Posted By Ark Tsisserev,
Tuesday, March 01, 2011
Updated: Wednesday, January 09, 2013
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Let’s say, you are undertaking design and installation or inspection of such electrical installation in patient care areas of a health care facility. Do you consider certain parts of patient care areas as wet locations, and which criteria do you use for such consideration?
In light of these questions — which wiring methods should be used, and which types of equipment construction should be specified in design? Is use of a solidly grounded system allowed in patient care areas or must only isolated systems be used?
Let’s check which electrical safety requirements are applicable for design and installation of electrical equipment in respect to these subjects, where consistency of design, installation and inspection is far from perfect.
First of all, let’s state the following undisputed facts:
1. Installation requirements in patient care areas of health care facilities are governed by Section 24 of the Canadian Electrical Code.
2. Application of electrical safety associated with provision of health care and application of essential electrical systems in a health care facility are covered by the CSA standard Z32 "Electrical Safety and Essential Electrical Systems in Health Care Facilities.”
Section 24 of the CE Code and the CSA standard Z32 mandate a variety of very specific conditions related to electrical installations and to application of electrical safety in health care facilities. However, the object of this discussion is to concentrate on two particular issues indicated at the outset of this article.
First of all, let’s discuss the subject of wet locations in patient care areas.
This question might surprise some readers. Why would we discuss wet locations when we deal with electrical installations in patient care areas of a typical health care facility (i.e., in patient care area of a major hospital)?
The readers may be referred to Rule 24-106(2) of the CE Code which states: "24-106(2) Receptacles located in areas that are routinely cleaned using liquids that normally splash against the walls shall be installed not less than 300 mm above the floor.”
The question is: "Does Rule 24-106(2) refer to areas that are defined as wet location in Section 0?”
Before offering the answer to this question, let’s check the definition of wet location in Section 0.
Section 0 offers the following definition ofwet location, "Wet location – a location in which liquids may drip, splash, or flow on or against electrical equipment.”
After reading this definition, the Code users may immediately review provisions of Section 22, where use of electrical equipment and wiring methods in the environment with liquids that may drip, splash or flow on or against electrical equipment is governed by specific provisions. Rule 22-102(4) mandates that "where the electrical equipment is, or likely to be, exposed to splashing of water, it shall be of a weatherproof or watertight type of construction.” Furthermore, Rule 22-200(1)(a) mandates that conductors that are exposed to moisture must be of the types specified in Table 19 for exposed wiring in wet locations.
Section 24, however, does not make any references to wet locations for the wiring methods or for selection of electrical equipment. Z32 also does not provide any references to wet location for the purpose of application of electrical systems in health care facilities.
Appendix B Note on Rule 24-116 states: "Areas subject to standing fluids on the floor or drenching of the work area can create a condition where a patient or staff member can become a path for ground-fault current under fault conditions. Routine housekeeping procedures and incidental spillage of liquids are not intended to be considered for the purpose of this Rule.”
Therefore, the answer to our highlighted question above is the definite: "NO.”
This answer is based on the following criteria:
1. If the areas described in Rule 24-106(2) should be classified as "wet locations,” such areas would have to be referenced in Appendix B on Rule 22-002 for Category 1 locations.
2. If these parts of a patient care area (where a routine cleaning takes place by using liquids that normally splash against the floor and wall surfaces) are intended to be classified as wet locations, Section 24 would impose requirements for wiring methods and installation of electrical equipment — to conform to Category 1 of Section 22.
It should be noted, for example, that the EMT is not allowed to be installed in wet locations by Rule 12-1402(1), and the EMT is a commonly used raceway in patient care areas.
3. Rule 24-106(2) deliberately mandates a minimum height restriction for receptacles in parts of patient care area that are routinely cleaned by use of liquids, as such areas are not considered to be "wet locations.” Otherwise, such restrictions would not exist, and the receptacles installed in these areas simply would have to comply with Rule 22-108.
4. This rule only mandates a clearance from a receptacle location and does not stipulate otherwise that the area of cleaning with liquids is a wet location.
5. Z32 does not mandate any specific conditions in this regard in Clause 4.2.6, Patient Care Area Classification, although this standard covers all relevant aspects of electrical safety in health care facilities. It should be also noted that Z32 requires use of medical electrical equipment that is designed, constructed, tested and certified to very stringent provisions of the CAN/CSA–C22.2 No. 60601 series standards, and that these standards take into account required mitigation of any leakage and risk currents associated with a specialized use of this type of equipment.
Proponents of classifying these areas as "wet locations” argue that a typical operating room is a prime example of a wet location, as an OR is subject to standing fluids or drenching of the work area. However, the CE Code addresses this matter in Rule 24-116, by mandating GFCI protection of receptacles installed in such areas or by mandating use of isolated systems conforming to Rule 24-200. Impact of routine standing fluids or drenching of the work area is different (from the CE Code and Z32 perspective) from the impact of incidental spillage of cleaning liquids in patient care areas. The latter impact is not intended to be addressed by provisions of Rule 24-116. In fact, Appendix B Note on Rule 24-116 states: "Areas subject to standing fluids on the floor or drenching of the work area can create a condition where a patient or staff member can become a path for ground-fault current under fault conditions. Routine housekeeping procedures and incidental spillage of liquids are not intended to be considered for the purpose of this Rule.”
It should be noted that some CSA C22.2 No. 60601 series standards might also mandatea GFCI protection in the design and construction of specific cord-connected medical electrical equipment, but such requirements are outside the scope of the installation Code.
So, by now we should be comfortable with the conclusion that the electrical equipment and wiring methods in patient care area do not have to be selected for use in a "wet location,” and that only the receptacles in areas subjected to standing fluids on the floor or drenching of the work area must be protected by a GFCI of the Class A type or must be suppliedby an isolated system. Now is the appropriate time to discuss the Code and Z32 provisions for isolated systems.
Isolated systems are not specifically mandated by the CE Code to supply all loads in patient care areas.
In general, isolated power in operating rooms represents an outdated design and installation approach. The concept of using isolated systems was traditionally utilized in the past in order to reduce the risk of a spark which could cause an explosion in the presence of flammable anesthetic agents. Flammable anesthetic agents have not been used for quite some time. As such, isolated systems are required as the power supply sourceonly as an alternativeto solidly grounded systems under provisions of Rule 24-110 of the CE Code. Rule 24-110 states: "The branch circuits supplying receptacles or other permanently connected equipment in intermediate or critical care areas shall be suppliedfrom either a grounded system meeting requirements of Rule 24-102, or an isolated system meeting the requirements of Rule 24-200….”
Appendix B Note on Rule 24-116 explains in part that use of a GFCI of the Class A type for receptacles in areas subject to standing fluids on the floor is intended for those "locations within a patient care area where interruption of power to the receptacles by actuation of a GFCI is deemed to be acceptable in accordance with the provisions of CAN/CSA-Z32.
These receptacles are intended to be supplied by an isolated system where such power interruption to the receptacles is not acceptable in accordance with CAN/CSA-Z32.
It is interesting to note that 2009 edition of CAN/CSA-Z32 "Electrical Safety in Health Care Facilities” offers the following statements:
Use of isolated power is not required by the Canadian Electrical Code, Part I, or by this Standard.
Note: The requirements of Section 24 of the Canadian Electrical Code, Part I, apply to the design and installation of isolated power systems.
The probability of persons receiving an unintended electric shock from a properly grounded system is very remote.
Because a grounded system does not require a line isolation monitor, isolating transformer, or special panelboard, additional space is not needed.
The capital cost is typically lower for grounded systems; however, additional testing is required on commissioning to ensure the safety of the system.
H.4 Choice of system
For intermediate and critical care areas, the decision to use a grounded system or an isolated system is made jointly by the provincial/territorial or federal body having jurisdiction, the HCF administration, and the professional engineer responsible for the electrical design.”
Many electrical designers and biomedical engineers responsible for operation of medical electrical equipment in patient areas of the health care facilities are of the opinion that an isolated system provides a very intangible additional level of safety to the patients and staff. Z32 mandates a very stringent testing protocolfor the electrical equipment and branch circuitssupplied by a solidly grounded system. Experience has demonstrated that the power supply provided by an isolated system may, in fact, camouflage electrical safety problems with medical electrical equipment. Thus, from a practical view point, use of an isolated system is not a desirable alternative to a solidly grounded system.
So, where the areas that are subjected to standing fluids on the floor or drenching of the work area can create a situation where a patient or staff member may become a path for ground-fault current under fault conditions, where means to mitigate such situation by the appropriate maintenance procedures are not deemed to be practicable and where a GFCI protection of receptacles in such areas is not acceptable due to a possible power interruption, a decision to use an isolated system as an alternative to a solidly grounded system is a combined decision by the HCF administration, respective regulators and design professionals.
Read more by Ark Tsisserev
Posted By Carey J. Cook,
Tuesday, March 01, 2011
Updated: Wednesday, January 09, 2013
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Inspectors, contractors and electrical engineers have used IEEE Color Books for decades to find practical solutions to questions on the design, installation, maintenance, and operation of industrial, commercial, and institutional electrical power systems.
The 13 Color Books — as virtually everyone in the industry knows — are a set of recommendations that reflect the best practices for calculating, coordinating, protecting and assuring the safety of power equipment and systems.
IEEE recently announced that the series is getting a makeover aimed at making the information easier to access and easier to revise. The books will still encompass the same content generally but they will be organized as 55+ IEEE "dot” standards. This will make revisions easier because the IEEE committee does not have to approve an entire volume of content when all that is needed is to promulgate just a few timely changes, ensuring that each "dot” standard version reflects the latest technologies and best practices for that topic.
