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 placeQ
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 SymbolsNO 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 = 5kANA
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 = 5kANA
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 utilizedQ
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. (
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