Here are some common questions regarding current-limiting fuses, hazard analysis and safe work practices, along with answers provided by Mersen engineers. Have a question you don't see answered? E-mail us or call Technical Services.
What is the reliability of overcurrent protection over time?
Amp-Trap 2000® fuses can be expected to provide reliable current-limiting performance for over 20 years if they are not physically damaged or continually utilized above their ampere rating. Since the current-limiting action of a fuse requires a fixed mass of copper or silver to melt, the fuse's speed of response is not affected with the passage of time. Consequently, there's no need for the periodic recalibration that might be required for an electromechanical device.
I've heard that under certain conditions, current-limiting fuses can allow for high incident energies when the fault current is low. What can we do in these cases?
Tests have shown that under most conditions, Class J, Class RK1 and Class T fuses can limit incident energies to low levels at typical working distances. The key to acceptable arc flash mitigation is to apply the fuse where the expected level of arc fault current will be large enough to drive the fuse into current-limiting mode.
Many times, the switch from Class RK5 fuses to Class RK1 or Class J fuses addresses the issue of lower fault currents. Going to lower ampere ratings where load currents allow can also address these issues. For applications where the expected arc fault current would be lower than current-limiting threshold of these fuses, consider Mersen's Amp-Trap® High-Speed J fuse.
For arc flash calculations, are fuses from various manufacturers interchangeable as long as the UL class stays the same?
For most applications this is true. However, there may be cases where certain brands may have superior performance compared to other fuses of the same class. An example is the Amp-Trap® High-Speed J.
Originally designed to provide protection for semiconductors in soft-starters, the High-Speed J has a low current-limiting threshold that provides a wider range of low arc flash energy protection. Plus, it's usually easier to ensure fuse coordination when you standardize on one brand of fuses.
It seems like selectivity is always lost when current-limiting fuses are used. True?
False. In fact, quite the opposite is true. Amp-Trap 2000® fuses will be selective for all levels of overcurrents, as long as the ampere rating of the upstream Amp-Trap 2000 fuse is twice that of the downstream fuse.
During a flash hazard analysis, is it necessary to calculate arc fault current when using current-limiting fuses?
When using Amp-Trap 2000® fuses, it's possible to perform the analysis knowing only the bolted-fault current, if that current is above the minimum shown in the incident energy charts. These charts are based on a model that was tested extensively in our lab under conditions believed to yield worst-case results. Be sure to read the criteria carefully to ensure that these charts apply to your applications. To get projected energies, use our online Arc Flash Calculator.
When using a current-limiting fuse, how can you calculate the arc flash current when you know the short circuit current?
Arc fault currents can be estimated through various models, such as the method identified in IEEE 1584, Guide for Performing Arc Flash Calculations. This would be necessary if the calculated bolted-fault current is lower than the minimum bolted-fault current in the incident energy charts provided for the current-limiting fuse.
We have a small organization with various 480V at 600 MCCs. Is it possible to perform our own study or do we need to enlist an engineering company?
Although it is certainly possible to perform your study using tools such as those provided with IEEE 1584, Guide for Performing Arc Flash Calculations, there may be benefits in working with an engineering firm. They include the extra manpower, the availability of expensive software tools, better familiarity with standards and regulations, and improved efficiency.
Are arc flash calculations required for control panels containing only finger-safe terminals and insulated cable?
At this time, most experts recommend calculations for such panels because of field experiences. Although IP20 grade finger-safe devices do minimize the probability of incidental contact, they are likely to be compromised in the presence of an arc flash explosion. If there is a possibility of an arc being established, you will need to take the steps necessary to protect workers from the potential hazard.
While checking for "no voltage" after deenergizing a circuit, do the requirements for PPE still apply?
Yes. Until it is proven that the equipment is electrically safe, workers must use the PPE that would be appropriate for the task if the equipment were in an energized state. Errors in one-line diagrams, labeling errors, opening the wrong disconnect device, and back-fed equipment are some of the situations where equipment could still be energized while workers are doing the verification. Without the proper PPE, workers could be seriously injured.
What is required of infrared thermographers who do not open or touch equipment, but only view the equipment through an IR imager (camera) after the panels have been opened?
If thermographers go within the safety boundaries delineated in NFPA 70E, they need to comply with the appropriate guidelines. If, for example, they need to operate within the flash-protection boundary, they need to wear the PPE and fire-resistive clothing dictated by the calculations at their closest working distance.
Articles and White Papers
© 2012 IEEE. This material is posted here with permission of the IEEE.
© 2010 IEEE. This material is posted here with permission of the IEEE.
© 2007 ICEFA. This material is posted here with permission of the ICEFA.
© 2007 IEEE. This material is posted here with permission of the IEEE.
© 2005 IEEE. This material is posted here with permission of the IEEE.
© 2004 IEEE. This material is posted here with permission of the IEEE.
