Circuit – breaker
Ib < In < Iz
Ib < In < 0.906Iz
If = 1.6In
If ≤ 1.45Iz
Circuit – breaker / Fuse (At 80% of the ampere rating)
Iz ≥ 1.25Icont
In < Iz
Circuit – breaker / Fuse (At 100% of the ampere rating)
Iz ≥ Icont
In < Iz
Ib = Operating current (A)
Icont = Continuous loads (A)
In = Rated current protection device (A)
Iz = Max wire ampacity (A)
If = Fusing current (A)
This tool calculates the rating of protective devices (circuit breakers) for electrical circuits according to IEC 60364-4-43, providing protection against overloads and short circuits. Suitable for industrial, commercial, and building electrical design.
Select the type of current in the circuit:
Direct Current (DC): Constant flow from positive to negative pole
Alternating Current (AC): Reverses direction and amplitude periodically at constant frequency
System configurations:
Single-phase: Two conductors (phase + neutral)
Two-phase: Two phase conductors; neutral may be distributed
Three-phase: Three phase conductors; four-wire system includes neutral
Electric potential difference between two points.
For single-phase: Enter Phase-Neutral voltage
For two-phase or three-phase: Enter Phase-Phase voltage
Power to be considered when determining the characteristics of circuit components.
Ratio of active power to apparent power.
Formula:cos φ = P / S
where φ is the phase angle between voltage and current. Value ranges from 0 to 1.
Installation method as defined in IEC 60364-5-52 (Table A.52.3). Examples include:
Free air
In conduit
Underground
Multiple circuits in a common duct
Note: Not all installation methods are recognized in every country's regulations.
Temperature of the surrounding medium when the conductor is not loaded.
Affects current-carrying capacity; commonly referenced at 30°C or 40°C.
Material of the conductor used:
Copper
Aluminum
Different materials have different resistivity and current-carrying capabilities.
Temperature rating of the insulation material:
PVC (Thermoplastic): 70°C at conductor
XLPE or EPR (Thermosetting): 90°C at conductor
Higher temperatures reduce insulation performance and require derating.
Cross-sectional area of the conductor, typically in mm².
Determines the maximum allowable current.
Conductors with the same cross-sectional area, length, and material can be connected in parallel.
The maximum permissible current is the sum of individual-core maximum currents.
Number of lines inside the duct powering different loads (e.g., 2 lines for 2 motors).
Reduction factors apply based on IEC 60364-5-52 Table B.52.17.
Total content of 3n harmonic current.
If the value of total 3n harmonic distortion is unknown, use the total harmonic distortion value.
High THD increases neutral current and affects breaker sizing.
Device responsible for protecting the cable from overload and short circuit, such as a circuit breaker or fuse.
Check this option if all sets of parallel cables are installed in one duct (derating factor will be applied).
Uncheck if each set is installed in a separate duct.
Definition: One "set" consists of one conductor per phase + one neutral conductor (if required) + one protective conductor.
This calculator follows IEC 60364‑4‑43 for AC and DC circuit‑breaker sizing to provide cable overload and short‑circuit protection. Input load parameters, installation method, ambient temperature, conductor material and cross‑section to obtain suitable protective‑device ratings for building, commercial and industrial electrical design.
Aluminum conductors have higher resistivity and lower ampacity than copper at the same cross‑section area.
Larger wire size is required for aluminum cables, and breakers shall be sized accordingly. Do not reuse copper‑cable breaker parameters for aluminum‑conductor circuits.
Non‑linear loads generate harmonics. Triplen harmonics notably increase neutral‑conductor current. THD values correct real‑circuit current. For high‑THD applications, do not size breakers only by fundamental‑wave load current, to prevent unwanted tripping or cable overheating.
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