Understanding short-circuit current rating (SCCR) assignment options for industrial control panels is the first step in avoiding risk.
Article 409 of the National Electric Code (NEC) is well known to many industrial control panel builders and facility managers. Effective on January 1, 2005, Article 409 requires industrial control panel assemblies to be clearly labeled with a respective short-circuit current rating (SCCR). The SCCR represents the maximum amount of instantaneous current the equipment can withstand without compromising the physical integrity of the panel. This rating must meet or exceed the available “fault current” for the installation.
The SCCR requirement was implemented as a safety consideration to prevent potential arc flash that could cause a fire, damage to the panel or property, or personal injury or even death. It is important to note that the SCCR is not represented by the overcurrent protective device’s interrupt rating. Supplement SB, “Short Circuit Current Ratings for Industrial Control Panels,” has been added to UL 508A to provide one method of addressing Article 409 of the NEC.
All panels that include one or more power circuit components as described in 49.5 of UL 508A require an SCCR, even if they are not otherwise designed for compliance with UL 508A. Excluded from this requirement are industrial panels that consist of only a control circuit. However, if the control circuit includes overcurrent protection that is connected to a power circuit, it does require an SCCR. If the panel includes a power circuit, in addition to control circuit with a separate supply, the control circuit also requires an SCCR.
Responsibility for compliance with SCCR requirements lies with multiple parties. The electrical contractor that will install the panel must work with the respective consulting and facility engineers to determine the appropriate SCCR based upon the fault current of the installation. This should be part of their process in gathering the requirements of the panel. It is important that this information is clearly communicated to the panel manufacturer early in the design stage. The panel manufacturer is required to properly label the panel with the SCCR.
The panel manufacturer is not required to confirm that the SCCR on the panel is sufficient for the installation. In compliance with the NEC, it is the responsibility of the authority having jurisdiction (AHJ) to confirm whether or not the panel’s SCCR is suitable for installation in a facility. In most facilities, the AHJ is the local electrical inspector. In the event of an accident or safety hazard due to an inadequate SCCR requirement on a panel, ultimate responsibility will lie with the electrical contractor who specified and installed the panel. The consulting engineer also will be held responsible as they are relied upon to determine or confirm the appropriate SCCR and fault current.