination Motor Controllers Used in Industrial Control Panels

Posted By Dan Neeser, Friday, March 01, 2013
Updated: Wednesday, February 13, 2013
Some of the most commonly used, but often misunderstood and misapplied devices in industrial control panels are manual motor controllers and self-protected combination motor controllers. The advantage of these devices is the reduced cost and size when compared to traditional motor controllers and combination motor starters.

The confusion with these devices results from the fact that the same device can be dual-listed as both a manual motor controller and a self-protected combination motor controller. On one side of the device, the listing and ratings are shown when applied as a manual motor controller. On the other side of the device, the listing and ratings are shown when applied as a self-protected combination motor controller. However, if applied as a self-protected combination motor controller, typically the ratings are reduced and additional accessories and marking requirements are needed. Hence, the question that results: is the device being applied as a manual motor controller or a self-protected combination motor controller? The answer is often unclear, which can complicate proper device application and equipment marking requirements for industrial control panel builders.

This article covers important safety criteria based on Code and Standard requirements for the proper application of manual motor controllers and self-protected combination motor controllers. As a field application engineer, the author finds these devices often misunderstood and misapplied. The objective of this article is to provide guidance to the reader to use the device’s instructions and markings to ensure proper application and marking when used in industrial control panels.

Figure 1: Traditional NEMA (left) and IEC (right) Motor Starters. Combination motor starters would incorporate a circuit breaker or fused switch ahead of the motor starter to provide motor branch circuit short-circuit and ground fault protection.



Manual Motor Controllers

Manual motor controllers, sometimes called manual motor protectors (MMP), are permitted to provide motor overload protection as required per NEC 430.32. MMPs may be also be used as a motor controller (ON-OFF Function) to meet NEC Article 430 Part VII. If marked "Suitable as Motor Disconnect” MMPs are permitted to serve as an "at the motor” disconnect per NEC 430.109, provided they are located between the final motor branch-circuit short-circuit and ground-fault protective device per 430.52 and the motor.

However, MMPs are not listed nor permitted to provide motor branch-circuit short-circuit and ground fault protection per NEC430.52. This is because their creepage and clearance distances are typically not sufficient as required by branch-circuit overcurrent devices such as UL 489 circuit breakers. Similarly, these devices do not have the creepage and clearance distances to be used as a motor branch-circuit disconnect. Thus, per NEC430.109 and UL 508A 30.3.3 , a motor branch-circuit short-circuit and ground-fault protective overcurrent device and branch-circuit disconnect are required on the line side of the MMP.

Figure 2: Examples of manual motor controllers (MMPs)

Figure 3: Possible applications of MMPs

Some MMPs have been tested and listed for group motor applications so that several of them may be able to be protected by a single motor branch-circuit short-circuit and ground-fault protective device, such as an upstream fuse or circuit breaker sized not to exceed the maximum ampere rating allowed per the device listing. In group motor applications, other limitations such as horsepower ratings and tap rule restrictions (per NEC 430.53 or UL 508A 31.4 for Industrial Control Panels) must also be investigated. Devices listed for use in group motor installations will be marked for such use to indicate that the device has undergone the appropriate testing to deem it suitable for such use. If investigated for tap conductor protection in group motor installations, they can additionally be marked "Suitable for Tap Conductor Protection in Group Installations.” The advantage of this marking is that the 1/10th rule for tap conductor protection per NEC430.53 and UL 508A 31.4 then applies versus the 1/3rd rule. This means the tap conductor to each manual motor protector must be sized suitable for the motor load but can be as small as 1/10th of the motor branch circuit short-circuit and ground-fault protective deviceversus 1/3rd of the branch-circuit conductors.

Figure 4: Example of MMP label

MMPs as listed to UL 508 will contain a marking near the agency symbol. This marking should read "Listed Manual Motor Controller” or an abbreviation such as "Man. Mtr. Cntlr.” MMPs listed for use within group motor applications, as the downstream, protected overload/controller device, will be marked for such use along with the required maximum ampere rating for the upstream fuses. MMPs, additionally listed for use as an "at the motor” disconnect, will be marked "Suitable as Motor Disconnect.” MMPs, additionally listed for use as protection of tap conductors in group installations, will be marked "Suitable for Tap Conductor Protection in Group Installations.”


Self-Protected Combination Motor Controllers

Self-protected combination motor controllers are often called self-protected combination controllers, Type E starters, Type E combination starters, or self-protected starters (SPS). SPSs are intended to provide motor overload per 430.32 and motor branch-circuit short-circuit and ground fault protection per 430.52 by combining a magnetic short-circuit trip and adjustable motor overload in one package. SPSs are a listed combination starter suitable for use without additional motor branch-circuit short-circuit and ground fault protection but limited to only single motor circuits.

