Switchgear, Panelboards & Electrical Distribution worked example

Short-Circuit Rating Margin with equipment short-circuit current rating of 310 units: a worked example

What does the result look like when equipment short-circuit current rating reaches 310 units? The full calculation is worked below with real intermediate numbers. Use it when short-circuit rating margin in switchgear, panelboards and electrical distribution needs a clean margin number for a switchgear, panelboards and electrical distribution go / no-go review.

The inputs for this scenario

  • Equipment short-circuit current rating (SCCR): 310 units (raised for this scenario; the documented default is 125)
  • Available fault current at the panel: 100 units (unchanged)
  • Reference fault current for percent basis: 100 units (unchanged)

Working through the calculation

  • Applying the documented formula (Short-Circuit Rating Margin margin = available value - required value) to the inputs above produces each figure below.
  • At this operating point the engine returns 210 % for margin, the number this scenario is built around.
  • At this operating point the engine returns 210 value for absolute margin.
  • At this operating point the engine returns 310 value for available amount.
  • At this operating point the engine returns 100 value for required amount.

How this compares with the baseline

  • Against the tool's baseline example, where equipment short-circuit current rating sits at 125 units and the headline result is 25 %, this scenario comes in 740% above the baseline at 210 %.
  • A figure at this level is achievable when equipment short-circuit current rating is genuinely sustained, not just peaked for a shift. It is a single-point arithmetic check; it does not perform a full fault study, account for series-rated combinations, or capture how motor contribution and utility changes shift available fault current over time.

Results at a glance

  • Margin: 210 % (headline result)
  • Absolute margin: 210 value
  • Available amount: 310 value
  • Required amount: 100 value

Run it with your numbers

  • Every input above is editable in the live Short-Circuit Rating Margin calculator, which recalculates instantly and can be shared with the inputs intact.

Last reviewed 2026-05-12.