Hi there,
we're finishing a design on a product, that can be powered from mains. After initial EMC tests we've concluded, that we need MOVs across L-PE and N-PE against surge and burst events. Now the problem is, that MOVs are known for failing short-circuit and in such event, there will be mains voltage on PE, which is user accessible and this is obviously a dangerous situation. I could not find a single standard, document or any other similar source, that would elaborate on that issue. All the focus seems to go towards fire hazard. I've seen schematic diagrams, where MOVs from L and N are connected to a single point, and that point is connected through a GDT to PE, which would solve the issie, be we hardly have any more space to squeeze in a GDT.
Have you ever had any problems with MOVs between mains and protective earth?