SPSs have additional test requirements for low level short-circuit interrupting tests followed by endurance tests that are not required for other combination motor controllers. SPSs can be either manual (Type E) or electro-mechanical (Type F – include a load side contactor for electrical operation). SPSs are often marked with a slash voltage rating that indicates the device is limited to use only on solidly grounded wye type systems. When marked with such a slash rating, they cannot be used on ungrounded, corner-grounded or impedance-grounded systems. Creepage and clearance on the line terminals has to be the same as UL 489 and UL 98 devices. Because of this, SPSs are often listed and marked for use with a terminal kit which is required to be installed to ensure line-side terminal spacings are adequate for the application. Additional accessory parts, such as lockable handles, may need to be used as an SPS. SPSs are suitable for use as a motor branch-circuit disconnect or "at the motor” disconnect per NEC 430.109, as a motor controller (On-Off Function) per NECArticle 430, Part VII, and as both a motor branch-circuit disconnect or "at the motor” disconnect and motor controller per NEC 430.111.


Figure 5: Example of SPS with required spacing adapter accessory.

SPSs, as listed to UL 508, will contain a marking near the agency symbol. This marking should read "Listed Self-Protected Combination Motor Controller” for factory assembled units. If separate components (accessories) are required, the manual self-protected combination motor controller must be marked "Self-Protected Combination Motor Controller when used with (manufacturer and part number of load side component)” or "Motor Controllers Marked For Use With This Component”. If not marked with manufacturer and part number, the other components of the assembly must be marked, "Suitable For Use On The Load Side Of __(B)__Manual Self-Protected Combination Motor Controller, or the equivalent, where (B) is replaced with the manufacturers name and part number of the manual self-protected combination motor controller.” In addition, SPS which are limited in application to only solidly grounded wye type systems will be marked with a slash voltage rating such as 480Y/277 or 600Y/347.

Figure 6: Example of SPS motor controller label

Use of busbar systems

Busbar systems are very commonly used with both MMPs and SPSs. The challenge with using busbar systems with devices applied as SPSs is that only the incoming terminals of the first device use feeder terminals that comply with the feeder circuit spacing required by UL 508A and the listing requirements of the device. The adjoining SPSs are not able to use the standard spacing adapters as marked and required to achieve adequate feeder circuit spacing in order to be applied as SPSs and at the same time allow installation of the busbar as shown in Figure 7.

Because of this issue, the author recommends only using the busbar accessories in group motor installations (where the devices are being applied as MMPs). A group motor application is considered a branch circuit application and feeder circuit spacing is only required on the line side of the branch circuit overcurrent device, not the MMPs. However, when applied in this manner, the additional requirements perNEC 430.53 or UL 508A 31.4 must be met.

Figure 7: Example of use of busbar systems


Protection of non-motor circuits

SPSs are only permitted to be used in single motor applications. They cannot be used as the branch-circuit protective device for a group motor application or branch circuit protection of other loads, such as lighting, heating, transformers, etc., unless they are listed to UL 489. Some manufacturers do provide products called motor protection circuit breakers which are evaluated per UL 489 (which look like a typical molded-case circuit breaker with an adjustable overload setting) and are suitable for branch circuit protection of all types of loads.


How are MMPs and SPSs applied?

As mentioned previously, the biggest challenge for these devices is to open an industrial control panel and answer the question: is a device being applied as an MMP or SPS? The author recommends analyzing the application of the device as an MMP first.

For a single motor, this is a simple question: is there a suitable motor branch-circuit short-circuit and ground-fault protective devices upstream (fuse or circuit breaker)?

For a group motor application, it becomes more complicated. In this case the user must verify the MMP is suitable for group motor applications: (1) is it protected by a motor branch circuit short-circuit and ground fault device (fuse or circuit breaker) that does not exceed the rating marked on the MMP for group applications, and (2) the tap rules are met per the NEC 430.53 or UL 508A (1/3rd or 1/10th rule discussed previously).

If the device cannot meet these requirements for group motor applications, then the user must look at adding needed accessories to apply the device as an SPS. Because of this, the user is likely recommended to avoid using busbar systems. Finally, the user must revise the ratings (typically go from 480V to 480Y/277V) for the device and assembly. Additional marking requirements are required per UL 508A when used as an SPS.


Assembly Marking Requirements

When a device is used with a slash rating, such as 480Y/277V, NEC 430.83(E) must be considered. Basically this section of the NEC allows the device to be applied only on a solidly grounded wye system. Therefore, it can only be installed on a solidly grounded 480Y/277V system. It cannot be applied on a 480V ungrounded or corner-grounded system or a 480Y/277V resistance grounded system. Section 49.6 of UL 508A would additionally require the industrial control panel to be marked 480Y/277V, as opposed to 480V. In addition, section 54.12 would require an additional marking on the input terminals of "For use on a solidly grounded wye source only.”

