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SCCR Codes and Standards Including: Basic Principles NEC ® 409 and UL 508A How to Determine the SCCR of an Industrial Enclosure.

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Presentation on theme: "SCCR Codes and Standards Including: Basic Principles NEC ® 409 and UL 508A How to Determine the SCCR of an Industrial Enclosure."— Presentation transcript:

1 SCCR Codes and Standards Including: Basic Principles NEC ® 409 and UL 508A How to Determine the SCCR of an Industrial Enclosure

2 2 Agenda Introduction and Basics National Electric Code 2005 Underwriters Laboratories Determining SCCR How to Increase SCCR Mersen Tools

3 3 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 Definitions

4 4 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 Why is SCCR important? QA &

5 5 Everybody Industrial Facilities Manufacturing Facilities Contractors Panel Builders System Integrators OEMs Etc… Who will be affected? QA &

6 6 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 The changes are already in place When will the changes be enforced? QA &

7 7 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

8 8 NEC Article Services Scope –This article covers service conductors and equipment for control and protection of services and their installation requirements – 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,…

9 9 NEC Article 409 – Industrial Control Panels – Scope –This article covers industrial control panels intended for general use and operating at 600 volts or less – 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

10 10 NEC Article 430 – Motors, Motor Circuits, and Controllers – 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 – Markings –A controller shall be marked with the manufacturers 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

11 11 NEC Article 670 – Industrial Machinery – Scope –This article covers the definition of, the nameplate data for, and the size and overcurrent protection of supply conductors to industrial machinery – 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

12 12 Underwriters Laboratories Independent Testing Company Offer 3 rd 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

13 13 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

14 14 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

15 15 Four Step Process How do you determine the SCCR of an industrial control panel? QA &

16 16 Its 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 over- current protection devices (OCPD) Before we apply the standard: Power Electrical Symbols Power Circuit vs. Control Circuit Branch Circuit vs. Feeder Circuit

17 17 Power Electrical Symbols Fuse PushbuttonElectric MotorMotor StarterCircuit Breaker RelayPower Transformer Fused Disconnect Switch NC NO NC

18 18 Control Circuit vs. Power Circuit Power Circuit Control Circuit

19 19 Branch Circuit vs. Feeder Circuit Branch Circuit #1 Branch Circuit #2 Feeder Circuit

20 20 Applying the Standard Lets analyze an example circuit

21 21 Example Circuit

22 22 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

23 23 QA & All Power Circuit Components What Components Do I Look For? 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

24 24 QA & In todays industry short circuit current ratings are usually listed in kilo-amperes, or kA On the product label or in the product manual Where do I find the SCCR of my components?

25 25 If the component SCCR is not listed on the product label or in the product manual use Table SB4.1

26 26 Mersen Resources for Determining SCCR

27 27 Control Circuit 10kA 200kA 5kA 200kA 65kA Unknown 100kA 200kA NA 200kA

28 28 12A (5HP = 3.7kW) Motor Starter does not have a labeled SCCR and is also not listed in product manual

29 29 SB4.1 5kA Control Circuit 10kA 200kA 5kA 200kA 65kA 100kA 200kA NA 200kA

30 30 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

31 31 Branch 1Branch 2 Branch 3 SB4.1 5kA Control Circuit 10kA 200kA 5kA 200kA 65kA 100kA 200kA NA 200kA

32 32 Branch 1 First Pass SCCR = 10kA 200kA Branch 1 10kA

33 33 Branch 2 First Pass SCCR = 5kA 200kA NA Control Circuit Branch 2 200kA

34 34 Branch 3 First Pass SCCR = 5kA Branch 3 SB4.1 5kA 65kA

35 35 Step 3: Assign a SCCR to the Feeder Circuit Make a pass of the feeder circuit and determine the lowest SCCR value

36 36 Feeder Circuit SCCR = 100kA Feeder 100kA 200kA

37 37 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 I p of the feeder OCPD to the SCCR of the feeder and each branch circuit –If the I p 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 I p column on SB4.2 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) What if we stopped now? QA &

