This webinar focuses on the fundamentals of arc flash mitigation and the standards required to keep workers safe. Additional questions from this live webcast are addressed here.
Arc flash and electrical safety are critical aspects in a manufacturing facility. Knowing and understanding the fundamentals often mean the difference between life and death. Companies and workers need to stay on top of the electrical codes so they can better protect themselves from a potential accident.
Watch “Electrical safety: Know the fundamentals of arc flash mitigation” and read this Q&A. Webcast presenters Lanny Floyd and Bibek Karki answered additional questions not addressed during this webcast.
Question: Can you provide examples of what defines adequate means of isolation within compartmentalized equipment such as MCCs and switchboards?
Floyd: Locating the 480 V power equipment (switch, circuit breaker, fuses, etc in a separate enclosure from 120 V or other control devices allows the 480 V equipment to be locked out and completely isolates other equipment from the circuits that could cause an arc flash.
Question: What year did arc flash become part of the engineering process in manufacturing and can anyone perform a UL 508A analysis? Also, if you have a piece of equipment that has been determined to be overdutied, what’s the time period for a solution?
Floyd: know that some manufacturers were address in arc flash mitigation in equipment designs in the early 1990s. I don’t have an answer for the last question other than overduties electric power equipment creates a dangerous condition.
Question: Is there a limit to the number of times a breaker can open on a fault before it’s interrupting rating is no longer valid?
Karki: I am not sure about the limit. However, I would recommend performing inspection and testing after each power interruption under fault.
Question: Arc resistance protection can be considerate like an arc flash mitigation protection? Or is different?
Karki: Personal protective equipment (PPE) or protection is the last resort. Arc flash hazard mitigation should be done before using PPE.
Question: How can I estimate my arc flash danger without an arc flash assessment?
Karki: I am not familiar with any other process except performing the arc flash hazard risk assessment. This assessment provides quantifiable incident energy.
Question: What is the difference between the NFPA 70E and the National Electrical Safety code? Which would be more applicable to follow?
Floyd: NFPA 70E addresses general industry and the NESC addresses electric and telecommunication utilities. There are situations where both standards can provide source material for developing an electrical safety program.
Question: Is it possible for arc flash in a single phase switchboard or panelboard and if so is it possible to have an arc flash at the controller at a downstream load?
Karki: Yes. A single-phase system can have multiple poles and all software have provision for hazard calculations. It is very much possible to have arc flash hazard anywhere in the power system above and including 50 V and greater.
Question: What working distance should be used for a switchboard? The IEEE 1584 working distance table only lists switchgear and panelboards.
Karki: There are various distances in the standard depending on fixed or movable.
Question: How one can maintain that three feet working clearance when a truck type breaker would need to be withdrawn?
Floyd: The working distance is measure from the energized bus bars and not from the exterior surface of equipment.
Question: Some customers’ request switchboard interbay barriers to reduce incident energy. Without testing, it is not believed that these claims can be made. What are your thoughts on this?
Karki: It is very difficult to say without testing/original equipment manufacturer (OEM) data. I would rely on the OEM on these data and would not follow any barrier method without specific test data and validations.
Question: Are there solutions that can be considered to reduce arc flash energy in low voltage (208 or 480 V) systems where selective coordination is required? Instantaneous trip settings often need to be pushed out to allow for selective coordination, which compromises arc flash energy reduction.
Karki: Using maintenance mode only compromises coordination while interacting with the electrical equipment. It is the best recommended to use some switching mechanism to switch between normal and reduced incident energy operations.
Question: How would you test to ensure the trip coil is operational?
Karki: You would have to perform resistance measurement and compare with original OEM suggested values.
Question: What provides the most comprehensive maintenance requirements for managing arc flash risk?
Karki: You could consult various IEEE, ANSI and NETA standards. NFPA 70B is valuable, as well.
Question: What approximate standard values of arc flash incident energy do we expect to see in industrial systems?
Karki: There is a wide range of values.
Question: Any suggestions for HV dc systems? We predominately use fuses but I’m concerned about the wide range of temperatures affecting the trip settings of fuses.
Karki: There are various circuit breakers and arc detection relays that I believe are better suited for wide temperature variations.
Question: What software do you think is best for arc flash analysis based on your experience?
Karki: I have used SKM, Easypower and ETAP. Each of them have specific capabilities and limitations. It really depends on your application and preference.
Question: Health care code requires coordination to 0.1 seconds. Are there plans to implement a similar requirement for other installations?
Floyd: I’m not aware of any movement in that direction.
Question: What overcurrent margin do you use in setting a lower set 50 relay or RELT or virtual main? (i.e. if short circuit is 20kA would you recommend setting the trip setpoint at 15 or 10kA?)
Karki: I like to calculate incident energy to make sure that I am getting a desired result. I would recommend setting at 15kA for this particular application.
Question: When ERMS mode is activated at a switchgear, does it affect just the switchgear itself or does it change trip settings of downstream equipment and devices?
Karki: It reduces the incident energy in downstream equipment; not the switchgear itself.
Question: I’ve read that when an arc fault occurs on one phase in an enclosure, the air can be ionized, and, consequently, faults occur between the other phases as well. Is this accurate or can you speak to this?
Floyd: You are correct. Most arcing faults start as a phase to ground fault, and within a fraction of a second, expand into a multiphase fault.
Question: Could you comment on the difference we can expect in the calculations results using the IEEE-1584 2002 vs IEEE-1584 2018? Any significant change in cal/cm² can occur?
Karki: In my experience, significant changes could be noticed if you select the electrode configuration instead of the default configuration. Also, the equipment dimension affects the incident energy, as well.
Question: Are electrical engineers automatically recommending arc flash reduction methods in plan submittals? Or do plan reviewers have to catch and make these recommendations?
Karki: I have not seen any reduction method suggested in plan submittals. I believe this is dependent on the engineering study results and recommendations.
Question: How frequently should an arc flash analysis be performed/reviewed in a facility? Is it only during a change or periodically?
Karki: NFPA 70E recommends every five years.
Question: How many cycles does it take for a LV breaker to interrupt the short circuit?
Karki: It depends on what the circuit breaker is set to. It could be few cycles in electronic trip units with instantaneous settings and few seconds in thermal magnetic circuit breakers.
Question: Will there be a certification of the equipments like UL about arc flash mitigation?
Karki: I have not seen any so far.
