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SCCR Estimator

Determine overall panel Short Circuit Current Rating.

Component SCCR Ratings (kA)

Enter the individual Short Circuit Current Rating for components in the primary power path.

Overall Panel SCCR

5 kA
Limiting Component (Weakest Link) Contactors / Motor Starters
Per UL 508A, the overall assembly SCCR cannot exceed the lowest rated component in the power circuit (unless protected by a current limiting fuse/breaker evaluated for series rating).
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Disclaimer of Liability: This calculator is provided for educational and estimation purposes only. By using this tool, you agree to discharge AutomationView of any liability for direct, indirect, or consequential damages resulting from its use. It is your strict responsibility to independently verify all calculations, validate the results against official manufacturer documentation, and ensure compliance with all applicable safety and engineering standards before implementing any parameters in a production environment.

Understanding Short-Circuit Current Rating (SCCR)

Determining the Short-Circuit Current Rating (SCCR) of an industrial control panel is a critical safety requirement per NEC Article 409 and UL 508A Supplement SB. The SCCR indicates the maximum fault current the panel can safely withstand without posing a fire or shrapnel hazard.

The ‘Weakest Link’ Methodology

Calculating panel SCCR is generally an analytical process rather than complex math. It involves identifying the lowest rated component in the power circuit.

  1. Identify Power Components: List all components in the power path, such as disconnects, breakers, contactors, and power distribution blocks. (Control circuit components are typically exempt).
  2. Determine Individual Ratings: Locate the marked SCCR or interrupting rating for each device. If a component is unmarked, you must use the conservative UL 508A default tables (e.g., Table SB4.1).
  3. Apply the Rule: The overall panel SCCR is restricted to the lowest rating of any individual component in the power circuit path.

Mitigation and Increasing SCCR

If your initial calculation yields an SCCR lower than the available fault current at the installation site, you can employ mitigation strategies:

  • Current-Limiting Fuses: Properly selected fuses limit the let-through current during a fault, allowing you to use downstream components with lower individual SCCR ratings.
  • Series Ratings: Manufacturers often test and list specific combinations of devices (like a breaker paired with a contactor) that achieve a higher combined SCCR than the devices would individually.

Compliance and Tools

Manually tracking component ratings and tested combinations can be tedious and prone to error. Using an SCCR Estimator tool is highly recommended to streamline UL 508A compliance, document your technical files accurately, and ensure a safe industrial automation installation.