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. 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 100kA @ 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, www.us.squared.com/ul508a.
*Note: See page 5 for details on drive SCCRs
2
IEC
NEMA
DRIVE*
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.
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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
Bus bars
Circuit breakers (including GFCI type)
Current meters
Fuseholder
Industrial control equipment
a. Auxiliary devices (overload relay)
b. Switches (other than mercury tube type)
c. Mercury tube switches
- Rated over 60 amperes or over 250V
- Rated 250 volts or less, 60 amperes
or less, and over 2 kVA
- Rated 250 volts or less and 2 kVA or less
Motor controller, rated in horsepower (kW)***
a. 0-50 (0-37.3)
b. 51-200 (38-149)
c. 201-400 (150-298)
d. 401-600 (299-447)
e. 601-900 (448-671)
f. 901-1500 (672-1193)
Meter socket base
Miniature or miscellaneous fuse
Receptacle (GFCI type)
Receptacle (other than GFCI type)
Supplementary protector
Switch unit
Terminal block or power distribution block
4
SCCR, kA
10
5
*
10
5
5
5
3.5
1
5***
10***
18***
30***
42***
85***
10
10**
2
10
0.2
5
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 60062.
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 2000
1418 Brook Drive
Downers Grove, IL 60515
USA
1-888-853-3503 in U.S. and Canada
415-352-2168 outside the U.S. and Canada
Fax: 1-888-853-3512 in U.S. and Canada
Fax: 1-630-932-7387 outside the U.S. and Canada
http://www.comm-2000.com
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.4.3.3. 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
Contactor
Overload Relay
Powerpact MCP
NEMA 1 to 5
NEMA
Powerpact UL 489 Powerpact MCP
NEMA 1 to 5
IEC
NEMA
IEC
GV2/3 Group Mount
D-Line
Included
GV2P
D-Line
Included
GV3M
D-Line
Included
GV7
–
Included
Max
Hp Range
40 Hp
75 Hp
125 Hp
150 Hp
10 Hp
40 Hp
75 Hp
100 Hp
40 Hp
60 Hp
125 Hp
125 Hp
10 Hp
10 Hp
20 Hp
30 Hp
7.5 Hp*
7.5 Hp*
15 Hp*
20 Hp
20 Hp
40 Hp
60 Hp
75 Hp
150 Hp
200 Hp
10 Hp
10 Hp
20 Hp
25 Hp
25kA-100kA
14kA-100kA
25kA-100kA
10kA-50kA
10kA-100kA
10kA-22kA
25kA-65kA
42kA-130kA
NEMA design
High SCCRs
Robust design
High SCCR
Precise motor
control
Lowest cost for
multiple motor loads
Low cost
Low Hp
Flexible
Low cost
Moderte Hp
Flexible
Low cost
High Hp
Small size
Precise
protection
208
240
480
600
SCCR
Strength
Self-protected
U-line
* 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.
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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 www.us.squared.com/mcp.
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 www.us.squared.com/ul508a 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 www.us.squared.com/ul508a 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.
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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 www.us.squared.com/ul508a 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 www.us.squared.com/ul508a and select the “Contact Us” option to e-mail us your questions or
you may call directly during our extended Customer Service contact hours of 7 AM - 8 PM (Eastern Time) at
1-888-778-2733.
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.
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jc
©2006 Schneider Electric All rights reserved
Schneider Electric – North America Operating Division
0101BR0601
1415 S. Roselle Road
Palatine, IL 60067
Tel: 847-397-2600
Fax: 847-925-7500
www.us.squared.com/ul508a
08-06