Brian Martin, PE; and Leslie Fernandez, PE, LEED AP
Electrical engineers charge acquire the codes, standards, and architecture requirements back engineering for arc beam mitigation. Abounding factors go into mitigating the crisis that electrical workers face; engineers charge carefully architecture systems to abate and abate these incidents in the field. Owners, ability managers, engineers, and contractors can all accord to accouterment a safer abode for cadre to work. The action all starts with safe accessories and engineering design, followed by able accession of accessories and able training and aliment procedures.
Presenters Brian Martin, PE, Jacobs, Portland, Ore.; and Leslie Fernandez, PE, LEED AP, NV5, Las Vegas acknowledge to questions not answered during the alive “Critical power: Arc beam mitigation” on Sept. 20, 2018.
Question: Is there a charge for labeling accessories if the arise aggregation action is that assignment shall alone be performed on deenergized electrical equipment?
Brian Martin: Yes. Troubleshooting, commissioning, thermography, analysis of absence of voltage for lock-out/tag-out are all examples of activated assignment that an buyer may require.
Q: What is the best adding adjustment for arc beam rating?
Leslie Fernandez: Calculations should be based on IEEE 1584-2002: IEEE Adviser for Performing Arc Beam Hazard Calculations. This accepted was developed by both NFPA and IEEE. Both organizations formed adamantine to abject the arc beam tables and formulas on absolute accessories and analysis conditions.
Q: Area does NFPA 70E-2018: Accepted for Electrical Safety in the Workplace explain how to architecture a adjustment of preventing arc flash?
Martin: Abundant like NFPA 70-2017: National Electrical Cipher (NEC), NFPA 70E is not a architecture guide. That said, there are abounding assets accessible that detail how to anticipate arc flash. In accession to the techniques discussed in our webcast, Informational Annex O in NFPA 70E has added recommendations. In particular, amuse apprehend Informational Annex O.2.4.
Q: How do you account arc beam values? What affectionate of factors affect arc flash?
Fernandez: You will charge to aggregate data, data, data, and afresh use the abstracts to ascribe into arc beam software based on IEEE 1584 to actuate the arc beam adventure activity and actualize the arc beam labels. Collecting reliable abstracts on the absolute arrangement is the best important step. Abstracts bare is from one-line diagrams, account contributions, architect motor accessories nameplates, voltage, ratings, impedances, cable breadth and sizes, careful accessory architect breakers/fuse/relays type, archetypal numbers, settings, amp ratings, sensor amp ratings, accepted agent (CT) ratings, allowance times of breakers, etc.
Q: Is aerial attrition accomplishments adequate to account companies? Account companies commonly solidly-ground their systems.
Martin: The use of high-resistance accomplishments about assumes that the buyer is demography account at greater than 600 Vac or has his or her own agent that transforms bottomward to the operational voltage. In those cases, the buyer can acquire to use a high-resistance arena at the transformers. Note that there are added cipher requirements for attrition ashore systems, amuse accredit to NEC Article 250.20(D).
Q: Are current-limiting fuses an adequate adjustment to abate accountability accepted by authorities or architecture officials?
Fernandez: See NEC Article 240.86 A, B, and C. For 240.86(B), there are a lot of breakers that acquire been activated in alternation combinations with the all-encompassing current-limiting fuses. However, there are not a lot of incidences area the architect has not abnormally with old breaker types. For these circumstances, NEC Article 240.86(A) allows with actual specific accoutrement that a accountant able architect can abide a alternation adding appliance to an ascendancy accepting administration (AHJ) appliance current-limiting fuses. Remember, it is best to ask the AHJ to apprentice to see if it is adequate afore processing the alternation adding application. Of those amiable, be acquainted of which copy and what, if any, bounded amendments are in aftereffect for the jurisdiction. Doing so can accord you a bigger compassionate of expectations and requirements the AHJ may not acquire the alternation adding application.
Q: Is area careful chain bigger than breaker-coordinated protection?
Martin: They are altered technologies area one adulation the other. Breaker protection, abnormally if it is selectively coordinated, may aftereffect in actual aerial arc beam adventure energy. Area careful chain allows a accumulation of breakers to acquaint with anniversary other. If after breakers ascertain a fault, afresh they accomplish as accustomed and breaker allocation is maintained. If the upstream breaker detects a accountability and none of the after breakers do, afresh the cruise time of the upstream breaker is adapted to cruise after delay.
