Think of it as a surge protector. It is intended to protect sensitive electronics from high voltage, which will burn them out.

If the DC voltage goes above a set level, called Over Voltage, the Over Voltage Protection (OVP) relay puts a short on the electronic bus, which blows the OVP fuse. Then, NO voltage is applied. The electronics can't burn out if there is no voltage...

Crude, crowbar technology, but simple, reliable and effective in protection.

Without voltage applied from the OVP circuit to your electronics, weird things happen. Replace the OVP fuse, and the OVP relay can again apply voltage to your electronics.

Best Regards,
Jim