USING CURRENT-LIMITING FUSES TO REDUCE HAZARDS DUE TO ELECTRICAL ARC-FLASHES Vincent Saporita Cooper Bussmann St. Louis, MO USA

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1 USING CURRENT-LIMITING FUSES TO REDUCE HAZARDS DUE TO ELECTRICAL ARC-FLASHES Vincent Sporit Cooper Bussmnn St. Louis, MO USA Abstrct: Numerous tests were conducted in which rcing fults were initited in open electricl equipment. s were run on circuits protected by both current-limiting fuses nd typicl industril circuit brekers. Results showed drmtic reduction in the mount of dmging energy relesed upon worker when current-limiting fuses were utilized. Mesurements included voltge, current, temperture, sound, nd pressure. High-speed 16mm film, video, nd infrred video were lso utilized to record the events. Results of the testing were used to develop n wrd winning IEEE pper[1] nd n electricl sfety trining pckge now being sold by the Electricl Sfety Subcommittee of the Petrochemicl Industries Committee (IEEE/PCIC). This pper explins the bckground for the testing, the tests themselves, nd how the fuse industry cn use the results of the testing to reduce the hzrds ssocited with electricl rcflshes. INTRODUCTION: The instlltion codes in North Americ require tht equipment be instlled in ccordnce with the wy it ws listed or certified. The instlltion codes however do not provide guidnce for mintennce workers, nd the product stndrds do not require testing for rcing fults tht might occur when the equipment door is open nd mintennce worker ccidentlly cretes n rcing short circuit. As result, numerous workers re injured nd killed ech yer while working on energized electricl equipment. An d-hoc working group ws formed within the IEEE/PCIC sfety committee to help ddress this sitution. The intent of the group ws to rise the wreness of electricl workers to the dngers ssocited with electricl rcs nd hopefully reduce the incidents of worker injuries nd deths. The d-hoc group consisted of 10 members, of which one ws medicl doctor with electricl burn expertise, two were consulting engineers, four were engineers for vrious petrochemicl compnies, nd three were with n electricl mnufcturer. The group hd no funding outside of the group itself. Everyone prticipted in the decision process, provided their expertise, nd donted ctul electricl equipment when possible. Some equipment ws brnd new. It hd never been put into service. Other equipment ws tken out of decommissioned plnts. Switchbords, pnelbords, buswy nd motor control centers were donted for these tests. In ddition, lb time ws donted by mnufcturer in high-power shortcircuit test lb in the Midwest. BACKGROUND/RELEVANT PAPERS: In 1982, Rlph Lee wrote pper titled, The Other Electricl Hzrd: Electric Arc Blst Burns [2]. In tht pper he developed formul for the distnce required for vrious degrees of burns s relted to the vilble MVA nd time of exposure. These formule were developed for rcs in open ir. D c = (2.65 X MVA bf X t) 1/2 (1) D c = (53 X MVA X t) 1/2 (2) D f = (1.96 X MVA bf X t) 1/2 (3) D f = (39 X MVA X t) 1/2 (4) Where D c = distnce for just curble burn, (feet) D f = distnce for just ftl burn, (feet) MVA bf = bolted fult MVA t point involved MVA = trnsformer rted MVA, 0.75 MVA nd over. For smller rtings, multiply by 1.25 t= time of exposure, (seconds) Lee s work showed, for exmple, tht skin temperture bove 96 degrees C for.1 second resulted in totl destruction of the tissue (incurble burn) nd tht skin temperture below 80 degrees C for.1 second llowed for skin which could be cured (just curble burn). NFPA 70E [3], Stndrd for Electricl Sfety Requirements for Employee Workplces, dopted the Lee Formule to define the sfe working distnce from potentil rc. While NFPA 70E is not generlly enforced s is the Ntionl Electricl Code (NFPA 70)[4], it is consensus document nd cn therefore be used in court of lw nd is considered redily vilble public knowledge. Rlph Lee followed in 1987 with nother pper titled Pressures Developed by Arcs [5]. In tht pper Rlph Lee explored the ffects of the expnding metl nd the heting of ir becuse of the rc pssing through it. Copper expnds by fctor of 67,000