Another advantage is that more experts are expected to share their knowledge under the new structure. In addition to the flexibility in the new review and publication process, IEEE is acknowledging the fact that publishing has evolved toward an online model, which besides being less expensive than printed books, allows numerous yet fast-turn update cycles, and makes the specific information users are looking for much more accessible to them.
Power engineering processes and procedures are evolving rapidly — particularly in light of the Smart Grid initiatives — and very specific information often needs to be retrieved in a timely manner. By creating a more user-friendly set of standards, IEEE will be able to meet those needs. Internally, IEEE will have a process that allows content to be revised, edited and balloted more quickly. In addition, the working groups that create the new standards will now have an opportunity to eliminate the redundant information that has found its way into multiple Color Books over time.
Eight working groups have already been formed, including one to write an introductory book that will provide an overview of the topics covered by the individual "dot” standards and provide references to the areas covered by each standard. The other seven working groups will develop or revise the dot standards.
Engineers recruited from across all power engineering disciplines will be needed to create the standards and while experts are welcomed, younger engineers can take advantage in a once-in-a-lifetime opportunity to help to create standards that will define the industry over the next few decades.
The original Color books followed two tracks. Some dealt with specific facilities such as industrial plants (Gray Book), commercial buildings (Red Book), or heath care facilities (White Book). Other Color Books cover specific technical topics such as emergency and standby power systems (Orange Book), protection and coordination (Buff Book), power systems analysis (Brown and Violet Books), grounding (Green Book), powering and grounding sensitive loads (Emerald Book), and reliability (Gold Book). The Yellow Book covered maintenance, operation, and safety of industrial and commercial power systems.
The new resource, released over time in "dot” standard sections, will begin publication early in 2011. For any volunteers wishing to participate, please contact: Patricia A. Gerdon at:email@example.com
Read more by Carey J. Cook
Posted By Leslie Stoch,
Tuesday, March 01, 2011
Updated: Wednesday, January 09, 2013
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This article reviews two very essential safety requirements of the Canadian Electrical Code for motor control circuits, grounding and why it’s so significant that control circuits be prohibited for use as motor disconnecting means.
Figure 1. Motor control circuit diagram
As a basic requirement, Rule 28-500 Control required specifies that every motor must be provided with a motor starter or controller for starting and stopping the motor. Sub-rule 1 also provides a list of exceptions to the rule, namely:
• A single-phase, 125-volt, cord-connected motor up to 1/3 horsepower;
• A motor controlled by a general use disconnect switch;
• A single-phase portable 125-volt motor, up to 1/3 horsepower controlled by a horsepower rated switch; or
• Several motors controlled by a single motor controller.
First addressing the motor control circuit grounding issue, Rule 28-506 Grounded control circuit requires that when a motor control circuit is supplied from a grounded electrical source, the grounded side of the motor control circuit must be arranged so that an accidental ground in the control wiring will not start the motor or prevent stopping of the motor.
Seems like a common sense requirement, but how is this to be accomplished? This simply means that the grounded side of the motor control circuit must be on the side of the motor starter coil opposite from the motor control contacts. Consider the motor control circuit diagram in figure 1. Which is the grounded side of the circuit? What do you think might occur if the other side of the control circuit happened to be the grounded side?
In this diagram, the rule requires that the right-hand side of the control circuit must be the grounded side. Should the grounding of the circuit accidentally be reversed, a short-circuit in the control wiring between the motor starter coil and the motor control contactor would energize the starter coil, causing the motor to start up on its own.
Alternatively, a short-circuit between the stop pushbutton and the motor control contactor would not cause the motor to start, but once started, the motor could not be stopped by means of the motor control circuit, since the STOP pushbutton would then be out of the control circuit and thereby prevented from stopping the motor.
Addressing our second point,Rule 28-602(4)specifies that a motor disconnecting means must not be electrically operated, either automatically or by remote control. This simply means that before working on a motor or the motor-driven machinery, we must always disconnect and lock-off the electrical power supply to the motor. Disabling the motor control circuit by using a lock-off switch is not a permissible or safe means of disconnecting the motor. A lock-off stop device in the control circuit will prevent the motor from starting. However, a short circuit in the control wiring could cause the motor to start unexpectedly and create an unsafe condition. For this reason, de-energizing the motor control circuit is not permitted as the motor disconnection means.
As with past articles, you should always consult the electrical inspection authority for a more precise interpretation of any of the above.
Read more by Leslie Stoch
Posted By Thomas A. Domitrovich,
Tuesday, March 01, 2011
Updated: Wednesday, January 09, 2013
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Flying by the seat of your pants when it comes to safety is not a good idea. A good safety plan can add value to your inspection program. Whether you have your own business or work for an organization, you should realize the value of a safety program. In the last few editions of IAEI News, this column focused on the results of a questionnaire where inspectors responded to questions related to conducting the inspection. One of the questions concerned itself with what an inspector takes to the job site and what is carried during the inspection. Although not focused on safety, some of the answers were intriguing.
The Unwritten Safety Plan
I have spoken to many inspectors and walked along with a few, it is quite clear that we all have our unwritten safety programs. We have our limitations on what we will and will not do, and we accept some level of risk. The equipment we carry to a job site speaks of our unwritten safety plan that drives our actions. When you go to a job site, if you automatically grab your gloves, safety glasses, hard hat and don your steel toe boots, you have a set of safety practices that may not be written down but, rest assured, they are in your head. You do this because of your experience, and you may be better at it than others. Write your safety plan on paper and share it with those with whom you work — you may be surprised at feedback that reveals items you may have missed. If your plan is complete, those you share it with will obtain an education and you will help ensure their work is performed to a higher standard. The bottom line in my book is that a well communicated safety program that is followed could save lives.
Table 2. It is clear from these results that this question should be a survey unto itself. The question was not formulated in such a manner as to stimulate the reviewer. A future article just may be in order to dig deeper in this area.
Table 2 is taken from the "Safety in Our States” column of the January/February 2011 issue of IAEI News. The question in the survey was twofold: What do you take to the inspection, and then what do you take during the inspection? The question was not formulated in such a manner as to stimulate the creativity of the reader and nor was it focused on safety. Some observations from these results include — out of 113 respondents:
- Only one respondent mentioned safety goggles – they were brought with them but not indicated to be an item carried during the inspection.
- Only two respondents mentioned a safety vest – one left it in the car but the other wore it during the inspection.
- Two respondents mentioned personal protective equipment (PPE) – keep in mind here that thirteen respondents noted that they inspect heavy industrials. Most inspectors should have PPE accessible to them. It may not be required for every inspection but when it is, it should be accessible. PPE can be expensive, especially when you are on a limited budget. It may not be required for every situation, but you should at least have access to protective equipment when you need it.
- Finally, there was one person who has a pair of steel toe boots – in the car, not on his feet while conducting the inspection.
The Safety Program
So what exactly is a safety program? It must be comprehensive and not only address OSHA requirements but also incorporate NFPA 70E, which was created to help bridge the gap between OSHA and the National Electrical Code. The business of working in and around electricity carries with it many responsibilities which include more than just electrical safety — your safety plan must be comprehensive.
Getting started on a good program may appear to be a daunting task. There are organizations that will help you implement a program, or you can assemble one yourself. The first step, no matter which direction you take, is to know and agree and commit to the fact that your organization needs a safety program. As a business owner, you must consider the following:
- OSHA has concluded that effective management of worker safety and health protection is a decisive factor in reducing the extent and the severity of work-related injuries and illnesses.
- Your return on investment can be great in the form of improved morale, decreased lost time, fewer workplace injuries and illnesses, lower insurance costs and possibly increased business from very safety conscience corporations.
Once you agree and accept the fact that a safety program is best for your organization, putting the plan together should not be all that difficult. There are many guides and references to help you. The following will get you started.
First assemble your library. Get your hands on a copy of these resources:
- NFPA 70E,Standard for Electrical Safety Requirements for Employee Workplaces,www.nfpa.org
- The Electrical Safety Program Book,www.nfpa.org
- Small Business Handbook, Occupational Safety and Health Administration (OSHA),www.osha.gov. This item is a free download.
Read through these documents and elevate your knowledge of the essentials around a good program. If you hire a professional, and it is probably a good idea to do so either just for this project or as a continued contract relationship, that group will build on this knowledge.
A good program on paper, in a binder, on a CD, is not enough. Safety is part of your daily routine. Safety meetings and reviews should be conducted on an ongoing basis — not to be left to on-the-job training. This program should be formalized in a manner that elevates the importance to your team, gives it the respect it deserves and ensures that while work is being performed your safety program is adhered to. Every employee has to understand the impact that your investment has to the business. Each person plays a role in the success of business and your safety program. It is a good idea to conduct safety review meetings on a periodic basis; make it a routine. Maintain all of your records to have evidence of your program and all safety activities and events. Track your performance and results.
Your customers may have a safety program in place that you may benefit from as well. They may have a site survey completed where high energy areas, PPE requirements, availability of safety labeling and equipment have been identified. Share your safety programs with each other.
Communication is very important on many levels within your organization and with others. There are many avenues to share your program information. Assemble the program in a few different formats to be most beneficial to your success.
Keep It Updated
So let’s assume that you have a safety plan and use it. This is a roadmap to a successful safe environment for both you and your employees. The safety landscape is continuously changing in many ways, so keep your safety goals clear and fresh with regular updates — make it a living document. Here are six reasons for keeping it up to date.