Arc Flash Note 1: Multiple Hazards of Arcing Faults
Arc Flash Note 2: Reducing Arc Energies with Current-Limiting Fuses
Arc Flash Note 3: Arc Flash Hazard Analysis
Arc Flash Note 4: Reduce Arc Flash Energies by Upgrading to A6D Class RK1 Fuses
Arc Flash Note 5: Reduce Arc Flash Energies by Reducing Fuse Ampere Rating
Arc Flash Note 6: Reducing Arc Flash Energies on Transformer Secondaries
Component Protection Note 2: Enhancing Short Circuit Safety with Type 2 Coordination for Motor Starters
Component Protection Note 4: Important Changes to UL 1449 Safety Standards for Surge Suppression
Photovoltaic Protection Note 5: Sizing Fuses for Photovoltaic Systems per the National Electrical Code
Standards & Codes Note 2: Critical Changes to the NFPA 70E Standard 2009 Edition
Standards & Codes, Note 4: Significant Changes to the NFPA70E Standard - 2012 Edition
Surge Protection Note 1: Introduction to Specifying Surge Protection
Surge Protection Note 2: Surge-Trap and the different kA Ratings
Arc Flash Articles
Calculating Arc Flash Hazard Levels, Pure Power, Winter 2008
Discover common mistakes in calculating arc flash hazard levels and how to avoid them.
Improving protection, reducing costs, PlantServices.com, March 2009
Every maintenance professional should know how to select the proper fuse for the application.
Is Your Electrical PPE Adequate?, Maintenance Technology, August 2007
Key Changes to the 2011 National Electric Code, IMARK NOW, November 2010
Mersen weighs in on the critical updates
Manage Your Fuse Inventory With 5S - Sort, set location, straighten, standardize and sustain to eliminate waste, Plant Services, 2011
Author: David Komm, Technical Services-Supervisor, Mersen
The Fuse Protection Review: Consolidating Inventory Reduces Costs and Upgrades Safety, Plant Services, June 2003
The time is now to implement 7 critical updates to NFPA 70E, Plant Engineering, July 2010
Books and Standards
To purchase any of these books and standards, simply click on the title.
Shock, electrocution, arc flash, and arc blast are responsible for one worker death per day and 3,600 disabling injuries per year on average in the United States. Now NFPA 70E — the Standard developed for OSHA — is revised to address safety gaps and increase electrical worker protection, while helping companies comply with OSHA 1910 Subpart S and OSHA 1926 Subpart K. Major changes recognize new hazards and address safety gaps.
Electricity and its dangers are not selective — they put both experienced and inexperienced workers at deadly risk. Every year some 3,600 workers are permanently disabled, and, on average, one worker per day is killed. Make sure you understand and can apply the strengthened safeguards in the 200129 NFPA 70E that can prevent electrical injuries and deaths. Protect your workers and your business with solid answers and advice in the 2009 NFPA 70E Handbook.
This guide provides designers and facility managers with techniques for determining arc flash hazard distances and the incident energy employees could be exposed to while working on or near electrical equipment.
Complete Guide to Arc Flash Hazard Calculation Studies, Jim Phillips
There are many codes and standards regarding electrical safety and the arc flash hazard. However, no individual standard ties together the requirements of an Arc Flash Hazard Calculation Study: Calculations, Practices, System Modeling, Analysis, Recommendations. Using a series of flow charts, examples and calculation worksheets, the study process is broken down into a detailed step by step approach.
A step-by-step guide to establishing a comprehensive electrical safety program.
This extensive guide from NFPA teaches individuals about safe work procedures and provides companies with a process for defining and implementing effective electrical safety programs.
This useful reference is provided by ESA, the company behind EasyPower® power engineering software.
For answers to your questions about arc flash hazards, current-limiting fuses and circuit protection in general, call or email any member of Mersen's Technical Services staff.
Technical Services: North America
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Email: Mike Lang
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Email: Dave Komm
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Email: Byron Jordan
- Short circuit hazards and protection
- Fundamentals of Arc Flash Hazards
- Fundamentals of low-voltage fuse classes
- Conductor protection
- Motor circuit protection
- Transformer protection
- Overcurrent protection coordination concepts
- Special considerations in series rating
- International fuses
- Fundamentals and application of medium-voltage fuses
- Fundamentals of semiconductor overcurrent protection
- DC circuit protection basics
Anyone, Anytime, Anywhere. That's Mersen's philosophy when it comes to ensuring that workers who specify or change fuses know the hazards of misapplications and the fundamentals of fuse safety.
When you standardize your fuse inventory on our Amp-Trap 2000® family of current-limiting fuses, we'll present customized in-house training sessions for your engineers, electricians and non-technical employees.
Whether you want to educate five people or 50, we'll provide you the training you want at times convenient to you — and at no charge. Here are just some of the topics we cover:
Click here to learn more about our training seminars.
National Electrical Code®, 2014 ed., National Fire Protection Association.
NFPA 70E: Standard for Electrical Safety Requirements for Employee Workplaces, 2012 ed., National Fire Protection Association.
