>...use C19-IEC320 Power cables
If the C7000 has six C20 connectors in the back it has single phase power. No need to talk about 3phase.
It should also have a minimum of 3 power supplies. Therefore you need to connec a minimum of three power cords in the back.
> ...connect them to a regular multisocket and go to a regular single fase power socket from there?
Each power supply requires 2880VA, that's 13-14A at 200-220V. Therefore each power cord must come from a separate separate power feed from your building power source.
A single powerfeed is not enough to support three power supplies.