What is 1.73 in electrical formula?

1.732 is the square-root of three (and is often written that way in the relevant equations), and the relationship between a three-phase, four-wire, system's phase and line voltages. That is, the line voltage is 1.732 times greater than the phase voltage, and the line current is 1.732 times

A three-phase, four-wire, system is provided by, for example, a transformer, whose secondary windings are connected in a consideration called 'star' or 'wye'. This configuration provides four conductors: three 'line conductors' and one 'neutral conductor'. The voltage measured between any pair of line conductors is called a 'line voltage', while a voltage measured between any one line conductor and the neutral conductor is called a 'phase voltage'. The relationship between these voltages is:

VL = 1.732 x VP

There is a similar relationship for the currents flowing through a 'delta' (or 'mesh') load -provided the load is balanced (i.e. each phase load is identical). That is, the line currents supplying that balanced load will be 1.732 times larger than the phase currents flowing through the individual loads.