Short-circuit current ratings of equipment

The interrupting rating and short-circuit current rating of equipment is an key consideration for the installation of equipment in electrical distribution systems. To emphasize this consideration, the 2005 National Electrical Code (NEC®) added short-circuit current rating marking requirements for various types of equipment, that previously was not required to be marked with the equipment short-circuit current rating. The marked short-circuit current rating of equipment is determined by the product standards as part of the listing and labeling process of the equipment or an approved method, such as UL 508A for industrial control panels. UL 508A Supplement SB is an analytical (non-tested) method of determining the short-circuit current rating of industrial control panels. This method basically determines the “weak-link” of all power circuit components in the industrial control panel and the lowest rated component then determines the assembly rating. Additional changes to the 2011 NEC have occurred to ensure equipment has short-circuit current ratings sufficient for the fault current where the equipment is installed.