Short Circuit Current Ratings
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Suggestion on How to Use • Industry Trainers are encouraged to use this material in their sessions • Download both the PowerPoint file (.ppt) and script file (.pdf) • Print the script file (.pdf) and read the script as you view the PowerPoint presentation in the “Slide Show” view. In this way you see the slides in large format and have animation (if there is any) • Must have PowerPoint and Adobe Reader application software on your system. ©2004 Cooper Bussmann ©2004 Cooper Bussmann 2005 National Electrical Code® Changes Affecting Overcurrent Protection ©2004 Cooper Bussmann ©2004 Cooper Bussmann 409 409.110 430.8 670.3(A) 440.4(B) 230.82(3) 100 700.27 701.18 517.26 240.86(A) 100 240.5(B) 240.60(D) 410.73(G) 430.52(C)(6) 430.83(E) New Article 409: Industrial Control Panels SCCR Marking for Industrial Control Panels SCCR Marking on Motor Controllers Industrial Machinery SCCR Marking HVAC Short Circuit Current Rating (SCCR) Marking SCCR Marking on Meter Disconnects Definition for Coordination (selective) Selective Coordination: Emergency Systems Selective Coordination: Legally Required Standby Sys. Selective Coordination: Healthcare Essential Circuits Existing Facilities: Series Rating Engineering Method Definition for Supplementary OCPD Appliance and Extension Cord Protection Renewable Fuses: Replacement ONLY Disconnecting Means: Electric Discharge Lighting Self Protected Comb. Ctrl 1 Pole Interrupting Capacity Motor Controllers Slash Voltage Requirement ©2004 Cooper Bussmann ©2004 Cooper Bussmann Summary of Changes Requiring Marked Short Circuit Current Rating • 409 • 409.110 • 430.8 • 440.4(B) New Article 409 Industrial Control Panels Marked on Industrial Control Panels Marked on Motor Controllers Marked on HVAC Greater than 60A Non Residential • 670.3 Marked on Industrial Machinery • 230.83(3) Marked on Meter Disconnect Switches ©2004 Cooper Bussmann ©2004 Cooper Bussmann Industrial Control Panels ©2004 Cooper Bussmann ©2004 Cooper Bussmann 2002 NEC® and Before • Required marking for interrupting rating of main Overcurrent Protective Device on Industrial machinery (670.3) • Industrial control panels, HVAC control panels, motor controllers, and meter disconnects were not required to be marked with SCCR ©2004 Cooper Bussmann ©2004 Cooper Bussmann Now - 2005 NEC ® Required to be marked with short circuit current rating: Components • Motor Controllers • Meter Disconnects Assembly • Industrial Control Panels • Industrial Machinery Electrical Panels • HVAC Panels above 60A nonresidential ©2004 Cooper Bussmann ©2004 Cooper Bussmann WHY???? ©2004 Cooper Bussmann ©2004 Cooper Bussmann Short Circuit Current Ratings (SCCR) What is a Short Circuit Current Rating? • The maximum short circuit current a component, assembly or equipment can safely withstand when protected by a specific overcurrent protective device, or for a specified time interval • SCCR pertains to protection of components, multiple component assemblies or entire control panels ©2004 Cooper Bussmann ©2004 Cooper Bussmann Short Circuit Current Ratings Short Circuit Current Rating is not the same as Interrupting Rating: • Interrupting Rating – Maximum available current a fuse or circuit breaker can safely interrupt under standard test conditions Class H Fuses 10kAIR • Interrupting Rating only pertains to the overcurrent protective device • Adequate Interrupting Ratings do not ensure protection of circuit components, assemblies or 50,000A Fault equipment Inadequate Interrupting Rating ©2004 Cooper Bussmann ©2004 Cooper Bussmann Marked Short Circuit Current Ratings Why are Marked Short Circuit Current Ratings Important? • Needed to ensure compliance with NEC® 110.10 • Helps to eliminate hazards where components and equipment are applied above their ratings • Simplifies inspection approval process ©2004 Cooper Bussmann ©2004 Cooper Bussmann Marked Short Circuit Current Ratings Component Marking Requirements • Short Circuit Current Rating may be established during testing as part of the listing and labeling process for individual components or multiple component assemblies ©2004 Cooper Bussmann ©2004 Cooper Bussmann Meter Disconnects Marked Short Circuit Current Rating 230.82(3) – Equipment Connected to the Supply Side of Service Disconnect. Only the following equipment shall be permitted to be connected to the supply side of the service disconnecting means: (3) Meter disconnect switches nominally rated not in excess of 600 volts that have a short-circuit current rating equal to or greater than the available short circuit current, provided all metal housings and service enclosures are grounded. ©2004 Cooper Bussmann ©2004 Cooper Bussmann 230.82(3) Meter Disconnects Marked Short Circuit Current Ratings Meter Disconnect Switches: • Must have a marked short circuit