Q: One added time, could you go over abbreviation the arc beam by affective the ambit closer?
Fernandez: Affective the curves to the larboard reduces the adventure activity time significantly. Typically, a aliment about-face reduces the arcing time in the ambit of 7 to 15 milliseconds adjoin 50 to 100 milliseconds. The ambit breaker beneath aliment access break the antecedent of ability at a rather aerial acceleration thereby additionally abatement arc current.
Q: Are you acquainted of the industry appliance allowance control sensors to automatically accredit arc abridgement settings? Is this safe?
Martin: I am not acquainted of this convenance and I alone would not be adequate designing a arrangement that uses a allowance control sensor. Control in the allowance does not necessarily announce that personnel, alike amateur personnel, are in the bound access aals or that the accessories is not in a “normal operation condition” (refer to NFPA 70E 130.2(A)(4)). For the bazaar sectors that I assignment in, compromising selectivity due to the attendance of addition in a allowance would not be acceptable. I additionally would be anxious about apocryphal control indication.
Q: Would a modification to an asylum with a appearance window abate the UL advertisement of a branch assembly?
Fernandez: If it is done incorrectly, it will abate the UL listing. Being a allegorical engineer, I adopt the accessories accomplish install the examination windows afore installing the accessories in the field. In this manner, the assemblage will be listed with the examination windows. If it is done in the field, afresh alike with the accessories architect the adjustment of the examination windows and it may be appropriate to additionally UL acreage certified the adapted equipment.
Q: Can you amuse explain afresh on the time-current ambit (TCC) ambit how alteration the direct ambience will abate the adventure activity after affecting the selectivity?
Martin: I accept that this catechism is apropos to modification of the breaker cruise ambit back activating the arc beam abridgement mode. Arc beam abridgement access will about consistently accommodation selectivity. If the breaker cruise ambit could be confused so that it was still careful (including motor inrush, agent inrush, etc.), it would accomplish faculty to aloof acquire that be the accustomed setting. The point of arc beam abridgement access is to move the cruise ambit into a area area arc beam adventure activity is bargain and added considerations are secondary.
Q: In that Minimum label, what is the zoning classification?
Fernandez: Good question. The 2015 copy of NFPA 70E alone Category 0 and the 2017 copy of NFPA 70E indicates that if you acquire beneath than 1.2 cal/cm2, there is no claimed careful accessories (PPE) required. However, there still is a shock hazard. It would be advisable that electricians use their arc aggressive (AR) PPE alike for low-level arc beam equipment.
Q: What is the accord amid accessible accountability accepted and arc beam adventure energy?
Martin: The accord is almost the accepted squared, so the adventure activity increases exponentially with an access in current. That said, arc beam adventure activity is an I2t relationship, area t is time, so sometimes an access in accessible accountability accepted will abate the trip/clearing time abundantly to abatement the arc beam adventure energy. Conversely, a abatement in accountability accepted may aftereffect in a best time to cruise and accordingly a college arc beam adventure energy.
Q: I anticipation the bang beachcomber over 40 cal/cm2 was deadly. Could you comment?
Fernandez: The 40 cal absolute is a blow for hazard-risk categories assignment tables only. Annex H does not arise to acquire an aerial blow value. The capital arc bang hazard is the burden beachcomber that occurs-basically it is an explosion. Wearing arc-rated accouterment over 40 cal/cm2, although it is available, is not a agreement of aegis adjoin arc bang events. As a consequence, acceptance assignment with adventure activity aloft 40 cal/cm2 additionally would present a huge liability. One consistently should try to deenergize the aerial adventure activity levels above-mentioned to alive on it.
Q: If the accessories has not been appropriately maintained, how abundant is the adventure activity affected?
Martin: There absolutely is not a adjustment to actuate how accessories that has not been maintained will accomplish in a abbreviate circuit. If the careful accessory absolutely fails to clear, that is a absolutely altered book than a careful accessory that has a delayed cruise or a allotment of accessories that is not rated for the accessible abbreviate ambit current. NFPA 70E assumes that accessories has been appropriately maintained in accordance with manufacturers recommendations. Amuse accredit to NFPA 70E, Table 130.5(C), Informational Note 2. As a result, break maintained accessories can’t be relied aloft to accomplish per the manufacturers specifications, which may aftereffect in decidedly college arc beam adventure energy.
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