Why three phases are used
Three-phase systems deliver power through three alternating voltages separated by 120 electrical degrees. This creates smoother power delivery than single-phase supply and is ideal for motors and larger commercial loads.
Because the phases share the load, three-phase equipment can deliver more power with less conductor material than an equivalent single-phase installation.
The square-root-of-3 factor
In balanced three-phase systems, apparent power is calculated as kVA = volts x amps x 1.732 / 1000 when using line-to-line voltage and line current.
To convert that apparent power to real power, multiply by power factor: kW = kVA x PF.
- Single-phase kVA = volts x amps / 1000
- Three-phase kVA = volts x amps x 1.732 / 1000
- Three-phase kW = kVA x power factor
Balanced and unbalanced loads
The simple formula assumes the phases are reasonably balanced. If one phase carries much more current than the others, engineers must evaluate each phase and neutral loading separately.
Good panel layout, load scheduling, and periodic measurements help keep three-phase systems healthy and efficient.