Calculateur de calibre de disjoncteur
Estimez un courant nominal standard à partir du courant de charge ou de P, V, phase et facteur de puissance. Charge continue 125 % optionnelle. Pas un substitut au code.
Courant connu. Vide pour estimer avec puissance et tension.
Ou estimer depuis la puissance
Puissance active (watts).
Monophasé : tension selon votre schéma.
1 pour résistif ; moteurs souvent 0,8–0,95.
Table of Contents
Outil de planification
Breakers (or fuses) protect conductors and equipment by opening when current is too high. Their ampere rating must be chosen using applicable codes, manufacturer listings, conductor ampacity, and site conditions.
This calculator picks the smallest common standard rating that is still at least your design current — the current you must not exceed on the protected circuit under your assumptions.
You may enter load current directly (from a nameplate, load calc, or engineer), or estimate it from real power, voltage, single- vs three-phase, and power factor.
Real projects need temperature correction, terminal limits, feeder vs branch rules, harmonic loads, motor inrush, GFCI/AFCI requirements, and utility or AHJ rules. Use this for quick estimates and education only.
Formulas used here
Operating current from power
Single-phase: I = P ÷ (V × PF). Three-phase: I = P ÷ (√3 × V_L-L × PF).
P is real power in watts, V is the voltage defined above for the selected phase mode, PF is power factor.
Continuous loads
If “continuous” is enabled: I_design = I_operating × 1.25, then choose the next standard breaker ≥ I_design.
Breakers are then matched to conductor ampacity and code requirements in the field.
Quick Reference (illustrative)
| Load | V | φ | Cont. | Breaker (A) | Note |
|---|---|---|---|---|---|
| 1,920 W | 240 | 1 | No | 10 | I = 8 A → often 10 A or 15 A minimum branch per local rules |
| 12,000 W | 240 | 1 | Yes | 70 | I ≈ 50 A, ×1.25 = 62.5 A → next standard 70 A |
| 15 kW | 400 | 3 | No | 32 | I ≈ 21.7 A at PF 1 → 25 or 32 A commonly stocked |
| 30 A | — | — | No | 30 | Direct amp entry; next size ≥ 30 A |
Real-World Examples
240 V single-phase heater
6,000 W, PF 1 → I = 6,000 ÷ 240 = 25 A. Non-continuous → next standard ≥25 A is often 30 A; verify conductor size and code minimums.
Small motor branch
Motors need Article 430 / local motor rules; this tool only converts watts to current. Use nameplate FLA and code tables for OCPD and conductor sizing.
Three-phase workshop
10 kW, 400 V L-L, PF 0.9 → I = 10,000 ÷ (√3 × 400 × 0.9) ≈ 16.0 A → common breaker 20 A or 25 A depending on supply and derating.
Continuous lighting load
If a load runs 3+ hours and is classified continuous, enable 125% so continuous current does not exceed 80% of the breaker rating in typical NEC-style planning.
FAQ
Conductor ampacity, ambient temperature, number of conductors in a raceway, terminal temperature limits, and listing instructions can require a larger wire or a different OCPD rating than this estimate suggests.
Use the voltage that matches how you computed or measured load current. A 240 V water heater uses 240 in this field; a 120 V branch uses 120. Three-phase always uses line-to-line voltage here.
If load current (A) is filled with a valid positive number, that value is used and the power fields are ignored until you clear amps.
No. It only suggests a common thermal-magnetic amp rating for planning. Device class (GFCI/AFCI/CAFCI), curves, and interrupting rating are separate selections.
Standard fuse amp ratings are often similar, but fuse curves and code rules differ. Treat the suggested amperes as an order-of-magnitude check, not a fuse part number.
Convert power and time with our electrical calculators (watts, amps, volts, kWh) to feed better numbers into this breaker planner.