4/1/2014 Equipment Short-Circuit Current Rating and Available Fault Current Dan Neeser – Field Application Engineer Eaton’s Bussmann Business [email protected] © 2013 Eaton. All rights reserved. Agenda • Interrupting rating (IR) • Series Ratings (SR) • Short-Circuit Current Ratings (SCCR) • Equipment Marking and Installation Requirements • Fault Current Calculations • Industrial Control Panels • UL 508A Supplement SB © 2013 Eaton. All rights reserved. 2 Interrupting Rating • 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 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 1910.303(b)(4) © 2013 Eaton. All rights reserved. 3 1 4/1/2014 Interrupting Rating - Proper Application Overcurrent device must have interrupting rating adequate for point of application. Circuit breakers IR varies by voltage and circuit breaker type. Fuses typically have high IR at rated voltage. © 2013 Eaton. All rights reserved. 4 Interrupting Rating • NEC 110.9: Device interrupting rating MUST be equal to or greater than the maximum available fault current. • Chapter 1 Video Clips - Interrupting Rating © 2013 Eaton. All rights reserved. 5 Series Rated Systems A 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. Downstream device will ALWAYS be a circuit breaker © 2013 Eaton. All rights reserved. 6 2 4/1/2014 Series Rated Systems • CB/CB • Fuse/CB © 2013 Eaton. All rights reserved. 7 Series Rated Systems • NEC® 240.86(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® 240.86(B) Tested Combinations • The combination of line side and load side devices must be tested and marked on the end-use equipment (panelboards & switchboards). © 2013 Eaton. All rights reserved. 8 Series Rated Systems • Additional Limitations and Requirements • Labeling Requirements • Manufacturer – NEC® 240.86(B) • Field Marking – NEC® 110.22(B)&(C) • Motor Contribution Limitations • NEC 240.86(C) • Motor FLA cannot exceed 1% of IR of protected CB. • Lack of Selective Coordination © 2013 Eaton. All rights reserved. 9 3 4/1/2014 Current 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) © 2013 Eaton. All rights reserved. 10 Current 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) © 2013 Eaton. All rights reserved. 11 Short-Circuit Current Ratings • NEC® Article 100 Definition • The highest current EQUIPMENT can withstand without extensive damage (fire or shock hazard). • Also known as component protection • May be based on a specific type of overcurrent device • NEC® 110.10 Circuit Impedance, Short-Circuit Current Ratings, and Other Characteristics. • Requires the equipment to have a short circuit current 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 1910.303(b)(5) © 2013 Eaton. All rights reserved. 12 4 4/1/2014 SCCR Marking Requirements • 430.8 – Marked on motor controllers • 440.4(B) – Marked on HVAC equipment • 409.110(3) – Marked on industrial control panels • 409.22 – Fault current cannot exceed marked SCCR • 670.3(A)(4) – Marked on industrial machinery control panel • 670.5 – Fault current cannot exceed marked SCCR • UL 508A, Supplement SB is an approved method to determine SCCR for industrial control panels and industrial machinery control panels • Typically Equipment is rated only 5kA unless higher ratings are requested! © 2013 Eaton. All rights reserved. 13 Fault Current Marking Requirement • 110.24 Available Fault Current. • (A) Service equipment must be marked with the maximum available fault current and date of calculation • (B) If fault current increases due to system modification, the marking must be updated. © 2013 Eaton. All rights reserved. 