Additionally, if a device is being applied as an SPS, section 55.7 of UL 508A requires cautionary markings to the assembly. An industrial control panel provided with an SPS shall be marked:

With the word "WARNING” and the following or the equivalent: "To maintain overcurrent, short-circuit, and ground-fault protection, the manufacturer’s instructions for selection of overload and short circuit protection must be followed to reduce the risk of fire or electric shock.”

With the word "WARNING” and the following or the equivalent: "If an overload or a fault current interruption occurs, circuits must be checked to determine the cause of the interruption. If a fault condition exists, the current-carrying components should be examined and replaced if damaged, and the integral current sensors must be replaced to reduce the risk of fire or electric shock.”


MMPs and SPSs can be cost-effective and space saving devices for use in industrial control panels. However, when using these devices, care must be taken to assure these devices are being applied properly per their listings. Often these devices are best applied as MMPs to take advantage of the use of accessories, such as busbar systems, higher voltage ratings, and reduced marking requirements. When used in a group motor installation, the group motor installation requirements must be followed. If used as an SPS, additional accessories, inability to use busbar systems, voltage limitations and special marking requirements are important application considerations.

Read more by Daniel R. Nesser

Tags:  Featured  March-April 2013 

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What Part Does IAEI Play in Disaster Relief?

Posted By David Clements, Tuesday, January 01, 2013
Updated: Thursday, December 13, 2012

Disasters are usually characterized by short reaction/response times, overwhelming devastation to infrastructure, and a strain on the tangible and intangible resources of the affected community.  Earthquakes, fires, floods, hurricanes, and tornadoes often damage electrical resources and severely impact communities economically, financially, and socially. Decision makers at local, state, and federal levels are expected to quickly implement plans to restore order and to mitigate the aftermath of these disasters.

Unfortunately, there are often not enough trained electricians and inspectors to protect homeowners from damaged wiring and equipment, to assess the most urgent needs and to restore the local electrical system quickly.  

IAEI has been particularly active in New Orleans after Hurricane Katrina and in New York and New Jersey after Hurricane Sandy.  The electrical industry helps homeowners and business owners identify and understand the hazards associated with water-damaged equipment, how it can cause serious fire hazards, where hidden fire hazards may be expected, how to deal with sediments and toxins and which water-damaged equipment must be replaced for their safety.

In order for IAEI to be effective in disaster relief programs, it is necessary for us to have a current disaster relief volunteer database. This will enable us to immediately respond to requests without having to take the time to build or update the database. We can then send out a disaster relief alert so that members who are committed in helping can respond on a timely basis.

Shortly after Sandy we were contacted by the state of New York to contact our members to see if they could help with the recovery effort in performing inspections on the thousands of properties that were damaged and without power. The response we received was overwhelming. Once again IAEI members and Inspection Authorities stepped up to offer their services and expertise in helping those suffering from the aftermath.

I want to personally say thank you to the hundreds that agreed to help and to let you know that I’m extremely proud to belong to such a great professional organization where members have empathy for those in need.  

If you are interested in being part of the IAEI Disaster Relief Team and have a minimum of five years experience in performing electrical inspections, here is the information you need to supply us:


Complete Address


Email address

Brief outline of experience

[IAEI inspector certification at the residential level is preferred, at a minimum.]

Please send the requested information to the following email address: Be sure to put "IAEI Disaster Relief Team” in the subject line of your email.

Aside from disaster relief, IAEI also participates in helping many others in need. For example, we learned during the Section Meetings that the Ontario Chapter makes donations to a couple of organizations that support persons recovering from electrical and burn injuries. The two organizations that were selected were Camp Bucko, which is a camp for children from 7 to 17 years of age who have serious burn injuries and St. John’s Rehabilitation Hospital Burn Unit, the site of Canada’s only dedicated electrical injury rehabilitation program. Western Section supports the Gregory Kistler Treatment Center in Fort Smith, Arkansas, a charity that provides therapy for children regardless of the family’s ability to pay.  Southern and Eastern Sections have scholarship programs for students pursuing training in the electrical industry. Southwestern Section has annual food drives for the needy and safety programs for children at the annual Home & Garden Show.

I am sure that this list just scratches the surface, because I’ve observed that IAEI members care—deeply, unselfishly and generously. I’d appreciate if you’d share the stories of your outreaches with me. Just send them to  Mark the subject line:  "Charitable outreaches.”

Together we are stronger as one. Let us build on our strength.

