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Circuit protection

Circuit Breaker Size Calculator

Enter design current and corrected cable ampacity to select a preliminary standard breaker and verify load, breaker, and cable coordination.Start calculating
A / mm²Current and protectionPDFStandalone reportSBC 401Method reference

Calculator

Enter your data and see the result immediately

Select a preliminary standard breaker rating and check load-to-breaker-to-cable coordination using IEC or NEC continuous-load treatment.

Calculator

Breaker size

Standard rating with cable check
Calculation inputsResults update instantly
Selection basis
Load duty
Study resultTAYAR TK
Tayar TK
Preliminary engineering studyBreaker size
Date: 2026-07-23Report reference: KWH-BREAKER-2026

Preliminary breaker size

The next standard rating after the continuous-load margin, when selected.

Load current24A
Design current24A
Suggested breaker25A
Cable ampacity checkPreliminarily passes
Entered cable ampacity34 A
Selection basisSBC 401 / IEC
Continuous-load multiplier100%
Calculation method

Preliminary overload coordination: load current Ib ≤ breaker In ≤ corrected cable ampacity Iz.

Engineering notes
  • Also verify fault current, interrupting rating, disconnection time, selectivity, trip curve, and load type.
Safety approval

Do not use this estimate for installation before checking nameplate data, site conditions, short-circuit protection, and earthing.

kwh.tirtk.com.satirtk.com.saC.R 1009172880

This is a planning and comparison estimate. Final protection and conductor selection requires review by a licensed engineer or electrician, site-condition checks, manufacturer instructions, and the applicable code.

Calculation guide

How is a circuit breaker selected?

Under the IEC method, design current Ib must not exceed breaker rating In, while In must not exceed corrected cable ampacity Iz. The calculator reports coordination instead of merely selecting the next rating above load.

Choose IEC treatment or NEC continuous-load treatment. Trip curve, motor starting, breaking capacity, and prospective fault current remain essential site-specific checks.

Breaker selection steps

  1. Enter the circuit design current.
  2. Identify continuous-load treatment.
  3. Enter corrected cable ampacity.
  4. Choose IEC or NEC basis.
  5. Verify Ib ≤ In ≤ Iz, then review curve and breaking capacity.

A breaker is more than an amp rating

  • Breaking capacity for prospective fault current.
  • Trip curve and motor inrush.
  • Upstream and downstream selectivity.
  • Residual-current protection where required.
Method references
SBC 401IEC 60364-4-43

Frequently asked questions

Circuit protection frequently asked questions

Should every load be multiplied by 125%?

Not as a blanket IEC rule. The 125% treatment is applied to continuous load when the NEC basis is selected.

Can I simply choose the next breaker above load?

The breaker must also remain within corrected cable ampacity and suit starting current and breaking capacity.

What breaker does an air conditioner need?

Use nameplate current, manufacturer instructions, starting behavior, and cable data rather than nominal power alone.

What does failed cable coordination mean?

The proposed breaker exceeds the entered corrected cable capacity, so the cable or circuit design must be reviewed.