Input
Result
3% / 5% limit—
The final value is the smaller of the 5% voltage-drop length and the short-circuit tripping length. For lighting, use the 3% figure.
How it is calculated
Current from power assumes a power factor
of 1 (I = P / U for one phase, I = P / (√3·U) for three).
The wire size is the smallest whose ampacity is at least the breaker rating; the
breaker is the nearest standard rating not below the load current. The voltage-drop
length comes from the voltage drop table, the
short-circuit length from the cable length table
for the chosen breaker type. Sizes and currents match the
wire size table. For leakage protection, see
choosing an RCD.
Important
The calculation is for reference, for copper and aluminium conductors with a resistive load (cos φ = 1); motors and other reactive loads draw more current. Installation method, temperature and cable grouping change the allowed current. The actual design should be done by a qualified electrician.