Industrial Control Panels Tested product combinations to meet NEC Article 409 and UL 508A Standard

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Eleanore Thomas
6 years ago
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1 Industrial Control Panels Tested product combinations to meet NEC Article 409 and UL 508A Standard

Short circuit current ratings and the new NEC Article 409 The 2005 Edition of the National Electrical Code, NFPA 70 contains a new Article 409 entitled Industrial Control Panels.

The requirement is that the components of the electrical power circuit meet a defined Short Circuit Current Rating (SCCR) for the application and that the panel is marked with the appropriate SCCR.

began enforcing the Supplement SB of the Standard for Industrial Control Panels, UL 508A.

2 Short circuit current ratings and the new NEC Article 409 The 2005 Edition of the National Electrical Code, NFPA 70 contains a new Article 409 entitled Industrial Control Panels. This article provides installer and enforcement authorities with the minimum requirements to facilitate the safe installation and inspection of industrial control panels. The requirement is that the components of the electrical power circuit meet a defined Short Circuit Current Rating (SCCR) for the application and that the panel is marked with the appropriate SCCR. A device marked with an interrupt rating or withstanding rating is considered to be the SCCR rating for the device. On April 25, 2006, Underwriters Laboratories Inc. began enforcing the Supplement SB of the Standard for Industrial Control Panels, UL 508A. This new addition to the standard is the only approved method for determining the SCCR of an industrial control panel. How do I obtain the needed SCCR? You have three options for determining the SCCR for the industrial control panel: 1. Test each panel construction and record the construction in the follow-up procedure. With the multitude of possible product combinations within a panel, this option can require a lot of testing and maintenance. Thirdparty testing and certification may also be required. 2. Purchase previously tested constructions (tested combinations) from a major supplier of equipment that can be tabulated in the control or machine panel builder s procedure. Once you have all the component ratings, either utilize an outside service or UL 508A, Supplement SB. 3. Utilize method described by Underwriters Laboratories Inc. in their UL 508A, Supplement SB. What are tested combinations? Tested combinations from Schneider Electric offer control panel builders, machine panel builders and end customers, such as facility engineers and managers, the ability to simplify this process significantly. Typical branch circuits as tested combinations Multiple products become one component as a tested combination (shown with 480V SCCR) Higher level SCCRs can be achieved through the use of UL-approved product combinations. This can represent several types of components used in a power circuit of an industrial control panel. This combination has been previously tested for a short circuit rating and can be applied to obtain the highest rating possible for a control panel s branch circuit versus individual component ratings. Common examples would be motor circuit protection and motor control devices. Schneider Electric posts its approved tested combinations along with the UL identification number on our website, *Note: See page 5 for details on drive SCCRs IEC NEMA DRIVE* 2

Advantages of tested combinations Tested combinations provide the opportunity to achieve higher level SCCR than individual component ratings.

Combined as a unit or group, the results are not calculated or derived; they are physically tested to ensure that they meet the SCCR that is approved.

3 Advantages of tested combinations Tested combinations provide the opportunity to achieve higher level SCCR than individual component ratings. Schneider Electric products are submitted to UL for testing as a standard part of our rating application. Combined as a unit or group, the results are not calculated or derived; they are physically tested to ensure that they meet the SCCR that is approved. One of the challenges facing panel builders or facility engineers is that in the past, intermixing of power circuit components has been commonplace. Under the new NEC Article 409 requirement, this practice is discouraged it is impossible to obtain higher level short circuit ratings as these products have never been laboratory tested in combination before. The end result is that the power circuit SCCR will be much lower than desired as the application of UL 508A, Supplement SB will reveal that the weakest link, such as a terminal block, may drag down the system rating. Intermixing power circuit components from various brands can also create lower SCCR values. Schneider Electric s tested and UL-approved ratings offer a quicker solution to achieving the ratings goal you seek. Manufacturer-provided tested combinations allow panel and machine builders to obtain higher SCCRs for branch circuits. Combined with the UL ID or identification number, the results are validated by UL to support your SCCR rating helping to mitigate issues that may surface during design phases or a later inspection during installation. The ID reference for each branch circuit makes inspection and listing easy. How do you obtain high fault rated branch circuit SCCRs? Circuit Breaker Contactor Overload Relay Historically, industrial control panels mix many types of components with various SCCR ratings inside the panel. The SCCR requirements in the 2005 NEC Article 409 and Supplement SB of UL 508A place stringent requirements on the ratings of each component inside the panel s power circuit. From an application perspective, the branch circuit has undergone a number of changes with the new code and standard. As you can see in the diagram, the area outlined in green is an example tested combination as a part of a motor control branch circuit. The SCCR is approved by UL and has a stand alone rating allowing for branch protection with starters, contactors and motor controllers along with high fault levels. Understanding what affects your SCCR evaluations There are a number of factors that can affect how your SCCR rating is derived. The following components are typically found in the power circuit of a control panel and should be included in your SCCR evaluation. Circuit Breakers Contactors Drives Fuses IEC Contactors Lighting Contactors Manual Motor Controllers Meter Sockets NEMA Contactors Receptacles Switch Units Terminal Blocks Transformers Devices used downstream of a control transformer tapped from the feeder circuit are not included in the calculation of the control panel SCCR. Do not include in your evaluation the following equipment as these devices are not typically found in your power circuits: Automation Devices Indicator Lights Limit Switches Push Buttons Relays Timers Unless otherwise modified by Supplement SB SB4.3, your panel is required to use the lowest level component SCCR in your power circuit. The table on page four from the UL 508A Supplement SB lists the ratings of common unmarked components and their default SCCR rating unless you have an alternative, such as a tested combination from Schneider Electric. 3

