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Circuit Breaker Rating Checks

Compare the entered Ib, In, Iz and prospective-fault/device-interrupt-capacity values as separate arithmetic checks without selecting a device or claiming compliance.

Inputs

Entered circuit and device data

Range: 0–100,000 A

Enter the design current after the relevant load and diversity assessment. This is the current the circuit is expected to carry.

Range: 0.1–100,000 A

Enter the device rated current from the selected breaker. This is not its interrupt capacity or instantaneous trip setting.

Range: 0.1–100,000 A

Enter the conductor current-carrying capacity after the applicable installation, ambient, grouping and thermal corrections. Do not use an uncorrected table value.

Range: 0–100,000,000 A RMS

Enter the prospective fault current at the protective device location on a consistent basis with the device rating and test method.

Range: 0.1–100,000,000 A

Enter the exact interrupting-capacity marking from the manufacturer data for the selected device and application. Do not substitute the breaker rated current In.

Result

Conductor capacity minus breaker rating (A)
8.00
Interrupt rating minus prospective fault current (A)
5,000.0
Breaker minus design current (A)
8.00
Smallest Ib/In/Iz chain margin (A)
8.00
Arithmetic checks
All three entered arithmetic checks pass. This is not a device selection or compliance determination.

Formula

Calculation logic

Formula definitions and substituted values.

Before relying on the result

  • Checking a proposed breaker and cable combination
  • Checking a breaker interrupt rating against available fault current
  • Review the displayed Ib/In/Iz and fault-capacity comparisons against the applicable rules and the exact manufacturer's device data.

Related calculators

Review the displayed Ib/In/Iz and fault-capacity comparisons against the applicable rules and the exact manufacturer's device data.