SCCR Codes and Standards Including: Basic Principles NEC® 409 and UL 508A How to Determine the SCCR of an Industrial Enclosure Agenda Introduction and Basics National Electric Code 2005 Underwriters Laboratories Determining SCCR How to Increase SCCR Mersen Tools 2 Definitions Short Circuit Current – An overcurrent usually defined as being in excess of ten times normal continuous rating usually caused by insulation breakdown or wiring error Short Circuit Current Rating (SCCR) – The prospective symmetrical fault current at a nominal voltage to which an apparatus or system is able to be connected without sustaining damage exceeding the defined acceptance criteria Available Fault Current – The maximum short circuit current that could flow in an unprotected circuit 3 Q Why is SCCR important? & A SCCR is now an important factor when considering UL 508A and the NEC. SCCR is important to you because: – By knowing about SCCR and available fault currents you will create safer working conditions for the personnel who work on or around electrical equipment – You will be able to ensure compliance with the NEC and UL – You can simplify your inspection approval process 4 Q & A Who will be affected? Everybody Industrial Facilities Manufacturing Facilities Contractors Panel Builders System Integrators OEMs Etc… 5 Q & A When will the changes be enforced? The changes are already in place NEC® Article 409 – Industrial Control Panels – Introduced in the 2005 NEC, “Industrial Control Panels” require panels to be clearly marked with a short circuit current rating, SCCR UL 508A – Industrial Control Panels – Listed panels will require the SCCR to be clearly marked on the panel effective April 25, 2006 6 National Electric Code – 2011 The National Electric Code is a standard for the safe installation of electrical wiring and equipment Part of the NFPA (National Fire Protection Association) Not a U.S. Law but is mandated by local or state officials Articles Related to SCCR – Article 230 – Article 409 – Article 670 7 NEC Article 230 - Services 230.1 - Scope – This article covers service conductors and equipment for control and protection of services and their installation requirements 230.82– 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,… 8 NEC Article 409 – Industrial Control Panels 409.1 – Scope – This article covers industrial control panels intended for general use and operating at 600 volts or less 409.110 – Marking – An industrial control panel shall be marked with the following information that is plainly visible after installation: • (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 9 NEC Article 430 – Motors, Motor Circuits, and Controllers 430.1 – Scope – This article covers motors, motor branch circuit and feeder conductors and their protection, motor overload protection, motor control circuits, motor controllers, and motor control centers 430.7(D) – Multimotor and Combination Load Equipment 430.8 – Markings – 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 other necessary data to properly indicate the applications for which it is suitable 10 NEC Article 670 – Industrial Machinery 670.1 – Scope – This article covers the definition of, the nameplate data for, and the size and overcurrent protection of supply conductors to industrial machinery 670.3 – Machine Nameplate Data – (A) Permanent Nameplate. 