Supplement SB from Underwriters Laboratories Inc. is one of the three methods that can be used to determine the SCCR of an industrial control panel. There are three distinct steps to establishing the rating:
Step 1. Determine the rating of the individual components within the control panel by using either:
- The component marking or instruction marking, which may require specific over-current protection
- The unmarked component rating determined by Table SB4.1 in the supplement
- A test of a component or combination of components per UL 508A
Step 2. When the current limiting protective devices are included in a feeder circuit, determine the modified rating (SB4.3) based upon the let-through values of the current limiting protective devices.
Step 3. Establish the overall rating (SB4.4) which cannot exceed the rating of the circuit, including the modified rating determined in Step 2 above. Each one of these steps is further detailed in the UL Supplement.