Circuit Breaker Selector
This calculator selects the rating and characteristic of a circuit breaker based on load type and power. Calculation per IEC 60898 and GOST R 50571. All computation is client-side.
Leave 0 to calculate from power
How the selection works
1. Calculated current: I = P / (U × cos φ) for single-phase, I = P / (√3 × U × cos φ) for three-phase. 2. Breaker rating — next standard value from the series: 6, 10, 16, 20, 25, 32, 40, 50, 63 A. 3. Characteristic: B — for lighting/sockets (instant trip 3–5×In), C — for motors/AC (5–10×In). 4. Cable cross-section — per IEC ampacity table.
Frequently asked questions
Which breaker characteristic: B, C or D?
B — for lighting and sockets (trip 3–5×In), C — for motors, compressors and AC units (5–10×In), D — for transformers and heavy motors (10–20×In). For an apartment: B for lighting, C for motor loads.
Why did a 10 A load get a 16 A breaker?
Breakers come in standard ratings: 6, 10, 16, 20, 25, 32, 40, 50, 63 A. The rating must be the next standard value not below the working current — 10.1 A exceeds 10 A, so 16 A is correct.
Which cable for a C16 breaker?
For a 16 A breaker, 2.5 mm² copper is sufficient (IEC 60364-5-52 / NEC 240.4). 1.5 mm² is only allowed up to 10 A.
Which main breaker for an apartment?
By the permitted power: 5.5 kW → 25 A, 7 kW → 32 A, 10.5 kW → 40 A (single phase, cos φ ≈ 1). Confirm the contracted capacity with the utility.