current rating equal to or greater than the available short circuit currents • Typically achieved by a fused disconnect utilizing current-limiting fuses ©2004 Cooper Bussmann ©2004 Cooper Bussmann 430.8 Motor Controllers Marked Short Circuit Current Ratings 430.8 – Motor Controllers A controller shall be marked with the manufacturer’s name or identification, the voltage, the current or horsepower rating, the short-circuit current rating, and such other necessary data to properly indicate the applications for which it is suitable. ©2004 Cooper Bussmann ©2004 Cooper Bussmann 430.8 Motor Controllers Marked Short Circuit Current Ratings Exceptions where the Short Circuit Current Rating is not required on the controller: • 1/8HP or less motors which are normally left running and constructed not to be damaged by overloads • 1/3HP or less portable motors where the controller is the attachment plug and receptacle • The rating is marked elsewhere on an assembly • The assembly into which the controller is to be installed is marked with a rating • Controller is rated 2HP or less at 300V or less and is listed exclusively for general purpose branch circuits ©2004 Cooper Bussmann ©2004 Cooper Bussmann Motor Controllers Marked Short Circuit Current Ratings • UL 508 has: • “Standard” fault current test • An optional “high available” fault current test • Optional Type 2 “no damage”, “high available” fault current (UL 508E) • “Standard” level: – 5kA for 0 - 50HP ratings – 10kA for 51 - 200HP ratings, etc. • Current limiting fuses are often used in the optional “high-available” fault current tests and Type 2 “no damage” tests to achieve high short circuit current ratings ©2004 Cooper Bussmann ©2004 Cooper Bussmann Marked Short Circuit Current Ratings Motor Controller Label Example (from an 80A, 40HP rated controller) GENERAL PURPOSE SWITCH INTERRUPTEUR, USAGE GENERAL Short circuit rating 100kA at 600VAC max when protected by 100A class J or T 5kA when protected by 150A class H or RK5 fuses LISTED 3E73 MAN MTR CNTRL ©2004 Cooper Bussmann ©2004 Cooper Bussmann Marked Short Circuit Current Ratings Equipment Marking Requirements • Short Circuit Current Rating can be established during testing as part of the Listing and Labeling process • Where testing is not feasible, Short Circuit Current Ratings can be determined using approved engineering methods ©2004 Cooper Bussmann ©2004 Cooper Bussmann Marked Short Circuit Current Ratings 409.110 – Industrial Control Panels – Marking. An industrial control panel shall be marked with the following information that is plainly visible after installation: (3) Short-circuit current rating of the industrial control panel based on one of the following: a. Short-circuit current rating of a listed and labeled assembly b. Short-circuit current rating established utilizing an approved method FPN: UL 508A-2001, Supplement SB, is an example of an approved method ©2004 Cooper Bussmann ©2004 Cooper Bussmann Industrial Control Panels: Now Marked with Short Circuit Current Rating ©2004 Cooper Bussmann ©2004 Cooper Bussmann Marked Short Circuit Current Ratings 670.3 – Industrial Machine Nameplate Data. (A) Permanent Nameplate. … shall be attached to the control equipment enclosure or machine and shall be plainly visible after installation. The nameplate shall include the following information: (4) Short-circuit current rating of the industrial control panel based on one of the following: a. Short-circuit current rating of a listed and labeled assembly b. Short-circuit current rating established utilizing an approved method FPN: UL 508A-2001, Supplement SB, is an example of an approved method ©2004 Cooper Bussmann ©2004 Cooper Bussmann Marked Short Circuit Current Ratings Example: Industrial Machinery Control Panel Label Plastics Processing Machine Short SN2356YUP77 Serial Number 87 Amperes Current 25 Horsepower Largest Motor H.P. 60 Ampere Max OCP Device 460 - 480 volts Voltage 3ph., 60 Hz Phase & Freq.. Amperes RMS Short Circuit Current Rating Circuit Current Rating100,000 100,000 Amperes Diagram Numbers CM 12.1 THRU CM 12.5 Quality Machine Tool Somewhere, USA ©2004 Cooper Bussmann ©2004 Cooper Bussmann RMS Marked Short Circuit Current Ratings 440.4(B) – Marking on Hermetic Refrigerant Motor-Compressors and Equipment (B) Multimotor and Combination-Load Equipment. Multimotor and combination-load equipment shall be provided with a visible nameplate marked with the maker’s name, the rating in volts, frequency and number of phases, minimum supply circuit conductor ampacity, the maximum rating of the branch-circuit short-circuit and ground-fault protective device, and the short-circuit current rating of the motor controllers or industrial control panel. ©2004 Cooper Bussmann ©2004 Cooper Bussmann Marked Short Circuit Current Ratings Combination Load and Multimotor HVAC and Refrigeration