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: (1)…(5) • (4) Short circuit current rating of the machine industrial control panel based on one of the following: – a. Short circuit current rating of a listed and labeled machine control enclosure or assembly – b. Short circuit current rating established utilizing and approved method 11 Underwriters Laboratories Independent Testing Company Offer 3rd Party Certification Consistent with NEC Relative Articles – – – – – – UL 98 Disconnect Switch UL 248 Low Voltage Fuses UL 508 Industrial Control Equipment UL 512 Fuse Blocks UL 1059 Terminal Blocks (PDB) UL 1449 Surge Protective Devices 12 UL 508A – Industrial Control Panels Guideline for construction and general design Manufacturers that adhere to the requirements are eligible for UL508A Listing of their product Four Parts of UL 508A – Part 1: General Use – Part 2: Specific Use • Enclosures, Elevator Control, Industrial Machinery, Flame Control, Crane Control, Marine Use, Service Equipment Use, AC and Refrigeration – Part 3: Specific Component Requirements – Part 4: Short Circuit Current Ratings 13 UL 508A – Industrial Control Panels Industrial control panel assemblies: – May include motor controllers, overload relays, fused disconnects, circuit breakers, pushbuttons, switches, timers, indicators, wiring, terminals, enclosures, etc… – Will be rated 600V or less – Where ambient temperatures do not exceed 40°C UL 508A does not include panels for Hazardous Locations “NRBX”, which are covered under UL 698A 14 Q & A How do you determine the SCCR of an industrial control panel? Four Step Process 15 It’s as easy as 1…2…3 Step 1: Assign a SCCR to each component in the power circuit Step 2: Assign a SCCR to each branch circuit Step 3: Assign a SCCR to the feeder circuit Step 4: Consider the current-limiting effects of the feeder overcurrent protection devices (OCPD) Before we apply the standard: Power Electrical Symbols Power Circuit vs. Control Circuit Branch Circuit vs. Feeder Circuit 16 Power Electrical Symbols NO Fuse Fused Disconnect Switch Power Transformer NC Relay NC NO Circuit Breaker Motor Starter 17 Electric Motor Pushbutton Control Circuit vs. Power Circuit Control Circuit Control Circuit Power Circuit Power Circuit 18 Branch Circuit vs. Feeder Circuit Feeder Circuit Branch Circuit #1 19 Branch Circuit #2 Applying the Standard Let’s analyze an example circuit 20 Example Circuit 21 Step 1: Assign a SCCR to each component in the power circuit SCCR of a component shall be established by one of the following: 1. SCCR marked on the component or on instructions provided with the component 2. SCCR can be determined by the voltage rating of the component and the assumed short circuit current from Table SB4.1 3. SCCR for a load controller, motor overload relay, or combination motor controller can be determined by type testing under the procedure specified by UL508 and as described in the manufacturers procedure 22 Q & What Components Do I Look For? All Power Circuit Components A Including disconnect switches, branch circuit protective devices, branch circuit fuse holders, load controllers, motor overload relays, terminal blocks, and bus bars, shall have a short circuit current rating expressed in amperes or kilo amperes and volts Exception No. 1: Power transformers, reactors, current transformers, dry-type capacitors, resistors, varistors, and voltmeters are not required to have a short circuit current rating 23 Q & A Where do I find the SCCR of my components? On the product label or in the product manual In today’s industry short circuit current ratings are usually listed in kilo-amperes, or kA 24 If the component SCCR is not listed on the product label or in the product manual use Table SB4.1 25 Mersen Resources for Determining SCCR 26 200kA 100kA 200kA NA 200kA 200kA 10kA 65kA Control Circuit 200kA 5kA 27 Unknown 12A (5HP = 3.7kW) Motor Starter does not have a labeled SCCR and is also not listed in product manual 28 200kA 100kA 200kA NA 200kA 200kA 10kA 65kA Control Circuit 200kA 5kA 29 SB4.1 5kA Step 2: Assign a SCCR to each Branch Circuit Make a pass of each branch circuit – The lowest component SCCR value will be equal to the branch SCCR In this case we have three branch circuits to analyze 30 200kA Branch 1 100kA Branch 2 Branch 3 200kA NA 200kA 200kA 10kA 65kA Control Circuit 200kA 5kA 31 SB4.1 5kA Branch 1 First Pass SCCR = 10kA Branch 1 200kA 10kA 32 Branch 2 First Pass SCCR = 5kA Branch 