P
Electrical Power
Rate of energy use: P = U × I (× power factor for AC).
Formulas
P = UI, P = I²R, P = U²/R. AC single phase: P = U I cosφ. Three phase: P = √3 × UL × IL × cosφ.
Example
A 9.2 kW shower at 230 V draws 40 A, so would typically need a 40 A or 45 A device and 10 mm² cable depending on installation method.
Key regulations
311.1 (maximum demand)