X2 capacitor warning

[Maarten]

Originally Posted by Radio Wrangler

An X capacitor across the mains may go shorted as the result of a high-voltage transient. 'It then relies on the current available from the mains to burn back the metalisation from the wound, clearing the short. As time goes by repeated zaps reduce the area of the capacitor and the capacitance is progressively reduced.

That is the preferred failure mode, but it may stay shorted as long as it doesn't burn or explode. For Y capacitors it would be problematic to fail shorted or even go short for a short time (pun by accident).