Shortcircuit current rating markings are not required for industrial control panels containing only control circuit components. Overview of ul508a supplement sb ul 508a is a safety standard for industrial control panels adopted by underwriters laboratory, which is an approved method in determining sccr referenced by nec article 409. Ul 508a industrial control panels power distribution and. Design of a motor circuit as per standard ul 508 part iv and ul 508a. Equipment intended to be connected to a source of supply greater. All components in power circuit must have ratings ratings of starters are typically based on hp rating supplement sb, table sb4. Determining sccr for industrial control panels and industrial. Ul508a, supplement sb describes three steps to determine the sccr of. Industrial control panels, supplement sb, is an example of an approved method. Many manufacturers and users started combining a manual ul 508 type e. Ul 508a, supplement sb is an approved method to determine sccr for industrial control panels and industrial machinery control panels.
Underwriters laboratory implemented ul508a supplement sb. Supplement sb, provides an analytical method to determine the shortcircuit current rating of an industrial control panel. Ul 508a supplement sb is the preferred option for nearly all industrial control panels. Determination of the short circuit current rating according to ul 508a supplement sb. A time delay they combine all the mandatory protection inversetime thermal. Excerpts from ul 508a standard for safety for industrial control panels are.
The test has to be witnessed by a ul project engineer. They are especially easy to integrate into distributed systems. It is a weakestlinkinthechain evaluation, meaning that the lowest sccr circuit within the panel. With the numerous possibilities for product combinations within a panel, this option will require a tremendous investment in testing and maintenance. Ul508a supplement sb4 is the approved method for determining short circuit current ratings for industrial control panels. They combine all the mandatory protection functions in a. This method is based upon the weakest link approach. Evaluate panel per ul508a, supplement b required by 406 if jurisdiction does not adopt 2005 nec earlier.
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