Equipment Exceptions: • Equipment used in one and two family dwellings • Cord-and-attachment-plug connected equipment • Equipment supplied by a branch circuit protected at 60A or less ©2004 Cooper Bussmann ©2004 Cooper Bussmann Marked Short Circuit Current Ratings Example of HVAC Label HVAC Control Panel Short Serial Number Current Min Circuit Ampacity Max Fuse Size Voltage Phase & Freq.. Short Circuit CurrentRating Rating Circuit Current HVDB708429521 72 Amperes 90 Amperes 125 Ampere 460 - 480 volts 3ph., 60 Hz 40,000 Amperes RMS 40,000 Amperes RMS HVAC Equipment, Inc. Anytown, USA ©2004 Cooper Bussmann ©2004 Cooper Bussmann Ensuring Compliance For equipment requiring Marked Short Circuit Current Ratings • Engineer provides: • Available short circuit currents at each installation point • Short circuit current rating of each piece of equipment or panel • During site inspection, inspector compares actual marked short circuit current ratings to the submitted data: planned SCCRs and available short circuit currents ©2004 Cooper Bussmann ©2004 Cooper Bussmann Ensuring Compliance This method requires proper engineering and analysis by the design engineers and proper review by inspectors. ©2004 Cooper Bussmann ©2004 Cooper Bussmann Ensuring Compliance: Simple Check For Short Circuit Current Rating • Determine the maximum, worst case short circuit current available at the terminals of the supply transformer • Verify that all required equipment is marked with a short circuit current rating sufficient for this maximum, worst case available current • If SCCRs are sufficient: installation approved. If this SCCRs insufficient by this quick check method, a detailed analysis may be required 500 KVA 5%Z 480/277V 1 1500 KVA 2%Z 480/277V 99,165 A 2 ©2004 Cooper Bussmann ©2004 Cooper Bussmann 13,222 A Achieving High Short Circuit Current Ratings High Short Circuit Current Ratings Make Equipment and Controllers: • Easier to specify and install for compliance • More flexible – can be moved from location to location safely ©2004 Cooper Bussmann ©2004 Cooper Bussmann Achieving High Short Circuit Current Ratings Current Limiting Fuses: • Reduce fault energy • Can be used to achieve high short circuit current ratings for motor controllers, assemblies of multiple components, disconnects, and industrial control panels ©2004 Cooper Bussmann ©2004 Cooper Bussmann Regulatory - 2005 NEC® Changes Marked Short Circuit Current Ratings Before Now Marked Plastics Processing Current Voltage 87 Amperes Current Rating 460 - 480 volts Phase & Freq.. 3ph., 60 Hz XYZ Machine Company Anywhere, USA Fuses and Disc PDB Plastics Processing Current 87 Amperes Voltage 460 - 480 volts Phase & Freq.. Short Circuit Current Rating 200 kA SCCR 3ph., 60 Hz 200 kA XYZ Machine Company Anywhere, USA 400A Class J Fuse Disconnect Listed 200,000A SCCR Power Distribution Block Listed 200,000A SCCR Protected by 400A Class J Fuses Branch circuits with current limiting fuses, contactors and overloads Listed 200,000A SCCR ©2004 Cooper Bussmann ©2004 Cooper Bussmann Marked Short Circuit Current Ratings Summary: The 2005 NEC® now requires short circuit current ratings to be marked on: • Meter Disconnect Switches • Motor Controllers • Industrial Control Panels • Industrial Control Panels for Industrial Machinery • Combination Load and Multimotor HVAC and Refrigeration Equipment ©2004 Cooper Bussmann ©2004 Cooper Bussmann Summary of Changes Selective Coordination of Overcurrent Protective Devices • 100 • 700.27 • 701.18 • 517.26 ©2004 Cooper Bussmann ©2004 Cooper Bussmann Definition: Coordination Selective Required for Emergency Systems Required for Legally Required Standby Systems Required for Essential Electrical Standby Systems Selective Coordination 2005 NEC® New Article 100 Definition Coordination (Selective) Localization of an overcurrent condition to restrict outages to the circuit or equipment affected, accomplished by the choice of overcurrent protective devices and their ratings or settings. ©2004 Cooper Bussmann ©2004 Cooper Bussmann What is Selective Coordination? Selective coordination • Isolates an overloaded or faulted circuit • Only the nearest upstream overcurrent protective device opens Why is it required? • Vital for critical systems • Increase system reliability OPENS NOT AFFECTED ©2004 Cooper Bussmann ©2004 Cooper Bussmann Fault Selective Coordination: Avoids Blackouts Lacking Selective Coordination With Selective Coordination Fault OPENS Fault UNNECESSARY POWER LOSS NOT AFFECTED Selective Coordination Requirements Articles affected • 700 Emergency Systems • 701 Legally Required Standby Systems • 517 Health Care Facilities ©2004 Cooper Bussmann ©2004 Cooper Bussmann Selective Coordination Requirements Other supporting requirements • 700.4 Maintenance and Testing Requirements • 700.9(B) Emergency circuits separated from normal supply circuits • 700.9(C) Wiring specifically located to minimize system hazards • 700.16 Failure of one component must not result in a condition where a means of egress will be in total darkness ©2004 Cooper Bussmann ©2004 Cooper Bussmann Selective Coordination Requirements 700.27 Coordination. Emergency system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protective devices. Blackout ©2004 Cooper Bussmann ©2004 Cooper Bussmann Emergency Systems • Required in places of assembly or where panic control is needed • Hotels, theaters, sports arenas, health care facilities and similar institutions • Provide power for: • Ventilation, fire detection, alarm systems, elevators, fire pumps, public safety communications, and continuous processes ©2004 Cooper Bussmann ©2004 Cooper Bussmann Selective Coordination Requirements 701.18 Coordination. Legally required standby system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protective devices. ©2004 Cooper Bussmann ©2004 Cooper Bussmann Legally Required Standby Systems • Supply power to selected loads when normal source fails • Serve loads to: • Heating and refrigeration, communications, ventilation and smoke removal, sewage disposal, lighting systems, and continuous processes ©2004 Cooper Bussmann ©2004 Cooper Bussmann Selective Coordination Requirements 517.26 Application of Other Articles. The essential electrical system shall meet the requirements of Article 700, except as amended by Article 517. Article 517 covers health care facilities Selective coordination required in essential electrical systems – • There are no amendments in Article 517 concerning selective coordination of overcurrent protective devices ©2004 Cooper Bussmann ©2004 Cooper Bussmann Essential Electrical Systems • In health care facilities • Designed to ensure service to lighting and power in critical areas • Essential systems include: • Critical branch, life safety branch, and equipment systems essential for life safety ©2004 Cooper Bussmann ©2004 Cooper Bussmann Objectives For These Important Circuits • Keep loads powered in the event of loss of normal power • Ensure system uptime • Ensure safety to human life in an emergency • Reduce the probability of faults • Provide reliable operation • Minimize the effects of an outage Selective coordination requirements fit well with these objectives ©2004 Cooper Bussmann ©2004 Cooper Bussmann Selective Coordination: Normal Supply Normal Source Emergency Source N ©2004 Cooper Bussmann ©2004 Cooper Bussmann E ATS Selective Coordination: Normal Supply Normal Source Emergency Source Unnecessary Feeder Outage N Fault X1 ©2004 Cooper Bussmann ©2004 Cooper Bussmann E ATS Opens Not Affected Unnecessary Power Loss Selective Coordination: Normal Supply Without Normal Source Emergency Source Unnecessary Main Outage N Fault X1 ©2004 Cooper Bussmann ©2004 Cooper Bussmann E ATS Opens Not Affected Unnecessary Power Loss Selective Coordination: Normal Supply Without With Normal Source Emergency Source N Fault X1 ©2004 Cooper Bussmann ©2004 Cooper Bussmann E Normal Source Emergency Source N ATS Opens Not Affected Unnecessary Power Loss E ATS Selective Coordination: Normal Supply Without With Normal Source Emergency Source N Fault X1 ©2004 Cooper Bussmann ©2004 Cooper Bussmann E Normal Source Emergency Source N ATS Opens Not Affected Unnecessary Power Loss E ATS Isolated to Branch Only Fault X1 Selective Coordination: Emergency Supply Normal Source Emergency Source N ©2004 Cooper Bussmann ©2004 Cooper Bussmann E ATS Selective Coordination: Emergency Supply Normal Source Emergency Source Unnecessary Feeder Outage N Fault X1 ©2004 Cooper Bussmann ©2004 Cooper Bussmann E ATS Opens Not Affected Unnecessary Power Loss Selective Coordination: Emergency Supply Without Normal Source Emergency Source N Fault X1 ©2004 Cooper Bussmann ©2004 Cooper Bussmann E Unnecessary Outage Entire Emergency Source ATS Opens Not Affected Unnecessary Power Loss Selective Coordination: Emergency Supply Without Normal Source Emergency Source N Fault X1 ©2004 Cooper Bussmann ©2004 Cooper Bussmann E Normal Source Emergency Source N ATS Opens Not Affected Unnecessary Power Loss E ATS Selective Coordination: Emergency Supply Without With Normal Source Emergency Source N Fault X1 ©2004 Cooper Bussmann ©2004 Cooper Bussmann E Normal Source Emergency Source N ATS Opens Not Affected Unnecessary Power Loss E ATS Isolated to Branch Only Fault X1 Selective Coordination Ensuring Compliance • Requires proper engineering, specification and installation • Designer must provide proper documentation of coordination • Site inspection should verify correct devices are installed per plans to achieve coordination ©2004 Cooper Bussmann ©2004 Cooper Bussmann What must to be considered? ©2004 Cooper Bussmann ©2004 Cooper Bussmann Selective Coordination - Fuses MELTING ENERGY Short Circuit Region Selectivity