Read more by David Clements

Tags:  Editorial  January-February 2013 

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Speed Control of Motors — An Introduction to Variable-Frequency Drives

Posted By Stephen J. Vidal , Tuesday, January 01, 2013
Updated: Thursday, December 13, 2012

Speed, torque, and horsepower are three interrelated parameters in motor control. The speed of a motor measured in revolutions per minute (RPM) defines a motor’s ability to spin at a rate per unit time. The torque of a motor measured in foot-pounds (ft-lb) is a rotational characteristic of the motor that is the algebraic product of force multiplied by distance. Electrically, one horsepower (hp) is equal to 746 watts. What is interesting about these motor parameters is that if you change one of the three variables, the other two are affected. For example, if you increase horsepower while keeping speed constant, torque increases.

An electric motor is a device that converts electrical energy into mechanical energy. An electrical signal is applied to the input of the motor and the output of the motor produces a defined amount of torque related to the characteristics of the motor. It is important to understand speed-torque characteristic curves as they show the relationship between speed as a percent of rated speed versus load torque as a percent of full rating. Motors are available in multi-speed configurations that can provide constant torque variable horsepower, constant horsepower variable torque, and variable torque variable horsepower.

Equation 1. Synchronous speed

Equation 1. Synchronous speed

Traditionally, dc motors have been used in precise speed control applications because of their ability to provide acceleration and deceleration from a dead stop position to full speed fairly easily. In a dc series motor (the field is in series with the armature), the speed is controlled by increasing or decreasing the applied voltage to the series field or armature by means of a field rheostat or an armature rheostat. Silicon controlled rectifiers (SCRs) have replaced rheostats as they can control large blocks of power without the heat dissipation problems of carbon or wire-wound variable resistors. Additionally, SCRs are much smaller in size than their earlier counterparts and interface well with programmable logic controllers.

The AC squirrel cage induction motor is essentially a constant speed device. The speed of the rotating magnetic field is referred to as synchronous speed. Equation 1 relates the synchronous speed (S) to the incoming line frequency (F) and number of poles (P) the machine is constructed of: [S = 120(F) ÷ P].

Here’s an example to illustrate this point. In the United States, the line frequency is 60 Hertz. A four-pole AC squirrel cage induction motor would therefore have a synchronous speed of 1800 RPM [(120 x 60) ÷ 4]. In practice, the motor will run at less than 1800 RPM as load is placed on the rotor. This difference in speed between synchronous speed and full-load speed is referred to as slip and is usually expressed as a percentage. Note that the only two variables in equation 1 that define speed are the incoming line frequency and the number of poles in the machine. Since the number of poles in a machine is fixed, the only variable that is left to change is the incoming line frequency. This is the basis for the operation of a variable-frequency drive (VFD).

It is important to understand the difference between the AC and the DC machine at this point. Earlier, we mentioned that a DC machine could have its speed changed by increasing or decreasing the applied voltage. This is not the case for an AC motor. In fact, you can damage an AC squirrel cage induction motor if you vary the incoming supply voltage.

The term variable-frequency drive is often used interchangeably with AC drive, inverter, or adjustable- frequency drive (AFD). The two most common circuits for adjusting the speed of an AC squirrel cage induction motor are the inverter and the cycloconverter.

The VFD using an inverter does two things: first, it takes the incoming AC signal and converts it to a DC signal through a process known as rectification, and then it takes the rectified DC signal and inverts it back to a variable voltage and variable-frequency AC signal. An inverter takes a waveform like a rectified DC signal and generates an equivalent time-varying waveform resembling a sinusoid. A block diagram for an inverter type VFD is shown in figure 1.

Figure 1. Block diagram of PWM VFD

Figure 1. Block diagram of PWM VFD

The VFD using a cycloconverter is a device that produces an AC signal of constant or controllable frequency from a variable-frequency AC signal input. The output frequency is usually one-third or less than the input frequency. The cycloconverter type of VFD is normally used with larger motors or groups of motors at once.

Typical specifications you might encounter with an inverter-type VFD are listed below:

Horsepower: 1–10 HP @ 230V

Input frequency: 50/60 Hz

Output frequency: 0–120 Hz standard; 0–400 Hz jumper selectable

Frequency setting potentiometer: 10 K ½ W

Ambient temperature: 0 – +40° C

Control method: PWM (pulse width modulation)

Transistor type: IGBT (insulated gate BJT)

Analog outputs: assignable

Digital Outputs: opto-isolated assignable

Terminal strips present on the VFD allow the device to interface to the outside world to familiar switching devices like start, stop, forward run, and reverse run. Instead of using a three-wire control circuit to start and stop a motor with momentary contact devices, the electronics of the drive control all those familiar operations.

Normally, the VFD also has a backlit liquid crystal display (LCD) that shows a variety of motor operational parameters that are fully programmable by the user. Solid-state devices like the silicon controlled rectifier, triac, and insulated gate bipolar junction transistor have allowed the variable-frequency drive to become the method of choice for AC motor speed control.

Read more by Stephen J. Vidal

Tags:  Featured  January-February 2013 

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