Hello Achim, nice pictures, how to access the thermal fuse, thankys for sharing. Sorry to say, but a poly-/multifuse is the totally wrong component for this purpose. It will neither help on overcurrent, nor on overheating. The trip current (where MF opens) will be ca. 3A @ 23°C, and ca. 1.5A @ 85°C, where the oven is running normally. I've taken these data from BOURNS MF-R type, should apply also to your special component. Datasheets end at 85°C, so I estimate that thermal derating of the MF would perhaps give about 750mA @ 145°C which also does not shut down further heating, but will for sure damage permamently all internal soldering junctions. Therefore, a regular thermal fuse (max. 105°C type) will ease your mind better, than this shunt. Frank