Equipment Short-Circuit Current Rating and Available Fault ...

1 8/27/20131 2013 Eaton. All rights Short-Circuit Current Rating and Available Fault CurrentDan Neeser Field Application EngineerEaton s Bussmann 2013 Eaton. All rights Interrupting Rating & Series Rating Short-Circuit Current ratings Maximum Fault Current Marking Fault Current Calculations UL 508A Industrial Control Panels Supplement SB - SCCR8/27/201323 2013 Eaton. All rights Rating NEC Article 100 Definition Highest Current an OVERCURRENT DEVICE (fuse or circuit breaker) is rated to safely interrupt. Self protection Rating only NEC Interrupting Rating . Requires the overcurrent device to have an interrupting Rating not less than the maximum Available Fault Current . The maximum Fault Current must be calculated and varies based on system size/location. Similar Requirements in OSHA (b)(4)4 2013 Eaton. All rights Rating NEC : Device interrupting Rating MUST be equal to or greater than the maximum Available Fault Current .

2 Chapter 1 Video Clips - Interrupting Rating8/27/201335 2013 Eaton. All rights Available Short-Circuit Current (Isca) at lineside terminals of each OCPDs with adequate Interrupting Rating - Proper Application6 2013 Eaton. All rights select circuit breaker with interrupting Rating adequate for point of application varies by voltage and circuit breaker Rating - Proper Application8/27/201347 2013 Eaton. All rights Interrupting Rating of Current -limiting fuses at full voltage reduces concerns about proper interrupting Rating at point of - Proper Application8 2013 Eaton. All rights combination of: - circuit breakers / circuit breakers OR- Fuses / circuit breakers ..that can be applied at Available Fault levels above the interrupting Rating of the load side circuit breaker, but not above that of the main or line side device will ALWAYS be a circuit breakerSeries Rated Systems8/27/201359 2013 Eaton.

3 All rights Rated Combination65,000 circuit Breaker65,000 ,000 A20 ACircuit BreakerISC=65,000 A10,000 Rated Systems: CB-CB10 2013 Eaton. All rights Rated Combination200,000 ,000 A20 ACircuit BreakerISC=300,000 A10,000 Rated Systems: Fuse-CBLPJ 400 SP300,000 2013 Eaton. All rights Rated Systems NEC (A) Selected Under Engineering Supervision in Existing Installations The series rated combination devices must be selected by licensed, professional engineer. Requires Documentation and Stamp. Series combination Rating and upstream device must be field marked on end use Equipment . Downstream circuit breaker must remain passive. NEC (B) Tested Combinations The combination of line side and load side devices must be tested and marked on the end-use Equipment (panelboards & switchboards).12 2013 Eaton. All rights Rated Systems Additional Limitations and Requirements Labeling Requirements Manufacturer NEC (B) Field Marking NEC (B)&(C) Motor Contribution Limitations NEC (C) Motor FLA cannot exceed 1% of IR of protected CB.

4 Lack of Selective Coordination8/27/2013713 2013 Eaton. All rights Limitation A Current limiting fuse will clear a Fault within one half of a cycle. Thermal energy is proportionate to the square of RMS Current multiplied by the time (Irms2t) Mechanical stresses are proportionate to the square of peak Current multiplied by the time (Ip2t)14 2013 Eaton. All rights Limitation Conductor protection for Fault of 45kA/480V (26kA with conductor) with non- Current -limiting device (1 cycle) vs. Current -limiting device (>1/2 cycle)8/27/2013815 2013 Eaton. All rights Current ratings NEC Article 100 Definition The highest Current EQUIPMENTcan withstand without extensive damage (fire or shock hazard). Also known as component protection May be based on a specific type of overcurrent device NEC circuit Impedance, Short-Circuit Current ratings , and Other Characteristics. Requires theequipment to have a short circuit Current Rating not less than the maximum Available Fault Current .

5 The maximum Fault Current must be calculated and varies based on system size/location. Similar Requirements in OSHA (b)(5)16 2013 Eaton. All rights Starter - SCCR High Fault Test: starter protected by an instantaneous trip circuit breaker (MCP) that only providesType 1 protection High Fault Test: starter protected by Low-Peak fuses that provides Type 2 (No Damage) protectionFault480V - 22,000 AFault480V - 22,000A8/27/2013917 2013 Eaton. All rights reserved. Marked on motor controllers (B) Marked on HVAC Equipment (3) Marked on industrial control panels Fault Current cannot exceed marked SCCR (A)(4) Marked on industrial machinery control panel Fault Current cannot exceed marked SCCR UL 508A, Supplement SB is an approved method to determine SCCR forindustrial control panels and industrial machinery control panelsSCCR Marking Requirements18 2013 Eaton. All rights Current Marking Requirement Available Fault Current .