The most obvious reason for updating your safety plan is a changing market. Changes in codes and standards documents and new operations within your own business will have an impact on your safety plan. A move from a residential focus to an industrial or commercial focus would warrant a review of your safety plan.
Codes and standards documents are typically on a review cycle changing periodically. The 2011 version of the National Electrical Code (NEC) is currently being reviewed by states and local jurisdictions and will be adopted throughout this and coming years. To date, North Dakota and Massachusetts have reviewed and adopted this new version of the NEC. North Dakota will begin to enforce NEC-2011 on September 1, 2011. Massachusetts began enforcement on January 1, 2011. Oregon, Idaho, Ohio and others have already begun their review process of the latest version of the NEC and adoption will be soon to follow.
Another document in the works by the National Fire Protection Association (NFPA) is NFPA 70E, Standard for Electrical Safety in the Workplace. The 2012 version of this document has some changes that may impact your plan. One of the tables used extensively, and unfortunately sometimes incorrectly, is targeted to be modified. Table 130.7(C)(9) is referenced to determine what personal protective equipment (PPE) is needed to protect from electric shock and arc-flash injuries. The proposed change that has been accepted to date includes the placement of maximum available short-circuit current and clearing times under each of the major equipment category headers. The major equipment headers will also include the potential arc-flash protection boundary. Some forget that the application of this table is permitted only where the maximum available short-circuit current and fault clearing time parameters specified in Notes 1 through 4 at the end of the table are followed; this is an important detail that should not be overlooked. As of this writing, NFPA 70E will be reviewed at the NFPA Annual Meeting later in June. It is at this meeting that the revised document will ultimately complete its process.
The NFPA web site has a complete schedule of all document revision cycles. You can flag those documents that you use most frequently so that an email is sent to you whenever there are changes to that document. This is a great feature of the NFPA web site, next to the free downloads of the Report on Proposals (ROP) and Report on Comments (ROC) documents. Make sure your plan references the latest codes and standards.
New Products / Solutions
The equipment or tools that you and your employees use, as well as the equipment they must work in and around, can and will periodically change. The electrical market is constantly in a state of flux not only to meet and address new demands in areas like alternative energy, but also to improve and offer new solutions around such safety concerns as arc-flash energy in the power system. Not only will you and your team be faced with new applications and products, there just may be new technologies you can utilize in your operations that help you work more safely.
Every year your organization will update a business plan; this is an important part of your overall business strategy and a necessity if you are about to approach your bank or investors for additional funds. There may be changes in your plan that requires the purchase of new equipment or educational materials. A review of your safety budget and plan at this time is very advisable. If you are involved with the financial planning for your safety program, your safety plan is a key part of your corporate message.
A safety plan in an organization needs to be funded appropriately. Do not let yours sit on a shelf year after year without being reviewed. Or worse yet, not have one at all. Ensure safety is appropriately funded and that everyone understands its importance. If you know that you don’t have the best equipment for your team and it is because of the lack of funding, take the first step to success by assembling your safety plan. Your plan will drive results.
The safety plan is there to keep your employees and those around them safe. When you first create your new safety plan, the employees in your organization will experience firsthand, through education and awareness programs, how important safety is to your organization. New employees added to your organization should understand the importance of safety as well. New releases of an updated safety plan can help keep existing and new employees well aware of your safety initiatives. Your work force constantly changes just like the markets, and these changes may require changes in your plan to ensure your safety plan properly addresses the needs of new personnel. Their level of knowledge and experience may be changing as you move into new markets or pull out of others.
Raising the Bar
Many organizations establish safety goals to go along with their safety program. Review those goals often. Add more, raise the bar, and keep the safety message alive. If you don’t have a safety plan, set the goal this year to get one in place. Then you can strive to make your safety program the model for the industry. Remember to communicate your program and measure its success as these are important aspects of growing the safety culture. You took the first step and created a safety plan, now grow your program.
The bottom line is that we should always strive to be better at safety in order to ensure it stays on track. Don’t let your organization get behind the safety eight ball. Just because you are an electrical inspector does not mean that you do not need a safety plan.
As always, keep safety at the top of your list and ensure that you and those around you live to see another day. If you have any tips or ideas you would like to share, please feel free to send them to me at firstname.lastname@example.org. I look forward to your input to these articles and guidance for future articles.
Read more by Thomas A. Domitrovich
Safety in Our States
Posted By Andrew Cochran,
Tuesday, March 01, 2011
Updated: Wednesday, January 09, 2013
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Managing Electrical Risk
The use of electricity has inherent risks, particularly electric shock and arc flash hazard. However management tools and technology are readily available to mitigate and manage these risks.
Figure 1. Risk Assessment Matrix
Hazards and risks are not the same thing. A hazard is something with the potential to cause harm and damages whether that be to equipment, processes or personnel. Risk is the likelihood that the event will occur and result in damages.
The relationship between hazard and risk can often be summarized via a Risk Assessment Matrix as per figure 1, which provides an easily understood, defined approach to hazard analysis and risk assessment.
Once the appropriate level has been determined then management action can be summarized using a simple response chart.
Category — Action
HIGH— Do not operate equipment or process until remedial action has been implemented.
SERIOUS— High priority, remedial action must be taken at the earliest opportunity.
MEDIUM —Take remedial action at the next convenient opportunity.
LOW— Risk level is acceptable, remedial action is discretionary.
Figure 2. Published Losses
We know from experience and empirical data that over 85% and probably closer to 98% of all electrical faults are phase-to-ground faults and we have documented and quantitative data from various studies summarizing the costs and impact of ground faults on industry.
One leading US based insurance company notes that over a 7 year period their clients reported 228 losses that were attributed to ground faults resulting in payments of $180 million. There were 72 occurrences in the commercial sector, hotels, universities, hospitals and shopping malls at an average cost of $830,000 each and 156 occurrences in manufacturing locations with an average cost of $769,000 per occurrence.
With the information available we can categorize the Risk Assessment of an electrical ground fault to be somewhere between HIGH and SERIOUS with financial damages according to one insurance company averaging $769,000 the majority of which is likely to be the costs associated with business interruptions and capital equipment damage. We can define the frequency as Occasional and thankfully the impact on personnel to be low as most ground faults simply result in process outages.
At the other extreme is the electrical arc fault which has a lower occurrence rate than a ground fault but the potential damage is significantly higher. According to statistics compiled by CapSchell Inc, a Chicago-based research and consulting firm that specializes in preventing workplace injuries and deaths, there are five to ten arc-flash explosions that occur in electric equipment every day in USA, resulting in medical treatment. Arc flash victims may suffer from chronic pain and scarring. Workers may also have difficulty re-integrating into the community, and may experience anxiety, depression, or other psychological symptoms. The social and economic costs may also be high. Workers’ compensation pays only a portion of lost wages. Some workers may not be able to return to their pre-injury job. Employers bear the costs associated with lost productivity, reduced competitiveness, employee rehiring and retraining, as well being subject to increases in workers’ compensation premiums. Published data from Washington State notes that from September 2000 through December 2005, 350 Washington workers were hospitalized for serious burn injuries occurring at work. Of these, 30 (9%) were due to arc flash/blast explosions. Total Workers’ Compensation costs associated with these 30 claims exceeded $1.3 million, including reimbursement for almost 1,800 days of lost work time.
Figure 3. Risk Assessment Matrix – Solidly Grounded System
An arc flash is a breakdown of the air resulting in an arc which can occur where there is sufficient voltage in an electrical system and a path to ground, neutral, or another phase. An arc flash, with a high level of current, in the range of 1000 amps or more, can cause substantial damage, fire or injury. The massive energy released in an arcing fault can instantly vaporize metal in the path of the arc, blasting molten metal and expanding plasma outward with extreme force. The result of the violent event can cause fire, destruction of equipment and serious injury to personnel in the vicinity of the blast.
An arc flash would likely have a Risk Assessment of MEDIUM to SERIOUS due to its low frequency but devastating impact on equipment and personnel.
There was a recent electrical fire at a recreational facility that resulted in consequential damages of $400,000, mostly in business interruption costs and as the forensic engineers and insurance investigators conducted their review, the focus was who and what was to blame for the losses.
The engineers and insurance representatives for all parties reviewed all aspects of the electrical equipment that was specified and installed including settings and commissioning reports. They questioned the integrity of the electrical switchgear, the protection relays and components specified in the electrical system, the installation practices of the electrical contractor, the maintenance schedule and its effectiveness etc.
The focus was not on whether the electrical system specified or used was correct or safe but simply who in the supply chain of electrical equipment and services would pay the damages. During the course of the investigation a simple question was raised. Was the grounding method chosen by the consulting engineer and the facility owner or operator a contributing factor?
The most common grounding method in use in North America for both commercial and industrial facilities and the method chosen in this specific instance is called solidly grounding. However, this grounding method is known to have the highest incident level of arc flash events and electrical fires. There are estimated to be around 210,000 industrial facilities that operate solidly grounded despite the higher level of risk.
Simply be using the Risk Assessment Matrix, the consulting engineer or business operator could have readily identified that choosing to specify a solidly grounded electrical system while economical and simple to implement, the associated hazard frequency level of OCCASIONAL and a hazard severity level of SERIOUS would result in a MEDIUM level of risk and that remedial action would need to be taken at the next convenient opportunity.
Figure 4. Hierarchy of Hazard Controls
In fact, since this was the design stage, preventative measure could have been implemented to ensure a REMOTE frequency and MARGINAL or MINOR impact to secure a LOW level of risk. Rather than point fingers post event looking to cast blame or recover damages, the responsible approach would be to proactively reduce the likelihood of the hazard and reduce the impact of the hazard at the design stage.
