Switchgear, Panelboards & Electrical Distribution worked example

Short-Circuit Rating Margin with equipment short-circuit current rating of 63 units: a worked example

Here is what the math looks like when conditions slip. We hold every other input steady and drop equipment short-circuit current rating to 63 units, then walk the calculation through step by step. Short-Circuit Rating Margin measures how much headroom a panelboard or switchgear assembly has between its rated short-circuit current rating (SCCR) and the actual available fault current at its location.

The inputs for this scenario

  • Equipment short-circuit current rating (SCCR): 63 units (the input this scenario stresses; the baseline uses 125)
  • Available fault current at the panel: 100 units (held at the documented default)
  • Reference fault current for percent basis: 100 units (held at the documented default)

Working through the calculation

  • The calculation starts from the formula this tool documents: Short-Circuit Rating Margin margin = available value - required value.
  • Margin works out to -37 % at these inputs, and this is the headline figure for the scenario.
  • Absolute margin works out to -37 value at these inputs.
  • Available amount works out to 63 value at these inputs.
  • Required amount works out to 100 value at these inputs.

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 248% below the baseline at -37 %.
  • The practical read: the gap between this scenario and the baseline is entirely attributable to equipment short-circuit current rating, so recovering it is worth quantifying in dollars before considering equipment or staffing changes. 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: -37 % (headline result)
  • Absolute margin: -37 value
  • Available amount: 63 value
  • Required amount: 100 value

Run it with your numbers

  • To rerun this with your own numbers, open the live Short-Circuit Rating Margin calculator, set equipment short-circuit current rating to your actual value, and adjust the remaining inputs to match your operation.

Last reviewed 2026-05-12.