Svar:
For each contactor, there is a short-circuit current and a time that it must withstand. If this is higher and longer than the specification, there is a risk that the contactor will weld together. What happens is that the magnetic field in the contact bridge forces the contact bridge apart and small arcs can form with the subsequent risk of the contactor welding the contact bridge. Alternatively, the heat in the contact points can be so high that they melt together.