If there are 3-220 volt elements in the oven, and they are wye connected (one side of each element is tied to a common point, usually the neutral), and each element is individually controlled, then the only difference in connecting them to a 3 phase supply vs. a single phase one is the current on the neutral.

Here's why. If the 3 elements are all powered by the same phase, neutral current will add. Suppose each element is 10 amps. With one element on, the current will be 10 amps on one of the hots, and 10 amps on the neutral. If 2 elements are on, the current is 10 amps on 2 of the hots, and 20 amps on the neutral. With all 3 elements on, the current is 10 amps on all 3 hots, and 30 amps on the neutral.

If the oven is connected to a 220/380 3 phase system, and all 3 phases are used, the neutral current will subtract, sort of. With one element on, the current will be 10 amps on phase R, and 10 amps on the neutral. With 2 elements on, the current will be 10 amps on phase R, 10 amps on phase S, and slightly less than 10 amps on the neutral. With all 3 elements on, the current will be 10 amps on R, 10 amps on S, and 10 amps on T. The neutral current will be around 2 amps. There will be 380 volts between the line side of each element, but this doesn't matter. Each element sees 220 volts.

The reason the neutral current doesn't fall much until all 3 phases are involved is difficult to explain, but it has to do with the 120 degree phase shift of a 3 phase system vs. the 180 degree phase shift of a single phase system.

All 3 of the elements can be powered by the same phase, but the neutral will need to be rated for 3X the breaker size.

Don't use the bridge if there are 3 breakers. It'll parallel the breakers, and you'll lose short circuit and overload protection. The bridge is meant to be used for one large single phase feed, not 3 small ones.

Rob

P.S. I had to laugh at myself, around here we use A, B, and C to identify 3 phase systems. I originally wrote A, B, and C. Then it dawned on me that Germany uses R, S, and T. So I went back and changed it all.