38 38 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 I p of the fuse –Class CC, G, J, L, RK1, RK5 or T

39 39 Feeder OCPD In this example the feeder overcurrent protection device is an AJT60 –Class J –60A –600V –Time Delay Feeder 100kA 200kA

40 40 Class J 60A –50kA peak I p = 8kA –100kA peak I p = 10kA –200kA peak I p = 16kA

41 41 I p = 100kA Branch 1 = 10kA Branch 2 = 5kA Branch 3 = 5kA SB4.1 5kA Control Circuit 10kA 200kA 5kA 200kA 65kA 100kA 200kA NA 200kA

42 42 Branch 1 Second Pass SCCR = 10kA 200kA Branch 1 = 10kA I p = 100kA Branch 1 = 100kA 100kA

43 43 Branch 1 = 100kA Branch 2 = 5kA Branch 3 = 5kA SB4.1 5kA Control Circuit 10kA 200kA 5kA 200kA 65kA 100kA 200kA NA 200kA I p = 100kA

44 44 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…

45 45 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 Power Transformer Specs –5KVA –480V – Pri –120V – Sec 5kA 200kA NA Control Circuit Branch 2 = 5kA 200kA

46 46 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:

47 47 Branch 2 Second Pass SCCR = 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 –ATQR25 200kA 5kA 200kA NA Control Circuit Branch 2 = 5kA 200kA Branch 2 = 200kA

48 48 Branch 1 = 100kA Branch 2 = 200kA Branch 3 = 5kA SB4.1 5kA Control Circuit 10kA 200kA 5kA 200kA 65kA 100kA 200kA NA 200kA I p = 100kA Panel SCCR is 5kA Limiting Factor is Branch 3

49 49 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!

50 50 1. Upgrade to components with higher SCCR 2. Add sub-feeder fuses 3. Upgrade feeder overcurrent protection device with a higher current limiting device 4. Consider type tested components, i.e., components that have been tested by the manufacturer under specific conditions and witnessed by UL There are four methods that could be utilized What can I do to increase my panel SCCR? QA &

51 51 Option 1: Upgrade to components with higher SCCR I p = 100kA Branch 3 = 5kA SB4.1 5kA 65kA 10kA Branch 3 = 65kA Solution –Replace the un-labeled motor starter with one that has a SCCR of 10kA Now we can utilize the current limiting capabilities of the feeder OCPD

52 52 Option 2: Add a sub-feeder fuse SB4.1 5kA 65kA Branch 3 = 5kA By adding a sub-feeder fuse, the standard allows you to use this fuse as your current limiting feeder protection In this case lets add a Class CC 20A Fuse –ATDR20

53 53 Class CC 20A –50kA peak I p = 3kA –100kA peak I p = 4kA –200kA peak I p = 5kA

54 54 Option 2: Add a sub-feeder fuse SB4.1 5kA 65kA Branch 3 = 5kA Branch 3 = 65kA Class CC, 20A –ATDR20 –I p = 100kA Fault This sub-feeder fuse will allow the panel SCCR to be increased to 65kA because once again the MCCB becomes the limiting device

55 55 Feeder 100kA 200kA Option 3: Upgrade feeder OCPD 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

56 56 Option 4: Consider type tested components 65kA SB4.1 5kA Branch 3 = 5kA 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

57 57 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

58 58 UL provides links to each manufacturers website displaying the SCCR testing results. (www.ul.com/controlequipment/shortcircuit.html)

59 59 This information is also available by viewing the Mersen USFM vs. Circuit Breaker Comparison Sheet available on our website

60 60 Option 4: Consider using type tested components Branch 3 = 5kA 200kA 5kA Branch 3 = 100kA Replace the 15A circuit breaker with the USFMCCI and the ATDR20 The USFMCCI + ATDR25 combined with the Telemecanique Motor Starter yields a SCCR of 100kA

61 61 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

62 62 Questions and Answers


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