The 2005 National Electrical Code (more information) now requires most control panels to be marked with their short-circuit current rating (SCCR). This change affects all industrial control panels (409.110), industrial machinery panels (670.3(A)), and non-residential HVAC equipment rated greater than 60A (440.4(B)). Furthermore, all industrial control panels listed to UL508A must be marked with their SCCR. Supplement SB in UL508A, which became effective on April 1, 2006, is referenced by the NEC as an approved method for establishing the SCCR of a panel. As with most every change to the NEC, safety is the primary concern of this new requirement. Under abnormal operating conditions, such as an electrical fault, a control panel may be subjected to thousands of amperes of let-through current before any protective device(s) inside the panel clears the fault. Such an event may cause severe damage to power components and electrical wiring, which can compromise the integrity of the Panel and result in injury to nearby personnel. Proper matching between the maximum available current from the power supply and the SCCR for the panel is fundamental to ensure safety. From the Panel users point of view, Panels with a higher SCCR allows them the flexibility to connect their Panel to electrical systems with different available currents. From the Panel builder’s point of view, establishing this higher SCCR may represent significant challenges and additional costs.