I suspect that one phase is used for the house and another phase for the HiFi.

Voltage phase to earth is 240v
Voltage phase to phase is 415v

Each phase's sinewave is 120 aways from the others.

If you have single phase outlets (240v) in the same room (might even be floor or house?) that are fed from different phases you need to label all the outlets, with phase / 415 volt warning notice.
As the (fatal) potential across phases is 415v (phase A - live to phase B live).

Regards,
Carl.


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