Why Three Phase Breaker Sizing Matters
A three phase breaker protects equipment, cables, and people. It must carry normal current without nuisance trips. It must also open safely during overloads or faults. Good sizing starts with load current. The calculator converts power, voltage, power factor, and efficiency into line current. It then applies duty, demand, service, spare capacity, and derating factors.
Balanced Load Planning
Most commercial motors, pumps, compressors, panels, and heaters use three phase supply. A balanced load shares current across all three conductors. The breaker rating still depends on line current, not the sum of all phase currents. That point avoids oversizing. It also keeps panel schedules clear.
Derating And Safety Margin
Real installations need adjustment. Continuous loads usually need a higher breaker allowance. Hot rooms, crowded panels, altitude, and enclosure limits can reduce device capacity. This tool lets you enter derating percentages, so the selected size reflects field conditions. Spare margin is useful when future expansion is likely.
Advanced Checks
Breaker choice is not only amperage. Voltage rating must meet or exceed system voltage. Interrupting capacity must exceed available fault current. The calculator compares these values. It also checks conductor ampacity when a cable value is entered. These checks help reveal unsafe combinations before installation.
Using Results In Design
Use the calculated current as the starting load value. Use the required breaker amps as the minimum protective rating. Use the selected standard size as the practical device rating. Review the safety margin before accepting the result. A very large margin may suggest oversized protection. A negative conductor margin needs cable review.
Professional Use
This calculator supports early design, estimates, and field notes. It does not replace local codes, manufacturer data, coordination studies, or engineer approval. Motor circuits, transformers, welders, elevators, and fire pumps may require special rules. Always verify temperature ratings, terminal limits, breaker curves, and selective coordination before final work.
The export buttons help keep records. Save the CSV for spreadsheets. Save the PDF for job files. Record project assumptions beside each result, especially demand factor and derating. Clear assumptions make later reviews faster and safer. Attach the result to panel schedules, purchase notes, maintenance logs, commissioning packs, and inspection reports for consistent documentation across teams.