Free Online Calculators
Find the right breaker & cable cross-section
Whether you're planning a new home build, renovating an existing property, or simply adding a new circuit for an appliance, choosing the right circuit breaker size and cable cross-section is essential for electrical safety. Our free Circuit Breaker Calculator makes this process simple, fast, and accurate – no electrical engineering degree required.
An undersized circuit breaker will trip repeatedly under normal load, causing frustration and interrupting power. An oversized breaker, however, won't protect the cable adequately – this can lead to overheating, insulation damage, or even electrical fires. Getting the sizing right is not just about convenience; it's a fundamental electrical safety requirement under standards like IEC 60364 and NEC (National Electrical Code).
Our circuit breaker calculator helps homeowners, electricians, and construction professionals quickly determine the optimal breaker rating and wire gauge before starting any electrical project.
The calculator uses Ohm's Law and standard electrical engineering formulas to determine the correct specifications. Simply enter the following details:
Based on these inputs, the calculator instantly outputs the recommended breaker amperage, the minimum cable cross-section, and flags whether your voltage drop stays within the safe 3% limit.
A standard electric range draws about 7,200 watts at 240V (two-phase in North America, three-phase in Europe). The calculator determines a current of approximately 30A in North America, recommending a 30A double-pole breaker with 10 AWG (or 6 mm²) copper wire. In Europe on a 400V three-phase system, a B16 breaker with 2.5 mm² cable is typically sufficient.
A 3,500W split-system air conditioner running on 230V draws around 15.2A. The calculator recommends a 16A circuit breaker with a minimum of 2.5 mm² copper cable. For cable runs exceeding 20 meters, it advises upgrading to 4 mm² to keep the voltage drop within acceptable limits.
An outdoor socket rated for up to 3,680W (16A at 230V) requires a 16A breaker and at least 1.5 mm² cable for short runs. The calculator will automatically alert you if the cable length causes the voltage drop to exceed 3%, protecting your equipment and ensuring energy efficiency.
Voltage drop refers to the reduction in electrical voltage as current travels along a cable. Most electrical codes limit this to 3% maximum for branch circuits in residential installations. Excessive voltage drop causes poor appliance performance, overheating, and increased energy waste.
Cable cross-sectional area directly affects current-carrying capacity. A 1.5 mm² copper cable can safely carry up to 15.5A when run in a wall, while a 2.5 mm² cable handles up to 21A. The calculator automatically references these capacity tables and recommends a compliant cable size every time.
Not all circuit breakers are the same. The trip curve defines how quickly a breaker responds to overcurrent:
The calculator recommends the appropriate trip curve based on the load type you specify, ensuring your installation is both safe and functional.
This tool is designed for DIY homeowners, licensed electricians, construction project managers, architects, and engineering students. While it provides accurate guidance based on standard formulas, it is intended as a planning aid. All electrical installations should be completed and inspected by a qualified electrician in accordance with local codes.
For a 20-amp outlet, you need a 20A circuit breaker with at least 12 AWG (2.5 mm²) copper wire. The calculator will confirm this and check that the cable length doesn't cause excessive voltage drop.
Yes! The circuit breaker calculator fully supports both single-phase and three-phase electrical systems. Simply select your voltage configuration and enter the total load power.
Using undersized wire creates excessive resistance, which causes heat buildup. In severe cases, this can melt insulation and start a fire. Always use the minimum cable size recommended by the calculator or go one size larger for safety.
No. This calculator is a planning and educational tool. A licensed electrician must design, install, and sign off on all electrical work in compliance with local electrical codes and safety standards.
Absolutely. Our circuit breaker calculator is completely free to use, with no registration or subscription required. Use it as many times as you need for any project.