14 How to Comply? Engineer – Calculate All equipment must comply with: NEC 110.9 (IR) &110.10 (SCCR) Isc = 60,142 A Contractor – Label Max Avail. Fault Current = 58,524 A Service Equipment Date Determined/Calculated: 9/2010 Required per NEC 110.24 Isc = 38,525 A HVAC SCCR = 40kA Isc = 42,153 A Isc = 27,532 A Industrial Machinery Panel Industrial Control Panel SCCR = 65kA SCCR = 30kA © 2013 Eaton. All rights reserved. Isc = 18,752 A Motor Controller SCCR = 25kA 15 5 4/1/2014 Fault 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-topoint, software) • Use “typical” fault current values as a reference only. © 2013 Eaton. All rights reserved. 16 Typical 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 greater © 2013 Eaton. All rights reserved. 17 Short-Circuit Current Factors • Typically highest at service point • Decreases in downstream equipment (due to impedance of transformers and conductors) © 2013 Eaton. All rights reserved. 18 6 4/1/2014 Calculation Example • 480V/3000A Service supplied from 2500 kVA Transformer • Find Isc at Transformer Secondary & Service Equipment 480V, 3000A Service Equipment Service Transformer Isc = 58,524A 2500 kVA 13.2kV – 480V 5% Impedance Isc = 60,142 A 7 – 600 Cu kcmil/phase 25 Feet in PVC © 2013 Eaton. All rights reserved. 19 Calculation Example • Step One: Calculate Secondary FLA of Transformer (3 phase) IFLA = KVA X 1000 EL-L X 1.732 KVA = KVA of Transformer EL-L = Secondary Phase to Phase voltage © 2013 Eaton. All rights reserved. 20 Calculation Example ISC 2500 KVA Transformer 13.2kV - 480V, 3 Phase Z = 5% IFLA = 2500 X 1000 480 X 1.732 IFLA = 3007 A © 2013 Eaton. All rights reserved. 21 7 4/1/2014 Calculation Example • Step Two: Calculate Multiplier • Z = Impedance of Transformer, refer to transformer nameplate or manufacturer data Mult = Mult = 100 %Z 100 5 Mult = 20 © 2013 Eaton. All rights reserved. 22 Calculation Example • Step Three: Calculate Secondary Short Circuit Current ISC = IFLA X Mult ISC = 3007 X 20 ISC = 60,140 A © 2013 Eaton. All rights reserved. 23 Calculation Example • Calculate Short Circuit Current at 480V Switchgear 480V Switchgear 7 – 600 Cu kcmil/phase 25 Feet in PVC ISC = 60,140A © 2013 Eaton. All rights reserved. 24 8 4/1/2014 Calculation Example • Isc known from previous calculation • Calculate multiplier for Cable • Step One: Calculate f value ISC 480V SWGR = ISC X Mult © 2013 Eaton. All rights reserved. 25 Calculation Example • Step One: Calculate f value f = 1.732 X L X ISC C X EL-L L = Length of conductor ISC = Short-circuit current at beginning of circuit C = “C” Value Constant for Cable From Table. Multiply by # of runs EL-L = Phase to Phase Voltage © 2013 Eaton. All rights reserved. 26 Calculation Example • C Value – 600 kcmil, CU, PVC = 28,033 © 2013 Eaton. All rights reserved. 27 27 9 4/1/2014 Calculation Example • Step One: Calculate f Value • L = 25 Feet • ISC = 60,140 A • C = 7 X 28,033 - See “C” Value Table • EL-L = 480V f = 1.732 X 25 X 60,140 7 X 28,033 X 480 = 0.0276 © 2013 Eaton. All rights reserved. 28 Calculation Example • Step Two: Use Calculated f Value • Calculate Multiplier Mult = Mult = 1 1+f 1 1 + 0.0276 = 0.9731 © 2013 Eaton. All rights reserved. 29 Calculation Example • Calculate Short Circuit Current at 480V Switchgear ISC 480V SWGR = ISC X Mult ISC 480V SWGR = 60,140 X .9731 ISC 480V SWGR = 58,522 A* * Add motor contribution if present © 2013 Eaton. All rights reserved. 30 10 4/1/2014 What if the System Changes? 480V, 4000A Service Equipment Service Transformer Isc = 70,587A 3000 kVA 13.2kV – 480V 5% Impedance Isc = 72,171 A 9 – 600 Cu kcmil/phase 25 Feet in PVC 480V, 3000A Service Equipment Service Transformer Isc = 72,667A 2500 kVA 13.2kV – 480V 4% Impedance Isc = 75,178 A 7 – 600 Cu kcmil/phase 25 Feet in PVC © 2013 Eaton. All rights reserved. 