If the second value of a two-voltage information is twice as high than the first value, it is a one phase three wire conductor system with one conductor between two others.(Example: 220 V/440 V).
If the second value of a two-voltage information is 1.73 times higher than the first value, it is a one phase three wire conductor system with mid point conductor. (Example: 230 V/400 V).
Single voltage values are three phasecurrent systems with tree conductors.(Example: 500 V).
* All informations are without obligation and have no claims on completeness.