Arc Flash NESC Utility

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  • 8/4/2019 Arc Flash NESC Utility


    An arc flash can occur when energized conductors touch each other or

    when one conductor makes contact with a grounded surface such as an

    equipment enclosure. The result can be a potentially dangerous and

    deadly arc that ionizes the air producing an explosion.

    oos! Wat was tat? t went ying rigt on bysome time ago. Weter you augt it, misse it orignore it, now it is far bein us in our rear viewmirror faing we off into te istane. Wat was

    it? ts te ationa Eetria afety coes (Ec) January 1,2009 eaine for ar as assessments.

    oring to te 2007 eition of te Ec: Article 410.A.3 Effective as of January 1, 2009, theemployer shall ensure that an assessment is performed todetermine potential exposure to an electric arc for employeeswho work on or near energized parts or equipment. Ifthe assessment determines a potential employee exposure

    greater than 2 cal/cm2 exists, the employer shall requireemployees to wear clothing or a clothing system that hasan effective arc rating not less than the anticipated level ofarc energy.

    Perform an assessment? r rate oting? Exposure greatertan 2 a/m2? January 1? at was so ong ago! Wat oes tisa mean?

    RC Fsh

    lets start by taking a ook at te probem. n ar as anour wen energize onutors tou ea oter or wen oneonutor makes ontat wit a groune surfae su as anequipment enosure. e resut an be a potentiay angerousan eay ar tat ionizes te air prouing an exposion.

    e worker an be engufe by a arge reba; bast pressurean rea tousans of pouns an ause bunt fore trauma

    injury; piees of expoing equipment an be aune as srapne;an te utravioet igt tat is te as an ause eye injury anbinness. Ea year tousans of peope are amitte to ospitasfor ar as reate injuries. Many of tem wi utimatey ie.

    CdE EERg

    e severity of an ar as is ene in terms of its inietnt(terma) energy, wi is measure as aories/entimeter2 (a/m2). is is te amount of energy tat an rea te workerstaning a spei istane away from te ar, known asteworking istane. ypiay, te working istane is 18 to


    OFIT!Arc Flash Assessment RequirementsBy Jim Phillips, President, T2G Technical Training Group/

    30 Electric Enery | Fall 2010

  • 8/4/2019 Arc Flash NESC Utility


    36 ines, epening on te task being performe as we as tetype of equipment being worke on. however, equipment su asot stiks an greaty inrease te working istane an reue teamount of inient energy tat reaes te worker.

    e amount of inient energy from an ar as is baseon many variabes. however, it is te magnitue of sort iruiturrent an te protetive evie earing time tat are te twomost important omponents. e sort iruit urrent is iretyreate to ow mu energy per time is reease an te protetiveevie earing time enes ow ong te uration of te ar as

    wi be.pRECVE Chg

    t is wiey aepte tat just 1.2 a/m2 an prouete onset of a seon egree burn, an tis vaue is use as tebenmark for persona protetion. oring to te Ec,anytime te potentia inient energy exposure to a worker anexee 2 a/m2, protetive oting or a oting system must beworn tat as an ar rating equa to or greater tan te avaiabeinient energy.

    e ar rating refers to te maximum inient energy tegarment an witstan wie proviing a terma barrier to imitte amount of energy tat an rea te worker to no more tan1.2 a/m2. Proteting a worker from te ar as usuay requires

    wearing oting mae from ame resistant (F) fabri as we asusing aitiona persona protetive equipment (PPE) su as aar at. F oting omes in various ar ratings su as 4 a/m2, 8 a/m2, 25 a/m2, 40 a/m2.

    hE RC Fsh ssEssME

    determining ow mu inient energy ou be avaiabe ata spei piee of equipment or oation on a ine is someting youo not want to isover from a e test (aienta or intentiona).is means te ony aternative is to preit it from auations.e most ommony use auation meto is base on EEE1584 EEE Guie for Performing r Fas hazar cauations.e EEE equations were empiriay erive from tests an are

    vai for systems operating from 208 vots up troug 15 kV witsort iruit urrents ranging from 700 up troug 106k.

    e EEE equations are base on te inient energy from atree-pase ar as. Even toug te majority of ar as eventsmay begin wit ontat from one pase to groun, it is assumete onuting pasma tat is proue wi quiky enguf teoter pases an esaate it into a arger tree-pase ar as.

    e EEE meto works we for istribution equipmentwit ose onutor spaing. however, were tere is argerspaing between te pases, su as on overea transmission anistribution ines, it is ess ikey tat a singe-pase ar as ouesaate into a tree pase event.

    t te present time, tere are imite auation metosavaiabe for a singe-pase ar as or for systems operating

    above 15 kV. commeriay avaiabe software using proprietarypysis-base moes is avaiabe for tese speia onitions.


    s an aternative to performing ar as auations, teEc aso aows te use of tabes base on:

    The effective arc rating of the clothing or a clothingsystem to be worn at voltages 1000 V and above shall bedetermined using Tables 410-1 and 410-2 or performingan arc hazard analysis.

    Ec abe 410-1 an 410-2 ist te ar ratings of F otingbase on various eves of sort iruit urrent an protetiveevie earing times. f te avaiabe sort iruit urrent anearing times are known at a given oation, te user an ook upte minimum oting rating from te tabes.

    hEp! hERE d BEg?

    emember one worBakwars.Begin by etermining wat answer you wou ike to see! es

    you rea tis orrety. e easiest way to begin te stuy is toetermine wat eve of F oting you tink migt be reasonabefor workers to wear. Often tis is oting rate 8 a/m2 orsometing simiar. One tis as been etermine, ten beginanayzing te smaest substation wit te simpest protetionseme so you an get starte more easiy an gain onene inyour efforts. ou an begin by using te Ec tabes to see if terating you seete wi work base on te sort iruit urrent anearing time.

    fter tis rst step as been ompete, move on an beginperforming atua auations to anayze oter senarios. eseou inue ases su as wat appens wen a transformeris out of servie, a ine is open, or if te ar as ours furterout on te ine resuting in a ower sort iruit an onger evie

    earing times. One you ave nise te rst substation you anmove on to oter oations.

    esoures su as provie a paewere peope sare information about ow to perform te ar asstuy. is an ep you move in te proper iretion an get infront of te ar as assessment requirement instea of watingit fae in te rear view mirror. n

    Jim Phillips, P.E., founder of and, is an internationally known educator on electrical power systems. You can reach Jim

    2010 Jim Phillips/T2G Technical Training Group.

    The NESC requires an arc flash assessment to protect propleworking on or near energized parts or equipment like this.