31 Bussmann Short-Circuit Calculator • NEW version • Apple or Android Apps • Web (run from homepage after entering contact info) © 2013 Eaton. All rights reserved. 32 Fault Current Calculation Example Isc = 50,000 A Marking Required per NEC 110.24 Isc = 54,688 A Isc = 42,575 A Main Switchboard SCCR=200kA Fault current at RTU1 > SCCR of RTU1 CODE VIOLATION! Isc = 8,562 A HVAC RTU1 SCCR = 5kA © 2013 Eaton. All rights reserved. 33 11 4/1/2014 How to Determine SCCR? • Short-Circuit Current Rating (SCCR) • Can be established by testing during the listing and labeling process OR • Can be determined using an approved (calculation) method • UL 508A Supplement SB is an approved method (industrial control panels and industrial machinery control panel) • AHJ Approved Method • NRTL field evaluation can also be used. © 2013 Eaton. All rights reserved. 34 Industrial Control Panel SCCR • Industrial Control Panel. An assembly of two or more components consisting of one of the following: 1) power circuit components only, such as motor controllers, overload relays, fused disconnect switches, and circuit breakers; 2)control circuit components only, such as push buttons, pilot lights, selector switches, timers, switches, and control relays; 3) a combination of power and control circuit components. These components, with associated wiring and terminals, are mounted on, or contained within, an enclosure or mounted on a subpanel. The industrial control panel does not include the controlled equipment. 35 © 2013 Eaton. All rights reserved. 35 UL 508A Supplement SB • What Needs to be Analyzed per UL 508A, Supplement SB? • All power circuit components (SB 4.1) • Feeder and branch circuit components that supply power to loads (motors, lighting, heating and appliances) • Includes disconnect switches, fuses, circuit breakers, load controllers, overload relays, power distribution/terminal blocks, bus bars, etc. • Control circuit components are NOT required to be analyzed • Pushbuttons, pilot lights, selector switches, timers, control relays, etc. © 2013 Eaton. All rights reserved. 36 12 4/1/2014 UL 508A Supplement SB • How to Determine Component SCCR (SB4.2.2)? • The SCCR marked on the component or on instructions. • The SCCR determined by the voltage rating of the component and the assumed short circuit current from Table SB4.1. • or • The SCCR for a load controller, motor overload relay, or combination motor controller that has been investigated in accordance with the performance requirements, including short circuit test requirements for standard fault currents or high fault currents specified in the Standard for Industrial Control Equipment, UL 508, and described in the manufacturer’s procedure. © 2013 Eaton. All rights reserved. 37 UL 508A Supplement SB • What are the Rules (Sweep 1)? • Lowest component SCCR limits assembly SCCR unless: • Combination ratings can be used to increase branch circuit component ratings (SB 4.2.2) • Component with marked/specified OCPD • Check with component manufacturer for combination ratings © 2013 Eaton. All rights reserved. 38 Combination Ratings - Branch Component SCCR OCPD I.R. Nameplate Voltage: 480 SCCR: 100kA • Use combination ratings with specified/marked OCPD to fix low rated branch components Combination ratings of overcurrent protective devices and components can be used © 2013 Eaton. All rights reserved. 39 13 4/1/2014 Combination Ratings - PDBs PDBFS220 (4 – 14 Load Side Conductors) – 100kA with 175A Class J fuse or less 40 © 2013 Eaton. All rights reserved. 40 Combination Ratings – Motor Starter & Contactor © 2013 Eaton. All rights reserved. 