2 times when vporized. Compre tht to the expnsion of wter, which is only 1670 times. In the pper, Protective Clothing Guidelines for Electric Arc Exposure [6], the uthors used incident energy s the bsis for choosing the correct protective clothing. The uthors stte tht n incident energy of 1.6 cl/cm 2 is the level t which second degree burns would occur on exposed skin. In follow-up pper, ing Updte on Protective Clothing & Equipment For Electric Arc Exposure [7], the uthors document mesured sound pressures of up to 163 db. For comprison, 12-gge shotgun produces n intensity level of 130 db. They stte tht enclosing three phse rc in box hs the potentil to increse the incident energy pproximtely three times, depending upon the box dimensions, s compred to n rc in open ir. The committee ws wre of the theoreticl ppers nd wnted to show how the potentilly dngerous rc flsh events could ffect workmen. It relized tht it is both equipment filure nd humn error tht contribute to rc flsh events. The tests were designed to be different thn previous theoreticl tests in two wys. First, the tests were to use mnnequin, with mesurements tken on or ner the mnnequin. Second, the tests were crried out with ctul electricl equipment, both new nd used, with rcs creted s they might likely occur in the rel world. The purpose of the tests ws not to compre equipment mnufcturers, but to rise the wreness of rc flsh hzrds in equipment tht ws pplied ccording to the mnufcturers recommendtions nd third-prty listing nd lbeling requirements. TESTS: A preliminry series of 11 tests were run on Mrch 26-28, The 27 min tests were run from September 10-12, The mnnequins were positioned in front of the rc s though they were working on the equipment. The closest worker ws positioned so tht his chest ws pproximtely two feet from the source of the rc, with his hnd reching in. The equipment used in the September tests is listed in Tble I. Avilble fult levels re shown in Tble IV. All tests were crried out within the rtings of the equipment, but there were severl mjor differences between the norml certifiction tests crried out by the equipment mnufcturers nd these tests. Norml certifiction testing is crried out with doors closed, wheres this testing ws done with the doors open. Norml testing is done with bolted short circuits, but this testing ws ccomplished with rcing short circuits. The resons for these differences re pretty obvious. Certifiction of the equipment lredy ssures tht the equipment will hndle reltively high short-circuit currents when the fults re bolted nd the doors re closed. But rel world troubleshooting techniques often require tht mintennce personnel work on hot equipment with equipment doors open. Thus the need for this series of tests. All equipment ws certified by Ntionlly Recognized ing Lbortory except for (1) field fbricted bus distribution box tht ws used to distribute power for n outdoor switchrck. (It ws removed from service specificlly for this testing.), nd (2), shop fbricted three phse, four wire bre copper bus structure with ¼ x 1 x 6 copper brs spced 1 prt (rcs were strted in the middle of the brs nd video-tped s they rn wy from the source.). Whenever possible, rcing fults were creted with screwdriver or wrench plced from phse to phse or phse to ground. Where it ws imprcticl to use screwdriver or wrench, smll piece of #18 copper wire ws used to initite n rc. The tests were stged in such mnner becuse reserch hd shown tht it ws s close s possible to ctul field conditions. TEMPERATURE MEASUREMENTS: Type T thermocouples were plced on the led mnnequin s extended hnd(t1), t the front of the neck(t2)nd under its shirt t chest level(t3). These thermocouples were connected to n Astromed GE Dsh-10 recorder. In ddition, temperture mesurements were cptured by mens of n infrred cmer nd recorded on tpe. These mesurements were used for the pek tempertures in Tble II. The infrred equipment included n Agem Thermovision Scnner 870 (Ctlog No , Seril No. 4175), monitor, control unit, power supply, dul lenses, nd Pnsonic VCR. A mirror ws used so tht the cmer could be positioned out of the direct line of the rc-blst.

