Hello!
So I strongly advise you to get a professional. It is not safe to handle three-phase current (I assume it is three-phase - 400V?). A professional simply has the necessary experience and the required measuring devices (Duspol etc.).
Especially when you use 3-phase, it is important, for example, that you have a 3-pole fuse. If you don’t have that and you make a mistake and only one or two fuses blow, your stove / oven can be damaged.
So, get a professional ;-)
Best regards
Nico