Breaker Sizing Calculator

Sizing the circuit breaker

Keep the breaker sandwiched between two limits, I_load ≤ I_breaker ≤ I_cable. Its rating has to cover the load current, yet it must never climb above what the cable can carry. Here is the reference table for copper with PVC insulation in conduit (NBR 5410): 1.5 mm² → 10 A; 2.5 mm² → 20 A; 4 mm² → 25 A; 6 mm² → 35 A. Take a 2200 W load at 220 V. It pulls 10 A, which means a 16 A breaker on 2.5 mm² cable does the job nicely. As for curves: use B for resistive loads and lighting, C for the usual mixed residential circuits, and D where motors throw a high inrush current at startup.

Applications

Think residential and commercial wiring done to NBR 5410, industrial panels, and dedicated runs for air conditioning, an electric shower, an oven or an EV charger. Beyond protection, the breaker doubles as a manual switch you can flip off to isolate a circuit during maintenance.

FAQ

Can I oversize the breaker to avoid tripping? Don't. The breaker is there to protect the cable, and a rating above the cable ampacity lets the wire overheat past its insulation rating, which is how fires start.

Which curve for an air conditioner? For most split units curve C handles it fine. Save curve D for the big motors that draw a heavy inrush current when they kick in.

Do I need a DR (RCD) too? Yes. NBR 5410 calls for a 30 mA RCD in bathrooms, kitchens, outdoor areas and at any outlet someone might touch with wet hands. The breaker on its own won't save you from a shock.