Three-phase sources and loads are commonly connected in star (wye) or delta configurations.

Star connection

In a star connection, one end of each phase is joined at a common neutral point. The other ends connect to the three line conductors.

For a balanced star system,

$$V_L=\sqrt3,V_{\mathrm{ph}},$$

while

$$I_L=I_{\mathrm{ph}}.$$

Here the subscripts $L$ and $\mathrm{ph}$ denote line and phase quantities.

Delta connection

In a delta connection, the three phase elements form a closed triangle and each line conductor connects to one corner.

For a balanced delta system,

$$V_L=V_{\mathrm{ph}},$$

and

$$I_L=\sqrt3,I_{\mathrm{ph}}.$$

Phase shift

The factors of $\sqrt3$ arise from vector addition of quantities separated by $120^\circ$, not from ordinary scalar addition. The corresponding line and phase quantities also have a $30^\circ$ phase relationship under standard phase sequences.

Star and delta connections therefore change how component ratings relate to the line voltages and currents seen by the power system.