How to connect a two-phase flow heater to an RCD?

Good afternoon! I purchased a stiebel eltron eil 7 plus instantaneous water heater (6.5 kV), but it turned out to have only three cables (2 phases + ground), but there was no zero. Please tell me how it can be connected using a difavtomat or ouzo to protect against current leakage and which machine to put. Connection diagram in the attachment. I can’t understand how to do this without zero. The apartment has three-phase voltage (13 kV)