CALCULOS FLASH

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SCCR Calculation Example – Individual SCCR’s : 

SCCR Calculation Example – Individual SCCR’s Main CB Control Relay Terminal Blocks Contactor W/ Overload Power Circuit SCCR at 480V Main CB 30kA Contactor 5kA Overload Relay 5kA Fuses on C-Trans 200kA Control Circuit Control Trans --- Control Relay --- Terminal Blocks --- Control Trans W/ fuses

SCCR Calculation Example – Individual SCCR’s : 

SCCR Calculation Example – Individual SCCR’s Main CB Control Relay Terminal Blocks Contactor W/ Overload Power Circuit SCCR at 480V Main CB 30kA Contactor 5kA Overload Relay 5kA Fuses on C-Trans 200kA If no additional information is available the the Industrial Control Panel must be rated at the lowest rating of any component: 5kA Control Trans W/ fuses

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SCCR Calculation Example – Tested Combinations Main CB Control Relay Terminal Blocks Contactor W/ Overload Power Circuit SCCR at 480V Main CB 30kA Contactor 5kA Overload Relay 5kA Fuses on C-Trans 200kA Control Circuit Control Trans --- Control Relay --- Terminal Blocks --- Control Trans W/ fuses

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SCCR Calculation Example – Tested Combinations Power Circuit SCCR at 480V Main CB Contactor 30kA Overload Relay Fuses on C-Trans 200kA UL508 component combination test results show that the CB and starter combination can be rated at 30kA. The Industrial Control Panel can now be rated at a higher SCCR: 30kA

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Ch. 1, Sec. 130.2 (A) Shock Hazard Analysis.“Shock hazard analysis shall determine the voltage to which personnel will be exposed, boundary requirements, and the PPE necessary in order to minimize the possibility of electric shock to personnel.”What is required?1. Determine the Operating Voltage of the System2. Determine Shock Protection Boundaries3. Determine the Personnel Protective Equipment

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SHOCK Hazard Analysis How to Comply with NFPA 70E?1.Determine the Operating Voltage.2.Determine the Three Shock Protection Boundaries by using Table 130.2(C) of NPFA 70E-2004 on P. 25a.Limited Approach Boundary•10 ft for 480 V for movable energized object•3 ft 6 in. for fixed energized objectb. Restricted Approach Boundary•12 in. for 480 Vc. Prohibited Approach Boundary•1 in. for 480 V

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Flash Hazard Ch. 1, Sec. 130.3 Flash Hazard Analysis. “A flash hazard analysis shall be done in order to protect personnel from the possibility of being injured by an arc flash. The analysis shall determine the Flash Protection Boundary and the personal protective equipment that people within the Flash Protection Boundary shall use.”How to Comply with NFPA 70E for FLASH Protection?1.Determine the Flash Protection Boundary2.Determine the incident energy exposure level3.Determine the Protective Clothing and PPE

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Flash Hazard How to Comply with NFPA 70E for FLASH Protection?1. Determine Flash Protection Boundary:Calculate using the IShort-Circuit Amperes& the clearing time for the overcurrentprotection(see Formula below & on Page 25 of NFPA 70E-2004ORdefault to four feet -600 V or less @ 300 kA cycles per 130.3(A) of NFPA 70E-2004)Flash Protection Boundary Formula (600 V or less) DC= [53 x MVA x t] 1/2where Dc = Arc Flash Boundary (AFB) in FeetMVA = Transformer capacity in MVA t = clearing time in seconds Second Degree Burn Threshold 1.2 cal/cm2

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Flash Hazard Analysis 2. Determine the Incident Energy Leverl:Calculate incident energy exposure level for the distance between worker’s face & chest from the potential arc source (18” typical) ORuse 130.7(C)(9) and 130.7(C)(10)Incident energy formula for Arc in a Cubic Box :EMB= 1038.7DA-1.4738tA[0.0093F2–0.3453F + 5.9675]Where EMB= cal/cm2in 20 inch Cubic BoxDA= distance from electrode in inches(typically this value would be 18”)tA= clearing timeF= Ishort-Circuit Amperes available (range of 16 kA to 50 kA)

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Flash Hazard Analysis3. Determine the Proper PPE :Once the incident energy is determined, the PPE has to have a rating equal to or greater than the incident energy available See 130.7(C)(11). If the alternate method is used:use 130.7(C)(9) for the task, then the proper PPE is selected from 130.7(C)(10) of NFPA 70E-2004.

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Flash Hazard Analysis Example 1 -An Electrician is to remove the covers to measure the voltage on a panelboardoperating at 480 V. Table 130.7(C)(9) > Hazard Risk Category (HRC)= 2*(V-Rated Gloves and V-Rated Tools Required )Table 130.7(C)(10) Specifies the following Required:* Untreated Natural Fiber T-Shirt & Undergarments* FR (8 cal/cm2) Long Sleeve Shirt & Pants* Hard Hat* Safety Glasses or Safety Goggles* Arc-Rated Face Shield w/ Flash Hood or Tube Sock (Balaclava)* Hearing Protection * Leather Gloves * Leather Work Shoes ELECTRICAL HOT WORK PERMIT REQUIRED? (Ans: NO)