The least common method but safest grounding method in use today in North America is Resistance Grounding where a resistor is connected between the neutral of the transformer secondary and the earth ground. The reasons supporting this option for electrical grounding can be found in several IEEE (Institute of Electrical and Electronic Engineers) Reference Guides.
IEEE Standard 141-1993 Recommended Practice for Electric Power Distribution for Industrial Plants
7.2.2 There is no arc flash hazard, as there is with solidly grounded systems, since the fault current is limited to approximately 5A. Another benefit of high-resistance grounded systems is the limitation of ground fault current to prevent damage to equipment.
The investigation continues and no blame or fault has been established nor damages awarded but the possible implication for the consulting engineering fraternity could be substantial. If the insurance investigation determines that the root cause was the specifying of a solidly grounded system which by its very nature contains a risk of arc flash occurring, then the responsibility lies with the specifying engineer.
The question for engineers, business owners, safety managers etc is what steps to take next after defining and categorizing the Risk and Hazard.
The first choice is to Eliminate the hazard, this is the most effective control measure and must always be considered first. If the hazard cannot be eliminated completely then there are a number of control options that can be used to prevent or minimize exposure to the risk.
- Substituting the risk for a lesser one
- Redesigning the equipment
- Isolating the hazard
- Establish safe work practices
- Personal Protective Equipment.
So why then do we start electrical safety with a focus on protection rather than prevention? We quite readily invest in and offer safety awareness training, we purchase and post warning signs, we insist on safety goggles and gloves and perhaps even PPE (Personal Protective Equipment) but we do not invest in prevention and take the steps necessary to eliminate or reduce the likelihood of a hazardous electrical incident.
Administration and the use of personal protective equipment are the lowest priority on the list of controls and should never be relied on as a primary means of risk control. Personal Protective Equipment should be used as a last resort when exposure to risk is not or cannot be minimized by other measures.
Elimination of the Hazard
In practice, the majority of electrical faults experienced in industrial low-voltage systems are phase-to-ground faults. For solidly grounded wye systems, the IEEE Red Book (Std 141-1993, Section 7.2.4) states that "A safety hazard exists for solidly grounded systems from the severe flash, arc burning, and blast hazard from any phase-to-ground fault.” The same standard recommends a solution to resolve this issue. Section 7.2.2 of the IEEE Red Book states that when using high resistance grounding, "There is no arc flash hazard, as there is with solidly grounded systems, since the fault current is limited to approximately 5 A.” The Red Book is referring here to phase-to-ground faults.
High resistance grounding (HRG) of AC electrical systems allows continuation of power to the circuit while maintenance personnel isolate the faulted equipment. This permits avoidance of an unplanned shutdown of a continuous process facility.
High resistance grounding, as a technology, was originally applied to industrial power distribution systems in industries as diverse as: food processing, mining, petrochemical and even commercial installations such as airports, data centers, etc. The main driver was to enhance the reliability and availability of power distribution equipment and prevent unplanned outages. HRG has also proven to be very effective in significantly reducing the frequency and severity of arc-flash accidents by limiting ground fault currents during the first phase to ground fault conditions.
Figure 5. Arc Flash Characteristics
Industry data indicates that 85% to 98% of electrical faults start as phase-to-ground faults. Resistance grounding inserts impedance between the transformer neutral and ground and limits the ground fault current to less than 5 amperes. With the ground fault limited to a low value, there is insufficient fault energy for the arcing to take effect. The hazard frequency is reduced during the first phase to ground fault. The first phase to ground fault normally initiates an alarm to allow isolation of the faulted equipment or circuit before the fault can escalate to phase to phase to ground fault. In fact, the NFPA 70E -2009 Standard for Electrical Safety in the Workplace states in section 130.2 FPN No.3 "Proven designs such as arc-resistant switchgear,…high-resistance grounding and current limitation….are techniques available to reduce the hazard of the system”. OSHA subpart S issued on February 14 2007, and effective on August 13, 2007 is based on NFPA 70E.
Substitution of the Hazard
An arc is developed in milliseconds and leads to the discharge of enormous amounts of energy. The energy discharged in the arc is directly proportional to the square of the short circuit current and the time the arc takes to develop, i.e. energy = I2t
The damage resulting from the arc depends on the arcing current and time and of these two factors time is the most easily controlled and managed. Rules of thumb for different arc burning times are:
- 35 ms or less – no significant damage to persons or switchgear which can often be returned to use after checking for insulation resistance
- 100 ms – small damage to switchgear that requires cleaning and possibly some minor repair. Personnel are could be at risk of injuries.
- 500 ms – catastrophic damage to equipment and personnel are likely to suffering serious injuries.
The goal of arc mitigation technology is to protect personnel and property and to effectively accomplish this we must first detect the arc and then cut the flow of current to the arc in as short a time as possible. As noted above the target is to achieve a total reaction time of 100ms or less from detection of the arc to isolation of the circuit.
Current-limiting fuses are often used in the design of electrical distribution systems to protect electrical equipment under high available short-circuit conditions (NEC110.10). They are able to protect the equipment from the significant thermal damage and magnetic forces associated with high short-circuit currents by actually reducing the current that flows and the time that it flows. Within their current-limiting range, they keep the current from reaching its peak during the first ½ cycle. And because they can react so quickly, the current is driven to zero in as little as ¼ cycle, or even less.
This great reduction in damaging current and time not only protects equipment from significant short-circuit currents, but naturally also helps protect workers that might be exposed to horrendous arc-flash energies. The difference between a 30,000-ampere arcing fault that lasts for 30 cycles, and a let-through arcing current of 1,000 amperes that lasts for ¼ cycle can be the difference between a worker driving home after work and a ride to the morgue.
An arc is accompanied by radiation in the form of light, sound and heat. Therefore the presence of an arc can be detected by analyzing visible light, sound waves, and temperature change. To avoid erroneous trips it is normal to use a short-circuit current detector along with one of the aforementioned arc indicators and the most common pairing in North America is current and light.
The burning of the arc heats up the ambient air causing it to expand and create a measurable increase in pressure inside the switchgear. In Europe it has become common practice to use the combination of light and pressure as positive indicators of an arc. The pressure sensor has an operating time between 8ms and 18ms and when combined with a circuit breaker with an operating time between 35ms and 50ms we have achieved our goal of 100ms or less.
However, many older circuit breakers operate closer to 80ms and these require to be paired with a faster acting arc detection device. Arcs produce light at intensity levels that excess 20,000 lux. This can be detected through special optical sensors connected to a relay system that has a typical operating time under 1ms and is the fastest arc flash detection technology currently available. The operating time is independent of the fault current magnitude since any current detector elements are used only to supervise the optical system.
With optical arc protection technology installed the relay operating time is essentially negligible compared to the circuit breaker operating time and the cost is fairly low since current transformers are only needed on the main breakers. Again, if we sum up the circuit breaker operating time and the optical arc detection time we are well below the goal of 100ms regardless of the age and speed of the circuit breaker and have mitigated the damage to a more reasonable level.
Isolating the Hazard
Arc resistance switchgear is designed to contain the hazard and vent the destructive energy away from personnel. The remains damage to the capital equipment but less than in conventional switchgear, there remains process interruptions but perhaps less than in conventional switchgear but personnel are isolated from the hazard.
Remote racking and remote switching ensures that personnel are not in close proximity to electrical switchgear in the event of an arc flash incident. Neither affects the frequency or severity of the hazard and the consequential impact on equipment damage and process interruptions but both ensure a lower risk of injury to personnel.
If we deploy proven technology such as High Resistance Grounding to reduce the frequency of the ground fault and arc flash hazard to OCCASIONAL or REMOTE and we take steps to reduce the impact of the hazard through the use of current limiting fuses or fast action optical relays to MARGINAL or MINOR, if we isolate personnel from the Hazard through arc resistant switchgear or remote racking then we can achieve a LOW risk from Electrical Hazards. We have the technology and the management tools to make the difference between sending 5 to 10 persons per day to hospital due to arc flash explosions to 5 to 10 per month.
Let’s get serious about Electrical Safety.
Read more by Andrew Cochran
Posted By Steve Douglas,
Tuesday, March 01, 2011
Updated: Wednesday, January 09, 2013
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CSA Standard C22.6 No. 1-11,Electrical Inspection Code for Existing Residential Occupancies,is a new Canadian standard developed to establish a minimum level of safety in existing residential occupancies and was published in February 2011.
The Electrical Inspection Code for Existing Residential Occupancies will be a National Standard of Canada, published in English and French. Although it has been drafted using Code format and language, this standard is a voluntary standard until adopted as regulation by an authority having jurisdiction. It was developed by a Technical Subcommittee with members representing the following industries and interest areas: the International Association of Electrical Inspectors, insurance, regulatory, fire marshals, forensic investigation, electrical product and wire and cable manufacturers, contractors, education, consumers, home inspectors, pool and hot tub industry, and certification organizations.
Aging electrical systems have been the subject of much research, and we would like to acknowledge David Dini of Underwriter Laboratories Inc. and the NFPA Fire Protection Research Foundation for their paper "Residential Electrical System Aging Research Project ”that helped frame some of the needs addressed by the new standard.
CSA Standard C22.6 No. 1-11
The body of the standard contains the main criteria for the evaluation of residential occupancies with related explanatory notes in Annex A. Annexes B and D feature a model checklist and guide for application and enforcement. The standard is limited to existing installations and does not overlap or conflict with the Canadian Electrical Code, Part I. The scope explicitly states that Electrical Inspection Code for Existing Residential Occupancies does not cover new installations or maintenance as covered by the Canadian Electrical Code, Part I.