Ratio Guide (based on I2T) LINE SIDE KRP-C-1200SP LOAD SIDE Loadside fuse must clear prior to lineside fuse melting ©2004 Cooper Bussmann ©2004 Cooper Bussmann Tm AVAILABLE SHORT-CIRCUIT CURRENT LPS-RK-600SP CLEARING ENERGY Ta Tc Tc Selective Coordination Fuses • Published selectivity ratios • Short circuit study unnecessary ©2004 Cooper Bussmann ©2004 Cooper Bussmann Selective Coordination - Fuses Circuit Selectively Coordinated Low Peak KRP-C-800SP Low Peak LPJ-100SP Loadside Fuse KRP-C_SP LPJ_SP LPS-RK_SP KRP-C_SP 2:1 2:1 2:1 LPJ_SP - 2:1 2:1 LPS-RK_SP - 2:1 2:1 Low Peak LPS-RK-20SP 800/100 = 8:1 only 2:1 needed Selective Coordination achieved Overloads or faults of any level up to 300,000A 100/20= 5:1 only 2:1 needed Selective Coordination achieved ©2004 Cooper Bussmann ©2004 Cooper Bussmann Selective Coordination – Circuit Breakers • Circuit Breakers • • • • • Depends on characteristics and settings Difficult to achieve May be higher cost Full short circuit study is necessary Proper analysis and interpretation a must ©2004 Cooper Bussmann ©2004 Cooper Bussmann Selective Coordination – Circuit Breakers 90A & 400A Molded Case Circuit Breakers • Inherent long delay between unlatching and interrupting due to mechanical means of breaking current • Upstream breaker can unlatch before the downstream breaker can clear the fault • Lack of Selective Coordination in the Short-Circuit Region ©2004 Cooper Bussmann ©2004 Cooper Bussmann Selective Coordination – Circuit Breakers Not Coordinated above 900A 800 A. CB STD @ 0.1 Seconds 1000 800 A w/ STD 100 10 1 TIME IN SECONDS 100 A. CB IT Non Adjustable CURRENT IN AMPERES 100 A 20 A 20 A. CB IT Non Adjustable 0.10 Coordinated for overloads and faults less than 900A ©2004 Cooper Bussmann ©2004 Cooper Bussmann 900A 0.01 1 10 100 1K 10K dteate.tcc Ref. Voltage: 480 Current Scale x10^0 100K Selective Coordination – Circuit Breakers Selectively Coordinated up to CBs’ Interrupting Ratings 800 A. CB STD @ 0.4 Seconds CURRENT IN AMPERES 1000 100 A. CB STD @ 0.1 Seconds 1 Overcurrents of any level up to CBs’ Interrupting Ratings ©2004 Cooper Bussmann ©2004 Cooper Bussmann TIME IN SECONDS 10 20 A. CB IT Non Adjustable 800 A w/ STD 100 100 A w/ STD 20 A 0.10 0.01 1 10 100 1K 10K dteate.tcc Ref. Voltage: 480 Current Scale x10^0 100K Summary of Changes Selective Coordination Required • 100 Definition • 700 Emergency Systems • 701 Legally Required Standby Systems • 517 Health Care Facilities: Essential Electrical Systems ©2004 Cooper Bussmann ©2004 Cooper Bussmann Summary of Changes Series Ratings for Existing Systems 240.86(A) ©2004 Cooper Bussmann ©2004 Cooper Bussmann Series Ratings Series Ratings The 2005 NEC®, section 240.86(A), will now permit selection of series rated combinations for existing systems when the selection is made by a licensed professional engineer. ©2004 Cooper Bussmann ©2004 Cooper Bussmann Series Ratings First … What is a Series Rated Combination? 110.22 & 240.86(A) Labeling Panel MDP1 Contractor Installed Label CAUTION Series Rated Combination with panel LDP1 Rated 200,000 Amperes Replace with Only 200 Amp Class J Fuses Panel Mfr’s Label Contractor Installed Label CAUTION Series Rated Combination with 200 Amp Class J fuses in MDP1 Rated 200,000 Amperes Replace with Only CB Co. XYZ Circuit Breaker ©2004 Cooper Bussmann ©2004 Cooper Bussmann NRTL Listing of Series Combination Rating of 200,000 amperes when CB Co. XYZ Circuit Breaker Protected by Maximum 400 A Class J Fuse Panel LDP1 Series Rating: Fuse/CB 400 A Class J Fuse 200,000 A Interrupting Rating Series Rated Combination 200,000 A. I.R. 20 A XYZ Circuit Breaker Best CB Company 10,000 A Interrupting Rating Up to ISC= 200,000 Amp Available Short Circuit Up to ISC= 200,000 Amp Available Short Circuit ©2004 Cooper Bussmann ©2004 Cooper Bussmann Series Rating: CB/CB 200 A ABC Circuit Breaker Best CB Company 65,000 A Interrupting Rating Series Rated Combination 65,000 A. I.R. 20 A XYZ Circuit Breaker Best CB Company 10,000 A Interrupting Rating Up to ISC= 65,000 Amp Available Short Circuit ©2004 Cooper Bussmann ©2004 Cooper Bussmann Up to ISC= 65,000 Amp Available Short Circuit Background Series Ratings for Existing System Building improvements and replacement transformers may have increased available short circuit currents to levels that exceeded existing circuit breakers’ interrupting ratings. • Serious safety hazard • Does NOT comply with NEC® 110.9 ©2004 Cooper Bussmann ©2004 Cooper Bussmann Background BEFORE 500 KVA 5%Z 480/277V 12,000 A Existing Equipment Circuit Breakers 14,000 A Interrupting Rating ©2004 Cooper Bussmann ©2004 Cooper Bussmann Background BEFORE 500 KVA 5%Z 480/277V AFTER 500 KVA 2% Z 480/277V 12,000 A 30,000 A Existing Equipment Circuit Breakers 14,000 A Interrupting Rating ©2004 Cooper Bussmann ©2004 Cooper Bussmann Safety Hazard Available Short Circuit Current