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Breaker Selectivity Limit Check

Compare a downstream prospective fault current with a manufacturer-published selectivity limit for one exact protective-device pair.

Inputs

Device pair and published data

Range: 0.1–100,000 A

Enter the downstream protective device rated current from the device data. This value alone does not establish discrimination.

Range: 0.1–100,000 A

Enter the upstream protective device rated current from the device data. A larger rating is only an ordering check, not a selectivity proof.

Range: 0–200 kA

Enter the published limit for the exact device models, trip settings, voltage, frequency and configuration. Identify whether the table value is for full or partial selectivity in your design record; no generic ratio is assumed.

Range: 0–200 kA RMS

Enter the prospective fault current at the downstream device using the same RMS basis and fault type as the manufacturer's coordination data.

Result

Upstream minus downstream rated current (A)
93.00
Selectivity-limit margin (kA)
4.000
Limit comparison
The entered fault current is below the user-supplied manufacturer selectivity limit for this pair.

Formula

Calculation logic

Formula definitions and substituted values.

Before relying on the result

  • Checking whether a fault level is within a published breaker-pair selectivity limit
  • Recording selectivity margin for a specified upstream and downstream pair
  • Use the exact manufacturer coordination table for the chosen device pair, then compare its published limit with the calculated fault level.

Related calculators

Use the exact manufacturer coordination table for the chosen device pair, then compare its published limit with the calculated fault level.