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The National Electric Code (NEC) and Underwriters Laboratories (UL) product standards underwent substantial changes in 2005. To help you understand how those changes relate to Industrial Control Panels, Eaton offers you our UL 508A resources. Get more information about how UL 508A affects you, how to select a short circuit current rating, and understanding UL 508A. For specific questions about how to apply UL 508A to your Industrial Control Panel, please email us.

The intent of Article 409 is to prevent the misapplication of control products and related equipment. This article will provide the minimum requirements to ensure safe installation and inspection of industrial control panels. Article 409 covers industrial control panels that are intended for general use and operate at a voltage of 600V or less. The entire panel and all components inside will be required to meet a defined Short Circuit Current Rating (SCCR) for the application, and the panel will have to be marked with the appropriate SCCR. The marking requirements of UL Standard 508A Industrial Control Panels for SCCR ratings took effect in April 2006.

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UL 508A – The Standard. UL 508A – Industrial Machinery “The following types of machines are identified as industrial machinery: − Metalworking machine tools, machines that cut or form metal − Plastics Machinery, including injection molding, extrusion, blow molding, specialized processing, thermoset molding and size reduction. Industrial Control Panels according to US codes and standards must be designed correctly for the required short circuit, in order to be put into operation.

Now that you know the dark secrets about UL508A and UL Listed Control Panels, here are a few important considerations when choosing your control panel vendor. Do NOT buy a control panel for your project unless it is: Made from UL-listed components recognized for their specific application, Built according to UL standards,.

UL508A is the UL standard for the construction of Industrial Control Panels. This document gives guidelines to panel builders on various issues including proper component selection, wiring methods and calculation of short circuit current ratings. If a customer follows UL508A’s construction requirements and recommendations, they can apply to have their panel listed by UL. Upon successful inspection, the panel would bear the UL label.

Eaton has created data tables, which will help you determine the SCCR for your industrial panel by providing the ratings for our products.

Eaton is committed to electrical safety and to providing our customers with UL listed & UL Recognized products and solutions. Eaton can add value by discovering mistakes before UL does, and prevent costly re-inspection. Re-inspection in the field can cost several thousand dollars. By purchasing coordinated components from Eaton, panel builders can simplify their SCCR compliance and take advantage of Eaton’s higher SCCR ratings for tested combinations.

To review commonly asked questions about UL508A and Eaton's products, please follow the instructions below for access to Product Expert:

Under Knowledge Center select Product Expert
Under Product Family select Codes and Standards
Under Product Line select Underwriters Laboratories (UL)
Then begin searching for solutions to questions.

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In the search field, type in UL508A and contributions including this keyword will populate.

For specific questions about how to apply UL508A to your Industrial Control Panel, please email our Technical Resource Center at StandardsePod@eaton.com.

A UL label signifies that the panel builder has met the requirements of UL508A, and that their panels are subject to inspection by UL field representatives. Not every panel is inspected by UL, but panels are subject to inspection by UL depending upon the quantity of UL Labeled panels made in a give time period. A UL Follow Up Services representative inspects the facility and reviews the panels to the UL508A Procedure for the particular panel shop being inspected. If the panels are found to be in compliance, they are permitted to continue production and apply the UL Label.

The NEC is the code accepted by most inspection agencies in the United States for safe installation of electrical equipment. While the UL standard looks at the construction of the OEM panel, the NEC looks at the manner in which this same panel is installed. This code is updated every 3 years, and typically takes 2-3 years before code enforcement begins. For instance, many cities still use the 1999 NEC as a basis for their electrical code.

Even if a manufacturer follows all of the guidelines implemented by UL at the time of manufacturing, the panel may not meet the requirements of the NEC, which are enforced by local electrical inspectors. For instance, the National Electric Code requires that equipment be labeled with the Short Circuit Current Rating, and that the SCCR of the equipment exceed the available short circuit current at the point of installation. While the NEC requires this, the UL standard for labeling took effect in April 2006. There may be situations, where an inspector will not allow the installation of this panel, even though it carries a valid UL listing. Many customers have been surprised by these changes, and by helping our customers understand the code, Eaton can help prevent costly errors and frustration.

A UL listed component bears the UL listing mark and has been subject to testing. The UL Listed label is evidence that the manufacturer submitted complete product samples for testing, witnessed by UL representatives. These products are subject to testing and evaluation by UL and were found to meet nationally recognized safety standards. Products can also be “UL Recognized”, which means that the product was found to be safe in particular instances when reviewed and accepted by UL in the final application. OEMs utilizing UL Recognized components in a control panel must ensure that their application meets additional requirements described in their UL procedure.

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There are three options:
1. Purchase previously tested combinations from a major supplier that can be tabulated in the panel builder’s procedure. Eaton is a major component supplier that is committed to providing this information to our customers. Once you have all of the component ratings, either use an outside service or UL508A Supplement SB.
2. Test each panel construction and record the construction in a follow-up procedure. With the numerous possibilities for product combinations within a panel, this option will require a tremendous investment in testing and maintenance. The test has to be witnessed by a UL project engineer.
3. Utilize the method described in UL508A Supplement SB.

There are three simple steps to calculating the SCCR Rating of a control panel. Step 1: Determine the individual short circuit current rating of each individual component in the system. 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 voltage. You can exclude transformers, dry-type capacitors, resistors, varistors and voltmeters. Step 2: Calculate the available short circuit current when taking into account current limiting components like control power transformers, fuses and circuit breakers. Step 3: Compare the values obtained in steps one and two to determine the overall short circuit current rating of the panel. The lowest rated SCCR of the device within the control panel must be the one that is marked on the panel.