The Canadian Electrical Code, Part I was first published in 1927. Since 1927, twenty-one editions of the code have been published and the next edition will be published January 2012. Throughout the years, the code has constantly evolved to improve the minimum level of safety. However, this evolution has made it more difficult for inspectors who must inspect existing installations constructed under previous editions of the Code. Most jurisdictions, when inspecting existing installations, will inspect to current code in the absence of any other requirements. The Electrical Inspection Code for Existing Residential Occupancies fills this need by providing a common standard for inspection. To assist with inspection of older installations, the standard features Annex C with a chronological history of code changes relative to residential occupancies. For example, readers will learn from Annex C that the Canadian Electrical Code first required a bonding connection for all non-metallic wiring methods and outlets in the 1958 edition.
Annex E provides a list of minimum safety requirements that the authority having jurisdiction can apply to existing residential occupancies. As an example, Clause E.4.2 would require receptacles installed outdoors and within 2.5 m of grade, other than automobile heater receptacles located in parking lots and intended solely for use as automobile heater receptacles, to be protected by a ground-fault circuit interrupter of the Class A type. It is recognized that the application of requirements in Annex E could be controversial, as they may necessitate upgrading of existing installations. For this reason, Annex E and Clause 4.5 have been structured to allow an authority adopting the standard as regulation to easily include or exclude the minimum safety requirements contained in this Annex.
Read more by Steve Douglas
Posted By Stephen J. Vidal ,
Tuesday, March 01, 2011
Updated: Wednesday, January 09, 2013
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A little bit of history is in order before we get into AC and DC circuit theory. In the latter part of the 19thcentury there were three principal players in the electrical generation and transmission industry. Thomas Edison, known as the "Wizard of Menlo Park” and most famous for his invention of the electric light bulb, was the main proponent of direct current (DC) transmission. George Westinghouse and Nikola Tesla were the main proponents of alternating current (AC) transmission. History documents this formative period in the development of electrical generation and transmission as the "War of Currents.”
Edison has been portrayed as the tireless inventor filing more than 1000 patent applications with the U.S. Patent Office. Since he was more of an inventor than a mathematician or physicist, he was not very receptive to the analytical complexities of alternating current. Tesla was quite the opposite in that he developed many theories concerning single-phase and polyphase systems. Westinghouse was an inventor like Edison, but he was also an engineer. He provided the financial backing for the development of a working AC network. It is noted in the literature that Edison went to great lengths to discredit AC power and its unsafe nature. He carried out many public relations campaigns by electrocuting animals with AC power. In the end, Westinghouse’s development of the transformer allowed alternating current to be the correct choice for power generation and transmission.
Every time you start your vehicle, run a cordless drill, or use any type of electronic equipment you are using DC. The battery in your vehicle uses chemical energy to separate positive and negative charge thereby developing a potential difference between its terminals to produce 12 VDC to crank the engine. The battery in your cordless drill uses a similar mechanism to power the drill’s motor. The electronic equipment you use every day, excluding portable equipment, converts the incoming AC supply to DC through a process known as rectification. Figure 1 is an example of a constant DC waveform.
The lights in your office, the receptacles you plug devices in within your home, and the large motors in a manufacturing facility are examples of equipment that use AC. AC power is generated and distributed in the United States at a frequency of 60 Hertz. The AC waveform is time varying and uses a sinusoidal function to model its behavior. Figure 2 illustrates a sinusoidal AC waveform.
There are five electrical properties that have to be introduced in circuit theory to help with the analysis. These are resistance, capacitance, inductance, reactance, and impedance. The standard symbols for resistors, capacitors, and inductors are shown in figure 3.
Resistance (R)can be defined as the property of a material to oppose movement of charge or current flow. The unit of resistance is the ohm. Resistors are components that oppose current flow. Figure 4 illustrates a circuit with resistors in series and a circuit with resistors in parallel. It is important to note that in a series circuit the current is the same through each element, and in a parallel circuit the voltage is the same across each element.
Capacitance (C)can be defined as the property of a material to oppose any change in voltage across the material. The unit of capacitance is the farad. Capacitance occurs when two conducting materials are separated by an insulator. In a parallel plate capacitor two conducting plates are separated by an insulator known as a dielectric. The capacitor has the ability to block DC signals and pass AC signals. Under steady state conditions the capacitor acts like an open circuit to DC and a frequency selective device to AC. Figure 5 illustrates a circuit with capacitors in series and a circuit with capacitors in parallel.
Inductance (L)can be defined as the property of a material to oppose any change in current through the material. The unit of inductance is the henry. All conductors even those not coiled have some inductance. Under steady state conditions the inductor acts like a short circuit to DC and a frequency selective device to AC. Figure 6 illustrates a circuit with inductors in series and a circuit with inductors in parallel with no mutual coupling.
Figure 3. Electrical Components
Reactance or more specifically capacitive reactance (Xc) and inductive reactance (Xl) can be defined as the opposition to current flow these components present under AC conditions. The unit of reactance is the ohm. These devices change their reactance based on the applied frequency.
Impedance (Z) can be defined as the total opposition to current flow presented by the combination of resistance and reactance in an AC circuit. The unit of impedance is the ohm. Under steady state conditions impedance allows for the analysis of a complex AC network in the frequency domain using the same techniques that would be used in a simple DC circuit.
Figure 4. Resistor Circuits
Useful Theorems.We have already mentioned Ohm’s Law. Two other very useful network theorems are Kirchhoff’s Voltage Law (KVL) and Kirchhoff’s Current Law (KCL). KVL states that in the closed loop of a circuit, also called a mesh, the algebraic sum of the voltage drops and voltage rises equals zero. KCL states that the algebraic sum of current at a node, where a node is defined as a junction of three or more current paths, equals zero.
Five other network theorems that are extremely useful for circuit simplification and analysis are:
- The Superposition Theorem
- Thevenin’s Theorem
- Norton’s Theorem
- The Maximum Power Transfer Theorem
- Delta/Wye – Wye/Delta Conversion Theorem
Figure 5. Capacitor Circuits
The Superposition Theorem allows you to solve complex networks with multiple voltage sources. Thevenin’s Theorem allows you to convert a complex network into a simple circuit with a Thevenin’s equivalent voltage source and a Thevenin’s equivalent series resistor. Norton’s Theorem allows you to convert a complex network into a simple circuit with a Norton’s equivalent current source and a Norton’s equivalent parallel resistor. These three network theorems are very useful in electronics applications. The Maximum Power Transfer Theorem states maximum power is transferred from the source to the load when the internal resistance of the load matches the internal resistance of the source. This theorem is very useful in power and communications applications. The Delta/Wye – Wye/Delta Conversion Theorem allows you to convert back and forth between a Delta-connected network and a Wye-connected network. This theorem is very useful in power and electronics applications.
This article provides an overview of basic circuit theory. The principles learned in DC circuit analysis with resistive networks can very readily be applied to AC networks with capacitors and inductors. Once the values of capacitance and inductance are converted to their corresponding values of capacitive reactance and inductive reactance at the specified frequency, the new values of complex impedance can be used to solve for circuit parameters with the same methods used in resistive networks.
Figure 6. Inductor Circuits
Read more by Stephen J. Vidal
Posted By Randy Hunter,
Tuesday, March 01, 2011
Updated: Wednesday, January 09, 2013
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Welcome back as we continue to discuss the 2011 National Electrical Code for the combination inspector. We are finally getting into the body of the code with Article 110, which covers the basic requirements for electrical installations and applies throughout the code, unless specifically overruled in any article in chapters 5 through 8. Some of the items covered in this article are the requirements for examination, installation and use, terminations, and access to and spaces about electrical equipment. Over the years I’ve often had inspectors and electricians ask me where in the code it states some basic rule, and more often than not it is a requirement in Article 110.
The first requirement is in 110.2, which is a very simple statement that conductors and equipment shall be acceptable only if approved. We’ve already covered whatapprovedmeans in a previous article, but for review it means identified, listed, labeled, or approved by the AHJ.
Next we learn the eight conditions considered for examination, identification, installation and use of equipment. Some of the more important considerations are: mechanical strength, electrical insulation, heating effects and arcing effects. For the complete list please refer to 110.3(A). Even the full list includes only some of the conditions that may need to be considered for equipment. The code can’t possibly cover all the requirements for all types of equipment, which is why equipment is made to a certain set of requirements known as astandard. These standards are created through a consensus process by various industry participants, and are a continuous work in progress as technology and manufacturing practices are always improving and changing. The last thing to consider in this area is that just because something is listed and labeled doesn’t mean that when it is installed it will be right. It is quite possible to install equipment in a manner not recommended or anticipated by the manufacturer. As a result, the code requires equipment to be installed in accordance with its listing and labeling and with any instructions included in the listing or labeling.
Voltages and Conductors
Photo 1. Common wire labeling information
We also have general rules for voltages, conductors and sizes of conductors. In summary, the voltage shall be the voltage at which the system operates and equipment must be rated not less than the voltage of the circuit it is used in. When the word "conductors” is used in the code, it is understood that it refers to copper conductors unless otherwise specified. This is done for simplicity when applying code, and it doesn’t infer that one type of conductor is superior to another or is preferred by the code. Wire is sized in either American Wire Gauge (AWG) or circular mils for the larger sizes. When we use circular mils, the size is generally listed as a number of "kcmil,” meaning a thousand circular mils. For instance 250 kcmil means 250,000 circular mils. Outside of the code, you might still see references to "mcm” or "MCM” which is an old designation that means the same thing as "kcmil.” (See photo 1 for wire legend.)
