Transcription

Industrial ControlsShort-circuit current rating (SCCR) of industrial control panelsReference ManualEdition06/2013Answers for industry.

1Short-circuit current rating (SCCR) ofIntroductionindustrial control panels2Overview of NEC Article 409NEC Article 409 and UL 508AShort-circuit current rating (SCCR)of industrial control panelsReference Manual06/2013A5E31896849002A/RS-AA/001Overview of Supplement SB3from the UL 508A standardBasic steps for calculating4the SCCR of a control panelFlow chart for calculating the5SCCR of a component

Legal informationWarning notice systemThis manual contains notices you have to observe in order to ensure your personal safety, as well as to preventdamage to property. The notices referring to your personal safety are highlighted in the manual by a safety alertsymbol, notices referring only to property damage have no safety alert symbol. These notices shown below aregraded according to the degree of danger.DANGERindicates that death or severe personal injury will result if proper precautions are not taken.WARNINGindicates that death or severe personal injury may result if proper precautions are not taken.CAUTIONindicates that minor personal injury can result if proper precautions are not taken.NOTICEindicates that property damage can result if proper precautions are not taken.If more than one degree of danger is present, the warning notice representing the highest degree of danger willbe used. A notice warning of injury to persons with a safety alert symbol may also include a warning relating toproperty damage.Qualified PersonnelThe product/system described in this documentation may be operated only by personnel qualified for the specifictask in accordance with the relevant documentation, in particular its warning notices and safety instructions.Qualified personnel are those who, based on their training and experience, are capable of identifying risks andavoiding potential hazards when working with these products/systems.Proper use of Siemens productsNote the following:WARNINGSiemens products may only be used for the applications described in the catalog and in the relevant technicaldocumentation. If products and components from other manufacturers are used, these must be recommendedor approved by Siemens. Proper transport, storage, installation, assembly, commissioning, operation andmaintenance are required to ensure that the products operate safely and without any problems. The permissibleambient conditions must be complied with. The information in the relevant documentation must be observed.TrademarksAll names identified by are registered trademarks of Siemens AG. The remaining trademarks in this publicationmay be trademarks whose use by third parties for their own purposes could violate the rights of the owner.Disclaimer of LiabilityWe have reviewed the contents of this publication to ensure consistency with the hardware and softwaredescribed. Since variance cannot be precluded entirely, we cannot guarantee full consistency. However, theinformation in this publication is reviewed regularly and any necessary corrections are included in subsequenteditions.Siemens AGIndustry SectorPostfach 48 4890026 NÜRNBERGGERMANYA5E31896849002A/RS-AA/001 06/2013 Technical data subject to changeCopyright Siemens AG 2013.All rights reserved

Table of contents1Introduction . 72Overview of NEC Article 409 . 93Overview of Supplement SB from the UL 508A standard . 114Basic steps for calculating the SCCR of a control panel. 134.14.1.14.1.24.1.34.25SB4.2 – Determining the short-circuit current ratings (SCCR) of individual power circuitcomponents .13Basic: Device markings or component instruction sheets .13Basic: Assumed short-circuit current rating .14Basic: Tested combination of devices according to UL508 .144.2.14.2.24.2.3SB4.3 – Adaptation of the available short-circuit current rating based on the peak letthrough currents when using current-limiting devices in the feeder circuit .18Current-limiting transformers .18Current-limiting circuit breakers (according to UL489) .18Current-limiting fuses .204.3SB4.4 – SCCR calculation of the industrial control panel .23Flow chart for calculating the SCCR of a component . 255.1Calculation of the short-circuit current rating of an individual power circuit componentaccording to UL 508A SB4.2.255.2Calculation of the short-circuit current rating of current-limiting feeder components .265.3Calculation of the short-circuit current rating of a control panel in accordance withUL 508A Supplement SB 4.4 .28Short-circuit current rating (SCCR) of industrial control panelsReference Manual, 06/2013, A5E31896849002A/RS-AA/0015

Table of contentsShort-circuit current rating (SCCR) of industrial control panels6Reference Manual, 06/2013, A5E31896849002A/RS-AA/001

