Dashcam voltage drop line input voltage DC12V-30V output voltage 5V\/1.5A, I would like to ask how large safety piece is suitable. Thank you?

The size of the safety piece is generally related to the maximum current of the appliance, but if you use the switching power supply step-down, there is no need to use the safety piece, the switching power supply chip is generally a built-in protection circuit, and once the switching power supply fails, there is no voltage at the output end.