Another alternative is to eliminate the need for a distribution block in a feeder circuit.

4 How to maintain high SCCRs using distribution and terminal blocks Power distribution and terminal blocks have default values of 10kA in the new UL 508A Standard, Supplement SB, Table SB4.1. Some manufacturers have now tested their products for various ratings and received approvals. Check with the specific supplier for details. Another alternative is to eliminate the need for a distribution block in a feeder circuit. This can be accomplished by directly connecting to our circuit breakers using our power distribution lugs that are approved for the short circuit rating of the breaker. This also helps to eliminate a component from the design. To maintain high SCCR levels, we recommend elimination of terminal blocks and utilize direct connections where possible to motors and other key circuits. This helps to avoid the standard default values in the UL 508A, Supplement SB, until such time as the manufacturers of these products obtain higher ratings for power circuit usage. Be wary of fuse performance claims vs. circuit breakers and tested combinations Some fuse manufacturers are claiming that you should replace circuit protection devices such as a circuit breaker with a fuse in order to comply with SCCR requirements. This is an incorrect statement. We offer a variety of tested and UL-approved combinations to meet and exceed most requirements in control panels. Another key fact to remember is that fuses cannot be used as a part of a tested combination unless they are tested as such, and individually listed with the manufacturer and UL. Direct substitution is not recommended. Fuses cannot provide the convenience and reset capability that you can obtain by using Schneider Electric s circuit protection components. Also, for added safety, there is no need to replace a breaker when it trips, further enhancing the safety of the employee in a powered equipment environment. The table below is extracted from the UL 508A Supplement SB, Table SB4.1 and is meant to be used as a guide only. Please refer to the UL website to view the most up-to-date Table SB4.1 information. Extract of Data from UL 508A Table SB4.1 Assumed maximum short circuit current rating for unmarked components (Eff. April 25, 2006) Component SCCR, ka Bus bars 10 Circuit breakers (including GFCI type) 5 Current meters * Fuseholder 10 Industrial control equipment a. Auxiliary devices (overload relay) 5 b. Switches (other than mercury tube type) 5 c. Mercury tube switches - Rated over 60 amperes or over 250V 5 - Rated 250 volts or less, 60 amperes or less, and over 2 kva Rated 250 volts or less and 2 kva or less 1 Motor controller, rated in horsepower (kw)*** a (0-37.3) 5*** b (38-149) 10*** c ( ) 18*** d ( ) 30*** e ( ) 42*** f ( ) 85*** Meter socket base 10 Miniature or miscellaneous fuse 10** Receptacle (GFCI type) 2 Receptacle (other than GFCI type) 10 Supplementary protector 0.2 Switch unit 5 Terminal block or power distribution block 10 * A short circuit current rating is not required when connected via a current transformer or current shunt. A directly connected current meter shall have a marked short circuit current rating ** The use of a miniature fuse is limited to 125-volt circuits *** Standard fault current rating for motor controller rated within specified horsepower range With the permission of Underwriters Laboratories Inc., material is reproduced from UL Standard 508A, Standard For Industrial Control Panels, which is copyrighted by Underwriters Laboratories, Inc., 333 Pfingsten Road, Northbrook Illinois UL shall not be responsible to anyone for the use of or reliance upon a UL Standard by anyone. UL shall not incur any obligation or liability for damages, including consequential damages, arising out of or in connection with the use, interpretation of, or reliance upon a UL Standard. UL s Standards for Safety are copyrighted by UL. Neither a printed copy of a Standard, nor the file for an electronic version of a Standard may copied, reproduced, and/or altered in any way. All of UL s Standards and all copyrights, ownerships, and rights regarding those Standards shall remain the sole and exclusive property of UL. Revisions of UL Standards for Safety are issued from time to time. A UL Standard for Safety is current only if it incorporates the most recently adopted revisions. Copies of the current edition of UL (Standard Number) may be purchased from: comm Brook Drive Downers Grove, IL USA in U.S. and Canada outside the U.S. and Canada Fax: in U.S. and Canada Fax: outside the U.S. and Canada 4