1IntroductionArticle 409 on Industrial Control Panels was added to the NEC (National Electrical Code) inits 2005 edition. This Article requires all Industrial Control Panels to be marked with a shortcircuit current rating. The short-circuit current rating (SCCR) requirements for UL 508A cameinto force in April 2006. These changes impact control panel builders, OEMs and end usersin a number of different ways: The correct choice of power circuit components of a control panel Specification of preferred device manufacturers Design and marking of panels Correct installation and modification of control panelsSiemens is committed to supplying best-in-class products and services to our customers.Siemens provides extensive product documentation to enable its customers to comply withNEC Article 409 and the UL 508A standard.GuideThis document includes the following information: Overview of NEC Article 409 Overview of Supplement SB of the UL 508A standard with relevant examples Process flow charts– Calculating the SCCR value of a component– Calculating the SCCR with current-limiting feeder components– Calculation of the SCCR of a control panelFurther information about UL / NFPAUnderwriters Laboratories UL (http://www.ul.com)UL online certifications directory (http://www.ul.com/database)National Fire Protection Association NFPA (http://www.nfpa.org)Short-circuit current rating (SCCR) of industrial control panelsReference Manual, 06/2013, A5E31896849002A/RS-AA/0017

IntroductionShort-circuit current rating (SCCR) of industrial control panels8Reference Manual, 06/2013, A5E31896849002A/RS-AA/001

Overview of NEC Article 4092The "NFPA 70: National Electrical Code" includes "Article 409" on the Construction ofIndustrial Control Panels operating at 600 volts or less.Section 409.2: definition of industrial control panelsSection 409.2 defines an industrial control panel as:"An assembly of two or more components consisting of one of the following:1. Power circuit components only, such as motor controllers, overload relays, fuseddisconnect switches, and circuit breakers2. Control circuit components only, such as pushbuttons, pilot lights, selector switches,timers, switches, control relays3. A combination of power and control circuit components"These components are mounted in an enclosure or panel with the associated wiring andterminals.The industrial control panel does not include the controlled equipment.Section 409.110: Marking of the short-circuit current ratingSection 409.110 requires a short-circuit current rating (SCCR) to be marked on all industrialcontrol panels. This rating must be based on the rating of a listed and labeled assembly oron another approved method for determining the rating. It also includes a fine print note(FPN) reference to UL 508A Supplement SB as an example of an approved method fordetermining the SCCR that may be marked on the panel.Short-circuit current rating (SCCR) of industrial control panelsReference Manual, 06/2013, A5E31896849002A/RS-AA/0019

Overview of NEC Article 409Short-circuit current rating (SCCR) of industrial control panels10Reference Manual, 06/2013, A5E31896849002A/RS-AA/001

Overview of Supplement SB from the UL 508Astandard3Components in the power circuitUL508A is the safety standard for industrial control panels.NEC Article 409 references UL508A Supplement SB as an approved method for determiningthe SCCR of an industrial control panel. The specific method is outlined in Section SB4.The SCCR of the control panel is based on the SCCR of each component in the powercircuit. The component with the lowest SCCR defines the SCCR of the entire panel.Paragraph SB4.2.1 and Table SB4.1 list the following components as part of the powercircuit:Disconnect switchesSupplementary protectorsBranch circuit protective devicesBusbarsFuseholdersCurrent metersLoad controllersCurrent shuntsMotor overload relaysSwitch unitsReceptaclesTerminal blocks or power distributionblocksParagraph SB3.2.1 states that the primary short-circuit protective device for the controlcircuit is also included in the calculation for the SCCR for the power circuit. Therefore, theSCCR of the overcurrent protective devices (except for supplementary protectors recognizedaccording to UL1077 or sets of supplemental fuses recognized according to UL248-13) areincluded in calculation of the SCCR of the control panel. Control circuit components on theload side of these devices are not included in calculation of the SCCR.Short-circuit current rating (SCCR) of industrial control panelsReference Manual, 06/2013, A5E31896849002A/RS-AA/00111

Overview of Supplement SB from the UL 508A standardShort-circuit current rating (SCCR) of industrial control panels12Reference Manual, 06/2013, A5E31896849002A/RS-AA/001