Now comes one of the most basic rules. I still get a chuckle when I read 110.7, which is titled "Wiring Integrity,” which requires that we make installations without having any shorts or ground faults. My first thought is,Well, that’s obvious, but I guess we still have to have it in writing.
The next item of discussion I generally have with my classes is regarding fault currents. Available fault current is the amount of current that is able to be delivered to a system at a certain point. Fault current can be affected by several factors, including the distance from the source, size of the source, and the various components in the system. Fault currents generally run into the thousands of amps. It is not unusual to have over 50,000 amps of current available in larger systems and between 4,000 and 8,000 amps in residential systems, depending on how close you are to your transformer. So how do we control that large amount of fault current? Overcurrent devices have a rating known as ampere interrupting capacity (AIC), which indicates the amount of current a device can safely interrupt without causing catastrophic damage to itself. Breakers generally range from 5 kAIC to 65 kAIC, and of course the price increases as the interrupting capacity increases. Fuses also have these ratings, but the most common fuses used today have 200 to 300 kAIC. So from this discussion, we learn that we have to be aware of the fault currents in a system and whether or not our equipment can handle that fault current. In the 2011 edition of theNEC, we have some new requirements in 110.24 regarding the labeling of an installation with the available fault current and some requirements when modifications are made to the installation.
In some cases, we use a process known as "series rating” to handle the fault current while avoiding having to use overcurrent devices that are fully rated for the fault current. In a series rated system, the manufacturer has tested certain equipment components with other components and found that the upstream devices will limit the pass-through fault current to an acceptable level to prevent damage to the downstream device. The tricky part of this is that you have to make sure you only use items specifically tested as a series combination, and you cannot deviate from the exact system as tested by the manufacturer. This method is often frowned upon due to its potential compliance issues and the inability to alter the installed system. I’ve never been a fan of it myself, as it leads to field issues during work performed later or service work by those who do not recognize that they are dealing with a series system. "Series combination systems” are at times used for existing locations to prevent costly equipment changeouts; however, this has to be done under the supervision of an engineer. In either case, these systems must now be marked in a readily visible location. The labeling shall state that the system is a "Series Combination System Rated _____ Amps. Identified Replacement Components Required.” (See photo 2 for an example of series rating in a residential service panel.)
We continue now with some installation rules, the first of which states that we cannot expose items to environments for which they are not listed to be used. This could include water, gases, fumes or other environmental factors which would or could cause damage. The most obvious example is equipment intended for dry locations that is exposed to a wet environment.
Section 110.12 requires that installations shall be installed in a neat and workmanlike manner. This raises the question: what is a neat and workmanlike manner? This is one of those items that can be subjective and at times totally unenforceable, since what looks good to one individual may not look good to another. However, we can get some guidance from NECA Standard 1,Standard for Good Workmanship in Electrical Construction.
Photo 3. Securely mounted
This section goes on to require that when we have unused openings in equipment, we have to secure these and make sure they are properly closed to maintain the original integrity of the equipment. We also have to keep the equipment from being damaged or contaminated. This applies throughout the entire project, since contamination by plaster or paint can cause overheating and arcing. Often when we have a contamination issue due to construction activities, the next step is someone attempting to clean it. This often exacerbates the problem instead of solving it. I once found painters soaking large frame breakers in paint remover to get paint off of them; needless to say, we had to have brand new gear to fix that situation. (Also see photo 2 for warning about contamination warning.)
We are required to securely mount equipment. I have seen one prohibition in this rule on a high percentage of tests that people have taken for certification, and that is that we are not allowed to use wood plugs in masonry, concrete, plaster or similar materials. The reasoning is that wood plugs simply don’t hold up and are likely to pull out, so we don’t have a securely mounted system when we use wood plugs. (See photo 3 for a securely mounted example.) The next requirement deals with cooling and ventilation of equipment. Some equipment depends on natural circulation and convection for cooling. If equipment is designed to be installed in a certain manner to allow cooling, we have to recognize this and insure we get the installation done in the recommended manner.
Photo 4. Typical markings on a wiring lug
Termination requirements are a part of the code that I emphasize strongly, as I believe that many of the failures we have in electrical installations are directly related to improper terminations. Having done a lot on mechanical work through the years, I understand the critical nature of connections for many items. Whether it is an engine in a car or a receptacle in a house, if it is not connected properly it will fail. It’s just a matter of time until this occurs, and the time to failure is proportional to how poorly the connection is done. One consideration for terminations is the connection of dissimilar metals. Some materials will work with others and some will not, specifically copper and aluminum shall not be intermixed in a terminal where such intermixing causes a reaction. If a termination device is rated for both copper and aluminum, then it can be done. Most of our larger conductor termination lugs are now made of aluminum and are plated so they can be used with copper. (See photo 4 for information on a termination lug.) On smaller devices, it depends on how they are tested, so the rule here is that we have to verify the listing and labeling to see exactly what each termination is listed for. Sometimes this will require the installation instructions from the carton to verify.
Now that we have the materials issue considered, we have to verify that we make the connection to the approved tightness. This is done by verifying the torque value for that device and utilizing the proper tool to ensure we make that connection to that torque value. So is a standard screw driver or a folding Allen wrench set sufficient to make sure we get the right torque value? I venture to say no. I know from testing performed recently that approximately 75 percent of the terminations made without using the proper tool were not within the specification recommended by the manufacturer. (For more information on this study, go to http://www.iaei.org/magazine/?p=5017 and read the article "The Difference Between Success and Failure – How a Torque Wrench Improves System Reliability,” published July 2010.) Over 30 percent of the connections were less than half the recommended torque. (See photos 5 and 6 to see a torque screwdriver and a factory label showing torque values for terminations)
Photo 5. Torque screwdriver
So we’ve learned we have to pay attention to connections of wire to equipment, and this includes both large and small connections. To do this properly, we have to check the equipment to verify the type of conductor, the size of conductor, and method of connection (set screw, crimp, solder lugs, wire binding screw, or studs and nuts that have upturned lugs). Each type of device has a unique manner of installation which must be performed properly. For a typical aluminum lug, the device will usually be marked as AL7CU or AL9CU. Receptacles will be labeled CU, CO/ALR or AL/CU. The AL means that that device is ok to use with aluminum; CU means it is ok with copper.
Did you notice the 7 and the 9 in the label of the lugs in the last paragraph? This leads into another factor to consider when making terminations, the temperature rating of the termination. The 7 stands for 75°C, and the 9 stands for 90°C. In 110.14(C) we cover the temperature requirements. This temperature rating matches the ampacity or size of the conductor to the rating of the connection. Again, we have some general rules, and the first is that for equipment rated 100 amps or less or marked for 14 through 1 AWG wire, conductors shall be used at the 60°C ampacities in Table 310.15(B)(16). I know we haven’t gotten to chapter 3 yet, but Table 310.15(B)(16) lists the loads that are permitted for various wire types at various operating temperatures. The second general rule states that for equipment over 100 amps, terminations shall be used with wire rated 75°C.
Now you know things just can’t be as simple as that, and of course there are more exceptions and requirements. First, you can always use wire rated at a higher temperature as long as you do not load it more than the rating of the lug. For instance, you may use 90°C wire for a termination on a 60°C lug as long as you protect that wire with an overcurrent device that will limit the load on the wire to the 60° range for that size wire. Now for the second allowance, you may use wire at the 75°C range below 100 amps if the wire and the lugs are rated for 75°C. This naturally leads to the next question, well can I use wire at the 90°C rating if I have 90°C lugs? Well, not so fast. That would make sense, but there’s always a little hitch, and here is the hitch on this: even though we have lugs rated 90°C, the equipment which houses the devices with the lugs is rated only for 75°C. Therefore, we are limited to the 75°C ampacities on those conductors.
The issue isn’t quite as simple as it appears on the surface. Part of the design and testing of equipment and terminations is evaluating the dissipation of the heat that builds up at a termination point and in the equipment. So in order to get rid of the heat, the manufacturers rely on the conductor to provide a heat sink to conduct heat away from the device in many cases. Standards for many types of electrical equipment, such as panelboards, limit their use to 75°C, so manufacturers can’t list the equipment for 90°C. Heat is a critical factor for electrical equipment and, generally speaking, we try to control the temperature of our equipment and make sure it isn’t subject to overheating as this will lead to premature failure or nuisance failure.
To sum up the temperature portion of this area of the code, it is the principle of the weakest link in a chain. If you have any portion of a circuit that is rated at 60°C, then you are not allowed to load that circuit above the 60° ampacity rating of that conductor. So a 60°C conductor with 75°C lugs is limited to 60°C; or 75°C wire terminated on a receptacle listed at 60°C is again limited to 60°C. If everything is listed at 75°C, you can load that wire to the 75°C ampacity. If we install 90°C wire on 75°C lugs, again we would be limited to 75°C ampacity. So the obvious question at this point is, why do we have 90°C wire? We will get to that in a later article, and there is an advantage to using wire with a higher temperature rating.
We’ve covered a good portion of Article 110 to this point. In the next article we will continue with Article 110, covering working clearances and space around electrical equipment and requirements for electrical rooms. Until then, remember to review the code as you review these articles. I’m covering what I consider to be the highlights of the code and some of the ways to apply it, but there is no way to hit every little detail in an article so you’ll need to at least read through each of the provisions on your own. See you in the next issue.