Beyond Circuit Breaker Interrupting Rating 14,000A IR, 480V, Circuit Breaker 50,000 Available ©2004 Cooper Bussmann ©2004 Cooper Bussmann Background Series Ratings for Existing System Up until NEC® 2005 The only option…remove and replace the CB panel with a new CB or fusible switch panel with overcurrent protective devices with sufficient Interrupting ratings. • Costly and Disruptive ©2004 Cooper Bussmann ©2004 Cooper Bussmann New Requirement 240.86(A) Series Rating 240.86(A) Selected Under Engineering Supervision in Existing Installations. The series rated combination devices shall be selected by a licensed professional engineer engaged primarily in the design or maintenance of electrical installations. The selection shall be documented and stamped by the professional engineer. This documentation shall be available to those authorized to design, install, inspect, maintain, and operate the system. This series combination rating, including identification of the upstream device, shall be field marked on the end use equipment. ©2004 Cooper Bussmann ©2004 Cooper Bussmann Series Ratings for Existing System With the 2005 NEC® 240.86(A): • A licensed professional engineer can determine if an upgrade of lineside fuses or circuit breakers can series rate with existing loadside circuit breakers. • This may save owner significant money and provide a safer system ©2004 Cooper Bussmann ©2004 Cooper Bussmann Ensuring Compliance: Series Ratings for Existing Systems Engineer: • Analyzes if lineside fuse or circuit breaker provides protection to the downstream circuit breakers • Provides stamped documentation that is readily available to those involved. ©2004 Cooper Bussmann ©2004 Cooper Bussmann Methods For Existing Systems There may be several analysis options for a licensed professional engineer to rectify situations where existing circuit breakers have inadequate interrupting ratings. Note: In some cases, a suitable method may not be feasible. New methods may surface in the future. ©2004 Cooper Bussmann ©2004 Cooper Bussmann Methods For Existing Systems 1. Check if new fused disconnect can be installed ahead of existing circuit breakers by using an existing, recognized series rated combination. 2. If existing system used series ratings with Class R fuses (RK5 Umbrella), analyze whether a specific Bussmann® Class RK1, J or T fuse may provide protection at the higher short-circuit current. ©2004 Cooper Bussmann ©2004 Cooper Bussmann Methods For Existing Systems 3. Supervise short circuit testing of lineside current-limiting fuses to verify protection is provided to circuit breakers that are identical to installed, existing circuit breakers. 4. Perform analysis to determine if currentlimiting fuses installed on lineside of existing circuit breakers provide adequate protection for circuit breakers. ©2004 Cooper Bussmann ©2004 Cooper Bussmann Suggest Bussmann® Low-Peak® Fuses For new installations, owners, designers, and contractors should consider using fusible switches in fully rated systems • Low-Peak® fuses have 300,000A interrupting rating so changes to electrical system will not cause the available short circuit current to increase beyond their interrupting rating • System reliability: no periodic maintenance and testing required on fuses to ensure their ability to operate as intended ©2004 Cooper Bussmann ©2004 Cooper Bussmann Solution Using Current Limiting Fuses BEFORE 500 KVA 5%Z 480/277V Bussmann Low Peak® Fuse 12,000 A 30,000 A Existing Equipment Circuit Breakers 14,000 A Interrupting Rating ©2004 Cooper Bussmann ©2004 Cooper Bussmann AFTER 500 KVA 2% Z 480/277V Series Ratings for New Systems For new installations, the process remains the same as the 2002 NEC®: • Tested • Listed • Marked • Use the Tables www.bussmann.com and SPD publication ©2004 Cooper Bussmann ©2004 Cooper Bussmann Summary of Changes Series Ratings for Existing Systems 240.86(A) ©2004 Cooper Bussmann ©2004 Cooper Bussmann Series Ratings 2005 NEC® Article 100 Definition Supplementary Overcurrent Protective Device. A device intended to provide limited overcurrent protection for specific applications and utilization equipment such as luminaires (lighting fixtures) and appliances. This limited protection is in addition to the protection provided in the required branch circuit by the branch circuit overcurrent protective device. ©2004 Cooper Bussmann ©2004 Cooper Bussmann Supplementary Overcurrent Protective Devices Examples UL248-14 Supplemental Fuses ©2004 Cooper Bussmann ©2004 Cooper Bussmann UL1077 Supplemental Protectors (Mini-breakers) Supplementary Overcurrent Protective Devices • Do not substitute where a branch circuit overcurrent protective device is required • Capabilities and spacings can be inadequate compared to branch circuit OCPD • Must be evaluated for appropriate application in every instance • Must investigate