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Flash Hazard Analysis Example 2 -An electrician is to operate a circuit breaker in the main switchgear (with all of the covers on the switchgear) to de-energize a circuit that is operating at 480 V for lock-out tagout. Table 130.7(C)(9) > Hazard Risk Category (HRC) = 0(No V-Rated Gloves & No V-Rated Tools Required )Table 130.7(C)(10) Specifies the following Required:* Untreated Natural Fiber long-sleeve shirt & pants* Safety GlassesNEXT STEP IS TO VERIFY VOLTAGE IS OFF!Electrician goes to machine disconnect to open and test for presence of voltage –What is the HRC level? (Ans: 2*) ELECTRICAL HOT WORK PERMIT REQUIRED? (Ans: NO)

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Flash Hazard Analysis Example 3 -An electrician is to operate a circuit breaker in the main switchgear (with some of the covers removed from the switchgear) to de-energize a circuit that is operating at 480 V for lock-out tagout. Table 130.7(C)(9) > Hazard Risk Category (HRC) = 1(No V-Rated Gloves & No V-Rated Tools Required )Table 130.7(C)(10) Specifies the following Required:* Untreated Natural Fiber pants* FR pants and long sleeve shirt* Hard Hat* Safety GlassesNEXT STEP IS TO VERIFY VOLTAGE IS OFF!Electrician goes to machine disconnect to open and test for presence of voltage –What is the HRC level? (Ans: 2*) ELECTRICAL HOT WORK PERMIT REQUIRED? (Ans: NO)

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Flash Hazard Analysis Example 4 -An electrician is to remove the covers on a panelboardto troubleshoot a 20 A lighting circuit that is not working. The circuit is operating at 208/120 V. Table 130.7(C)(9) > Hazard Risk Category (HRC) = 1(V-Rated Gloves & V-Rated Tools Required )Table 130.7(C)(10) Specifies the following Required:* Untreated Natural Fiber pants* FR pants and long sleeve shirt* Hard Hat* Safety GlassesELECTRICAL HOT WORK PERMIT REQUIRED? (Ans: NO)

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Flash Hazard Analysis Example 5 -An electrician is to install a 100 A, 480 V I-Line circuit breaker on a panelboardfor a new bailer machine. If the panel is shutdown, all the lines will stop and the warehouse will be without lighting.Table 130.7(C)(9) > Hazard Risk Category (HRC) = 2*(V-Rated Gloves & V-Rated Tools Required )Table 130.7(C)(10) Specifies the following Required:* Untreated Natural Fiber T-Shirt & Undergarments* FR (8 cal/cm2) Long Sleeve Shirt & Pants* Hard Hat* Safety Glasses or Safety Goggles* Arc-Rated Face Shield w/ Flash Hood or Tube Sock (Balaclava)* Hearing Protection* Leather Gloves* Leather Work ShoesELECTRICAL HOT WORK PERMIT REQUIRED? (Ans: YES)

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Flash Hazard Analysis

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Flash Hazard Analysis -Example 2 This Example Provided Bussmann® •Flash Protection Boundary CalculationCircuit using non-current limiting circuit breaker480 Volt,3 phase Main Lug Only Panel40896 Amperes AvailableOvercurrent protective devicewith clearing time of 6 cyclesAnswerDC= 3 ft

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Flash Hazard Analysis -Example 2 This Example Provided Bussmann® •Flash Protection BoundaryCalculationCircuit using current limiting fuses480 Volt,3 phase Main Lug Only Panel40896 Amperes Available6000 Equivalent RMS Let-ThroughClass J, 200 A fuse clearing time of 1/4 cycle undershort circuit conditions.AnswerDC= .23 ft

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Flash Hazard Analysis This Example Provided Bussmann® Incident Energy Calculation Formula: Based on CUBIC BOXEMB= 1038.7 DB-1.4738tA[0.0093F2-.3453F+5.9675]cal/cm2EMB = Incident Energy (cal/cm2)DB = Distance, (in.) [for Distances >18 inches]tA = Arc Duration, (sec.)F= Bolted Fault Short Circuit Current [16KA to 50kA]

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Flash Hazard Analysis -Example 2This Example Provided Bussmann®Incident Energy Calculation @ 18”Circuit using non-current limiting circuit breaker480 Volt,3 phase Main Lug Only Panel40896 Amperes AvailableOvercurrent protective devicewith clearing time of 6 cyclesAnswerEMB = 10.92 cal/cm2

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Flash Hazard Analysis This Example Provided Bussmann®Incident EnergyCalculation @ 18”Example 2: 40896 ampsof available fault current, 480 volt 3 phase system, Non-current limitingovercurrent device 6 cycle (0.1 sec) opening time.EMB= 1038.7 DB-1.4738tA[0.0093F2-.3453F+5.9675]EMB = 1038.7 (18)-1.4738(.1)[0.0093(41)2-.3453(41)+5.9675]EMB = 10.92 cal/cm2

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Flash Hazard Analysis -Example 2 This Example Provided Bussmann®Incident EnergyCalculation @ 18”Circuit using current limiting fuses480 Volt,3 phase Main Lug Only Panel40896 Amperes Available6000 Equivalent RMS Let-ThroughClass J, 200 A fuse clearing time of 1/4 cycle under short circuit conditions.AnswerEMB < .17 cal/cm2

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