41 Combination Ratings - MMP • OL Protection Only • Fuse or Circuit Breaker Required for SC Protection • Suitable for Group Installations • Straight Ratings (480V) © 2013 Eaton. All rights reserved. 42 14 4/1/2014 Combination Ratings – Type E/F • Combination Motor Controller • SC & OL Protection • Line Side Adapters Required • Slash Ratings (480/277V) © 2013 Eaton. All rights reserved. 43 UL 508A Supplement SB • What are the Rules (Sweep 1)? • Lowest component SCCR limits assembly SCCR unless: • Feeder components are used that limit the shortcircuit current reducing the need for higher branch circuit component SCCR (SB 4.3) • Current limiting overcurrent protective devices • Transformers rated 10kVA or less © 2013 Eaton. All rights reserved. 44 Feeder vs. Branch Circuits Feeder Circuit Branch Circuit Branch Circuit © 2013 Eaton. All rights reserved. 45 15 4/1/2014 Use of CL Devices - OCPD • CL Device must be in the feeder circuit • For CL Fuses or Circuit Breakers • Use PEAK Let-through, Not RMS Let-Through (more conservative) • Fuses - cannot use manufacturer specific fuse data – only tables based on performance requirements from UL 248 (more conservative - apply to all manufacturers) • Circuit Breakers - must be Listed and marked “currentlimiting” and use published let-thru curves (most circuit breakers are not CL) • Can only raise downstream BRANCH circuit components (not overcurrent protective devices – fuses/circuit breaker IR or Combination motor controllers SCCR) © 2013 Eaton. All rights reserved. 46 Use of CL Devices - OCPD Component SCCR OCPD I.R. Nameplate Voltage: 480 SCCR: 14kA F • Current limiting feeder OCPD can be used to increase branch component SCCR. B Use of CL OCPD can only fix components © 2013 Eaton. All rights reserved. 47 Use of CL Devices - Transformers • CL Device must be in the feeder circuit • For Transformers • If 10kVA with secondary devices (components and overcurrent devices) of 5kA or higher, apply the IR of the primary overcurrent protective device • If 5kVA (120V Secondary) with secondary devices (Components and overcurrent devices) of 2kA or higher, apply the IR of the primary overcurrent protective device © 2013 Eaton. All rights reserved. 48 16 4/1/2014 Use of CL Devices - Transformers Component SCCR OCPD I.R. Nameplate Voltage: 480 SCCR: 200kA 10 kVA • Transformers can be used to limit the short-circuit current available • If 10kVA & sec comp = 5kA+ • If 5kVA/120V & sec comp = 2kA+ • Then assign entire circuit I.R. of primary overcurrent device Use of Small Transformers (10kVA or less) can increase secondary component/OCPD ratings © 2013 Eaton. All rights reserved. 49 UL 508A Supplement SB • What are the Rules (Sweep 2)? • Lowest overcurrent protective device interrupting rating (or SCCR for some devices) always limits assembly SCCR • All Feeder and branch circuit overcurrent devices • Tested series combination ratings or series ratings (fuse-circuit breaker or circuit breaker-circuit breaker) are NOT allowed. • Branch circuit overcurrent devices tapped from the feeder circuit supplying a control circuit. • Supplemental protective devices protecting the control circuit transformer in a motor branch circuit. © 2013 Eaton. All rights reserved. 50 Why High SCCR? • NEC & Equipment standards only require the SCCR to be marked • NEC requires the marked value to be adequate for the maximum available fault current • Although not required, high SCCR is often preferred • Flexibility of application • Multiple installations • Fault current unknown • Insufficient SCCR can delay installation © 2013 Eaton. All rights reserved. 51 17 4/1/2014 Fix It - Solutions • High I.R. Protective Devices • Class R • Class J • Class J Drive Fuse • Class T • Class CC • CubeFuse • High Speed • High IR/CL CBs © 2013 Eaton. All rights reserved. 