differences and limitations for the specific application ©2004 Cooper Bussmann ©2004 Cooper Bussmann Supplementary Overcurrent Protective Devices Example of difference between UL489 circuit breaker and UL1077 supplemental protector: Spacings: UL1077 3/8” thru air, 1/2” over surface UL489 1” thru air, 2” over surface ©2004 Cooper Bussmann ©2004 Cooper Bussmann Supplementary Overcurrent Protective Devices Example of difference between UL489 circuit breaker and UL1077 supplemental protector: Time current characteristics UL1077 no standard overload characteristics UL489 standard overload characteristics ©2004 Cooper Bussmann ©2004 Cooper Bussmann Supplementary Overcurrent Protective Devices 10 reasons why UL1077 supplementary devices can not be used for branch circuit protection 1. Not intended for, nor evaluated for branch circuit protection 2. Spacings are inadequate 3. Do not have standard overload characteristics 4. Multipole, 3 phase UL1077 devices not evaluated for all types of overcurrents 5. Most UL1077 devices tested with and rely upon upstream branch circuit device for protection ©2004 Cooper Bussmann ©2004 Cooper Bussmann Supplementary Overcurrent Protective Devices 10 reasons why UL1077 supplementary devices can not be used for branch circuit protection 6. Not required to be tested by closing into fault 7. Not tested for calibration or reusability after fault interruption 8. Considerable damage allowed after short circuit interruption test 9. Not intended for branch circuit protection or disconnecting means 10. Not evaluated for energy let-thru or protection of conductors under short circuit current tests ©2004 Cooper Bussmann ©2004 Cooper Bussmann 240.5(B) Protection of Flexible Cords, Flexible Cables and Fixture Wires • Prior to 2005 NEC®, supply cords of listed appliances, portable lamps, and extension cords assumed protected by branch circuit device However, many fires caused by small wire • With 2005 NEC, these supply cords are considered protected when applied within listing requirements NRTLs & cord and equipment manufacturers determine if small wire protected If specific cords or equipment has poor record, protection may be required If protection needed, could be fuse, GFCI, AFCI, LCDI or combination ©2004 Cooper Bussmann ©2004 Cooper Bussmann 240.5(B) Protection of Flexible Cords, Flexible Cables and Fixture Wires One solution - fused line cords • Cost effective • Good protection • Used extensively in UK and Japan Fused plug ©2004 Cooper Bussmann ©2004 Cooper Bussmann 240.60(D) Renewable Fuses Now Replacement Only 240.86(D) Renewable Fuses. Class H cartridge fuses of the renewable type shall only be permitted to be used for replacement in existing installations where there is no evidence of overfusing or tampering. Not to be used on new installations Reason: renewable fuses have only 10,000A interrupting rating ©2004 Cooper Bussmann ©2004 Cooper Bussmann 240.60(D) Renewable Fuses Now Replacement Only Supports overcurrent protective devices with high interrupting rating For new equipment use: • Low Peak® Fuses 300,000A IR LPJ_SP KRP_C_SP LPS-RK_SP & LPN-RK_SP LP-CC (200,000A IR) • CUBEFusesTM 300,000A IR TCF • Additional fuse types available with high IR ©2004 Cooper Bussmann ©2004 Cooper Bussmann 240.60(D) Renewable Fuses Now Replacement Only Modern current limiting fuses with high interrupting rating also provide: • Best equipment protection • Selective coordination • Reliability over life of system • Minimal maintenance • Possible arc flash hazard reduction • Physical size rejecting features ©2004 Cooper Bussmann ©2004 Cooper Bussmann 410.73(G) Disconnecting Means for Electric Discharge Lighting (1000V or less) 2005 NEC® new section requiring disconnecting means for certain types of luminaires: • That use double-ended lamps • Indoor other than dwellings • Ballasts that can be serviced in place Disconnecting means accessible to qualified person prior to servicing the ballast Effective Jan. 1, 2008 Rationale: safer system for electricians ©2004 Cooper Bussmann ©2004 Cooper Bussmann 430.52(C)(6) Self-Protected Combination Controller Single-Pole Interrupting Capability Limitation New 2005 NEC® 430.52(C)(6) FPN: Proper application of self-protected combination controllers on 3-phase systems, other than solidly grounded wye, particularly on corner grounded delta systems, considers the selfprotected combination controllers’ individual pole-interrupting capability. ©2004 Cooper Bussmann ©2004 Cooper Bussmann 430.52(C)(6) Self-Protected Combination Controller Single-Pole Interrupting Capability Limitation • This limitation can be a safety hazard • The single-pole interrupting capability is not marked on the device • Must check UL508 Standard Device 0 to 200 hp up to 600V: tested only for 8,660A single-pole short circuit current interruption, even though the device may have a three-phase