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SCCR Codes and Standards

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

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

3 Definitions Short Circuit Current Short Circuit Current Rating (SCCR)
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

4 Q A SAFETY Why is SCCR important?
& SAFETY 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

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

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

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 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,…

9 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 – 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 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

11 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

12 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

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

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

17 Power Electrical Symbols
NO NC Fuse Fused Disconnect Switch Power Transformer Relay NC NO Circuit Breaker Motor Starter Electric Motor Pushbutton

18 Control Circuit vs. Power Circuit
Control Circuit: The circuit of a control apparatus or system that carries the electric signals directing the performance of the controller but does not carry the main current. Power Circuit: Carries the main current of the circuit Power Circuit Power Circuit

19 Branch Circuit vs. Feeder Circuit
Branch Circuit: A portion of a wiring system in the interior of a structure that extends from a final overload protective device to a plug receptacle or a load such as a lighting fixture, motor, or heater Feeder Circuit: all circuit conductors between the service equipment, the source of a separately derived system, or other power supply source and the final branch-circuit overcurrent protective device Branch Circuit #1 Branch Circuit #2

20 Applying the Standard Let’s analyze an example circuit

21 Example Circuit

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: SCCR marked on the component or on instructions provided with the component SCCR can be determined by the voltage rating of the component and the assumed short circuit current from Table SB4.1 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 Q A What Components Do I Look For? All Power Circuit Components
& All Power Circuit Components 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 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 Generic fuse block label USFM label

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

26 Mersen Resources for Determining SCCR
From left to right: FS SCCR Quick Select Guide (now available on website under “Resources”  “Reference”), NEW US Website, Increase SCCR with USFM

27 Control Circuit 200kA 100kA 200kA NA 200kA 65kA 200kA
First – Identify Control Circuit – anything in the control circuit can be neglected when determining the panel SCCR Start from top to bottom, left to right FBJ60 + AJT60 – 200kA FSPDB2A – 100kA 60308SJ + AJT210 – 60308SJ has a 200kA SCCR, AJT20 has an IR of 200kA = Combined SCCR of 200kA 18A Contactor and OVLD – Manufacturer manual states the motor starter has a SCCR of 10kA ATQR25 + USCC1 – 200kA CPT – Does not require a SCCR US3J + HSJ15 – 200kA Electronic Motor Controller – Product manual states 5kA ST4803PY – 100kA MCCB – Product label 65kA 12A contactor and OVLD – No listing, Use table SB4.2 10kA 200kA 5kA Unknown

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

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

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 Branch 1 Branch 2 Branch 3 Control Circuit 200kA 100kA 200kA NA 200kA
Identify the Branch Circuits 10kA 200kA 5kA SB4.1 5kA

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

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

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

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

36 Feeder Circuit SCCR = 100kA Feeder 200kA 200kA 100kA
For this example we will include the TVSS as part of our Feeder Circuit because there is no load on the TVSS 100kA

37 Q A What if we stopped now?
& 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

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 Ip of the fuse Class CC, G, J, L, RK1, RK5 or T

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

40 Class J 60A 50kA peak  Ip = 8kA 100kA peak  Ip = 10kA

41 Ip = 10kA @ 100kA Branch 1 = 10kA Branch 2 = 5kA Branch 3 = 5kA
NA 200kA 65kA Control Circuit 200kA By looking at the three branch circuits we can determine that Branch 1 will be affected by the current limiting effects of the feeder OCPD. 10kA 200kA 5kA SB4.1 5kA

42 Branch 1 Second Pass SCCR =
100kA Branch 1 = 100kA Branch 1 = 10kA Ip = 100kA 200kA According to our rule, the peak let-thru of the feeder OCPD is less than the SCCR of the branch so we increase the branch SCCR to the appropriate value from Table SB4.2 10kA

43 Ip = 10kA @ 100kA Branch 1 = 100kA Branch 2 = 5kA Branch 3 = 5kA
NA 200kA 65kA Control Circuit 200kA Panel SCCR is still 5kA based on the branch 2 and branch 4 10kA 200kA 5kA SB4.1 5kA

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 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 Branch 2 = 5kA 200kA NA Control Circuit 200kA 5kA

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: Use rating of primary OCPD ATQR25

47 Branch 2 Second Pass SCCR =
200kA Branch 2 = 5kA Branch 2 = 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 ATQR25 200kA NA Control Circuit 200kA As long as every device after the Power Transformer has a SCCR not less than 2kA then we can increase the branch rating to the SCCR of the primary overcurrent device 5kA

48 Limiting Factor is Branch 3
Panel SCCR is 5kA Limiting Factor is Branch 3 Ip = 100kA 200kA Branch 1 = 100kA Branch 2 = 200kA Branch 3 = 5kA 100kA 200kA NA 200kA 65kA Control Circuit 200kA We have followed the standard and the panel is only rated for 5kA 10kA 200kA 5kA SB4.1 5kA

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 There are four methods that could be utilized
Q What can I do to increase my panel SCCR? A & 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

51 Option 1: Upgrade to components with higher SCCR
Branch 3 = 65kA Branch 3 = 5kA 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 65kA Branch circuit then has a SCCR of 65kA because of the MCCB Ip = 100kA SB4.1 5kA 10kA

52 Option 2: Add a sub-feeder fuse
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 65kA SB4.1 5kA

53 Class CC 20A 50kA peak  Ip = 3kA 100kA peak  Ip = 4kA

54 Option 2: Add a sub-feeder fuse
Branch 3 = 65kA Branch 3 = 5kA Class CC, 20A ATDR20 Ip = 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 65kA SB4.1 5kA

55 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

56 Option 4: Consider type tested components
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 65kA We publish some of this data in the USFM vs. Circuit Breaker Document SB4.1 5kA

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 UL provides links to each manufacturers website displaying the SCCR testing results. (www.ul.com/controlequipment/shortcircuit.html) By logging onto UL.com and searching for SCCR test results we can find a link to Schneiders results. Look for the part numbers mentioned on the previous slide: 12A IEC Contactor Part # LC1D12 OVLD Relay, 5.5–8A Part # LRD12 15A Circuit Breaker Part # GJL36015 Then compare the combination SCCR of using an ICB and Class CC fuses (65kA and 100kA respectively)

59 This information is also available by viewing the Mersen USFM vs
This information is also available by viewing the Mersen USFM vs. Circuit Breaker Comparison Sheet available on our website We list all the major control manufacturers combinations in one sheet 12A IEC Contactor Part # LC1D12 OVLD Relay, 5.5–8A Part # LRD12 15A Circuit Breaker Part # GJL36015 Find the IEC contactor LC1D12 and combination SCCR with GJL breaker at 480V vs Class CC and USFM We can increase combination SCCR from 65kA to 100kA

60 Option 4: Consider using type tested components
Branch 3 = 100kA Branch 3 = 5kA 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 200kA Replace breaker with USFM + ATDR Now with a combination SCCR of 100kA we can increase our branch SCCR to 100kA Which then allows the whole panel to be 100kA USFMCCI + ATDR has a SCCR of 200kA Telemecanique motor starter has a SCCR of 5kA 5kA

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 Questions and Answers


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