5 Current limiting provision in the UL 508A Standard Within the Supplement SB, you can modify a panel rating using approved current limiting feeder components. What this means is that transformers, circuit breakers and fuses can help you obtain high SCCRs when lower fault components are specified in the design. As stated below, circuit breakers can provide this capability. According to the UL 508A SB4.3.2 For branch circuits supplied by a listed circuit breaker marked current limiting in the feeder circuit, the short circuit current rating on the line side of the circuit breaker shall be one of the following: a) The short circuit current rating of the feeder circuit breaker, when all of the components in the branch circuit have a short circuit current rating not less than the published peak let-through current of the circuit breaker, see Figure SB4.1, and the short circuit current rating of all branch circuit protective devices on the load side are not less than the short circuit current rating of the feeder circuit breaker; b) The smallest short circuit current rating of any branch circuit protective device on the load side of the feeder circuit breaker, when the conditions of SB4.3.2(a) exist except the short circuit current rating of the branch circuit protective devices on the load side are less than the short circuit current rating of the feeder circuit breaker; c) The smallest short circuit current rating of any branch circuit on the load side of the feeder circuit breaker, when the conditions of SB4.3.2(a) or SB4.3.2(b) are not met. As you can see above, current limiting breakers from Schneider Electric can supplant the need for a current limiting fuse. In order to utilize the current limiting approach, your application design must meet the specifics of SB4.3.2 or SB As highlighted above in bold print, simply inserting current limiting provisions will not elevate your panel s overall SCCR value. In order to do that, you must insure that your branch overcurrent protective devices or tested combination have an SCCR that is equal to or greater than the current limiting device employed in the feeder circuit. Otherwise, you will be limited to the lowest SCCR of your branch devices. Short circuit ratings and options for motor circuits The following table can help you select the appropriate mix of product combinations to meet your control panel requirements. As you can see, the variety of breakers, starters and relays offered by Schneider Electric can meet most SCCR application demands. Breaker + MC + OLR Manual Starter and Protector U-Line Circuit Protection Powerpact MCP Powerpact UL 489 Powerpact MCP GV2/3 Group Mount GV2P GV3M GV7 Self-protected Contactor NEMA 1 to 5 NEMA 1 to 5 IEC D-Line D-Line D-Line U-line Overload Relay NEMA NEMA IEC Included Included Included Included Max Hp 10 Hp 40 Hp 10 Hp 7.5 Hp* 20 Hp 10 Hp Hp Range Hp 40 Hp 60 Hp 10 Hp 7.5 Hp* 20 Hp 75 Hp 10 Hp Hp 75 Hp 125 Hp 20 Hp 15 Hp* 40 Hp 150 Hp 20 Hp Hp 100 Hp 125 Hp 30 Hp 60 Hp 200 Hp 25 Hp SCCR 25kA-100kA 14kA-100kA 25kA-100kA 10kA-50kA 10kA-100kA 10kA-22kA 25kA-65kA 42kA-130kA Strength NEMA design Robust design High SCCR Lowest cost for Low cost Low cost Low cost Small size High SCCRs Precise motor multiple motor loads Low Hp Moderte Hp High Hp Precise control Flexible Flexible protection * 480/277V Variable Frequency Drives and Softstarts Underwriters Laboratories does not currently have a UL 508A category that recognizes a tested product combination that includes a variable frequency drive and a branch circuit protective device. While both have SCCR ratings as stand alone products, there is currently no category for a tested combination with either a circuit breaker or fuse device. If your installation requires the use of these products you must use the VFD manual to determine the overcurrent protective device required and its associated SCCR. 5

Motor circuit protectors and high short circuit current ratings If you need high fault levels up to 100 ka when using either IEC or NEMA style starters, the Square D Powerpact Motor Circuit Protector

The new Powerpact MCP offers simple solutions that deliver more reliable start-ups, better protection for your equipment, and complete adjustment range for your motor starters.

safety Lower life cycle costs To learn more about this unique product and design, visit our website at www.us.squared.com/mcp.

