For mains input you can use a varisor for over voltage or surge voltage. This element has a specified threshold voltage of which it will go short circuit when the specified voltage is reached and normally blows a fuse. Usually for a mains input voltage of 230vac we use a varistor rated at around 275vac.
The guy takes people for granted, maybe he thought he deserves to answered and for him not show gratitude, well like my mum used to say appreciation lost only in a worst people, cheers not every are the same