Three-phase power
Three AC supplies 120° apart sharing conductors. The sum of balanced phase currents is zero (slim or no neutral), instantaneous total power is constant (no torque pulsation), and √3 shows up in every line-vs-phase conversion.
In practice
V_line = √3 × V_phase in wye; I_line = √3 × I_phase in delta; P = √3 × V_L × I_L × PF for balanced loads either way. Keep the √3 with the line quantities and the algebra stays self-consistent.