General Notations used in 3-phase:

In three phase circuits, normally the phases are recognized by the colours of insulation on wires utilized, i.e. R for red, Y for yellow and B for blue. Often the phases are also marked as A, B, C or 1, 2, 3. These nomenclatures that mean R-Y-B, A-B-C or 1-2-3 are universally accepted.

The voltage in circuit V_RY is positive from R to Y. the order of the subscripts defining the direction of the voltage. So

                    V_RY= V_YR

Similarly,    I _RY = - I_YR

This form of double subscript notation makes the calculations in 3-phase circuits simple and less ambiguous.