Breaker Size Calculator ⚡

Select a standard MCB/MCCB breaker size from amps or kW. Optional IEC and NEC verification checks using cable ampacity (Iz), fault level, ambient temperature, grouping, and altitude factors.

🧮 Inputs

Auto calculate enabled (no Calculate button).
📈 Results
Load Current (Ib):
0.00 A
Required Breaker Current:
0.00 A
Recommended Breaker:
0 A
IEC Check (Ib ≤ In ≤ Iz):
NEC Check:
Correction Factor (Kt):
Effective Iz (Iz × Kt):
Fault Level Requirement:

How to Use Breaker Size Calculator

  1. Select calculation mode: Amps or Power (kW).
  2. Enter your load value and choose Load Type.
  3. Enable IEC or NEC verification if you want to validate cable ampacity and correction factors.
  4. Results update automatically (no calculate button).

FAQ

What is Ib, In, and Iz?

Ib is load current, In is breaker rated current, and Iz is cable current carrying capacity.

Why do I see continuous load 125% in NEC mode?

In NEC workflows, continuous loads are often sized at 125% to reduce nuisance trips and keep margin.

What is kA / kAIC?

It indicates the minimum interrupting (breaking) capacity required for the breaker based on fault level.

📚 References

  • IEC principle: Ib ≤ In ≤ Iz (with correction factors)
  • NEC continuous load practice (125%)
  • Standard breaker rating series (typical IEC/NEC values)