That's somewhat common in bodged wiring upgrades in central Europe. Cookers (ranges) usually have the elements connected L-N but take three phases to spread the load, either on a 3-pole 16 amp or three single poles. Two hob elements per phase and the oven on the third (it's rare to see anything with more than four elements and a single oven here, the typical load is 6.5-8 kW). However, if the incoming mains is only single-phase 2w but the installer sets up the cooker circuit for three-phase 4w, the neutral could see up to 3x16 amps. In Austria that's somewhat de-fused by the typical 25 amp limit on the incomer but in Germany the incomer could be fused at up to 63 amps.
I've seen that once or twice in Austria but decided to leave it - 2.5 mm2 and a 25 amp bottle fuse is marginal because of the slower overload trip of the fuse compared to a B/C MCB but unlikely to burn the house down and it was decidedly temporary - the installer had put back the original single-phase meter, jumpering all the load-side lives until the grid operator's subcontractor installed the new three-phase meter. Usually that shouldn't take more than a few days but in this instance it was about two months.