D.R. Doan and R.A. Sweigart, "A Summary of Arc Flash Energy Calculations," IEEE Transactions on Industry Applications, Vol. 39, No. 4, July-August 2003, pp. 1200-1204.
T. Gammon and J. Matthews, "Conventional and Recommended Arc Power and Energy Calculations and Arc Damage Assessment," IEEE Transactions on Industry Applications, Vol. 39, No. 3, May-June 2003, pp. 594-599.
A.D. Stokes and D.K. Sweeting, "Electric Arcing Burn Hazards," International Conference on Electric Fuses and Their Applications, Gandsk, 2003.
R. Wilkins, M. Allison and M. Lang, "Time-Domain Analysis of Arc Fault Hazard," International Conference on Electric Fuses and Their Applications, Gandsk, 2003.
IEEE 1584: Guide for Performing Arc-Flash Hazard Calculations, IEEE, September 2002.
R.L. Doughty, T.E. Neal, G.M. Laverty and H. Hoagland, "Minimizing Burn Injury: Electric Arc Hazard Assessment and Personal Protection," IEEE Industry Applications, May-June 2002, pp. 18-25.
R.A. Jones, L.B. McClung and J.J. Andrews, "NFPA 70E Changes for Year 2000," IEEE Transactions on Industry Applications, Vol. 37, No. 4, July-August 2001, pp. 1167-1173.
T. Gammon and J. Matthews, "Instantaneous Arcing-Fault Models Developed for Building System Analysis," IEEE Transactions on Industry Applications, Vol. 37, No. 1, January-February 2001, pp. 197-203.
R.L. Doughty, T.E. Neal, T.L. Macalady and V. Saporita, "The Use of Low-Voltage Current-Limiting Fuses to Reduce Arc Flash Energy," IEEE Transactions on Industry Applications, Vol. 36, No. 6, November-December 2000, pp. 1741-1749.
R.L. Doughty, T.E. Neal, T.A. Dear and A.H. Bingham, "Testing Update on Protective Clothing and Equipment for Electric Arc Exposure," IEEE Industry Applications, January-February 1999, pp. 37-49.
S. Jamil, H.L. Floyd and D.A. Pace, "Implementing Electrical Safety Regulations and Standards," IEEE Industry Applications, January-February 1999, pp. 16-21.
R.L. Doughty, T.E. Neal and H.L. Floyd II, "Predicting Incident Energy to Better Manage the Electric Arc Hazard on 600V Distribution Systems," Proc. IEEE PCIC, September 1998, pp. 329-346.
M. Capelli-Schellpfeffer, R.C. Lee, M. Toner and K.R. Diller, "Correlation Between Electrical Accident Parameters and Injury," IEEE Industry Applications, March-April 1998, pp. 25-31.
R.A. Jones and other members of IEEE-PCIC working group, "Staged Tests Increase Awareness of Arc-Flash Hazards in Electrical Equipment," IEEE Petroleum and Chemical Industry Conference Record, September 1997, pp. 313-332.
T.E. Neal, A.H. Bingham and R.L. Doughty, "Protective Clothing Guidelines for Electric Arc Exposure," IEEE Transactions on Industry Applications, Vol. 33, No. 4, July-August 1997, pp. 1043-1054.
R. Wilkins, "Standard Fuse Model for System Short-Circuit Studies." 8th International Symposium on Switching Arc Phenomena, TU Lodz, Poland, 1997, pp. 163-166.
H. Schau and D. Stade, "Requirements to Be Met by Protection and Switching Devices From the Arcing Protection Point of View," Proceedings of 5th International Conference on Electric Fuses and Their Applications, Technical University of Ilmenau, Germany, September 1995, pp. 15-22.
J. Paukert, "The Arc Voltage and the Resistance of LV Fault Arcs," 7th International Symposium on Switching Arc Phenomena, TU Lodz, Poland, 1993, pp. 49-51.
R.L. Doughty, R.A. Epperly and R.A. Jones, "Maintaining Safe Electrical Work Practices in a Competitive Environment," IEEE Transactions on Industry Applications, Vol. 28, No. 1, January-February 1992, pp. 196-204.
A.D. Stokes and W.T. Oppenlander, "Electric Arcs in Open Air," J. Phys. D: Appl. Phys., Vol 24, 1991, pp. 26-35.
R.H. Lee, "Pressure Developed by Arcs," IEEE Transactions on Industry Applications, Vol. IA-23, No. 4, July-August 1987, pp. 760-764.
R. Wilkins, "3-Phase Operation of Current-Limiting Power Fuses," 3rd International Conference on Electric Fuses and Their Applications, Eindhoven, 1987, pp. 137-141.
M.N. Ozisik, "Heat Transfer," McGraw-Hill, 1985.
R.H. Lee, "The Other Electrical Hazard: Electric Arc Blast Burns," IEEE Transactions on Industry Applications, Vol. IA-18, No. 3, May-June 1982, pp. 246-251.
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