2 200kA NA 200kA 5kA 33 Control Circuit Branch 3 First Pass SCCR = 5kA Branch 3 65kA SB4.1 5kA 34 Step 3: Assign a SCCR to the Feeder Circuit Make a pass of the feeder circuit and determine the lowest SCCR value 35 Feeder Circuit SCCR = 100kA Feeder 200kA 200kA 100kA 36 Q What if we stopped now? & A The panel SCCR would be equal to that of the component with the lowest SCCR; in this case 5kA (Electronic Motor Controller & 12A Motor Starter) Step 4 is pivotal when attempting to increase panel SCCR UL 508A, SB4.3 – Feeder Components that limit the short circuit current available – Power Transformer – Circuit Breaker – Fuse Compare the Ip of the feeder OCPD to the SCCR of the feeder and each branch circuit – If the Ip of the feeder OCPD is not greater than the SCCR of the feeder or branch then the feeder or branch will have an SCCR equal to the appropriate Ip column on SB4.2 37 Step 4: Consider the current-limiting effects of the feeder over-current protection devices Power Transformer – Use SB4.3.1 Circuit Breaker – The panel builder must select the current limiting breaker based on the published peak let-thru curve data provided by the breaker manufacturer. Listed breakers rated 15A or 20A, 600V or less, also labeled “current limiting” are able to limit the current to 5kA and 10kA respectively. Fuse – Refer to UL 508A Table SB4.2 to determine the Ip of the fuse – Class CC, G, J, L, RK1, RK5 or T 38 Feeder OCPD In this example the feeder overcurrent protection device is an AJT60 – – – – Class J 60A 600V Time Delay 200kA Feeder 200kA 100kA 39 Class J 60A – 50kA peak Ip = 8kA – 100kA peak Ip = 10kA – 200kA peak Ip = 16kA 40 Ip = 10kA @ 100kA 200kA Branch 2 = 5kA Branch 1 = 10kA Branch 3 = 5kA 100kA 200kA NA 200kA 200kA 10kA 65kA Control Circuit 200kA 5kA 41 SB4.1 5kA Branch 1 Second Pass SCCR = 100kA Branch 1 = =100kA 10kA Ip = 10kA @ 100kA 200kA 10kA 42 Ip = 10kA @ 100kA 200kA Branch 1 = 100kA Branch 2 = 5kA Branch 3 = 5kA 100kA 200kA NA 200kA 200kA 10kA 65kA Control Circuit 200kA 5kA 43 SB4.1 5kA Panel SCCR is still 5kA Summary – – – – Feeder SCCR = 100kA Branch 1 SCCR = 100kA (was 10kA) Branch 2 SCCR = 5kA Branch 3 SCCR = 5kA Branches 2 and 3 are limiting our panel SCCR Lets examine Branch 2 in more detail… 44 Branch 2 In this case the Power Transformer is a component that limits short circuit current available Using UL508A SB4.3.1 we can determine the current limiting capabilities of the power transformer Branch 2 = 5kA 200kA NA 200kA Power Transformer Specs – 5KVA – 480V – Pri – 120V – Sec 45 5kA Control Circuit The current limiting effects of a Power Transformer UL508A SB4.3.1 – For branch circuit supplied by a power transformer with an isolated secondary winding, the short circuit current rating on the line side of the transformer shall be one of the following: XFMR Rating less than or = 10kVA less than or = 5kVA greater than 10kVA Secondary Voltage Secondary Devices SCCR on line side of transformer not specified greater than or = 5kA Use rating on primary overcurrent device 120V maximum greater than or = 2kA Use rating on primary overcurrent device - - Use lowest SCCR of secondary current components 46 Branch 2 Second Pass SCCR = 200kA According to SB4.3.1 our branch power transformer will limit the let-thru current to 2kA Branch SCCR is equal to our primary overcurrent device Branch 2 200kA = 5kA 200kA NA 200kA – ATQR25 5kA 47 Control Circuit Panel SCCR is 5kA Ip = 10kA @ 100kA Limiting Factor is Branch 3 200kA Branch 2 = 200kA Branch 1 = 100kA Branch 3 = 5kA 100kA 200kA NA 200kA 200kA 10kA 65kA Control Circuit 200kA 5kA 48 SB4.1 5kA Panel SCCR is still 5kA Summary – – – – Feeder SCCR = 100kA Branch 1 SCCR = 100kA (was 10kA) Branch 2 SCCR = 200kA (was 5kA) Branch 3 SCCR = 5kA Branch 3 is the limiting factor in our panel! 49 Q 1. 2. 3. 