Assuming that ø-g votlages are always balanced {or “zero”} in ungrounded-delta systems can be hazardous to your health. Phases have inherent capacitance to ground formed across system insulation; can be quite variable based on insulation quality and affected by transient and resonant conditions. ‘Neutral shift’ with respect to ground can an does result in temporary overvoltages well above system ø-ø voltage, wreaking havoc to “600-volt” insulation.
The characteristics of a low-voltage ungrounded-delta {or sometimes ungrounded-wye} systems are discussed in chapter 6 of Beeman’s
Industrial Power Systems Handbook or chapter 1 of IEEE standard 142. [green book]
See discussion in
https://www.electrical-contractor.net/ubb/Forum9/HTML/000043.html and short reference at
http://6L6.net/localuser/bjarn/ecn.beemaIPSH6z..htm
