PRELIMINARY ENGINEERING TOOL
Preliminary breaker-size helper
Find a nominal standard rating that satisfies the basic Ib ≤ In ≤ Iz relation.
Inputs
Calculation steps
Ib = 25 A × 1 = 25.00 A
25.00 A ≤ 25 A ≤ 32.00 A
Formula ID: BREAKER_SUGGESTION_V1
Assumptions and references
Preliminary calculation only. Verify inputs, manufacturer data, applicable standards, fault levels, and local requirements before construction or procurement.
UNDERSTAND THE TOOL
What this calculator does
The breaker helper identifies rating-series options that satisfy the narrow preliminary relationship Ib ≤ In ≤ Iz. It does not determine breaking capacity, selectivity, fault protection, coordination or compliance.
How to use it
- Enter the design current and the corrected cable capacity.
- Choose the supplied rating series and pole count appropriate to your concept.
- Review candidate ratings and the relation shown for each.
- Use a qualified protection study and applicable product data before selecting equipment.
Fields and meanings
- Ib
- Design current expected for the circuit.
- Iz
- Corrected cable current-carrying capacity from a separately reviewed assessment.
- Rating series
- The available nominal breaker ratings you want to compare.
- Poles / curve
- Descriptive preliminary inputs; they do not complete a protection design.
Review required. Fault level, breaking capacity, RCD requirements, discrimination, conductor protection and local rules are not solved here.
Read the full protection relation article →