Voltage surge protection for MOSFET

[rogerm123]

Researching using a depletion mode MOSFET as a voltage indicator for 115V line by attaching an antenna to the gate and having it in close proximity to the outgoing side of a fuse. If the fuse blows, no voltage would be sensed, the MOSFET would turn on supplying battery voltage to a PicAxe chip whereby I could "do-stuff".
My thinking is the depletion mode MOSFET would keep batteries turned off conserving them until needed.
My concern is if a spike that blows a 0.5amp/250v fast blow fuse might damage the MOSFET even though it is physically disconnected from the fused circuit and is insulated from ground.

Any thoughts on things I need to consider?

 

[papaof2]

Wire an appropriate optocoupler across the fuse and the isolated side of the optocoupler to the MOSFET with any needed biasing resistors?
Not zero drain but probably very low drain with the proper choice of components.

 

[Technoman]

Only an overcurrent spike would blow your fuse, so not harmfulI for your MOSFET.
I would prefer the papaof2's solution.
Using an antenna, which may collect from other sources, a 60 Hz low pass filter would be recommended in your design.

 

[rogerm123]

Thanks. I will research.