Mains transformer failure

Originally put down to powering 2 ohm rather than 4 ohm speakers but had survived 3 days of running like that. A short in the primary. But on replacing the Tx it became obvious there was a break in the mains cable (owner knew this but failed to tell me until now). So if repeated breaking carrying mains current , depite X class cap over the mains switch , would that be a more likely reason for the failure. ? Back EMF going well into the KV, punching through the insulation in the primary section.