The OVP relay has a zener diode in the circuit (see diagram on relay case) which means it is an over voltage device as zeners fire on a preset voltage not current...the fuse blows when the zener fires as it (the zener) now presents a short to ground so drawing excessive current..so... the fuse blows because there is an overvoltage condition...a zener and a fuse always go together in any over voltage protection circuitry...hope that clears up the function of the OVP...note that the OVP RELAY when removed should not affect performance (bUt u then don't have OV protection!!) I HAVEN'T TRIED THIS THO..
Peter
300sel