6 Motor circuit protectors and high short circuit current ratings If you need high fault levels up to 100 ka when using either IEC or NEMA style starters, the Square D Powerpact Motor Circuit Protector (MCP) from Schneider Electric may be your solution. It is the ultimate solution for flexibility, code compliance and performance for protecting motor circuits. The new Powerpact MCP offers simple solutions that deliver more reliable start-ups, better protection for your equipment, and complete adjustment range for your motor starters. Key features and attributes include: Settings for standard or energy efficient motors More reliable start-ups of your equipment Easier installations High SCCR ratings Better equipment protection and safety Lower life cycle costs To learn more about this unique product and design, visit our website at Schneider Electric tested combination solutions and UL approval Schneider Electric has been working with Underwriters Laboratories to obtain tested combinations that are more than manufacturer endorsed, but physically tested and proven to work in the environment in which we recommend. Our UL-approved tested combinations have their own UL record number to provide you with the data required to support your panel and any subsequent inspection. You can find these approved and tested combinations on our website at as you search our database. Don t be fooled with claims that combination SCCRs are not validated or approved by UL. The field approval of your panel may be jeopardized by taking shortcuts with untested product mixes. You can be sure that Schneider Electric has you covered with our tested combination testing program. Key attributes to note when using tested combinations When you use a tested combination within your control panel, it is important to note a few key database attributes in both the design and labeling phases. First, on the UL and SCCR databases, you ll note several key conditions of use in the SCCR report. The first is the Enclosure Volume value. This is a minimum volume as determined through the physical testing process. Choosing an overall enclosure volume smaller than this cubic foot rating would put you in violation of the UL category as this dimension minimum is required to assure a safe operation should there be any type of fault current incident. UL 508A, Supplement SB does not specifically address other key control panel attributes, such as latch types, NEMA vs. IEC enclosures, environmental concerns, etc. as those specifics are presented within other areas of UL 508A and other UL Standards, such as UL 50. Please consult with UL s guidelines via their website for more specifics. Another key attribute to note is the UL identification or UL ID number. This number should be placed on the final drawings and SCCR label, if possible, as a reference to the inspector as to where they can find specific information on this tested combination of products from Schneider Electric. In our online SCCR database, each tested combination has a unique UL ID number. This could be for something as minor as a voltage or horsepower rating variance from another similar combination. Please make sure to cite this UL ID number on your finished documentation and label. 6

Using the Schneider Electric Internet Databases for SCCR searches Schneider Electric has created a special website to help customers understand the significant impact the changes in the 2005 National

Whether you are an industrial control manufacturer, panel or machine builder or an individual business looking to modify existing panels or learn what you need to know before buying a new one, the

Some of the key pieces of information on our site include: General code and standard information NEC adoption map that is interactive so you can search a state s code requirements Steps on how to

7 Using the Schneider Electric Internet Databases for SCCR searches Schneider Electric has created a special website to help customers understand the significant impact the changes in the 2005 National Electrical Code and Underwriters Laboratories product standards will have on their business. Whether you are an industrial control manufacturer, panel or machine builder or an individual business looking to modify existing panels or learn what you need to know before buying a new one, the code and standards changes may affect your installation. This website hosts a number of education and product search tools. Some of the key pieces of information on our site include: General code and standard information NEC adoption map that is interactive so you can search a state s code requirements Steps on how to establish a short circuit current rating Schneider Electric Square D, Telemecanique and Merlin Gerin brand product SCCRs are available in searchable online databases as both individual products and in tested combinations Online training Extensive FAQs, updates, literature and much more Visit website to obtain more information on our SCCR data. Additional assistance for product combinations not listed in SCCR databases If you are unable to locate through our website or the UL database approved Schneider Electric tested combinations for our Square D, Telemecanique and Merlin Gerin brand products, please contact us via our website at and select the Contact Us option to us your questions or you may call directly during our extended Customer Service contact hours of 7 AM - 8 PM (Eastern Time) at Our tested combination database is a living environment where periodic updates and speciality combinations are being uploaded regularly. However, our product development teams can assist you in determining how to help meet your special need if our tested product combinations do not. 7

Understanding SCCR. THE BEST ELECTRICAL CONTROLS BUSINESS ON THE PLANET! Unmatched Service Superior Product Quality Advantage Pricing

Understanding SCCR. THE BEST ELECTRICAL CONTROLS BUSINESS ON THE PLANET! Unmatched Service Superior Product Quality Advantage Pricing Understanding SCCR What is SCCR? When it comes to industrial machinery, it s critical to ensure that electrical panels are designed and built with the proper SCCR to maintain the system, eliminate downtime