Basic steps for calculating the SCCR of a controlpanel4.14SB4.2 – Determining the short-circuit current ratings (SCCR) ofindividual power circuit componentsThe short-circuit strength of individual power circuit components can be calculated usingthree possible methods: Based on device markings or component instruction sheets Based on assumed short-circuit current rating Based on tested combinations of devices according to UL5084.1.1Basic: Device markings or component instruction sheetsMost Siemens power control and circuit protection components include a standard shortcircuit rating on the front or on the nameplate.Example of marking on a 3RT contactorFigure 4-1NameplateExceptionThe short-circuit current rating of Siemens frequency converters is stated in the operatinginstructions or the relevant catalogs. This complies with the requirements of NEC Article 409and is therefore entered in the relevant UL test reports.Moreover, in the case of frequency converters that are protected with fuses, circuit breakersaccording to UL489 or self-protected combination motor controllers per UL508 type E, theshort-circuit current rating of the drive in conjunction with the line-side protective device isstated.Short-circuit current rating (SCCR) of industrial control panelsReference Manual, 06/2013, A5E31896849002A/RS-AA/00113

Basic steps for calculating the SCCR of a control panel4.1 SB4.2 – Determining the short-circuit current ratings (SCCR) of individual power circuit components4.1.2Basic: Assumed short-circuit current ratingFor unmarked components, the assumed maximum short-circuit current rating in accordancewith Table SB4.1 (see extract) can be used for calculating the short-circuit current rating.Figure 4-24.1.3Table SB4.1: Assumed maximum short-circuit current rating for unmarked components(extract)Basic: Tested combination of devices according to UL508To increase the short-circuit current rating of a device, an appropriate protective device mustbe connected on the line side of it. Which protective device is suitable is stated in therelevant UL test report of the device whose short-circuit current rating is to be increased.UL test reportExample: A 3RT2015 contactor has a default value of 5 kA according to its rating plate. TheUL test report states the protective devices with which the short-circuit current rating can beincreased.Figure 4-3Extract from the UL test reportShort-circuit current rating (SCCR) of industrial control panels14Reference Manual, 06/2013, A5E31896849002A/RS-AA/001

Basic steps for calculating the SCCR of a control panel4.1 SB4.2 – Determining the short-circuit current ratings (SCCR) of individual power circuit componentsDownload: certificates of complianceCertificates of Compliance (http://www.siemens.com/sirius/support) for switching devices canbe downloaded on the Internet. These contain the contents of the UL test reports that arerelevant for configuration.Figure 4-4Support: certificate download 1Figure 4-5Support: certificate download 2Short-circuit current rating (SCCR) of industrial control panelsReference Manual, 06/2013, A5E31896849002A/RS-AA/00115

Basic steps for calculating the SCCR of a control panel4.1 SB4.2 – Determining the short-circuit current ratings (SCCR) of individual power circuit componentsFigure 4-6Support: certificate download 3Figure 4-7Support: certificate download 4General information and relevant product documentation (including configuration manuals)relating to North America are also available on the .Short-circuit current rating (SCCR) of industrial control panels16Reference Manual, 06/2013, A5E31896849002A/RS-AA/001

Basic steps for calculating the SCCR of a control panel4.1 SB4.2 – Determining the short-circuit current ratings (SCCR) of individual power circuit componentsExampleThe following example shows a circuit breaker according to UL489 in a feeder circuit and atested combination according to UL508 Type F. The circuit breaker has been tested andapproved for 100 kA and the self protected combination motor controller per UL 508 Type Ehas also been tested and approved for 65 kA.The combination shown below complies with 65 kA according to the UL rules.Figure 4-8Example combinationShort-circuit current rating (SCCR) of industrial control panelsReference Manual, 06/2013, A5E31896849002A/RS-AA/00117

