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What is the Short-Circuit Current Rating (SCCR)?
The Short-Circuit Current Rating (SCCR) is a parameter for electrical components or assemblies. According to the definition in the National Electrical Code (NEC), the SCCR is the maximum short-circuit current that a component or system must be able to safely withstand.
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Why is the SCCR needed?
Calculating the SCCR makes it possible to assess whether a main circuit can withstand a short-circuit load until the upstream protective device trips. It also allows engineers to identify what the maximum short-circuit load is at the installation site. Short-Circuit Current Ratings are an important criterion for the safety of industrial and commercial switchgear systems and control panels in accordance with the UL standard. When used correctly, switchgear systems should be able to withstand a short-circuit without exposing employees to a fire hazard, flying debris, an arc fault or an electric shock.
How does the rating affect the North American market?
Of course, when exporting machines containing electrical equipment to North America, the applicable standards and rules there must be observed. This means that machines and systems must achieve the specified SCCR value at the connection point.
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The North American National Electrical Code (NEC), the US Federal Office for Occupational Safety and Health Administration (OSHA) and the Underwriters Laboratories (UL) create guidelines relating to the SCCR.
The NEC safety standard also lists other requirements, including that documentation or a dated marking (depending on the type of switchgear system) for the available fault current (also called the available short-circuit current) must be provided at the installation point of a control panel or switchgear system. These modifications allow installers, testers, and inspectors to verify that the SCCR is equal to or greater than the available short-circuit current for the installed device, meaning it also complies with the other sections of standards which deal with device installations.
The SCCR of a switchgear system is equal to the lowest-rated value for the SCCRs of all the components, the potentially increased SCCRs of components in the branch circuits or the short-circuit breaking capacity of the overcurrent protection devices. For more information on how to calculate the SCCR, see the whitepaper "Current-limiting components: Improving Eaton's Short-Circuit Current Rating (SCCR)."
The SCCR for a machine should be calculated during the machine control panel's early engineering phase—this works out to be the most efficient. Eaton offers a variety of resources to make it easy to calculate the SCCR.
Calculating the SCCR value for systems is an essential part of the applicable safety standards in the North American market. If you want to sell machines and systems there, the SCCR value must be calculated and marked on the system. But calculating the SCCR isn't witchcraft—and if it's worked out early enough in the planning phase, it can also be increased relatively easily.
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