Read more by Randy Hunter
Posted By Steve Terry, Mitch Hefter, Ken Vannice,
Tuesday, March 01, 2011
Updated: Wednesday, January 09, 2013
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Editor’s Note: this article first appeared in the Spring 2010 issue ofProtocol, the journal of PLASA (formerly known as ESTA), the lead international association for those who supply technologies and services to the event, entertainment and installation industries. Minor revisions have been made due to the publication of the 2011 edition of theNational Electrical Code®.
For some time, the proper control of emergency lighting circuits has been a topic of debate for manufacturers, systems integrators, and specifying electrical engineers. Much of the debate has centered on the proper application of the many codes and standards that apply to emergency lighting. These include:
ANSI/NFPA 70, National Electrical Code (NEC),Article 700, Emergency Systems
NEC Article 701, Legally Required Standby Systems
NEC Article 702, Optional Standby Systems
NFPA 110, Standard for Emergency and Standby Power Systems
NFPA 101, Life Safety Code
Underwriters Laboratories (UL) Standard 924, Emergency Lighting and Power Equipment
Underwriters Laboratories (UL) Standard 1008,Transfer Switch Equipment.UL1008 covers transfer switches that are rated for use in emergency systems and for other applications. Unless noted otherwise in this article, we are examining UL1008 transfer switches for emergency systems only.
Figure 1. Case 1 - Normal
(See sidebar at the end of the article for more information about theNECand these UL standards).
Each of these standards focuses on a specific area of emergency or standby lighting and power, or describes a specific piece of equipment somewhere in the path of the emergency or standby lighting or power circuit. However, it is not always easy to answer all application questions by searching these standards since they often point at each other, creating a circular answer, or in many cases, a lack of an answer. For the entertainment and architectural lighting industries, one of the burning questions has been: "Where is it appropriate to use a UL1008 emergency transfer switch, and where can a simpler UL924 load control relay be used to energize an emergency lighting circuit?”
Due to the relative cost and complexity of UL1008 emergency transfer switches, for many years the industry kept asking whether such a switch was really necessary for dimmer branch circuits, especially since in all likelihood there was another UL1008 switch somewhere in the building, transferring a main feeder between normal and emergency power. The answer to this question is not a simple one, and it requires a review of the full spectrum of options in the emergency lighting toolbox. Each of the following cases has a place in the design of emergency lighting systems. It should be noted that these case drawings have been simplified to illustrate functionality, and do not contain every detail of the circuits they describe.
Figure 2. Case 1 - Emergency
Case 1. Emergency-only lights on an emergency-only circuit
The Case 1 arrangement is probably the simplest possible way to energize emergency lighting fixtures. A number of emergency-only fixtures are dedicated to providing the minimum illumination levels required by the NFPA 101, Life Safety Code, or local building codes. The lighting fixtures are fed from a dedicated emergency-only breaker panel fed directly from the emergency power source, which may be a generator or uninterruptable power supply (UPS). When the source comes on line, the lights are energized without any switching or transfer equipment. The one disadvantage to this arrangement is that the emergency fixtures will be dark when normal power is present. This may be a visually unacceptable situation for the architect or lighting designer.
Case 2. Designated emergency lights with self-contained power source
Case 2 is familiar to anyone who has used self-contained battery pack emergency lights, sometimes called "unit equipment.” These units are listed under UL924 and contain a power source (usually a battery), a charger, and a load control relay. The unit is connected to normal power, which provides charging current for the battery. When normal power fails, the load control relay energizes the load. When normal power returns, the load is extinguished. For many years, battery packs were the norm for emergency lighting. They are inexpensive, but battery maintenance and the "car-headlight” look of the unit can be problematic. Case 2 can also use similar unit equipment that utilizes a recessed emergency luminaire which is more esthetically pleasing than a car-headlight battery pack.
Figure 3. Case 2 - Normal
Case 3. Normal/emergency lights on switches or wallbox dimmers
Case 3 introduces the concept of using the same fixture for both normal and emergency use. Normal/emergency lights are fed via a normal/emergency breaker panel and a wall switch, wallbox dimmer or other wallbox-mounted control device. When normal power fails, an upstream UL1008 emergency transfer switch automatically transfers the feeder of the breaker panel to an emergency power source. At the same time, a UL924 load control relay senses the loss of normal power upstream from the transfer switch and bypasses the switch or dimmer, forcing the load on, no matter what the position of the switch or dimmer. Note that the UL924 load control relay is not performing a transfer function, but merely a bypass or shunt function. Thus it is only required to switch the hot leg of the branch circuit. Some normal-power control devices, however, do not allow shunting (e.g., an autotransformer), and thus require a double-throw load control relay to disconnect the load from the normal control device before applying power to the load. While the double-throw construction of the relay can be misleading, this break-before-make bypass is not a transfer function. Case 3 always relies on the upstream UL 1008 emergency transfer switch for the transfer function.
Figure 4. Case 2 - Emergency
Case 4. Normal/emergency lights on a UL 924 listed dimmer rack or relay cabinet
Case 4 extends the use of the same fixtures for both normal and emergency use, because the fixtures are fed by a dimmer rack or relay cabinet that is listed for emergency use under UL924, as well as the more conventional UL508/UL891 listing. The dimmer rack contains a load control relay, or an electronic bypass method. When normal power fails, the entire feeder to the dimmer rack is transferred to an emergency source by an upstream UL1008 emergency transfer switch. Controls sensing normal feeder failure upstream from the transfer switch cause the internal load control relays or electronic bypass devices to energize selected circuits by bypassing dimmers, and forcing loads on, no matter what the state of the dimmer control system. Only those loads needed to reach minimum emergency illumination are energized, as allowed by NEC 700.23 (a new section in 2008). Note that the behavior of other circuits in the dimmer rack needs to be known when using this approach. If non-emergency circuits continue to respond to the control system when the rack is in emergency mode, then the size of the emergency source needs to accommodate these loads as well. A better solution is to use a UL 924 dimmer rack with load-shedding capability. This will insure that non-emergency dimmers are forced into an off condition at the same time that emergency dimmers are forced into an on condition when the rack is in emergency bypass mode. Note that NEC 700.23 requires all circuits leaving the dimmer cabinet to comply with Article 700 as emergency circuits, i.e., wired separately from all normal-only circuits, whether or not they are energized to get to the required illumination.
Figure 5. Case 3 - Normal
Case 4A. Normal/emergency lights on a dimmer system with an external UL 924 load control relay
Recently, external stand-alone UL924 load control relays have become available for bypassing circuits in a dimmer rack that does not have a native UL924 listing. It is this Case 4A that generates the most confusion, because, at first glance, the function performed by the relay looks like a transfer (which actually must be performed by a UL1008 emergency transfer switch), not a bypass. However, that is not the case, and here’s why: In this case, the load control relay switches the load between the dimmer output and an external circuit breaker connected to the same phase and power source as the dimmer. The single feeder to the dimmer rack is transferred by an upstream UL1008 emergency transfer switch, making one feeder operate as both the normal and emergency source for the dimmer rack. Therefore, the UL924 load control relay is providing a bypass rather than transfer function. As in Case 4, the state of the non-emergency circuits in the dimmer rack must be forced to off when in emergency mode. If not, the emergency power source must accommodate the full load connected to the rack, not just the emergency bypassed circuits. In practical terms, this gets tricky, because it requires interaction between the emergency system and the dimmer control system. A better solution may be found in Case 5.
Figure 6. Case 3 - Emergency
Case 5. Normal/emergency lights on a UL1008 branch circuit automatic (emergency) transfer switch
Case 5 describes a design widely adopted by the industry. The dimmer rack is fed by normal power only, and shuts down during a normal power failure. For each normal/emergency load, both the neutral and the hot conductor are transferred to a separate emergency source via a UL1008 branch circuit (emergency) automatic transfer switch (BATS). The switch is designed to insure that it can withstand the available fault current during transfer, and can never interconnect the normal and emergency power sources. In addition, the switch must work safely when the normal and emergency sources are on different phases and not synchronized. Case 5 is useful when a dimmer rack is fed by a very large feeder, but only a small portion of the branch circuits will be used for emergency. The use of the BATS allows those circuits to be selectively transferred to the emergency source without worrying about sizing the emergency source to deal with the full capacity of the dimmer rack feeder. The downside to Case 5 is the size, cost, and complexity of the UL1008 switch.
Figure 7. Case 4 - Normal
What does UL say about emergency circuits, UL924 and UL1008?
Recently, a number of manufacturers of UL924 load control relays have produced products with installation manuals that suggested the relays could be used for Case 5 applications, where the load was transferred rather than bypassed. In the Spring 2005 issue of The Code Authority (UL’s newsletter on code issues), the article "Focus on Emergency Lighting Equipment” appears on page 3. In the second paragraph, that article states, "An important issue to recognize is that an LCR does not switch the load between the normal and emergency supplies. Load switching of this type should only be performed by a[n emergency] transfer switch listed in accordance with UL1008, Standard for Safety for Transfer Switch Equipment. An LCR has only one power input source, and that is connected to the emergency power supply.”
Figure 8. Case 4 - Emergency
In addition the UL White Book clearly differentiates Automatic Transfer Switches for Use in Emergency Systems (product category WPWR), Automatic Transfer Switches for Use in Optional Standby Systems (WPXT), and Automatic Load Control Relays (product category FTBR).