4. & A What can I do to increase my panel SCCR? There are four methods that could be utilized Upgrade to components with higher SCCR Add sub-feeder fuses Upgrade feeder overcurrent protection device with a higher current limiting device Consider type tested components, i.e., components that have been tested by the manufacturer under specific conditions and witnessed by UL 50 Option 1: Upgrade to components with higher SCCR Solution Branch 3 5kA ==65kA – Replace the un-labeled motor starter with one that has a SCCR of 10kA 65kA Now we can utilize the current limiting capabilities of the feeder OCPD Ip = 10kA @ 100kA SB4.1 10kA 5kA 51 Option 2: Add a sub-feeder fuse By adding a sub-feeder fuse, the standard allows you to use this fuse as your current limiting feeder protection Branch 3 = 5kA 65kA In this case lets add a Class CC 20A Fuse – ATDR20 SB4.1 5kA 52 Class CC 20A – 50kA peak Ip = 3kA – 100kA peak Ip = 4kA – 200kA peak Ip = 5kA 53 Option 2: Add a sub-feeder fuse Class CC, 20A Branch 3 = =65kA 5kA – ATDR20 – Ip = 4kA @ 100kA Fault 65kA This sub-feeder fuse will allow the panel SCCR to be increased to 65kA because once again the MCCB becomes the limiting device SB4.1 5kA 54 Option 3: Upgrade feeder OCPD 200kA Feeder Not applicable for this example. We are using the most current limiting device Use option 3 if you are using a circuit breaker as your feeder overcurrent protective device 200kA 100kA 55 Option 4: Consider type tested components Some manufacturers “type test” fuses or circuit breakers with their motor starters to achieve a higher SCCR rating when used in combination Each major controller manufacturer type tests their components on an annual basis. Results are available on UL.com Branch 3 = 5kA 65kA SB4.1 5kA 56 Option 4: Consider type tested components Example: – 12A Motor Starter and 15A MCCB are both Schneider products (Square D, Telemecanique) – 12A IEC Contactor • Part # LC1D12 – OVLD Relay, 5.5–8A • Part # LRD12 – 15A Circuit Breaker • Part # GJL36015 57 UL provides links to each manufacturers website displaying the SCCR testing results. (www.ul.com/controlequipment/shortcircuit.html) Com ponent Type Com ponent Manufacturer ICB MC OLR OLR OLR OLR OLR OLR OLR OLR Square D Telemecanique Telemecanique Telemecanique Telemecanique Telemecanique Telemecanique Telemecanique Telemecanique Telemecanique GJL36015M03 LC1D12 LRD10 LRD12 LRD14 LRD16 LRD1510 LRD1512 LRD1514 LRD1516 F MC OLR OLR OLR OLR OLR OLR OLR OLR OLR OLR OLR OLR OLR OLR OLR OLR OLR Any Telemecanique Telemecanique Telemecanique Telemecanique Telemecanique Telemecanique Telemecanique Telemecanique Telemecanique Telemecanique Telemecanique Telemecanique Telemecanique Telemecanique Telemecanique Telemecanique Telemecanique Telemecanique Class CC LC1D12 LRD01 LRD02 LRD03 LRD04 LRD05 LRD06 LRD07 LRD08 LRD10 LRD12 LRD14 LRD16 LRD1508 LRD1510 LRD1512 LRD1514 LRD1516 58 Com ponent Catalog Designation Com ponent kA Com ponent Am ps Com bination Com bination kA Volts 5 5 5 5 5 5 5 5 5 15 12 4-6 5.5 - 8 7 - 10 9 - 13 4-6 5.5 - 8 7 - 10 9 - 13 65 480 200 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 30 12 0.10 - 0.16 0.16 - 0.25 0.25 - 0.40 0.40 - 0.63 0.63 - 1 1 - 1.6 1.6 - 2.5 2.5 - 4 4-6 5.5 - 8 7 - 10 9 - 13 2.5 - 4 4-6 5.5 - 8 7 - 10 9 - 13 100 480 This information is also available by viewing the Mersen USFM vs. Circuit Breaker Comparison Sheet available on our website 59 Option 4: Consider using type tested components Replace the 15A circuit breaker with the USFMCCI and the ATDR20 Branch 3 ==100kA 5kA 200kA The USFMCCI + ATDR25 combined with the Telemecanique Motor Starter yields a SCCR of 100kA 5kA 60 Panel SCCR is now 100kA Summary – – – – Feeder SCCR = 100kA Branch 1 SCCR = 100kA (was 10kA) Branch 2 SCCR = 200kA (was 5kA) Branch 3 SCCR = 100kA (was 5kA) By using option 4 we were able to remove the circuit breaker in Branch 3 and replace it with fusing in order to increase our panel SCCR 61 Questions and Answers 62
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