SCCR is defined by NEC (National Electrical Code) as the maximum short-circuit current a component or assembly can safely withstand. NEC requires control panels and other equipment to be marked with SCCR.
Equipment with insufficient SCCR can pose a risk to personnel and equipment or create a fire hazard. In 2017 the NEC (National Electrical Code) had included several new short-circuit protection requirements. The most significant changes will require that the available fault current at the location where the equipment is installed is marked and documented. These changes will allow installers, inspectors to verify that the installed equipment SCCR is equal to or greater than the available fault current. When it comes to control panels, UL 508A Supplement SB establishes an approved method that defines how equipment SCCR is determined.
The UL 508A Supplement SB provides an analysis method that considers the “weakest link” as the basis for the determining equipment SCCR; the equipment SCCR is limited to the lowest rated component SCCR or lowest rated overcurrent protective device interrupting rating in the control panel.
There are three key considerations to determining equipment SCCR
According to UL 508A SB4.3, current-limiting devices in the feeder circuit can be used to increase branch-circuit component ratings. The peak let-through current of a current-limiting overcurrent protective device in the feeder circuit is compared to the downstream branch circuit component SCCR. If the peak let-through at a selected prospective short-circuit current is less than or equal to the component SCCR, then the component SCCR can be raised to the selected prospective short-circuit current.
Current-limiting fuses shall be approved according to UL 248 and be marked with “Current Limiting” for example class J, CC, RK1, RK5, T and L fuses. The value for the peak let-through current must be determined from Table SB4.2 in UL 508A.
Another alternative is the use of current limiting MCCBs according to UL 489. The MCCB shall be marked “Current Limiting”, the value for the peak let-through current is provided by the manufacturer.
We provide a full range of fuses and fusible switch disconnectors from Eaton Bussmann Series and UL 489 current limiting MCCBs from Eaton.