I am designing a circuit to protect a load from over-voltage. The voltage at the load must be around 380VDC and the current consumption will be around 2A. In normal operation the Power Supply must increase the voltage as the load pulls more current so that the voltage drop across the cable is compensated. However, if by any reason the power supply shoots the voltage to 800VDC, the circuit on the load must be opened, avoiding the load to see such a high voltage. The power supply is capable of delivering 8A.
I tried the circuit in the picture, it works pretty well as it opens at 400VDC (triggered by the two zeners in series). But at 500VDC the zeners blow up even with a 150k resistor.
Would a crowbar work in this situation ? I really don't want to use glass fuses to avoid opening the enclosure where the load is installed.