3 Tble I [1] Equipment used in tests nd overcurrent device opertion w/ 50 A MCP 20 Size 1 combo strter w/ 35 A MCB No. Equipment Overcurrent device Fult Initition Overcurrent device result 1 Size 1 combo strter 601A Clss L, 30A RK 1 Lod side screwdriver C 30 A RK 1 opened 2 Size 1 combo strter 601 A Clss L Lod side screwdriver C None 3 Size 1 combo strter 601 A Clss L Lod side screwdriver C Clss L opened 4 Size 1 combo strter 640 A - Pwr CB Lod side screwdriver C 9 MCC # 2 w/insulted bus 601 A Clss L, 30 A MCP Lod side #18 wire C 30 A MCP tripped 10 MCC # 2 w/ insulted bus 601 A Clss L, 70 A MCP Lod side #18 wire C 70 A MCP tripped 11 MCC # 2 w/insulted bus 601 A Clss L, 70 A MCP Lod side #18 wire B to C 70 A MCP tripped 12 MCC # 2 w/insulted bus 30 A MCP Lod side #18 wire B to C 30 A MCP tripped 13 MCC # 2 w/insulted bus 640 A - Pwr CB Line side bucket #18 wire A, B, C 14 MCC # 2 w/insulted buss 640 A - Pwr CB Line side bucket #18 wire A, B, C A distribution duct 640 A - Pwr CB #18 wire A, B, C A power pnel 30 A MCB 3 Phse Lod side screwdriver C 30 A MCB tripped A distribution duct 640 A - Pwr CB # 8 wire A, B, C 18 Size 2 combo strter 601 A, Clss L, 50 A Lod side screwdriver C 50 A MCP opened 200 A 170 Limiter nd w/ 50 A MCP MCP 200 A 170 Limiter 19 Size 2 combo strter 601 A Clss L, 50 A MCP Lod side screw- 50 A MCP did not open driver C 601 Clss L, 35 A MCP Lod side MCB #18 wire C to gnd 21 Size 2 combo strter 50 A MCP Lod side MCP #18 wire A, B, C 22 MCC # A Clss L, 50A MCB Lod side strter A, B, C #18 wire 23 MCC # A Clss L Incoming lugs wrench 24 MCC # A - Pwr CB Incoming lugs wrench 25 MCC # 3 Size 2 strter with limiters 601 A Clss L, 50 A MCB, M limiter Lod side strter A, B, C #18 wire 26 MCC # 3 Size 2 combo strter 601 A Clss L, 50A MCB Lod side strter A, B, C #18 wire 27 MCC # A - Pwr CB Line side A, B, C #18 wire s 5, 6, 7, nd 8 were product tests nd were not recorded. 35 A MCP did not open 50 A MCP did not open 50A MCB tripped Clss L opened 50A M

4 Tble II [1] Mesured tempertures C Time in ms C Time in ms C Time in ms Infrred T1 90% 90% to to 90% 90% No.,b Temp. pk rise fll 80 C 70 C T2 90% 90% 90% 90% rise fll 90% to 90% to T3 rise fll pk time time 80 C 70 C pk time time > > >250 >2500 > > Temperture mesurements were not recorded for tests 1,2, 5, 6, 7, 8, 9, 10, 11, 12, 15, 17, 22, 23, 25, nd 26. The number 18 ws not used. SOUND MEASUREMENTS: Sound mesurements were recorded in two different wys: 1. Pressure probes were instlled on the led mnnequin. These were Omeg DPX piezo-electric sensors. After mplifiction, the signls were sent to the Astromed Dsh-10. Probes were plced distnces of 2 nd 6 from the rc source. 2. Condenser microphones from Bruel nd Kjer were locted on tripods t distnces of 20 (D 1 ) nd 25 (D 2 ) from the source of the rc. See Tble III. It ws felt tht the resons for the difference between the idel nd mesured distnce effect were due to nonsphericl pressure wve, reflective lbortory, nd nonidel source. For comprison of the dvntges of using currentlimiting fuses, the mesured pressure, in 3, when the 22,600 mpere short ws clered by 601 mp Clss L fuse ws 504 lbs/ft 2 while, in 4, the pressure ws mesured t greter thn 2160 lbs/ft 2 when the circuit ws protected by the 640 mp Power Circuit Breker. Erdrum rupture occurs t pressure of 720 lbs/ft 2, while the threshold for lung dmge is 1728 lbs/ft 2. Tble III[1] Pressure No. b P1 c P2 c 20 ft 25 ft 2 ft d No. P1 c P2 c Sound Sound ft d > > Mesured in psi. b Pressure mesurements were not recorded for tests 1, 2, 5, 6, 7, 10, 15, 16, nd 24. The number 18 ws not used. c Some of the test dt is missing becuse the pressure-sensing device ws destroyed, due to extreme pressure nd temperture. d Clculted by extrpoltion.