It is also important to note that NEC 700.5(C) states two clear requirements: "Automatic transfer switches shall be electrically operated and mechanically held. Automatic transfer switches, rated 600 VAC and below, shall be listed for emergency system use” (authors’ emphasis). Be aware that some products marketed as automatic transfer switches and listed under UL 1008 are for optional standby systems (NECArticle 702), not emergency use. These same devices may be also listed under UL924 as an emergency bypass device. See sidebar for further discussion on the difference between an emergency circuit, a legally required standby circuit, and an optional standby circuit.
New Sections in NEC-2011
Figure 9. Case 4A - Normal
New language was added to the 2011 edition of the NEC.
"Relay, Automatic Load Control.A device used to energize switched or normally-off lighting equipment from an emergency supply in the event of loss of the normal supply.
"Informational Note: For requirements covering automatic load control relays, see ANSI/UL924, Emergency Lighting and Power Equipment.”
"700.24 Automatic Load Control Relay.If an emergency lighting load is automatically energized upon loss of the normal supply, a listed automatic load control relay shall be permitted to energize the load. The load control relay shall not be used as transfer equipment.”
Figure 10. Case 4A - Emergency
How do I choose the right emergency control method for my application?
For each project, the emergency system designer must review the field conditions and examine the pros and cons of each approach to arrive at the most economical but safe system. The first step is usually to determine whether a true Article 700 emergency system is required or whether something less, like an Article 702 optional standby system, is acceptable. If the project includes specifying the primary automatic emergency transfer switch at the service entrance and generator, then UL1008 equipment is required and NFPA110 will most likely apply. If the project requires a branch circuit emergency transfer switch (BATS), the expense of a UL1008 emergency transfer switch is still required but the auxiliary equipment specified in NFPA110, such as generator start-up controls, is not. This auxiliary equipment will be provided by the primary UL1008 transfer switch at the service entrance. If the project is to turn on an emergency circuit controlled by a wallbox dimmer, a UL1008 emergency transfer contactor is a bit expensive, while a UL924 bypass relay is sufficient.
Figure11. Case 5 - Normal
After selecting the proper approach to the project, equipment must be selected that functions together as a system to meet the safety objectives of the project. A UL1008 automatic emergency transfer switch is designed for the conditions found on feeder circuits. In addition to being safe, it must have sensing circuitry to automatically transfer on failure of the normal source to assure the transfer happens automatically and reliably.
On the other hand, UL924 equipment covers a broader range of devices and applications, is subject to less rigorous testing and may be subject to misapplication unless the system designer is careful. Unit equipment, exit luminaires and recessed emergency luminaires will probably have all the elements required to make a functional emergency system. Other stand-alone UL924 components may not. For instance, Listed UL924 metering devices are available to sense normal feeder failure, but they will not be of much use if not mated with a suitable power switching device. There are listed UL924 power switching devices that, if not connected to correctly sense the upstream normal feeder, will turn the emergency illumination on when the branch circuit loses normal power but will turn off again when the generator takes over. How each piece of equipment functions must be researched in order to make the design work as a system. What doesn’t work is to haphazardly choose UL1008 listed equipment or UL924 listed equipment and assume you have successfully completed the project.
From the above, it can be seen that there are a number of code-compliant methods for energizing emergency lighting circuits. Whichever method is used, the system must meet the following rules:
Figure 12. Case 5 - Emergency
When transferring a load between a normal and emergency power source, either in a feeder or branch-circuit application, a listed UL1008 emergency transfer switch must be used.
A dimming system with a dual listing under UL924 and UL508/UL891 may be used to energize emergency lights.
An external UL924 load control relay may be used to bypass a switch or dimmer to energize emergency lights, but may never be used to transfer emergency lights between a normal and emergency power source.
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Posted By Paul Molitor,
Sunday, January 02, 2011
Updated: Thursday, September 06, 2012
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There are many terms used in the context of Smart Grid: demand response, distributed generation, advanced metering infrastructure, home-to-grid, and electric transportation to name a few. Meanwhile, the U.S. government has committed $3.4 billion in stimulus grant funding and upwards of $11 billion (depending on how you read the federal budget numbers) to the development of Smart Grid.
Focusing on the technical level can lead to a very confusing landscape of bits, bytes, and applications. It makes it difficult to understand just what the heck is happening as we move toward the concept of a "Smart Grid.” This confusing technical picture and boat load of funding in the pipeline really begs the question, "What is Smart Grid and what are we getting for our money?”
When you start shopping for a definition of the Smart Grid, you will find that for every website you visit, you will find a different (albeit somewhat similar) answer. Mike Oldak of the Utilities Telecom Council said, "If you put 10 consultants in a room, you’ll come out with 15 different definitions for Smart Grid.”
Even the Smart Grid Interoperability Panel, a public-private partnership formed by the National Institute of Standards and Technologies (NIST) for the specific purpose of identifying standards for Smart Grid, has avoided the problem of trying to create a definition. In NIST Special Publication 1108 NIST Framework and Roadmap for Smart Grid Interoperability Standards, Release 1.0, there are discussions of key concepts, applications, and requirements, but no formal definition of a "Smart Grid.” Although it seems illogical on the surface, this is really the right thing to do.
In general, we speak of "the grid” as though it were a single object, when really it is a collection of systems and devices that serve a single purpose, namely the delivery of electricity. True grid-heads might try to tack on more industry-based concepts including "generation,” "transmission,” and "distribution” to the idea of delivering electricity, but I propose that it’s only natural, and understood, that it is impossible to really deliver something unless it’s been previously made and moved. Just as we have come to speak of the Internet with no real understanding of all the things that must come together in order to provide the content and applications that each of us accesses every day, so too is there a grid-head concept that by some magical means, electricity is delivered to the plug in the wall. In that sense, it’s somewhat of an injustice to even attempt to create a definition for "Smart Grid.”
Home Energy Dashboard
So what are we doing?
To put it into perspective, think about another technological advancement—the automobile. When cars were first developed, they had no instrumentation. It wasn’t until some time later that gas, oil, and temperature gauges, as well as speedometers, tachometers, and turn-signal indicators were installed. I would venture to guess that every person reading this article has at least as much interaction with the electric grid—if not more, on a daily basis—as with a car. But what kind of information do you have about your electricity usage?
Thomas Edison is credited with launching the first electric grid in Manhattan in 1882, while Karl Benz invented the automobile in 1894. Even with a 12-year head start, we know much less about our electricity consumption than we do about the fuel consumption in our automobiles. This fact is easily illustrated through two simple questions: What would you expect to pay for a gallon of gas today? What would you expect to pay for a kilowatt-hour of electricity today?
Keeping the automobile example in mind, one of the first goals of Smart Grid is to add instrumentation to the grid. What makes this possible, and therefore the first enabling feature for Smart Grid, is our ability to provide two-way communication flows. With the ability to communicate effectively, we can not only feed more information back to the utility operators to improve the grid’s overall performance, but also provide direct and immediate feedback to the consumers about their electricity usage—a home energy dashboard, if you will.
With additional instrumentation inside the home through the development of smart appliances and manageable plug-in devices, every consumer will have the ability to observe, on a near real-time basis, exactly where the money is being spent on the electricity bill. Coupling this with additional data from the utility, a homeowner could compare the current day’s usage to a previous day, week, month, or year. With just a modest level of cooperation from the utility company, a home-owner could also compare individual data with the average residential consumption within his or her ZIP code. All of this knowledge, all of this control, all of this useful information is made possible by the simple act of enabling two-way communication on the grid.
But wait, there’s more.
In many utility areas, various tax credits and other benefits are being offered to homeowners who install wind turbines or solar panels. If you would have done this in the past, any electricity generated by those devices that went unused by the homeowner would have simply been wasted. Now, however, the means exist whereby a consumer can actually sell that unused power back to the utility company. This "feed-in” service permits the homeowner to more quickly recover the cost of installing a renewable energy device. This is huge!
This concept not only works with residential renewables, but also with electric vehicles (EV). When not needed for transportation, the electricity stored in an EV battery could be used to deliver power to some other person or device that really needs it. Picture a hospital parking garage filled with electric vehicles, each of which holds various amounts of electric charge. If the power goes out, those vehicles could be used to supply electricity to the hospital until the local emergency generator is started. What if the original power outage was caused by a lightning strike to that generator permanently disabling it? Tapping the nearby EVs could literally be a life-saving technology
The second enabling feature of Smart Grid is the ability to support two-way power flows. This enables a consumer to become a producer when producing (or storing) excess power, and then revert to being a consumer when in a power deficit. A homeowner with a rooftop solar device can sell power to the grid during the day while at work and home demand is low, then buy power back at night when it is time to power the microwave, big screen television, or even the cell phone charging station.
The Grid of the Future
With the two enabling features in place, practically everything we want to accomplish with the Smart Grid starts to fall in line:
On a hot summer day, when facing a possible shortage of electric power, the utility company can send a signal that causes a number of residential thermostats to adjust, thus preventing a blackout (demand response).
Appliances, such as the defroster in your refrigerator, can program themselves to run at night when the demand for electricity is lower and therefore cheaper ("smart” appliances and time-of-use pricing).
Faults in the electric current can be detected and reported to the utility, thus minimizing downtime. At the same time, power can be re-routed around those faults so that the fewest number of customers are affected (distribution automation).
Renewable sources are readily incorporated in the grid, and EVs become widely adopted (greenhouse gas reduction).
Fewer electric generating plants are necessary in order to maintain power quality for the customer base (grid optimization).
In the grand scheme of things, we’re just getting started in terms of enabling the Smart Grid. Clearly the vision of a better electrical future exists, but the path to that future remains somewhat unclear. The challenge that the electricity industry faces, is how to apply what we know about technology in order to realize that vision.
Read more by Paul Molitor