How the cable and fuse estimate is built.
The tool first calculates design current. For power entries, single-phase current uses I = P ÷ (V × power factor), while three-phase current uses I = P ÷ (√3 × V × power factor). The shared supply voltage therefore changes the calculated current when power rather than amperage is entered.
How the breaker or fuse is selected.
The calculator chooses the smallest standard protective-device rating that is at least the design current but does not exceed the corrected cable current capacity. If no supported rating satisfies both conditions, the result deliberately reports that manual design review is required instead of recommending an oversized device.
Length and supply voltage are both checked.
For single-phase circuits the estimate uses 2 × I × L × R. For three-phase circuits it uses √3 × I × L × R. The voltage-drop percentage is then calculated against the selected supply voltage, so the same volt loss represents a larger percentage on a lower-voltage system.
This is a planning estimate, not electrical approval.
Electrical cable and protective-device selection also depends on exact cable construction, grouping, installation method, fault-loop impedance, short-circuit withstand, disconnection time, RCD requirements, equipment starting current and local rules. Final design and installation must comply with the applicable electrical code, manufacturer instructions and site conditions, and should be checked by a qualified electrical professional.
Common questions.
Why can a longer cable require a larger size?
Longer conductors have more resistance, so voltage drop increases even when current stays the same. The calculator therefore reports ampacity and voltage-drop checks separately.
Can I simply fit the next larger fuse?
No. A protective device must be coordinated with the conductor and load. This tool will not recommend a standard device whose rating exceeds the corrected cable capacity.
Which supply voltages can I use?
FigureNest provides common international presets from 110 V through 480 V plus a custom voltage option. Select single-phase or three-phase separately and verify that the chosen value matches the actual system being designed.
What is not included.
The current version does not calculate grouping factors, harmonic loading, motor starting protection, fault-loop impedance, RCD selection, short-circuit energy withstand or required disconnection time. These are intentionally excluded rather than hidden behind a false “safe” result.