Protection relation
A preliminary Ib ≤ In ≤ Iz breaker relationship check
Explore the basic relation between design current, nominal breaker rating and corrected cable capacity.
Open preliminary breaker-size helper →
What this calculation is for
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 the calculator
- 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.
Useful for
- • Early circuit concept
- • Comparing nominal rating choices
- • Documenting a preliminary relationship in a local project
Fields explained
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.
Important limits and next checks
Preliminary engineering aid only. This article and its calculator do not provide an approval, certificate, compliance determination or installation instruction.
- Fault level, breaking capacity, RCD requirements, discrimination, conductor protection and local rules are not solved here.
- Do not purchase or install a breaker on this helper alone.
Verify applicable laws, rules, standards, manufacturer data and project conditions with a qualified electrical professional before construction, procurement or regulatory submission.