Basic steps for calculating the SCCR of a control panel4.2 SB4.3 – Adaptation of the available short-circuit current rating based on the peak let-through currents whenusing current-limiting devices in the feeder circuit4.2SB4.3 – Adaptation of the available short-circuit current rating basedon the peak let-through currents when using current-limiting devicesin the feeder circuitWhen short-circuit-current-limiting components are used in the feeder circuit, all componentsin the branch circuit must be rated for the peak let-through current of the short-circuit-currentlimiting components used in the feeder circuit.4.2.1Current-limiting transformersFor branch circuits powered through a load transformer with an isolated secondary winding,the following applies to the short-circuit current rating on the secondary side: Transformer 10 kVA max. 5 kA on the secondary side, i.e. all devices on thesecondary side must be rated for 5 kA or higher Transformer 5 kVA and max. 120 V max. 2 kA on the secondary side, i.e. all deviceson the secondary side must be rated for 2 kA or higher All other transformers are not current-limiting, i.e. they have the same short-circuit currenton the secondary and the primary side4.2.2Current-limiting circuit breakers (according to UL489)To be able to use a circuit breaker in accordance with UL489 as a current-limitingcomponent in the feeder circuit, it must be marked "current limiting".In this case, the let-through currents of the circuit breaker must be considered. The letthrough current can be obtained from the circuit breaker characteristic.ExampleThe SCCR of the assembly is the breaking capacity of the circuit breaker in the feeder circuitunder the following conditions: The SCCR of all individual components in the branch circuit is not lower than the peak letthrough current of the circuit breaker in the feeder circuit. The breaking capacity of all branch circuit protective devices or the SCCR of allcombination motor controllers is not lower than the breaking capacity of the circuitbreaker in the feeder circuit. The SCCR of the assembly is the lowest breaking capacity of a branch circuit protectivedevice or combination motor controller connected on the load side of the circuit breaker inthe feeder circuit if this is smaller than the breaking capacity of the circuit breaker in thefeeder circuit. The SCCR of the assembly is the lowest SCCR of each branch circuit on the load side ofthe circuit breaker if the above conditions do not apply.Short-circuit current rating (SCCR) of industrial control panels18Reference Manual, 06/2013, A5E31896849002A/RS-AA/001

Basic steps for calculating the SCCR of a control panel4.2 SB4.3 – Adaptation of the available short-circuit current rating based on the peak let-through currents whenusing current-limiting devices in the feeder circuitThe selected circuit breaker lets 22 kAthrough at a short-circuit of 100 kA. In other words, all components in thebranch circuit must be designed for atleast 22 kA. The control panel is suitablefor a maximum let-through value of100 kA.Short-circuit current rating (SCCR) of industrial control panelsReference Manual, 06/2013, A5E31896849002A/RS-AA/00119

Basic steps for calculating the SCCR of a control panel4.2 SB4.3 – Adaptation of the available short-circuit current rating based on the peak let-through currents whenusing current-limiting devices in the feeder circuit4.2.3Current-limiting fusesOnly fuses from UL508A, Tab. SB4.2 may be used as current-limiting fuses. This tableshows the relevant peak let-through currents (see column Ip x 10³).Figure 4-9Table SB4.2The SCCR of the assembly is the breaking capacity of the fuse in the feeder circuit under thefollowing conditions: The SCCR of all individual components in the branch circuit is not lower than the peak letthrough current of the fuse in the feeder circuit. The breaking capacity of all branch circuit protective devices or the SCCR of allcombination motor controllers is not lower than the breaking capacity of the fuse in thefeeder circuit. The SCCR of the assembly is the lowest breaking capacity of a branch circuit protectivedevice or combination motor controller connected on the load side of the fuse in the feedercircuit if this is smaller than the breaking capacity of the fuse in the feeder circuit. The SCCR of the assembly is the lowest SCCR of each branch circuit on the load side ofthe fuse if the above conditions do not apply.Short-circuit current rating (SCCR) of industrial control panels20Reference Manual, 06/2013, A5E31896849002A/RS-AA/001

Basic steps for calculating the SCCR of a control panel4.2 SB4.3 – Adaptation of the available short-circuit current rating based on the peak let-through currents whenusing current-limiting devices in the feeder circuitExamplesThe following two examples show a fuse as the feeder circuit protective device. Theprocedure described also applies if a circuit breaker according to UL489 is used as thefeeder circuit protective device.Example 1 SCCR 35 kA since the circuit breaker is only suitable for 35 kA.The contactor and overload relays are protected by the fuse in the feeder circuit since 5 kA(SCCR of contactor and overload relays) is 3 kA (let-through value of the fuse).Short-circuit current rating (SCCR) of industrial control panelsReference Manual, 06/2013, A5E31896849002A/RS-AA/00121