52 Fix It - Solutions • High SCCR Components © 2013 Eaton. All rights reserved. 53 Terminal Blocks & Power Distribution Blocks • Power Distribution Blocks • High SCCR. • Feeder (larger) spacings. • UL Listed • Terminal Blocks • High SCCR • Branch Circuit Spacings • UL Recognized © 2013 Eaton. All rights reserved. 54 18 4/1/2014 Class J • “Junior” • Class J – Low-Peak® • LPJ-(AMP)SP • 600V, 1A – 600A, 300kA • Characteristics • Dual Element Time Delay • Better time delay than CC • Less time delay than RK1/RK5 • Very current limiting • Smaller than RK1/RK5 • Open fuse indication Optional • Applications • Feeder and branch circuits • OEM & Building Systems • Type 2 Protection © 2013 Eaton. All rights reserved. 55 New Fuseblocks • • • • Class R, H, K & J fuse blocks (70A+) High SCCR Modular, snap-together design UL Listed with creepage and clearance distances for feeder and branch circuits. 200A+ meet requirements for service entrance, feeder, and branch circuits. • Optional high-clarity, see-through, fingersafe covers with optional blown fuse indication • Built-in lockout-tagout feature The only modular design on the market with finger-safe covers across the entire line © 2013 Eaton. All rights reserved. 56 New PDB Fuseholder • UL Recognized Class J fuseholder with PDB • Optional IP20 Finger-Safe Covers • 100A, 200A or 400A, 1Pole – 3Pole • 50% space savings, 33% labor savings The only combination PDB/Fuseblock on the market © 2013 Eaton. All rights reserved. 57 19 4/1/2014 Class CF • “CUBE FUSE” • Class CF - TCF(amp), TCF(amp)RN or FCF(amp)RN • TCF - 600Vac/300Vdc, 1-100A, 300kA/100kA • FCF - 600Vac/dc, 1-100A 200kA/50kA • Characteristics • • • • • • DE Time Delay or Fast Acting Class J Performance Very Current Limiting Small physical Size Finger safe IP20 Optional Indicating version time-delay only • Applications • General purpose; e.g. motor circuits (Type 2 Protection, transformers, heaters, feeders and branch circuit protection © 2013 Eaton. All rights reserved. 58 Class CC • “Control Circuit” or “Charlie Chaplin” (little hat) • Class CC - General Features • • • • 600V, up to 30A 200kA Interrupting rating Very Current Limiting Space Saving Design - 13/32” X 1½” • Grooved ferrule provides rejection feature from supplementary fuses with same dimensions (midget fuses) when Class CC fuseholders are used • Offer 3 different fuse types • Time delay (for motor circuit: LP-CC) • Time delay (for control transformer primary: FNQ-R) • Non-time delay (Non-inductive loads: KTK-R) © 2013 Eaton. All rights reserved. 59 Compact Circuit Protector • Compact Circuit Protector (CCP) • 200kA SCCR • 600V • 30A with Class CC Fuses • 30A, 60A or 100A with CUBEFuse® • Smallest fusible disconnect available • Finger-safe design • UL98 branch circuit disconnect • PROVIDES ISOLATION OF CIRCUITS AND LOCK-OUT/TAG-OUT © 2013 Eaton. All rights reserved. 60 20 4/1/2014 Bussmann Surge Protection Devices • UL Product Lineup • • • • • UL 1449 3rd Edition Recognized Di-rail SPDs Surge Protector for Single, Split, Wye and Delta Phases 120V to 600V Type 2 SPD Data/Field Bus Product Lineup • • • • LV/Controls Product Lineup • • • • Surge Protection for low voltage/Control Applications 24v to 240v AC and DC Type 2 or 3 SPD Data communication SPD © 2013 Eaton. All rights reserved. UL 497B Listed BNC Coax Cable, RJ45 / Ethernet Data Cable and Universal 4Pole versions available for popular data signal applications DIN-Rail mount makes installation easy Universal 4-pole SPD is easy to apply in most instrumentation applications up to 180V 61 Questions? © 2013 Eaton. All rights reserved. 21
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