A blind spot display apparatus presents a situation at a blind spot occurring at an intersection from a driver’s viewpoint, in a method of presenting the situation to a driver. It serves for the purpose of protecting apparatus or installations against electromagnetic pulses, overvoltages andor lightning strokes. Advantageously, each capillary tube has a respective end outside threaded to engage in a mating thread-way provided in the sensitive element; moreover, a perimeter weld is provided for safety around each capillary tube near the connection to the sensitive element.