Basic steps for calculating the SCCR of a control panel4.2 SB4.3 – Adaptation of the available short-circuit current rating based on the peak let-through currents whenusing current-limiting devices in the feeder circuitExample 2 SCCR 50 kA since the breaking capacity of the circuit breaker is not lower than that of thefuse.The contactor and overload relays are protected by the fuse in the feeder circuit since 5 kA(SCCR of contactor and overload relays) is 3 kA (let-through value of the fuse).Short-circuit current rating (SCCR) of industrial control panels22Reference Manual, 06/2013, A5E31896849002A/RS-AA/001

Basic steps for calculating the SCCR of a control panel4.3 SB4.4 – SCCR calculation of the industrial control panel4.3SB4.4 – SCCR calculation of the industrial control panelThe SCCR of the industrial control panel is calculated with limitation to the lowest value of acomponent or a circuit according to SB4.2 or SB4.3.ExampleThe first calculation is based on SB4.2 and looks as the individual SCCR values with whichthe components are marked or that appear on the list of unmarked components.Industrial control panelComponentsNo.Power circuit①Circuit breaker②Contactor③Overload relays④Fuses on the primary side of thecontrol transformerNo.Control circuit⑤Control transformer⑥Control relay⑦Terminal blocks⑧Display lamp⑨HAND-OFF-AUTO selector switchThe components listed under control circuit do not have to be included in the SCCRcalculation for the industrial control panel.The individual SCCR values of the individual power circuit components are as follows:No.Power circuitSCCR at 480 V①Circuit breaker25 kA②Contactor5 kA③Overload relays5 kA④Fuses on the primary side of the controltransformer200 kABoth the contactor and the overload relay have an SCCR of 5 kA at 480 V. If no furtherinformation is available, this industrial control panel would be marked with an SCCR of 5 kAat 480 V AC.Short-circuit current rating (SCCR) of industrial control panelsReference Manual, 06/2013, A5E31896849002A/RS-AA/00123

Basic steps for calculating the SCCR of a control panel4.3 SB4.4 – SCCR calculation of the industrial control panelShort-circuit current rating (SCCR) of industrial control panels24Reference Manual, 06/2013, A5E31896849002A/RS-AA/001

Flow chart for calculating the SCCR of a component5.1Figure 5-15Calculation of the short-circuit current rating of an individual powercircuit component according to UL 508A SB4.2SB4.2Short-circuit current rating (SCCR) of industrial control panelsReference Manual, 06/2013, A5E31896849002A/RS-AA/00125

Flow chart for calculating the SCCR of a component5.2 Calculation of the short-circuit current rating of current-limiting feeder components5.2Figure 5-2Calculation of the short-circuit current rating of current-limitingfeeder componentsSB4.3 (1)Short-circuit current rating (SCCR) of industrial control panels26Reference Manual, 06/2013, A5E31896849002A/RS-AA/001

Flow chart for calculating the SCCR of a component5.2 Calculation of the short-circuit current rating of current-limiting feeder componentsFigure 5-3SB4.3 (2)Short-circuit current rating (SCCR) of industrial control panelsReference Manual, 06/2013, A5E31896849002A/RS-AA/00127

Flow chart for calculating the SCCR of a component5.3 Calculation of the short-circuit current rating of a control panel in accordance with UL 508A Supplement SB4.45.3Figure 5-4Calculation of the short-circuit current rating of a control panel inaccordance with UL 508A Supplement SB 4.4SB4.4Short-circuit current rating (SCCR) of industrial control panels28Reference Manual, 06/2013, A5E31896849002A/RS-AA/001

Service & SupportDownload catalogs and information tter - always up to date:www.siemens.com/sirius/newsletterE-Business in the Industry .siemens.com/sirius/supportContact for all technical information:Technical AssistanceTel.: 49 (911) 895-5900e-mail: rius/technical-assistanceSiemens AGIndustry SectorPostfach 23 5590713 FUERTHGERMANYwww.siemens.com/automationSubject to change without prior noticeOrder No.: A5E31896849002 Siemens AG 2013IndustrialControlsSIRIUS

Section 409.110: Marking of the short-circuit current rating Section 409.110 requires a short-circuit current rating (SCCR) to be marked on all industrial control panels. This rating must be based on the rating of a listed and labeled assembly or on another approved method for d