Fault Current Calculationsand NEC RequirementsDan Neeser – Field Application [email protected]: (314) 753-2514 2013 Eaton. All rights reserved.

Question? How many attendees have had a customerdesigning or owning a commercial or industrialfacility ask for the fault current provided by theutility? Why are they asking this question and whatanswer do you provide? 2013 Eaton. All rights reserved.2

Answer Depends on Concern Proper Application of Equipment Interrupting Rating Short-Circuit Current Ratings Meeting Requirements of SelectiveCoordination Arc Flash Protection of Employees 2013 Eaton. All rights reserved.3

OCPD - Interrupting Rating (I.R.) NEC Article 100 Definition Highest current an OVERCURRENT DEVICE(fuse or circuit breaker) is rated to safely interrupt. Self protection rating only NEC 110.9 Interrupting Rating. Requires the overcurrent device to have aninterrupting rating not less than the maximumavailable fault current. The maximum fault current must be calculated andvaries based on system size/location. Similar Requirements in OSHA 1910.303(b)(4) 2013 Eaton. All rights reserved.4

Equipment - Short-Circuit Current Ratings NEC Article 100 Definition The highest current EQUIPMENT can withstand withoutextensive damage (fire or shock hazard). May be based on a specific type of overcurrent device NEC 110.10 Circuit Impedance, Short-Circuit CurrentRatings, and Other Characteristics. Requires the equipment to have a short circuit currentrating not less than the maximum available faultcurrent. The maximum fault current must be calculated andvaries based on system size/location. Similar Requirements in OSHA 1910.303(b)(5) 2013 Eaton. All rights reserved.5

Equipment - Short-Circuit Current Ratings NEC 110.10: Equipment short-circuit currentratings must be adequate for maximum availablefault current. Must Assure Proper SCCR for all equipment Panelboards/SwitchboardsMotor Control Centers/MCCsDisconnects/Transfer SwitchesIndustrial Control PanelsHVAC EquipmentConductors/Busway 2013 Eaton. All rights reserved.66

New Code Change – 2011 NEC110.24 Available Fault Current.(A) Service equipment must be marked with themaximum available fault current and date ofcalculation(B) If fault current increases due to systemmodification, the marking must be updated. 2013 Eaton. All rights reserved.7

How to Comply?Engineer – CalculateAll equipment must complywith: NEC 110.9 (IR) &110.10(SCCR)Isc 60,142 AService EquipmentContractor – LabelMax Avail. Fault Current 58,524 ADate Determined/Calculated: 9/2010Required per NEC 110.24Isc 42,153 AIsc 27,532 AIsc 18,752 AIsc 38,525 AHVACSCCR 40kAIndustrialMachinery PanelIndustrialControl PanelSCCR 65kASCCR 30kA 2013 Eaton. All rights reserved.Motor ControllerSCCR 25kA8

Selective Coordination In the Past: Not required by Code, but “Coordination” Studies wereperformed to improve system reliability – they did notassure “total” coordination (best you can get) As of 2005:National Electrical Code (NEC) Article 100 Definitions Coordination (Selective) Localization of an overcurrentcondition to restrict outages to the circuit or equipmentaffected, accomplished by the choice of overcurrentprotective devices and their ratings or settings. Overcurrent overloads, ground faults & short-circuitsSELECTIVE COORDINATION “TOTAL” COORDINATION 2013 Eaton. All rights reserved.9

Selective CoordinationWithout Selective CoordinationWith Selective CoordinationOPENSOPENSNOT AFFECTEDNOTFaultAFFECTEDFaultUNNECESSARYPOWER LOSSWHY? IMPROVES SYSTEM RELIABILITY TO CRITICAL LOADS 2013 Eaton. All rights reserved.10

Selective CoordinationSummary of NEC Selective Coordination Requirements 620.62 Required for Circuits with multiple Elevators (1993) 700.28 Required for Emergency Systems (2005-2014) 701.27 Required for Legally Required Standby Systems (20052011) 708.54 Required for Critical Operations Power Systems (2008) 517.26 Required for Essential Electrical Systems (2005) 695.3(C)(3) Required for Campus Style Fire Pumps (2011) 645.27 Required for Critical Operation Data Systems (2014) 2013 Eaton. All rights reserved.11