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Sizing - Additional branch circuit protection - Fuseholder

31.3.1 The ampere rating and type of branch circuit protection for a single motor circuit, other than covered in 31.3.2 and 31.3.3, shall be determined based on the smaller of:

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a) Sizing in accordance with Table 31.1, by:
1) Determining the full-Ioad ampere rating corresponding to the motor horsepower rating from Table 50.1 or Table 50.2;
2) Determining the maximum percentage of full-Ioad amperes corresponding to the type of branch circuit device selected from Table 31.1; and
3) Multiplying (1) and (2);

b) Sizing based on component restrictions, as indicated by markings on components, the heater table of an overload relay, or in the instructions provided with components. In this case, the branch circuit protection selected shall be coordinated with all power circuit components on the load side of the protective device and shall:
1) Have an ampere rating not exceeding the manufacturers maximum specified rating; and
2) Be the same type of device specified by the manufacturer.

When used in instructions for a component, heater tables, or instruction manuals, the term 'fuse' shall refer to a branch-circuit type fuse and 'circuit breaker' shall refer to an inverse-time circuit breaker.

31.3.2 The branch circuit protection for a single-motor circuit provided with a variable-speed drive shall be of the type and size specified by the manufacturer's instructions provided with the drive. When the instructions do not specify the type and size, a branch-circuit fuse or inverse-time circuit breaker shall be used and shall be sized in accordance with 31.3.1(a) based upon the full-Ioad motor output current rating of the drive.

Exception N.1: Additional branch circuit protection is not required for a drive provided with integral inverse-time circuit breaker, branch-circuit, or semiconductor fuses in all ungrounded input conductors.

Exception N.2: Unless specified in the installation instructions for a variable-speed drive, a 'common bus' drive is not required to have individual branch circuit protective devices installed in the dc input conductors. See 31.4.2 for branch circuit protection for the power supply converter unit supplying dc bus power to the 'common bus' inverter sections.

31.3.3 Additional branch circuit protection is not required for a self-protected combination motor controller or a manual self-protected combination motor controller supplying a single motor load. The adjustable range of the self-protected combination motor controller shall be set for the motor full load current rating as determined from 31.3.1. The cautionary markings in 55.7 shall be provided.

31.3.4 Additional branch circuit protection is not required to be provided when an instantaneous-trip circuit breaker and all of the load side power components have been evaluated as a combination motor controller as specified in 31.1.1 and supply a single motor load. The adjustable range of the instantaneous-trip circuit breaker shall be able to be set for the rating determined from 31.3.1. The cautionary markings of 55.6 shall be provided.

31.3.5 A fuseholder shall be sized to accept a fuse in accordance with 31.3.1. The fuseholder shall be provided with the replacement fuse marking of 56.1 when:
a) The fuseholder accepts a fuse with an ampere rating greater than specified in 31.3.9;
b) The fuseholder accepts a fuse with an ampere rating Ihat exceeds a component restrlction as specified in 31.3.1(b); or
c) The fuseholder is intended for a semiconductor fuse.

31.3.6 The branch circuit protective device(s) provided in an industrial control panel for a multi-speed motor having two or more windings or a part winding motor shall have:
a) Individual branch circuit protection for each winding that complies with 31.3.1 based on the full load current rating of the protected winding; or
b) A single branch circuit protective device or set of branch circuit protective devices supplying all windings that complies with 31.3.1 based on the full load current rating of the smallest winding.
31.3.7 When the calculated ampere rating of the branch circuit protection as specified in 31.3.1 (a) does not correspond to a standard size fuse or circuit breaker, the next higher size fuse or inverse-ti me circuit breaker as specified in 31.3.8 shall be used.

Exception N.1: When the calculated ampere rating of the branch circuit protection specified in 31.3. 1(b) does not correspond to a standard size fuse or circuit breaker, the next lower standard size shall be used.

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Exception N.2: When a circuit breaker is used as branch circuit protection of a motor circuit that is rated 3. 75 amperes or less in accordance with 31.3. 1, a 15-ampere circuit breaker is able to be used.

31.3.8 Standard ampere ratings for fuses and inverse-time circuit breakers are 15, 20, 25, 30, 35, 40, 45, 50,60,70,80,90,100,110,125,150,175,200,225,250, 300, 350, 400, 450, 500, 600, 601, 700,800, 1000,1200,1600,2000,2500,3000,4000,5000, and 6000. Additional ratings for fuses include 1,3,6, and 10.

31.3.9 Where the starting current of the motor opens the branch circuit protective device specified based on 31.3.1(a), the maximum rating or setting of the branch circuit protective device shall not exceed:
a) 400 percent of full-Ioad motor current for a non-time delay fuse or a Class CC time delay fuse not exceeding 600 amperes;
b) 300 percent of full-Ioad motor current for a non-lime delay fuse rated 601 amperes or greater;
c) 225 percent of full-Ioad motor current for a lime delay (dual element) fuse;
d) 400 percent of full-Ioad motor current for an inverse-time circuit breaker not exceeding 100 amperes;
e) 300 percent of full-Ioad motor current for an inverse-time circuit breaker rated more than 100 amperes; or
f) 1300 percent of full-Ioad motor current for an instantaneous-trip circuit breaker or 1700 percent of motor full load current for an instantaneous trip circuit breaker used with a high efficiency Design B motor.

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