>... connect them to a regular multisocket and go to a regular single fase power socket from there?
>... A single powerfeed is not enough to support three power supplies.
Let me qualify my answer to your question about the multisocket. A single C19/C20 outlet probably does not have enough power to support three C7000 power supplies. If you have a high amperage (50AMP) circuit with a C19/C20 multisocket PDU then you could connect it to the three power connections of the C7000.