Single-Phase power

kW is what an energy meter bills; kVA is what sizes conductors, breakers, and transformers. Both are real quantities, and neither measures efficiency: power factor is about phase, not loss, so a motor at 0.8 pf is not running at 80 percent of anything. Reactive power sloshes between load and supply without doing work, and it is the reason a 2.3 kVA appliance can hide 1.2 kVAr. Where a single-phase figure stops being enough: bigger loads run three phase, where power is √3 × V × I × pf per line and the arithmetic on this page no longer applies. Cable sizing practice sits in IEC 60364-5-52.