MCCB Selection Calculator

Develop a preliminary MCCB selection by checking continuous load current, adjustable protection settings, cable capacity, and fault interrupting capability.

What this utility does

The MCCB Selection Calculator brings together load current, adjustable thermal or long-time settings, conductor coordination, and Icu-related fault-current checks for preliminary molded-case breaker selection. It is useful for organizing the key values that should be reviewed when comparing a candidate MCCB with its feeder and expected fault level.

How to use

  1. Enter the circuit load and conductor information requested by the calculator.
  2. Select or enter the candidate MCCB frame rating, adjustable Ir setting, cable ampacity Iz, Icu, and prospective fault current.
  3. Review the displayed checks for load current versus breaker rating, overload setting versus cable capacity, and breaking capacity versus prospective fault current.
  4. Use the result as a screening reference, then verify the final device and settings against the exact manufacturer model, installation conditions, coordination requirements, and applicable standard.

Practical notes

  • The basic current relationships help identify obvious mismatches, but they do not prove complete selectivity, discrimination, or protection performance.
  • Adjustable Ir settings are not a substitute for checking conductor ampacity and the complete protection scheme. Cable ampacity must reflect the real installation method and correction factors.
  • Icu and Ics values are device- and test-condition-specific; use the manufacturer catalogue for the exact breaker, voltage, and application. Prospective fault current should come from the appropriate system study or validated engineering input.
  • Motor, transformer, generator, UPS, and distribution feeders can have different starting, inrush, or operating characteristics that may require additional protection analysis.
  • The calculator is a preliminary engineering aid and should not be treated as a final breaker selection or commissioning approval.

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