Selective CoordinationAlternateNormalSourceSourceNEATSPanel 2013 Eaton. All rights reserved.12

Selective Coordination – Circuit Breakers How to Selectively Coordinate with CircuitBreakers? Answer: Do short-circuit current study and coordinationstudy investigating various types and optionsof CBs for specific project 2013 Eaton. All rights reserved.13

Selective Coordination – Circuit BreakersHow to Selectively Coordinate with Circuit Breakers? Do short-circuit current study and coordination study Use time current curves to identify types and options of CBs required toachieve selective coordination (select breaker needed eliminate overlapof curves for fault current available) Even small changes in fault current can result in lack of complianceCURRENT IN AMPERES1.10001023 4 5 6 7 89 1002CURRENT IN AMPERES AT 480 VOLTS3 4 5 6 7 89 1000 2 3 4 5 6 7 89 10000 23 4 5 6 7 89 1000007002.30A MCCB 18kAIR500400300800A200100200100200A MCCB 35kAIR10070Short-Circuit Current Study70504030TIME IN SECONDS10By1Ace EngineeringTIME IN SECONDS800A MCCB .03.02.02TIME IN SECONDS10000.100.01101001K10K100K.0130 200 800 MCCB.tcc Ref. Voltage: 480 Current in Amps x 1 30 200 800 MCCB.drw 2013 Eaton. All rights reserved.1023 4 5 6 7 89 10023 4 5 6 7 89 1000 23 4 5 6 7 89 10000 23 4 5 6 7 89 100000.01CURRENT IN AMPERES AT 480 VOLTS14

Selective Coordination – Fuses How to Selectively Coordinate with Fuses? Answer: Use fuse selective coordination ratio tablesand new fusible branch panels 2013 Eaton. All rights reserved.15

Selective CoordinationLine Side FuseLoad Side FuseLOW-PEAK : LOW-PEAK 2:1 Line:Load Ratio No plotting required! Valid up to 200kA 2013 Eaton. All rights reserved.16

Branch Panel w-Peak All Low-Peak Fuses Minimum Ratio 2:1 met Use the Quik-Spec Coordination Panelboardat branch level Also used by Utilities in125Vdc MV ControlApplicationsTCF20 2013 Eaton. All rights reserved.17

Arc Flash Energy Arc flash Energy Is Dependent On: Arcing fault duration or time to clear Speed of the overcurrent protective device Arcing fault current magnitude Available fault current Current-limitation can reduce 2013 Eaton. All rights reserved.18

Arc Flash Hazards – Circuit Breakers 2013 Eaton. All rights reserved.19

Arc Flash Hazards - Fuses 2013 Eaton. All rights reserved.20

Bussmann Short-Circuit Calculator NEW version Apple or Android Apps Web (run from homepageafter entering contact info) 2013 Eaton. All rights reserved.21

Fault Current Calculation ExampleIsc 50,000 AMarking Required per NEC 110.24Isc 54,688 AIsc 42,575 AMainSwitchboardSCCR 200kAFault current at RTU1 SCCR of RTU1CODE VIOLATION!Isc 8,562 AHVAC RTU1SCCR 5kA 2013 Eaton. All rights reserved.22

Selecting Protective Devices Handbook (SPD) This comprehensive guide to electricalovercurrent protection and electricaldesign considerations is based on the2014 NEC .With over 250 pages, this industryleading handbook has new or expandedinformation on the following: OCPD servicing and maintenanceIndustrial control panelsElectrical safetyFuses for hazardous locationsPhotovoltaic systems and fusesData centersFuse sizing for buildingsSurge protective devicesView on-line or save as PDF 2013 Eaton. All rights reserved.23

Questions?Dan NeeserField Application [email protected] 2013 Eaton. All rights reserved.