short circuit current rating of 65,000A. ©2004 Cooper Bussmann ©2004 Cooper Bussmann 430.83(E) Slash Voltage Rating for Motor Controllers New 2005 NEC ® 430.83(E) Applications. A motor controller with a slash rating, such as 120/240V or 480Y/277, shall be permitted to be applied in a solidly grounded circuit where the nominal voltage of any conductor to ground does not exceed the lower of the two values of the motor controller’s voltage rating and the nominal voltage between any two conductors does not exceed the higher value of the motor controller’s voltage rating…” ©2004 Cooper Bussmann ©2004 Cooper Bussmann Motor Controller 480Y/277 slash voltage rating 480 volts Line-to-line 480Y/277 Volt Three phase Four wire Solidly grounded wye system A B C N Ground 277 volts Line-to-ground ©2004 Cooper Bussmann ©2004 Cooper Bussmann Slash Rated Exercise Can 480Y/277 Controller Be Used? System Voltage Secondary System Type L-L Volt L-G Volt 480Y/277 Solidly Grounded WYE 480 277 Yes No 480 Resistance Grounded WYE 480 277 Yes No 480 Delta Corner Grounded B Phase 480 480 Yes No 480 Delta Ungrounded 480 * Yes No * Ungrounded delta systems - phase conductors are capacitively coupled to ground ©2004 Cooper Bussmann ©2004 Cooper Bussmann Slash Rated Exercise Can 480Y/277 Controller Be Used? System Voltage Secondary System Type L-L Volt L-G Volt 480Y/277 Solidly Grounded WYE 480 277 Yes No 480 Resistance Grounded WYE 480 277 Yes No 480 Delta Corner Grounded B Phase 480 480 Yes No 480 Delta Ungrounded 480 * Yes No * Ungrounded delta systems - phase conductors are capacitively coupled to ground ©2004 Cooper Bussmann ©2004 Cooper Bussmann Slash Rated Exercise Can 480Y/277 Controller Be Used? System Voltage Secondary System Type L-L Volt L-G Volt 480Y/277 Solidly Grounded WYE 480 277 Yes No 480 Resistance Grounded WYE 480 277 Yes No 480 Delta Corner Grounded B Phase 480 480 Yes No 480 Delta Ungrounded 480 * Yes No * Ungrounded delta systems - phase conductors are capacitively coupled to ground ©2004 Cooper Bussmann ©2004 Cooper Bussmann Slash Rated Exercise Can 480Y/277 Controller Be Used? System Voltage Secondary System Type L-L Volt L-G Volt 480Y/277 Solidly Grounded WYE 480 277 Yes No 480 Resistance Grounded WYE 480 277 Yes No 480 Delta Corner Grounded B Phase 480 480 Yes No 480 Delta Ungrounded 480 * Yes No * Ungrounded delta systems - phase conductors are capacitively coupled to ground ©2004 Cooper Bussmann ©2004 Cooper Bussmann Slash Rated Exercise Can 480Y/277 Controller Be Used? System Voltage Secondary System Type L-L Volt L-G Volt 480Y/277 Solidly Grounded WYE 480 277 Yes No 480 Resistance Grounded WYE 480 277 Yes No 480 Delta Corner Grounded B Phase 480 480 Yes No 480 Delta Ungrounded 480 * Yes No * Ungrounded delta systems - phase conductors are capacitively coupled to ground ©2004 Cooper Bussmann ©2004 Cooper Bussmann Slash Voltage Rating • System must be solidly grounded • Larger device voltage rating greater than system L-L voltage • Smaller device voltage rating greater than system L-G voltage 480Y / 277 V ©2004 Cooper Bussmann ©2004 Cooper Bussmann Single-Pole Interrupting Capability and Slash Voltage Rating Examples The next seven slides demonstrate the limitations of single-pole interrupting capabilities and slash voltage rating. These are examples with circuit breakers. The same issues are applicable to self protected combination controllers for single-pole interruption and slash voltage ratings and motor controllers for slash voltage ratings ©2004 Cooper Bussmann ©2004 Cooper Bussmann Solidly Grounded WYE System SERVICE PANEL BRANCH PANEL 277V Steel Conduit A A 480V B C B 480V C N ©2004 Cooper Bussmann ©2004 Cooper Bussmann N Solidly Grounded WYE System Single Pole Must SERVICE BRANCH Interrupt Fault Current PANEL PANEL 277V Steel Conduit A A 480V B C B 480V C N ©2004 Cooper Bussmann ©2004 Cooper Bussmann N Fault to Conduit Corner Grounded Delta System SERVICE PANEL BRANCH PANEL Steel Conduit A A B C 480V B C ©2004 Cooper Bussmann ©2004 Cooper Bussmann Corner Grounded Delta System Single Pole Must Interrupt Fault Current SERVICE BRANCH PANEL PANEL Steel Conduit A A B C 480V B C ©2004 Cooper Bussmann ©2004 Cooper Bussmann Fault to Conduit Single Pole Interrupting Capability UL 489 Circuit Breaker Procedure UL Single Pole Short-Circuit Test CB Frame Rating 100 A Maximum 101 – 800 A. 480/277V 480V 10,000 Amps 8,660 Amps 10,000 Amps 8,660 Amps Example: 20 A, 480V CB having 65,000 A.I.R. (3 Pole Test). Single pole tested at 8,660 Amps ©2004 Cooper Bussmann ©2004 Cooper Bussmann 480 Volt, 25,000 Amp Line to Ground Single Pole Test UL489 tests single pole at only 8660A 4 Feet 4/0 225 Amp, 480 V Circuit Breaker 35, 000 Amp Three Phase Interrupting Rating Photos on following slide ©2004 Cooper Bussmann ©2004 Cooper Bussmann ©2004 Cooper Bussmann ©2004 Cooper Bussmann 2005 Code Changes THE END