6 (A) Service Equipment must be markedwith the maximum Available Fault currentand date of calculation (B) If Fault Current increases due to system modification, the marking must be 2013 Eaton. All rights to Comply?Service EquipmentIsc = 60,142 AIsc = 27,532 AIsc = 42,153 AMax Avail. Fault Current = 58,524 ADate Determined/Calculated: 9/2010 Isc = 18,752 AIsc = 38,525 ARequired per NEC ControllerSCCR = 25kAIndustrial Control PanelSCCR = 30kAIndustrial Machinery PanelSCCR = 65kAHVACSCCR = 40kAAll Equipment must comply with: NEC (IR) & (SCCR)Engineer CalculateContractor Label20 2013 Eaton. All rights Inspection Check-List8/27/20131121 2013 Eaton. All rights Current Calculations To determine the Fault Current : Draw the one-line diagram Identify sources of Short-Circuit Current (utility, generation, motors) Include system component information (tranformers, conductors, busway, overcurrent devices are not considered) Use calculation method (ohmic, per unit, point-to-point, software) Use typical Fault Current values as a reference 2013 Eaton.

7 All rights Short-Circuit Current Values Short-Circuit Current at service entrance Equipment varies by type/size of system: Small residential systems (100A to 200A) 10,000A to 15,000A or less Small commercial building systems (400A to 800A) 20,000A to 30,000A Larger commercial and manufacturing building systems (2,000A to 3,000A) - 50,000A to 65,000A Higher Short-Circuit currents are possible where low impedance (energy-efficient) transformers are used (or where larger transformers (kVA) feed multiple services. Commercial buildings directly connected to utility grid system 200,000A or greater8/27/20131223 2013 Eaton. All rights Current Factors Typically highest at service point Decreases in downstream Equipment (due to impedance of transformers and conductors)24 2013 Eaton. All rights Example 480V/3000A Service supplied from 2500 kVA Transformer Find Isc at Transformer Secondary & Service Equipment480V, 3000A Service EquipmentService Transformer2500 480V5% Impedance7 600 Cu kcmil/phase25 Feet in PVCIsc = 60,142 AIsc = 58,524A8/27/20131325 2013 Eaton.)

8 All rights X 1000EL-LX KVA = KVA of TransformerEL-L= Secondary Phase to Phase voltageCalculation Example Step One: Calculate Secondary FLA of Transformer (3 phase)26 2013 Eaton. All rights KVA - 480V, 3 PhaseZ = 5%ISCIFLA=2500 X 1000480 X IFLA= 3007 ACalculation Example8/27/20131427 2013 Eaton. All rights =100% ZMult =1005 Mult = 20 Calculation Example Step Two: Calculate Multiplier Z = Impedance of Transformer, refer to transformer nameplate or manufacturer data28 2013 Eaton. All rights IFLAX MultISC= 3007 X 20 ISC= 60,140 ACalculation Example Step Three: Calculate Secondary short circuit Current8/27/20131529 2013 Eaton. All rights Switchgear7 600 Cu kcmil/phase25 Feet in PVCISC= 60,140 ACalculation Example Calculate short circuit Current at 480V Switchgear30 2013 Eaton. All rights 480V SWGR= ISCX MultCalculation Example Isc known from previous calculation Calculate multiplier for Cable Step One: Calculate f value8/27/20131631 2013 Eaton.

9 All rights = X L X ISCC X EL-LL = Length of conductor ISC= Short-Circuit Current at beginning of circuitC = C Value Constant for CableFrom Table. Multiply by # of runsEL-L= Phase to Phase VoltageCalculation Example Step One: Calculate f value32 2013 Eaton. All rights Example C Value 600 kcmil, CU, PVC = 28,0338/27/20131733 2013 Eaton. All rights = X 25 X 60,1407 X 28,033 X 480= Example Step One: Calculate f Value L = 25 Feet ISC = 60,140 A C = 7 X 28,033 - See C Value Table EL-L = 480V34 2013 Eaton. All rights =11 + f Step Two: Use Calculated f Value Calculate MultiplierCalculation ExampleMult == + 2013 Eaton. All rights 480V SWGR= ISCX MultISC 480V SWGR= 60,140 X .9731 ISC 480V SWGR= 58,522 A** Add motor contribution if presentCalculation Example Calculate short circuit Current at 480V Switchgear36 2013 Eaton. All rights if the System Changes?480V, 4000A Service EquipmentService Transformer3000 480V5% Impedance9 600 Cu kcmil/phase25 Feet in PVCIsc = 72,171 AIsc = 70,587A480V, 3000A Service EquipmentService Transformer2500 480V4% Impedance7 600 Cu kcmil/phase25 Feet in PVCIsc = 75,178 AIsc = 72,667A8/27/20131937 2013 Eaton.

10 All rights Bussmann Short-Circuit Calculator New version Apple or Android Apps Web (run from homepage) Old version Download for Window XP38 2013 Eaton. All rights reserved. Choose three phase or single phase systemCalculating Available Fault Current and creating labels has never been easier!123 Click on Add to my System Select a component you want to addCreate a System8/27/20132039 2013 Eaton. All rights reserved. Select Add TransformerCalculating Available Fault Current and creating labels has never been easier!123 If you have a known primary Fault Current you can add it here. If not, select assume infinite Enter values into the appropriate fieldsAdd a Transformer40 2013 Eaton. All rights reserved. After adding a Transformer, you will be asked if you want to add motor contributionCalculating Available Fault Current and creating labels has never been easier!123 Yo u can complete a quick calculation by selecting a % of your transformer s FLA or add it manually Add these calculations to your systemAdd Motor Contribution8/27/20132141 2013 Eaton.