5 VIDEO/FILM: s were filmed(16mm) t 10,000 frmes per second using Photec IV cmer no. PSI This required only 1.5 seconds for 450 of film. Color VHS video ws lso utilized t ground level nd from n observtion deck 15 bove the test floor. ELECTRICAL MEASUREMENTS: Electricl mesurements re shown in Tble IV. Note the significnt reduction in let-through I 2 t between s 3 (22.6kA clered by 601 mp Clss L fuse) nd 4 (22.6kA protected by 640 mp Power Circuit Breker) nd between s 23 (65kA clered by 601 mp Clss L fuse) nd 24 (65kA protected by 640 mp Power Circuit Breker). This is due to the fct tht the Clss L fuse ws current-limiting while the Power Circuit Breker ws set t 12 cycles (to discriminte with downstrem overcurrent protective devices). The rc flsh energy ws gretly reduced, s cn be witnessed in the high speed film nd VHS video. This reduction in rc flsh energy is tremendous benefit for the fuse industry. It minimizes workmen s exposure, surely sving lives in the long run. No. Avil. Current (ka) Tble IV[1] Mesured current Pek let-through X 1,000 I 2 T let-through X 1,000 Aφ Bφ Cφ N Aφ Bφ Cφ N >65.85 > > > b Current mesurements were not recorded for tests 14, 15, 16, nd 21. The number 18 ws not used. ADVANTAGE FOR THE FUSE INDUSTRY: Becuse of the incresed requirement for worker sfety, consulting engineers nd industril plnts re more frequently specifying fuses in their distribution systems. This is due to the tremendous reduction in rc-flsh energy tht is ssocited with the use of current limiting fuses. (Workmen still need to wer proper protective clothing while working on or ner live equipment becuse not ll fults will be of high enough vlue to be within the current-limiting rnge of the fuse.) Fuse mnufcturers cn tke dvntge of this opportunity by promoting the IEEE pper nd video, or by producing nd promoting similr sfety oriented pckge. CONCLUSION: A volunteer d-hoc committee ws formed to try to increse the wreness of rc-flsh hzrds in the workplce. After the testing ws complete, it becme obvious tht the current limittion provided by modern current-limiting fuses

6 provided rel reduction in rc-flsh energy, nd ssocited tempertures, pressures, nd let-through I 2 t. Vrious mesurements were documented, including very drmtic video nd high speed film. Becuse of the incresed level of employee sfety, this dvntge of current-limiting fuses cn be used to help persude consulting engineers nd plnt engineers to specify current-limiting fuses s the preferred overcurrent protective devices. References: [1] Ry A. Jones, Mry Cpelli-Schellpfeffer, Robert E. Downey, Shhid Jmil, Dnny P. Liggett, Terry Mcldy, L. Bruce McClung, Vincent J. Sporit, Lynn F. Sunders, nd Arthur Smith, Stged s Increse Awreness of Arc-Flsh Hzrds in Electricl Equipment, IEEE Petroleum nd Chemicl Industry Conference Record, September 1997, pp A copy of the video (VHS), pper, nd CD (trining presenttion) of Stged s Increse Awreness of Arc-Flsh Hzrds in Electricl Equipment is vilble for $75.00 (US), from: IEEE/PCIC Sfety Subcommittee, c/o Kim Estwood, Thermon Mnufcturing Compny, 100 Thermon Drive, Sn Mrcos, TX 78666, Phone: (512) , Fx: (512) Mke checks pyble to PCIC Electricl Sfety Workshop. [2] Rlph Lee, The Other Electricl Hzrd: Electricl Arc Blst Burns, IEEE Trnsctions on Industry Applictions, Vol. 1A-18, No. 3, P. 246, My/June [3] NFPA 70E Stndrd for Electricl Sfety Requirements for Employee Workplces, 1996 Ed. Quincy, Msschusetts: Ntionl Fire Protection Assocition, 1995 [4] NFPA 70 Ntionl Electricl Code, 1999 Ed. Quincy, Msschusetts: Ntionl Fire Protection Assocition, 1998 [5] Rlph Lee, Pressures Developed by Arcs, IEEE Trnsctions on Industry Applictions, Vol. 1A-23, No. 4, July/August [6] Dr. T. Nel, A. H. Binghm nd R. L. Doughty, Protective Clothing Guidelines For Electric Arc Exposure, IEEE Petroleum nd Chemicl Industry Conference Record, September 1996, pp [7] R. L. Doughty, Dr. T. E. Nel, T. A. Der nd A. H. Binghm, ing Updte On Protective Clothing & Equipment For Electric Arc Exposure, IEEE PCIC Conference Record, September 1997, pp

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DPST-NO None 2 channels Auto-reset Inverse 24 VAC/VDC G9SB-2002-A 4 1 channel or 2 Sfety Rely Unit Ultr Slim Sfety Rely Unit Models of width 17.5 mm vilble with 2 or 3 poles. Models of width 22.5 mm with 3 poles lso vilble. Conforms to EN stndrds. (TÜV pprovl) DIN trck mounting possible.